From bertram.felgenhauer at googlemail.com  Sun Jun  1 00:29:02 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Sun Jun  1 00:21:54 2008
Subject: [Haskell-cafe] type-level integers using type families
In-Reply-To: <48416FA4.7040402@gmail.com>
References: <483E1FCF.9000101@gmail.com>
	<66615E96-5F85-4DAD-A280-1CEBF356B682@cse.unsw.edu.au>
	<483FEFB0.3060904@di.unipi.it> <48416FA4.7040402@gmail.com>
Message-ID: <20080601042902.GA4221@zombie.inf.tu-dresden.de>

Peter Gavin wrote:
> Roberto Zunino wrote:
>> Maybe he wants, given
>>   cond :: Cond x y z => x -> y -> z
>>   tt :: True
>>   true_exp  :: a
>>   false_exp :: <<<untypable>>>
>> that
>>   cond tt true_exp false_exp :: a
>> That is the type of false_exp is "lazily inferred", so that type errors
>> do not make inference fail if they show up in an unneeded place.
>
> Yes, that's exactly what I want, but for type families (not MPTC). I think 
> it could be done if the type arguments were matched one at a time, across 
> all visible instances.

What do you think of the following idea?

Using naive type level natural numbers,

> data Zero
> newtype Succ a = Succ a

Booleans,

> data True
> data False

comparison,

> type family (:<:) x y
> type instance (Zero   :<: Succ a) = True
> type instance (Zero   :<: Zero  ) = False
> type instance (Succ a :<: Zero  ) = False
> type instance (Succ a :<: Succ b) = a :<: b

difference,

> type family Minus x y
> type instance Minus a        Zero     = a
> type instance Minus (Succ a) (Succ b) = Minus a b

and a higher order type level conditional,

> type family Cond2 x :: (* -> * -> *) -> (* -> * -> *) -> * -> * -> *
> type First2  (x :: * -> * -> *) (y :: * -> * -> *) = x
> type Second2 (x :: * -> * -> *) (y :: * -> * -> *) = y
> type instance Cond2 True  = First2
> type instance Cond2 False = Second2

we can define division as follows:

> type family Div x y
> type DivZero x y = Zero
> type DivStep x y = Succ (Div (Minus0 x y) y)
> type instance Div x y = Cond2 (x :<: y) DivZero DivStep x y

It's not exactly what you asked for, but I believe it gets the effect
that you wanted.

Enjoy,

Bertram
From thomas.dubuisson at gmail.com  Sun Jun  1 02:11:22 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Sun Jun  1 01:59:44 2008
Subject: [Haskell-cafe] [ANN] Bindings to Xen Control (xenctrl.h)
Message-ID: <1212300682.2448.14.camel@Clunker>

All,
I'm just getting started with hsXenCtrl [1] as both a fun way to play
with Xen and become proficient with Haskell FFI.  Once I get my
community.haskell.org account squared away I'll likely setup a public
darcs repo (and a homepage somewhere).

As for modules: I intend to expand on the trival FFI bindings in
System.Xen.CBindings and there'll be a higher level interface in
System.Xen (functions will standardize on returning Either or throwing
exceptions, hiding the xc_handle open/close, etc).

Typical Disclaimers:
The _only_ thing I've actually done with this, just tonight, is pause /
unpause domains.  API is subject to change!  Only my exact build of Xen
is sure to work, and no promise even then.

TomMD

[1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl

From dons at galois.com  Sun Jun  1 02:31:40 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  1 02:24:41 2008
Subject: [Haskell-cafe] [ANN] Bindings to Xen Control (xenctrl.h)
In-Reply-To: <1212300682.2448.14.camel@Clunker>
References: <1212300682.2448.14.camel@Clunker>
Message-ID: <20080601063140.GA1200@scytale.galois.com>

thomas.dubuisson:
> All,
> I'm just getting started with hsXenCtrl [1] as both a fun way to play
> with Xen and become proficient with Haskell FFI.  Once I get my
> community.haskell.org account squared away I'll likely setup a public
> darcs repo (and a homepage somewhere).
> 
> As for modules: I intend to expand on the trival FFI bindings in
> System.Xen.CBindings and there'll be a higher level interface in
> System.Xen (functions will standardize on returning Either or throwing
> exceptions, hiding the xc_handle open/close, etc).
> 
> Typical Disclaimers:
> The _only_ thing I've actually done with this, just tonight, is pause /
> unpause domains.  API is subject to change!  Only my exact build of Xen
> is sure to work, and no promise even then.
> 
> TomMD
> 
> [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl

Good stuff. Perhaps the synopsis should include a link or description of
the typical use cases/ thinks we might achieve?

-- Don
From apfelmus at quantentunnel.de  Sun Jun  1 03:37:39 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Sun Jun  1 03:30:40 2008
Subject: [Haskell-cafe] Re: appending an element to a list
In-Reply-To: <48414C2B.9010606@daimi.au.dk>
References: <483EE208.2010601@inf.fu-berlin.de>	<483EF36B.5040100@daimi.au.dk>	<48404039.6030605@cisco.com>	<48405717.20206@daimi.au.dk>	<87r6bja609.fsf@hbox.dyndns.org>	<3c4d5adf0805302159o23113ad2sb24754e02789bb06@mail.gmail.com>
	<48414C2B.9010606@daimi.au.dk>
Message-ID: <g1tjk4$c4i$1@ger.gmane.org>

Tillmann Rendel wrote:
> Abhay Parvate wrote:
>> I think I would like to make another note: when we talk about the complexity
>> of a function, we are talking about the time taken to completely evaluate
>> the result. Otherwise any expression in haskell will be O(1), since it 
>> just creates a thunk.
> 
> I don't like this notion of complexity, since it seems not very suited 
> for the analysis of composite expression in Haskell.
> 
> Is this intuitive view generalizable to arbitrary datatypes (instead of 
> lists) and formalized somewhere?

See also the thread section beginning with

   http://thread.gmane.org/gmane.comp.lang.haskell.cafe/34398/focus=34435



Regards,
apfelmus

From vigalchin at gmail.com  Sun Jun  1 04:00:27 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sun Jun  1 03:53:13 2008
Subject: [Haskell-cafe] modelling C in Haskell ..
In-Reply-To: <F77D2BD2-3BF5-48FA-8B51-723305860036@fastmail.fm>
References: <5ae4f2ba0805292346y217d799du8a3e097a1e004e7a@mail.gmail.com>
	<B38D65AC-A9E6-4C12-B9D3-A2285477BBEE@fastmail.fm>
	<5ae4f2ba0805300029s69b1a1fdn73e07fe17b458b10@mail.gmail.com>
	<F77D2BD2-3BF5-48FA-8B51-723305860036@fastmail.fm>
Message-ID: <5ae4f2ba0806010100j3788d29bj4aa0f5f4e3a8c5a8@mail.gmail.com>

my knowledge of point-free is from category theory. in what sense is Haskell
point-free handle namespace pollution?

Kind regards, Vasili

On Fri, May 30, 2008 at 3:23 AM, Jonathan Cast <jonathanccast@fastmail.fm>
wrote:

> On 30 May 2008, at 12:29 AM, Galchin, Vasili wrote:
>
>  compactness in writing and also namespace pollution .. ;^)
>>
>
> I know what the advantages of C's notation are.  But getting the best
> notation out of Haskell generally doesn't happen by trying to make your code
> look like C.
>
> So the general answer to questions of the form `C can do x; can Haskell' is
> `No'.  Don't do it like in C.  It won't be idiomatic, it won't be elegant,
> and neither of us will like the results.  Understand the features of Haskell
> that make your program compact, point-free (how Haskell handles namespace
> pollution), and elegant and use those.  This will require a different
> factoring of your program vs. C.  Sorry, but that's life.
>
> jcc
>
>
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From aruiz at um.es  Sun Jun  1 06:20:03 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Sun Jun  1 06:12:51 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
Message-ID: <484277D3.9020604@um.es>

Anatoly Yakovenko wrote:
> What is the most efficient way to update a position in a matrix or a
> vector?  I came up with this:
> 
> updateVector :: Vector Double -> Int -> Double -> Vector Double
> updateVector vec pos val = vec `add` v2
>    where
>       v2 = fromList $ (replicate (pos) 0.0) ++ ((val - (vec @>
> pos)):(replicate ((dim vec)- pos - 1) 0.0))
> 
> but this seems pretty inefficient to me.
> 
> thanks,
> Anatoly
> 

It is probably more efficient to use subVector and join (implemented by 
copyArray):

updateVector' v pos val
     | pos == 0        = join [b,c]
     | pos == dim v -1 = join [a,b]
     | otherwise       = join [a,b,c]
     where a = subVector 0 pos v
           b = fromList [val]
           c = subVector (pos+1) (dim v -pos-1) v

 > updateVector' (fromList [1,2,3,4,5]) 2 57
5 |> [1.0,2.0,57.0,4.0,5.0]

(The three cases are required because empty vectors are not currently 
allowed.)

Something similar can be done for matrices using flatten and reshape.

Although vectors and matrices in this library are immutable and intended 
to be manipulated as a whole by higher level functions, this kind of 
update functions may often be useful. I will include them soon.

Alberto
From bertram.felgenhauer at googlemail.com  Sun Jun  1 14:44:46 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Sun Jun  1 14:37:38 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
Message-ID: <20080601184446.GA27750@zombie.inf.tu-dresden.de>

Hi,

I'm pleased to announce yet another tool for importing darcs repositories
to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in
Haskell, on top of the darcs2 source code. The result is a much faster
program - it can convert the complete ghc 6.9 branch (without libraries)
in less than 15 minutes on my slightly dated machine (Athlon XP 2500+),
which is quite fast [3]. Incremental updates work, too.

The program is still rough around the edges, and there's some cosmetical
work to do, especially with respect to converting author names. The
program should recover from most errors, as long as nobody else modifies
the destination repository.

Nevertheless, it seems quite useable already. I hope somebody finds
this useful.

You can grab the source at

   http://int-e.home.tlink.de/haskell/git-darcs-import-0.1.tar.bz2

Look at the README for further information.

Credits go to:
    David Roundy and all contributors for darcs2. The code base is
    surprisingly pleasant to work with.

    And of course, Linus Torvalds, Junio Hamano and all other git
    contributors.

Enjoy,

Bertram

[1] http://repo.or.cz/w/darcs2git.git?a=shortlog
[2] http://git.sanityinc.com/?p=darcs-to-git.git
[3] http://nominolo.blogspot.com/2008/05/thing-that-should-not-be-or-how-to.html
From aeyakovenko at gmail.com  Sun Jun  1 14:45:09 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Sun Jun  1 14:37:55 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <484277D3.9020604@um.es>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
Message-ID: <e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>

do you have any plans to provide an interface for inplace updates?

On Sun, Jun 1, 2008 at 3:20 AM, Alberto Ruiz <aruiz@um.es> wrote:
> Anatoly Yakovenko wrote:
>>
>> What is the most efficient way to update a position in a matrix or a
>> vector?  I came up with this:
>>
>> updateVector :: Vector Double -> Int -> Double -> Vector Double
>> updateVector vec pos val = vec `add` v2
>>   where
>>      v2 = fromList $ (replicate (pos) 0.0) ++ ((val - (vec @>
>> pos)):(replicate ((dim vec)- pos - 1) 0.0))
>>
>> but this seems pretty inefficient to me.
>>
>> thanks,
>> Anatoly
>>
>
> It is probably more efficient to use subVector and join (implemented by
> copyArray):
>
> updateVector' v pos val
>    | pos == 0        = join [b,c]
>    | pos == dim v -1 = join [a,b]
>    | otherwise       = join [a,b,c]
>    where a = subVector 0 pos v
>          b = fromList [val]
>          c = subVector (pos+1) (dim v -pos-1) v
>
>> updateVector' (fromList [1,2,3,4,5]) 2 57
> 5 |> [1.0,2.0,57.0,4.0,5.0]
>
> (The three cases are required because empty vectors are not currently
> allowed.)
>
> Something similar can be done for matrices using flatten and reshape.
>
> Although vectors and matrices in this library are immutable and intended to
> be manipulated as a whole by higher level functions, this kind of update
> functions may often be useful. I will include them soon.
>
> Alberto
>
From pieter at laeremans.org  Sun Jun  1 18:18:36 2008
From: pieter at laeremans.org (Pieter Laeremans)
Date: Sun Jun  1 18:11:20 2008
Subject: [Haskell-cafe] Ghc / cgi static linking
Message-ID: <ddacd4a70806011518v2b65d010r56e60ca9bf0a530c@mail.gmail.com>

Hello,

I'm researching the use of Haskell to replace some perl scripts (in a web app).
The app is deployed with a webhosting provider.

CGI scripts can be executed =>  I can use Haskell. I've tried some
hello world cgi scripts, compiled them on the same linux
the hosting company uses and deployed them. It worked!

But I would like to implement a search feature for the website.  For
Java/php/perl there 's lucene.
For haskell there 's holumbus. Unfortunately, sqlite is a requirement
for holumbus. It is not installed at the server of the
hosting company.

Is it possible to staticly link the sqlite3 library using ghc ?

And are there other lucene like libs available like holumbus for haskell ?

thanks in advance,

Pieter



-- 
Pieter Laeremans <pieter@laeremans.org>
From dons at galois.com  Sun Jun  1 18:26:00 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  1 18:18:48 2008
Subject: [Haskell-cafe] Ghc / cgi static linking
In-Reply-To: <ddacd4a70806011518v2b65d010r56e60ca9bf0a530c@mail.gmail.com>
References: <ddacd4a70806011518v2b65d010r56e60ca9bf0a530c@mail.gmail.com>
Message-ID: <20080601222600.GE4759@scytale.galois.com>

pieter:
> Hello,
> 
> I'm researching the use of Haskell to replace some perl scripts (in a web app).
> The app is deployed with a webhosting provider.
> 
> CGI scripts can be executed =>  I can use Haskell. I've tried some
> hello world cgi scripts, compiled them on the same linux
> the hosting company uses and deployed them. It worked!
> 
> But I would like to implement a search feature for the website.  For
> Java/php/perl there 's lucene.
> For haskell there 's holumbus. Unfortunately, sqlite is a requirement
> for holumbus. It is not installed at the server of the
> hosting company.
> 
> Is it possible to staticly link the sqlite3 library using ghc ?

Yes, it is entirely possible to statically link entire CGI apps.

For example, this simple program,

    import Database.SQLite
    main = print "hey, test this"

when compiled as $ ghc A.hs --make is dynamically linked against:

    $ ldd A
    A:
        Start            End              Type Open Ref GrpRef Name
        0000000000000000 0000000000000000 exe  1    0   0      A
        0000000041a85000 0000000041ee5000 rlib 0    1   0      /usr/local/lib/libsqlite3.so.9.0
        0000000049b04000 0000000049f1d000 rlib 0    1   0      /usr/lib/libm.so.2.3
        0000000042213000 000000004264f000 rlib 0    1   0      /usr/local/lib/libgmp.so.7.0
        0000000047d0e000 00000000481e0000 rlib 0    1   0      /usr/lib/libc.so.42.0
        0000000047900000 0000000047900000 rtld 0    1   0      /usr/libexec/ld.so

Now, we can just pass some linker flags through to statically link this lot,

    $ ghc A.hs --make -optl-static -no-recomp
    $ ldd A                                  
    ldd: A: not a dynamic executable
    $ file A
    A: ELF 64-bit LSB executable, AMD64, version 1, for OpenBSD, statically linked, not stripped

I've added this information to the web programming FAQ,

    haskell.org/haskellwiki/Practical_web_programming_in_Haskell#Deploying_statically_linked_applications

Note it also works for fastcgi, which when combined with Haskell's lightweight
threads, makes a good option for performance-oriented web apps.

-- Don
From peteg42 at gmail.com  Sun Jun  1 21:27:56 2008
From: peteg42 at gmail.com (Peter Gammie)
Date: Sun Jun  1 21:21:09 2008
Subject: [Haskell-cafe] Ghc / cgi static linking
In-Reply-To: <20080601222600.GE4759@scytale.galois.com>
References: <ddacd4a70806011518v2b65d010r56e60ca9bf0a530c@mail.gmail.com>
	<20080601222600.GE4759@scytale.galois.com>
Message-ID: <12F6690C-C370-4C25-B080-ADC3975318EC@gmail.com>

On 02/06/2008, at 5:26 AM, Don Stewart wrote:

> pieter:
> Yes, it is entirely possible to statically link entire CGI apps.

You might want to watch out for a bug in GHC 6.8.2 that means GHC's "- 
static" flag doesn't work. (At least for me, at least on Debian: the "- 
lpthread" flag is passed before the "-lrt" one, and symbols are left  
unresolved as a result.) Apparently the near-to-release 6.8.3 will fix  
this issue.

Presumably dons is using a more recent GHC than 6.8.2, or other (BSD?)  
platforms are not affected.

Note also you may have to tweak sundry .cabal files to add "extra- 
libraries" fields. As an example, I added this to HSQL's PostgreSQL  
backend to get it to statically link:

extra-libraries: pq, crypt, pthread

(If anyone cares you need to build PostgreSQL without kerberos as that  
doesn't seem to statically link any more.)

cheers
peter

-- 
http://peteg.org/

From dons at galois.com  Sun Jun  1 21:31:00 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  1 21:23:45 2008
Subject: [Haskell-cafe] Ghc / cgi static linking
In-Reply-To: <12F6690C-C370-4C25-B080-ADC3975318EC@gmail.com>
References: <ddacd4a70806011518v2b65d010r56e60ca9bf0a530c@mail.gmail.com>
	<20080601222600.GE4759@scytale.galois.com>
	<12F6690C-C370-4C25-B080-ADC3975318EC@gmail.com>
Message-ID: <20080602013100.GJ4759@scytale.galois.com>

peteg42:
> On 02/06/2008, at 5:26 AM, Don Stewart wrote:
> 
> >pieter:
> >Yes, it is entirely possible to statically link entire CGI apps.
> 
> You might want to watch out for a bug in GHC 6.8.2 that means GHC's "- 
> static" flag doesn't work. (At least for me, at least on Debian: the "- 
> lpthread" flag is passed before the "-lrt" one, and symbols are left  
> unresolved as a result.) Apparently the near-to-release 6.8.3 will fix  
> this issue.
> 
> Presumably dons is using a more recent GHC than 6.8.2, or other (BSD?)  
> platforms are not affected.

Yeah, that's the case.
  
> Note also you may have to tweak sundry .cabal files to add "extra- 
> libraries" fields. As an example, I added this to HSQL's PostgreSQL  
> backend to get it to statically link:
> 
> extra-libraries: pq, crypt, pthread
> 
> (If anyone cares you need to build PostgreSQL without kerberos as that  
> doesn't seem to statically link any more.)
> 

Hey Pete,

Can you add these caveats to the wiki page?

    haskell.org/haskellwiki/Practical_web_programming_in_Haskell#Deploying_statically_linked_applications
From donn at avvanta.com  Sun Jun  1 22:08:38 2008
From: donn at avvanta.com (Donn Cave)
Date: Sun Jun  1 22:00:44 2008
Subject: [Haskell-cafe] haskell compiler on NetBSD amd64
In-Reply-To: <20080510093512.GA27361@matstaff04.nuigalway.ie>
References: <20080509222119.cfe30daa.donn@avvanta.com>
	<20080510093512.GA27361@matstaff04.nuigalway.ie>
Message-ID: <20080601190838.61e222e3.donn@avvanta.com>

On Sat, 10 May 2008 10:35:12 +0100
Emil Skoeldberg <emil.skoldberg@nuigalway.ie> wrote:

> On Fri, May 09, 2008 at 10:21:19PM -0700, Donn Cave wrote:
> > So here I am with 64 bit Athlon hardware, running amd64
> > NetBSD (a.k.a. x86_64), reasonably motivated to compile
> > Haskell.
> 
> So, we are in the same boat then!

OK, for you and me and probably no one else in the world, I have
built 6.8.2, and for a short time I have it on-line - at my ISP's
site, http://www.avvanta.com/~donn/   ... append file name, which
is ghc-6.8.2-netbsd-amd64.tar.bz2   Size is ca. 54 Mb.

When you want to use this to build future ghc releases, you'll
probably have to modify libbfd.so to get GNU ar to index one
or two of the larger libraries.  I believe the release itself
will work fine without this mod - ld uses the same library, but
I think only ar has the problem.

That cost me a lot of time.  The other thing that cost me some
time was the gmp dist in ghc-6.6.1, which didn't fully configure
for the platform.  The rest was reasonably straightforward.
I built 6.6.1 .hc files on OpenBSD.

-- 
Donn Cave <donn@avvanta.com>
From dons at galois.com  Sun Jun  1 22:34:10 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  1 22:27:22 2008
Subject: [Haskell-cafe] haskell compiler on NetBSD amd64
In-Reply-To: <20080601190838.61e222e3.donn@avvanta.com>
References: <20080509222119.cfe30daa.donn@avvanta.com>
	<20080510093512.GA27361@matstaff04.nuigalway.ie>
	<20080601190838.61e222e3.donn@avvanta.com>
Message-ID: <20080602023410.GK4759@scytale.galois.com>

donn:
> On Sat, 10 May 2008 10:35:12 +0100
> Emil Skoeldberg <emil.skoldberg@nuigalway.ie> wrote:
> 
> > On Fri, May 09, 2008 at 10:21:19PM -0700, Donn Cave wrote:
> > > So here I am with 64 bit Athlon hardware, running amd64
> > > NetBSD (a.k.a. x86_64), reasonably motivated to compile
> > > Haskell.
> > 
> > So, we are in the same boat then!
> 
> OK, for you and me and probably no one else in the world, I have
> built 6.8.2, and for a short time I have it on-line - at my ISP's
> site, http://www.avvanta.com/~donn/   ... append file name, which
> is ghc-6.8.2-netbsd-amd64.tar.bz2   Size is ca. 54 Mb.
> 
> When you want to use this to build future ghc releases, you'll
> probably have to modify libbfd.so to get GNU ar to index one
> or two of the larger libraries.  I believe the release itself
> will work fine without this mod - ld uses the same library, but
> I think only ar has the problem.
> 
> That cost me a lot of time.  The other thing that cost me some
> time was the gmp dist in ghc-6.6.1, which didn't fully configure
> for the platform.  The rest was reasonably straightforward.
> I built 6.6.1 .hc files on OpenBSD.

Great work, let's get it up on the download page,

    http://haskell.org/ghc/download_ghc_682.html

-- Don
From donn at avvanta.com  Sun Jun  1 23:50:12 2008
From: donn at avvanta.com (Donn Cave)
Date: Sun Jun  1 23:42:18 2008
Subject: [Haskell-cafe] haskell compiler on NetBSD amd64
In-Reply-To: <20080602023410.GK4759@scytale.galois.com>
References: <20080509222119.cfe30daa.donn@avvanta.com>
	<20080510093512.GA27361@matstaff04.nuigalway.ie>
	<20080601190838.61e222e3.donn@avvanta.com>
	<20080602023410.GK4759@scytale.galois.com>
Message-ID: <20080601205012.6973f74a.donn@avvanta.com>

On Sun, 1 Jun 2008 19:34:10 -0700
Don Stewart <dons@galois.com> wrote:

> Great work, let's get it up on the download page,
> 
>     http://haskell.org/ghc/download_ghc_682.html
>

Suits me, but now that I've had a chance to compile a little
more Haskell with it, I think I might like to fix up a couple
things.  I'm not promising to make ghci work, though that would
be nice, but mainly I'm talking about linker warnings attached
to a couple of "compatibility" functions that got linked in
when the more POSIX compliant versions would have been found
if e.g. stdlib.h had been included.  opendir(), unsetenv(), etc.
So if that's agreeable, don't take the file I put on-line, I'll
build up another one.

thanks

-- 
Donn Cave <donn@avvanta.com>
From thomas.dubuisson at gmail.com  Mon Jun  2 00:19:24 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Mon Jun  2 00:07:35 2008
Subject: [Haskell-cafe] [ANN] Bindings to Xen Control (xenctrl.h)
In-Reply-To: <20080601063140.GA1200@scytale.galois.com>
References: <1212300682.2448.14.camel@Clunker>
	<20080601063140.GA1200@scytale.galois.com>
Message-ID: <1212380364.2448.39.camel@Clunker>

Don,
I'll throw future work ideas in the next releases cabal.  The most
obvious doors opened are Haskell rewrites of the current Xen
infrastructure (virt-install, xm, xend).  Slightly more interesting
tasks could be (warning: random thoughts):

1) HAPPS server that can manage Xen domains (without requiring python
libs or System.cmd)
2) Network or BSD socket based remote management programs in Haskell.
haxr or session-types might be of use here.
3) With the functions that can alter the CPUs availability, more complex
rules or sharing arrangements could be implemented.  Same concept
applies to other resources such as PCI and memory allocation.  Seeing as
Xen doesn't over-commit memory, a guest VM program that detects low/high
memory situations and reports to the host for policy controlled
balloning (adjustment of VM allocated memory) would be kind of fun...
but probably complete overkill for any user of Xen.

Right now I think the bindings are enough for an 'xm' replacement but
nothing more.  I've over doubled the number of functions bound just now.
There will probably be regular releases for the next few weeks as I find
time.

Thomas

On Sat, 2008-05-31 at 23:31 -0700, Don Stewart wrote: 
> thomas.dubuisson:
> > All,
> > I'm just getting started with hsXenCtrl [1] as both a fun way to play
> > with Xen and become proficient with Haskell FFI.  Once I get my
> > community.haskell.org account squared away I'll likely setup a public
> > darcs repo (and a homepage somewhere).
> > 
> > As for modules: I intend to expand on the trival FFI bindings in
> > System.Xen.CBindings and there'll be a higher level interface in
> > System.Xen (functions will standardize on returning Either or throwing
> > exceptions, hiding the xc_handle open/close, etc).
> > 
> > Typical Disclaimers:
> > The _only_ thing I've actually done with this, just tonight, is pause /
> > unpause domains.  API is subject to change!  Only my exact build of Xen
> > is sure to work, and no promise even then.
> > 
> > TomMD
> > 
> > [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl
> 
> Good stuff. Perhaps the synopsis should include a link or description of
> the typical use cases/ thinks we might achieve?
> 
> -- Don

From abhay.parvate at gmail.com  Mon Jun  2 01:04:07 2008
From: abhay.parvate at gmail.com (Abhay Parvate)
Date: Mon Jun  2 00:56:51 2008
Subject: [Haskell-cafe] Re: appending an element to a list
In-Reply-To: <g1tjk4$c4i$1@ger.gmane.org>
References: <483EE208.2010601@inf.fu-berlin.de> <483EF36B.5040100@daimi.au.dk>
	<48404039.6030605@cisco.com> <48405717.20206@daimi.au.dk>
	<87r6bja609.fsf@hbox.dyndns.org>
	<3c4d5adf0805302159o23113ad2sb24754e02789bb06@mail.gmail.com>
	<48414C2B.9010606@daimi.au.dk> <g1tjk4$c4i$1@ger.gmane.org>
Message-ID: <3c4d5adf0806012204p25133bdaxbc22955b70f094ff@mail.gmail.com>

I somehow thought it would be easy to talk about complexity of calculating
individual elements in an infinite list should be sufficient, but that seems
to be involved, and my over-generalization doesn't seem to work. Thanks for
the link; particularly it has reference to Wadler's papers exactly on this
problem.

Abhay

On Sun, Jun 1, 2008 at 1:07 PM, apfelmus <apfelmus@quantentunnel.de> wrote:

> Tillmann Rendel wrote:
>
>> Abhay Parvate wrote:
>>
>>> I think I would like to make another note: when we talk about the
>>> complexity
>>> of a function, we are talking about the time taken to completely evaluate
>>> the result. Otherwise any expression in haskell will be O(1), since it
>>> just creates a thunk.
>>>
>>
>> I don't like this notion of complexity, since it seems not very suited for
>> the analysis of composite expression in Haskell.
>>
>> Is this intuitive view generalizable to arbitrary datatypes (instead of
>> lists) and formalized somewhere?
>>
>
> See also the thread section beginning with
>
>  http://thread.gmane.org/gmane.comp.lang.haskell.cafe/34398/focus=34435
>
>
>
> Regards,
> apfelmus
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
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From vigalchin at gmail.com  Mon Jun  2 01:07:11 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun  2 00:59:54 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
Message-ID: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>

Hello,

      I have been developing new code for the "unix" package. I have run
into what I think are ghc 6.8.2 anomalies but couldn't see a pattern.
Possibly now I do. I have been using the 32-bit x86 ghc binary that I
downloaded from http://www.haskell.org and running on Ubuntu Linux. I am
pretty I can repeat now. Everything is ok until I do "sudo runhaskell
Setup.hs install" which installs a new "unix" package that I just built. Of
course the "intall" installs into /usr/local/lib/unix-2.3.0.0/ghc-6.8.2. The
"install" seems to destroy some ghc compiler state under /usr/local ... This
is of course just a theory. However, once I re-install ghc et. al. from the
binary download then things are ok again. I have tried the ghc re-install at
least 4 times. Hope I am not misleading anybody .. just trying to help!

Kind regards, Vasili
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From yann at kierun.org  Mon Jun  2 03:48:21 2008
From: yann at kierun.org (Yann Golanski)
Date: Mon Jun  2 03:41:08 2008
Subject: [Haskell-cafe] Re: Images and GUIs in Haskell
In-Reply-To: <20080601040910.545853dc@solaris>
References: <62728db30805311530x6c28431fwf2615a18fac343cb@mail.gmail.com>
	<20080601014052.5658743f@solaris>
	<62728db30805311800s472cc708rf50bd77a70c65eb3@mail.gmail.com>
	<20080601040910.545853dc@solaris>
Message-ID: <20080602074821.GC1271@kierun.org>

Quoth Achim Schneider on Sun, Jun 01, 2008 at 04:09:10 +0200
> I would go for GL(U(T)), as it's as good for 2d primitives as SDL will
> ever be, has excellent cross-platform support and allows you to go 3d
> if you want to. There's also some very decent event handling.

You can use R as well. http://www.r-project.org/

-- 
yann@kierun.org             -= H+ =-             www.kierun.org
   PGP:   009D 7287 C4A7 FD4F 1680  06E4 F751 7006 9DE2 6318
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From jules at jellybean.co.uk  Mon Jun  2 05:10:16 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Mon Jun  2 05:02:59 2008
Subject: [Haskell-cafe] GHCi panic
In-Reply-To: <48406AC1.4090003@btinternet.com>
References: <48406AC1.4090003@btinternet.com>
Message-ID: <4843B8F8.9070309@jellybean.co.uk>

Andrew Coppin wrote:
> I don't suppose this will surprise anybody greatly, but...
> 
> Apparently if you write a Haskell module that is 400 KB in size and 
> defines a single CAF consisting of a 45,000-element [String], GHCi 
> panics when attempting to load it interpretted, and hits a stack 
> overflow attempting to load it compiled.

qv http://hackage.haskell.org/trac/ghc/ticket/2002
From aruiz at um.es  Mon Jun  2 05:37:14 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Mon Jun  2 05:29:57 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>	
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
Message-ID: <4843BF4A.2080800@um.es>

Anatoly Yakovenko wrote:
> do you have any plans to provide an interface for inplace updates?

Yes, I will try to write a simple version of Data.Array.ST...

> On Sun, Jun 1, 2008 at 3:20 AM, Alberto Ruiz <aruiz@um.es> wrote:
>> Anatoly Yakovenko wrote:
>>> What is the most efficient way to update a position in a matrix or a
>>> vector?  I came up with this:
>>>
>>> updateVector :: Vector Double -> Int -> Double -> Vector Double
>>> updateVector vec pos val = vec `add` v2
>>>   where
>>>      v2 = fromList $ (replicate (pos) 0.0) ++ ((val - (vec @>
>>> pos)):(replicate ((dim vec)- pos - 1) 0.0))
>>>
>>> but this seems pretty inefficient to me.
>>>
>>> thanks,
>>> Anatoly
>>>
>> It is probably more efficient to use subVector and join (implemented by
>> copyArray):
>>
>> updateVector' v pos val
>>    | pos == 0        = join [b,c]
>>    | pos == dim v -1 = join [a,b]
>>    | otherwise       = join [a,b,c]
>>    where a = subVector 0 pos v
>>          b = fromList [val]
>>          c = subVector (pos+1) (dim v -pos-1) v
>>
>>> updateVector' (fromList [1,2,3,4,5]) 2 57
>> 5 |> [1.0,2.0,57.0,4.0,5.0]
>>
>> (The three cases are required because empty vectors are not currently
>> allowed.)
>>
>> Something similar can be done for matrices using flatten and reshape.
>>
>> Although vectors and matrices in this library are immutable and intended to
>> be manipulated as a whole by higher level functions, this kind of update
>> functions may often be useful. I will include them soon.
>>
>> Alberto
>>
> 
From duncan.coutts at worc.ox.ac.uk  Mon Jun  2 06:38:20 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Mon Jun  2 06:28:00 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
Message-ID: <1212403100.15010.133.camel@localhost>


On Mon, 2008-06-02 at 00:07 -0500, Galchin, Vasili wrote:
> Hello,
> 
>       I have been developing new code for the "unix" package. I have
> run into what I think are ghc 6.8.2 anomalies but couldn't see a
> pattern. Possibly now I do. I have been using the 32-bit x86 ghc
> binary that I downloaded from http://www.haskell.org and running on
> Ubuntu Linux. I am pretty I can repeat now. Everything is ok until I
> do "sudo runhaskell Setup.hs install" which installs a new "unix"
> package that I just built. Of course the "intall" installs
> into /usr/local/lib/unix-2.3.0.0/ghc-6.8.2. The "install" seems to
> destroy some ghc compiler state under /usr/local ...

That sounds right. You're replacing the unix-2.3.0.0 library that comes
with ghc-6.8.2 with your own version. It is highly unlikely to be ABI
compatible with the one you are replacing and so all the other packages
that already depends on the existing unix-2.3.0.0 library end up broken.
You'd expect this kind of breakage to be exposed as link errors and
segfaults.

I suggest you do not replace any of the libraries that come with ghc. To
be more precise, it is perfectly ok to *add new versions* but it is not
ok to *replace existing versions* without rebuilding all the other libs
that depend on it.

Make sense?

So if you really want to make changes to the unix lib, make sure you
change the version number too. I also suggest not installing the
packages as root, just install them locally. That way you can guarantee
you never mess up your ghc install. You would be able to revert to a
clean ghc install just by removing your
~/.ghc/$arch/ghc-6.8.2/package.conf file which will unregister *all*
locally registered packages. To unregister individual packages use
ghc-pkg --user unregister $pkgname

Duncan

From nominolo at googlemail.com  Mon Jun  2 06:42:15 2008
From: nominolo at googlemail.com (Thomas Schilling)
Date: Mon Jun  2 06:35:12 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
Message-ID: <8D4BA8BD-D3A2-4B56-B18E-FD6EA7A81D45@googlemail.com>


On 1 jun 2008, at 20.44, Bertram Felgenhauer wrote:

> Hi,
>
> I'm pleased to announce yet another tool for importing darcs  
> repositories
> to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in
> Haskell, on top of the darcs2 source code. The result is a much faster
> program - it can convert the complete ghc 6.9 branch (without  
> libraries)
> in less than 15 minutes on my slightly dated machine (Athlon XP 2500 
> +),
> which is quite fast [3]. Incremental updates work, too.
>
Nice!  Do you happen to also have a darcs (or Git) repository somewhere?

/ Thomas
--
Monkey killing monkey killing monkey over pieces of the ground.
Silly monkeys give them thumbs they forge a blade
And where there's one they're bound to divide it
Right in two

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From bertram.felgenhauer at googlemail.com  Mon Jun  2 08:05:03 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Mon Jun  2 07:57:51 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <8D4BA8BD-D3A2-4B56-B18E-FD6EA7A81D45@googlemail.com>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<8D4BA8BD-D3A2-4B56-B18E-FD6EA7A81D45@googlemail.com>
Message-ID: <20080602120503.GB4258@zombie.inf.tu-dresden.de>

Thomas Schilling wrote:
>
> On 1 jun 2008, at 20.44, Bertram Felgenhauer wrote:
[git-darcs-import]
>
> Nice!  Do you happen to also have a darcs (or Git) repository somewhere?

I've uploaded my (git) repo to repo.or.cz, see
    http://repo.or.cz/w/git-darcs-import.git

Patches are welcome.

enjoy,

Bertram
From devriese at cs.tcd.ie  Mon Jun  2 09:05:11 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Mon Jun  2 08:57:56 2008
Subject: [Haskell-cafe] hs-plugins compile error
Message-ID: <20080602130511.GA24905@netsoc.tcd.ie>

Hi,

I'm getting the compilation error that is actually logged on Hackage:

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/plugins

Below is a small diff file that resolves these problems; I don't know
what the proper protocol is for submitting these diffs but it may be
useful to someone.

- E 

diff -ur plugins-1.2-orig/src/System/Plugins/Env.hs plugins-1.2/src/System/Plugins/Env.hs
--- plugins-1.2-orig/src/System/Plugins/Env.hs	2008-06-02 14:57:59.000000000 +0100
+++ plugins-1.2/src/System/Plugins/Env.hs	2008-06-02 15:00:25.000000000 +0100
@@ -73,7 +73,7 @@
 
 import Control.Concurrent.MVar  ( MVar(), newMVar, withMVar )
 
-import Distribution.Package
+import Distribution.Package hiding (packageName)
 import Text.ParserCombinators.ReadP
 
 import qualified Data.Map as M
diff -ur plugins-1.2-orig/src/System/Plugins/PackageAPI.hs plugins-1.2/src/System/Plugins/PackageAPI.hs
--- plugins-1.2-orig/src/System/Plugins/PackageAPI.hs	2008-06-02 14:57:59.000000000 +0100
+++ plugins-1.2/src/System/Plugins/PackageAPI.hs	2008-06-02 14:59:49.000000000 +0100
@@ -40,7 +40,7 @@
 
 #if CABAL == 1 || __GLASGOW_HASKELL__ >= 604
 import Distribution.InstalledPackageInfo
-import Distribution.Package
+import Distribution.Package hiding (depends, packageName)
 #else
 import System.Plugins.Package
 #endif
diff -ur plugins-1.2-orig/src/System/Plugins/ParsePkgConfCabal.hs plugins-1.2/src/System/Plugins/ParsePkgConfCabal.hs
--- plugins-1.2-orig/src/System/Plugins/ParsePkgConfCabal.hs	2008-06-02 14:57:59.000000000 +0100
+++ plugins-1.2/src/System/Plugins/ParsePkgConfCabal.hs	2008-06-02 14:58:56.000000000 +0100
@@ -6,7 +6,7 @@
   ) where
 
 import Distribution.InstalledPackageInfo
-import Distribution.Package
+import Distribution.Package hiding (depends)
 import Distribution.Version
 
 import Data.Char             ( isSpace, isAlpha, isAlphaNum, isUpper, isDigit )

From richardg at richardg.name  Mon Jun  2 09:39:39 2008
From: richardg at richardg.name (Richard Giraud)
Date: Mon Jun  2 09:32:24 2008
Subject: [Haskell-cafe] Mutually Recursive Modules
Message-ID: <4843F81B.7060808@richardg.name>

Hello

I'm using GHC 6.8.2 with mutally recursive modules.  I'm familiar with 
how to do simple cases in GHC ({-# SOURCE #-} and .hs-boot files) but I 
can't figure out how to get it to work for a particular set of modules.

Is it known (i.e., proven) that GHC 6.8.2 can compile any set of 
mutually recursive modules without refactoring?  Are there known 
limitations?

Thanks,

Richard G.
From isaacdupree at charter.net  Mon Jun  2 09:55:25 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Mon Jun  2 09:48:05 2008
Subject: [Haskell-cafe] Mutually Recursive Modules
In-Reply-To: <4843F81B.7060808@richardg.name>
References: <4843F81B.7060808@richardg.name>
Message-ID: <4843FBCD.8000001@charter.net>

Richard Giraud wrote:
> Hello
> 
> I'm using GHC 6.8.2 with mutally recursive modules.  I'm familiar with 
> how to do simple cases in GHC ({-# SOURCE #-} and .hs-boot files) but I 
> can't figure out how to get it to work for a particular set of modules.
> 
> Is it known (i.e., proven) that GHC 6.8.2 can compile any set of 
> mutually recursive modules without refactoring?  Are there known 
> limitations?

With the old (6.2 and before) .hi-boot scheme where there was no 
abstraction in boot-files, it could probably do anything that it could 
do.  But I'm not convinced with .hs-boot... it can resolve one level of 
cycle, and I don't know how to *prove* that it *can't* do any given 
thing, but I strongly suspect there are things it can't do.  Luckily, it 
is very often the case that your code will be better off anyway if 
refactored to have less module recursion. (though not always.)

-Isaac
From g9ks157k at acme.softbase.org  Mon Jun  2 10:08:38 2008
From: g9ks157k at acme.softbase.org (Wolfgang Jeltsch)
Date: Mon Jun  2 10:01:32 2008
Subject: [Haskell-cafe] Re: Damnit, we need a CPAN.
In-Reply-To: <20080530220930.6dff9dfa@solaris>
References: <20080529173830.3aae4434@solaris>
	<200805301834.16537.g9ks157k@acme.softbase.org>
	<20080530220930.6dff9dfa@solaris>
Message-ID: <200806021608.39009.g9ks157k@acme.softbase.org>

Am Freitag, 30. Mai 2008 22:09 schrieb Achim Schneider:
> [?]

> I'm generally very interested in declarative GUI programming, but not
> nearly enough acquainted with the whole topic to judge one project's
> approach over the other. I just followed standard scientific evaluation
> technique to select the projects to consider: The ones with the most and
> most recent activity win.
>
> So far, my impression is that documentation is severely lacking, but
> then I'm too busy watching Babylon 5 right now and did not get more
> than half an hour or so looking at grapefruit.

Okay, I think we?ll improve API documentation and then make a release, despite 
Grapefruit not being production quality yet.  I hope, you?ll find it 
useful. :-) 

Best wishes,
Wolfgang
From aditya_siram at hotmail.com  Mon Jun  2 10:37:11 2008
From: aditya_siram at hotmail.com (Aditya Siram)
Date: Mon Jun  2 10:29:57 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
Message-ID: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>


I am building a web-app that, in broad strokes, allows a leader to assign tasks to team members and allows team members to accept/reject/pick tasks that they want to do. 

I really like Haskell and I would like to use it to implement the solution. Are frameworks like Happs ready? Not so much in terms of documentation, but in functionality and stability. 

-Deech
_________________________________________________________________
Give to a good cause with every e-mail. Join the i?m Initiative from Microsoft.
http://im.live.com/Messenger/IM/Join/Default.aspx?souce=EML_WL_ GoodCause
From isaacdupree at charter.net  Mon Jun  2 10:45:31 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Mon Jun  2 10:38:12 2008
Subject: [Haskell-cafe] Default definitions for associated type synonyms
In-Reply-To: <52f14b210805300710k366731d6w340231d6eef3ef19@mail.gmail.com>
References: <52f14b210805300710k366731d6w340231d6eef3ef19@mail.gmail.com>
Message-ID: <4844078B.1010201@charter.net>

Dreixel wrote:
> Hello,
> 
> Does anyone know if it is possible to specify a default definition for an
> associated type synonym? When I tried:
> 
> class A a where
>>   type B a = a
>>
> 
> GHC (version 6.9.20080309) told me: "Type declaration in a class must be a
> kind signature or synonym default". However, when I look at the parser I see
> no way to specify such synonym default. Is this possible?

I'm curious... so, cc'ing glasgow-haskell-users mailinglist because the 
question is more likely to be noticed by relevant people there.

> Thanks,
> Z? Pedro
From stefan at cs.uu.nl  Mon Jun  2 10:50:00 2008
From: stefan at cs.uu.nl (Stefan Holdermans)
Date: Mon Jun  2 10:42:48 2008
Subject: [Haskell-cafe] Default definitions for associated type synonyms
In-Reply-To: <4844078B.1010201@charter.net>
References: <52f14b210805300710k366731d6w340231d6eef3ef19@mail.gmail.com>
	<4844078B.1010201@charter.net>
Message-ID: <9AAEC7D1-A1C3-4124-B2B0-E1F9F3E4675D@cs.uu.nl>

Isaac,

>> Does anyone know if it is possible to specify a default definition  
>> for an
>> associated type synonym?


According to http://hackage.haskell.org/trac/ghc/wiki/TypeFunctionsStatus 
  defaults for associated types is still a TODO.

Cheers,

   Stefan
From daniel at dbpatterson.com  Mon Jun  2 10:57:04 2008
From: daniel at dbpatterson.com (Daniel Patterson)
Date: Mon Jun  2 10:47:10 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
Message-ID: <20080602105704.1e4dc5ed@patagonia.local>

You definitely could use HAppS for that, but considering that it sounds like a
pretty small/lightweight app, you might want to check out hvac
( http://fmapfixreturn.wordpress.com/2008/03/23/ ), which is a newer (but
still surprisingly full-featured) web framework. It is pretty
lightweight, and might be easier to get working for your purposes.

Daniel

On Mon, 2 Jun 2008 09:37:11 -0500
Aditya Siram <aditya_siram@hotmail.com> wrote:

> 
> I am building a web-app that, in broad strokes, allows a leader to assign
> tasks to team members and allows team members to accept/reject/pick tasks
> that they want to do. 
> 
> I really like Haskell and I would like to use it to implement the solution.
> Are frameworks like Happs ready? Not so much in terms of documentation, but
> in functionality and stability. 
> 
> -Deech
> _________________________________________________________________
> Give to a good cause with every e-mail. Join the i?m Initiative from
> Microsoft. http://im.live.com/Messenger/IM/Join/Default.aspx?souce=EML_WL_
> GoodCause_______________________________________________ Haskell-Cafe mailing
> list Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From marco-oweber at gmx.de  Mon Jun  2 11:16:36 2008
From: marco-oweber at gmx.de (Marc Weber)
Date: Mon Jun  2 11:09:20 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
Message-ID: <20080602151636.GA20757@gmx.de>

On Mon, Jun 02, 2008 at 09:37:11AM -0500, Aditya Siram wrote:
> 
> I am building a web-app that, in broad strokes, allows a leader to assign tasks to team members and allows team members to accept/reject/pick tasks that they want to do. 
> 
> I really like Haskell and I would like to use it to implement the solution. Are frameworks like Happs ready? Not so much in terms of documentation, but in functionality and stability. 
Me too, but in this case if it's only about assigning tasks you should
consider using existing solutions such as flysrpay or mantis http://www.mantisbt.org/
Maybe they fit your needs ?

mit freundlichem Gruss
Marc Weber
From nominolo at googlemail.com  Mon Jun  2 12:13:33 2008
From: nominolo at googlemail.com (Thomas Schilling)
Date: Mon Jun  2 12:06:27 2008
Subject: [Haskell-cafe] Damnit, we need a CPAN.
In-Reply-To: <20080529161307.GA17931@scytale.galois.com>
References: <20080529173830.3aae4434@solaris>
	<404396ef0805290847w41cb7635ud6f655a9c096f28e@mail.gmail.com>
	<20080529110555.3d08fcb6@Eridanus.javasnob.homelinux.net>
	<20080529161307.GA17931@scytale.galois.com>
Message-ID: <E3E18D96-B25B-4287-885F-8D3CCCD1F757@googlemail.com>


On 29 maj 2008, at 18.13, Don Stewart wrote:

>> Hackage and Cabal are nice, but a command line tool for automatically
>> searching Hackage and installing Hackage packages (like the cpan
>> program, or easy_install) would be nice.  Unless I haven't done my
>> homework and this tool exists...
>>
>
> This tool exists. It is called 'cabal-install'. To try out one of
> today's new packages:
>
>     $ cabal update
>     $ cabal install category-extras
>


Another nice feature:  Say you want to hack on the darcs version of a  
project, but you need to install the dependencies.  If the project is  
Cabalised you can build and install the darcs version as well as all  
dependencies by calling 'cabal install' with no arguments inside the  
project directory.

   $ darcs get <project>
   $ cd <project>
   $ cabal install

/ Thomas
--
Push the envelope.  Watch it bend.



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From tphyahoo at gmail.com  Mon Jun  2 12:42:08 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Mon Jun  2 12:34:51 2008
Subject: [Haskell-cafe] cabal install fail for happs-hsp-template
Message-ID: <910ddf450806020942n4bc2fac8kc454aeda446b77ee@mail.gmail.com>

Can cabal install be made to work for this package?
*****
thartman@thartman-laptop:~>sudo cabal install happs-hsp-template
[sudo] password for thartman:
cabal: internal error: could not construct a valid install plan.
The proposed (invalid) plan contained the following problems:
Package Cabal is required by several packages, but they require
inconsistent versions:
  package ghc-6.8.2 requires Cabal-1.2.3.0
  package plugins-1.2 requires Cabal-1.5.2


thartman@thartman-laptop:~>cabal --version
cabal-install version 0.4.7
using version 1.3.11 of the Cabal library
thartman@thartman-laptop:~>ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.8.2
thartman@thartman-laptop:~>ghc-pkg list | grep -i ghc
/usr/local/lib/ghc-6.8.2/package.conf:
    (ghc-6.8.2), haskell-src-1.0.1.1, haskell98-1.0.1.0, hpc-0.5.0.0,
From tphyahoo at gmail.com  Mon Jun  2 12:59:24 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Mon Jun  2 12:52:06 2008
Subject: [Haskell-cafe] Re: cabal install fail for happs-hsp-template
In-Reply-To: <910ddf450806020942n4bc2fac8kc454aeda446b77ee@mail.gmail.com>
References: <910ddf450806020942n4bc2fac8kc454aeda446b77ee@mail.gmail.com>
Message-ID: <910ddf450806020959i368abde0ud1080acc23734a0b@mail.gmail.com>

I just noticed this is also reported as a 6.8 build failure on hackage itself.

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-hsp-template

2008/6/2 Thomas Hartman <tphyahoo@gmail.com>:
> Can cabal install be made to work for this package?
> *****
> thartman@thartman-laptop:~>sudo cabal install happs-hsp-template
> [sudo] password for thartman:
> cabal: internal error: could not construct a valid install plan.
> The proposed (invalid) plan contained the following problems:
> Package Cabal is required by several packages, but they require
> inconsistent versions:
>  package ghc-6.8.2 requires Cabal-1.2.3.0
>  package plugins-1.2 requires Cabal-1.5.2
>
>
> thartman@thartman-laptop:~>cabal --version
> cabal-install version 0.4.7
> using version 1.3.11 of the Cabal library
> thartman@thartman-laptop:~>ghc --version
> The Glorious Glasgow Haskell Compilation System, version 6.8.2
> thartman@thartman-laptop:~>ghc-pkg list | grep -i ghc
> /usr/local/lib/ghc-6.8.2/package.conf:
>    (ghc-6.8.2), haskell-src-1.0.1.1, haskell98-1.0.1.0, hpc-0.5.0.0,
>
From aeyakovenko at gmail.com  Mon Jun  2 13:06:40 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Mon Jun  2 12:59:21 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <4843BF4A.2080800@um.es>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
Message-ID: <e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>

>> do you have any plans to provide an interface for inplace updates?
>
> Yes, I will try to write a simple version of Data.Array.ST...
>

I can try to help you, although I still dont quite grok monads.
Wouldn't it be more efficient to use StorableArray, so you can cast
from and to C?  I am not sure how vectors and matrixes are represented
in C, but I imagine it should be possible to manipulate them without
resorting to copying between haskell and C.
From dons at galois.com  Mon Jun  2 13:21:31 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun  2 13:14:14 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
Message-ID: <20080602172131.GA7534@scytale.galois.com>

aditya_siram:
> 
> I am building a web-app that, in broad strokes, allows a leader to
> assign tasks to team members and allows team members to
> accept/reject/pick tasks that they want to do. 
> 
> I really like Haskell and I would like to use it to implement the
> solution. Are frameworks like Happs ready? Not so much in terms of
> documentation, but in functionality and stability. 

HAppS is nice (see hpaste.org for example, which is nice and simple, and
has been running for over a year).

Another nice option in Haskell is using something like HStringTemplate
or the xhtml combinators  with fastcgi hooked into GHC's concurrency
mechanisms.

You can find *many* more things here,

    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Network
    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Web
From bulat.ziganshin at gmail.com  Mon Jun  2 13:21:34 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Mon Jun  2 13:16:45 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
Message-ID: <814976210.20080602212134@gmail.com>

Hello Anatoly,

>> Yes, I will try to write a simple version of Data.Array.ST...
> Wouldn't it be more efficient to use StorableArray, so you can cast

there is some difference between them - MutableByteArray# (used for
STUArray) is movable Haskell object which is subject to GC while
StorableArray has a fixed address and allocated through C malloc().
this makes MBA more appropriate for small arrays while SA should be
used for large ones because GC makes memory usage of program 3 times
larger


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From dons at galois.com  Mon Jun  2 13:24:01 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun  2 13:16:50 2008
Subject: [Haskell-cafe] hs-plugins compile error
In-Reply-To: <20080602130511.GA24905@netsoc.tcd.ie>
References: <20080602130511.GA24905@netsoc.tcd.ie>
Message-ID: <20080602172401.GB7534@scytale.galois.com>

Thanks, 

if possible, could you construct this as a patch against the darcs
branch, which lives here:

    http://code.haskell.org/~dons/code/hs-plugins

Cheers,
  Don

devriese:
> Hi,
> 
> I'm getting the compilation error that is actually logged on Hackage:
> 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/plugins
> 
> Below is a small diff file that resolves these problems; I don't know
> what the proper protocol is for submitting these diffs but it may be
> useful to someone.
> 
> - E 
> 
> diff -ur plugins-1.2-orig/src/System/Plugins/Env.hs plugins-1.2/src/System/Plugins/Env.hs
> --- plugins-1.2-orig/src/System/Plugins/Env.hs	2008-06-02 14:57:59.000000000 +0100
> +++ plugins-1.2/src/System/Plugins/Env.hs	2008-06-02 15:00:25.000000000 +0100
> @@ -73,7 +73,7 @@
>  
>  import Control.Concurrent.MVar  ( MVar(), newMVar, withMVar )
>  
> -import Distribution.Package
> +import Distribution.Package hiding (packageName)
>  import Text.ParserCombinators.ReadP
>  
>  import qualified Data.Map as M
> diff -ur plugins-1.2-orig/src/System/Plugins/PackageAPI.hs plugins-1.2/src/System/Plugins/PackageAPI.hs
> --- plugins-1.2-orig/src/System/Plugins/PackageAPI.hs	2008-06-02 14:57:59.000000000 +0100
> +++ plugins-1.2/src/System/Plugins/PackageAPI.hs	2008-06-02 14:59:49.000000000 +0100
> @@ -40,7 +40,7 @@
>  
>  #if CABAL == 1 || __GLASGOW_HASKELL__ >= 604
>  import Distribution.InstalledPackageInfo
> -import Distribution.Package
> +import Distribution.Package hiding (depends, packageName)
>  #else
>  import System.Plugins.Package
>  #endif
> diff -ur plugins-1.2-orig/src/System/Plugins/ParsePkgConfCabal.hs plugins-1.2/src/System/Plugins/ParsePkgConfCabal.hs
> --- plugins-1.2-orig/src/System/Plugins/ParsePkgConfCabal.hs	2008-06-02 14:57:59.000000000 +0100
> +++ plugins-1.2/src/System/Plugins/ParsePkgConfCabal.hs	2008-06-02 14:58:56.000000000 +0100
> @@ -6,7 +6,7 @@
>    ) where
>  
>  import Distribution.InstalledPackageInfo
> -import Distribution.Package
> +import Distribution.Package hiding (depends)
>  import Distribution.Version
>  
>  import Data.Char             ( isSpace, isAlpha, isAlphaNum, isUpper, isDigit )
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From ben.franksen at online.de  Mon Jun  2 14:40:14 2008
From: ben.franksen at online.de (Ben Franksen)
Date: Mon Jun  2 14:33:09 2008
Subject: [Haskell-cafe] Re: modelling C in Haskell ..
References: <5ae4f2ba0805292346y217d799du8a3e097a1e004e7a@mail.gmail.com>
	<B38D65AC-A9E6-4C12-B9D3-A2285477BBEE@fastmail.fm>
	<5ae4f2ba0805300029s69b1a1fdn73e07fe17b458b10@mail.gmail.com>
	<F77D2BD2-3BF5-48FA-8B51-723305860036@fastmail.fm>
	<5ae4f2ba0806010100j3788d29bj4aa0f5f4e3a8c5a8@mail.gmail.com>
Message-ID: <g21eqe$aig$1@ger.gmane.org>

Galchin, Vasili wrote:
> my knowledge of point-free is from category theory. in what sense is
> Haskell point-free handle namespace pollution?

In the sense that you can write e.g.

  f = g . h

instead of

  f x = g (h x)

thereby avoiding the need to give a name the argument to f.

Cheers
Ben

BTW,
A: No.
Q: Should I include quotations after my reply?

From ben.franksen at online.de  Mon Jun  2 14:53:30 2008
From: ben.franksen at online.de (Ben Franksen)
Date: Mon Jun  2 14:46:22 2008
Subject: [Haskell-cafe] Re: modelling C in Haskell ..
References: <5ae4f2ba0805292346y217d799du8a3e097a1e004e7a@mail.gmail.com>
Message-ID: <g21fja$enk$1@ger.gmane.org>

Galchin, Vasili wrote:
>
> typedef struct blah
> {
>        int val1;
> 
>        union {
> 
>            int  val2;
> 
>            struct {
> 
>                  int val3;
> 
>                  int val4;
>            }
>        }
> }    C_type;
> 
> question: in Haskell, can I embed definition of the "union" inside of the
> C typedef, i.e. recursion definition? Or must I have a separate definition
> for the "union" which I "instantiate" inside the Haskell "typedef", i.e.
> Haskell "data"?

No. Each definition of a data type must occur at the top-level. Also,
Haskell has only a very weak record system, a deficit that is generally
agreed to be one of Haskell's greatest weaknesses.

Like jcc, I'd also be interested what concrete problem prompted your
question. While I have often found it annoying that in Haskell e.g. record
labels are global in scope, I have never encountered a situation where I
wanted to have lexically nested data type declarations.

Cheers
Ben

From keith at oreilly.com  Mon Jun  2 14:56:46 2008
From: keith at oreilly.com (Keith Fahlgren)
Date: Mon Jun  2 14:49:29 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <20080602172131.GA7534@scytale.galois.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
Message-ID: <4844426E.7010101@oreilly.com>

On 6/2/08 10:21 AM, Don Stewart wrote:
> aditya_siram:
>> I am building a web-app that, in broad strokes, allows a leader to
>> assign tasks to team members and allows team members to
>> accept/reject/pick tasks that they want to do. 
>>
>> I really like Haskell and I would like to use it to implement the
>> solution. Are frameworks like Happs ready? Not so much in terms of
>> documentation, but in functionality and stability. 
> 
> HAppS is nice (see hpaste.org for example, which is nice and simple, and
> has been running for over a year).
> 
> Another nice option in Haskell is using something like HStringTemplate
> or the xhtml combinators  with fastcgi hooked into GHC's concurrency
> mechanisms.

If you're interested in the background of rolling your own web stuff, I like 
Paul Brown's description of building perpubplat here: http://mult.ifario.us/t/blog


HTH,
Keith

From devriese at cs.tcd.ie  Mon Jun  2 15:23:32 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Mon Jun  2 15:16:15 2008
Subject: [Haskell-cafe] hs-plugins compile error
In-Reply-To: <20080602172401.GB7534@scytale.galois.com>
References: <20080602130511.GA24905@netsoc.tcd.ie>
	<20080602172401.GB7534@scytale.galois.com>
Message-ID: <20080602192332.GB24905@netsoc.tcd.ie>

Hi Don,

Is this the kind of thing you mean (I'm not really a darcs user; this is
the patch created by darcs record):

[Hide some names to remove ambiguity errors
Edsko de Vries <edsko@edsko.net>**20080602202001] {
hunk ./src/System/Plugins/Env.hs 76
-import Distribution.Package
+import Distribution.Package hiding (packageName)
hunk ./src/System/Plugins/PackageAPI.hs 43
-import Distribution.Package
+import Distribution.Package hiding (depends, packageName)
hunk ./src/System/Plugins/ParsePkgConfCabal.hs 9
-import Distribution.Package
+import Distribution.Package hiding (depends)
}

Edsko
From ekmett at gmail.com  Mon Jun  2 15:25:28 2008
From: ekmett at gmail.com (Edward Kmett)
Date: Mon Jun  2 15:18:12 2008
Subject: [Haskell-cafe] Re: [ANN] bloomfilter 1.0 - Fast immutable and
	mutable Bloom filters
In-Reply-To: <4841CFB2.1020203@cs.pdx.edu>
References: <48408014.30401@serpentine.com> <20080531005127.4b330ff7@solaris>
	<slrng433li.olb.wnoise@ofb.net> <20080531202904.45054b49@solaris>
	<4841CFB2.1020203@cs.pdx.edu>
Message-ID: <7fb8f82f0806021225l7bccc5det817cd572b1f0ca14@mail.gmail.com>

On Sat, May 31, 2008 at 6:22 PM, Jim Snow <jsnow@cs.pdx.edu> wrote:
> In practice, one might use something like 32 hash tables.  This yields a
> false positive rate of 1/(2^32).  Their most obvious application is to store
> the dictionary for a spell checker in a space-efficient way, though I have a
> friend who wrote a paper on using them for router caches.

One minor technicality is that you don't actually use k separate hash
tables. You use k separate hash functions, and hash using different
functions into the same physical table with a goal of having
approximately half of
the bits in the table set when all of your data is hashed.
From jstrait at moonloop.net  Mon Jun  2 15:48:12 2008
From: jstrait at moonloop.net (Jon Strait)
Date: Mon Jun  2 15:51:46 2008
Subject: [Haskell-cafe] Vancouver Haskell users meeting
Message-ID: <48444E7C.7050602@moonloop.net>

An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/haskell-cafe/attachments/20080602/205dcae6/attachment-0001.htm
From kr.angelov at gmail.com  Mon Jun  2 16:35:22 2008
From: kr.angelov at gmail.com (Krasimir Angelov)
Date: Mon Jun  2 16:28:04 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
Message-ID: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>

Hi,

I have to write ParseChart implementation with Data.Map/Set. The chart
is type like this:

type Chart k v = Map k (Set v)

now I need operation like:

insert :: k -> v -> Chart k v -> Maybe (Chart k v)

where the result is (Just _) if the (k,v) is actually added to the
chart or Nothing if it was already there and nothing have to be done.
The straight forward implementation is:

case Map.lookup k chart of
  Nothing -> Just (Map.insert k (Set.singleton v) chart)
  Just set | Set.member v set -> Nothing
               | otherwise            -> Just (Map.insert k
(Set.insert v set) chart)

The problem with this is that both the Map and the Set are traversed
twice. The first time from lookup/member and the second time from
insert. Does someone have an idea how to do this with the current
libraries?

There are the Map.updateLookupWithKey and the Map.alter functions:

updateLookupWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a ->
(Maybe a,Map k a)
alter :: Ord k => (Maybe a -> Maybe a) -> k -> Map k a -> Map k a

which are the closest that I need. The problem is that the first
doesn't allow the client function to be called if there isn't matching
key in the map and the second is doesn't allow to return value from
the client function. What I really need is an alterLook?p function:

alterLook?p :: Ord k => (Maybe a -> (b,Maybe a)) -> k -> Map k a -> (b,Map k a)

The chart manipulation is in the tight loop of my application so I
need fast code. Any other ideas?

Regards,
   Krasimir
From jstrait at moonloop.net  Mon Jun  2 16:45:26 2008
From: jstrait at moonloop.net (Jon Strait)
Date: Mon Jun  2 16:48:58 2008
Subject: [Haskell-cafe] Vancouver Haskell users meeting
Message-ID: <48445BE6.4090108@moonloop.net>

Anyone else here from Vancouver (Canada)?  I thought it would be great 
to have a little informal get-together at a local cafe and share how 
we're currently using Haskell, or really anything (problems,  
comparisons, useful software tools, etc.) in relation to Haskell.

I'm scheduling a meeting for this Thursday, June 5th. for 7PM at 
<http://www.waazubee.com/content/directions.php> Waazubee Cafe - 
http://www.waazubee.com/content/directions.php  (at Commercial Dr. and 
1st Ave.) 

They have wireless internet access.  I'll get a table near the back, 
bring my laptop, and will have a copy of Hudak's SOE book (the front 
cover is impossible to miss) out on the table.

If anyone wants to meet, but this Thursday is not a good day for you, 
let me know what days are better and we'll move the meeting.  If anyone 
is sure that they will come this Thursday, you might let me know, so I 
can have an idea about the resistance in changing the day, if needed.

Thanks,

Jon
From dons at galois.com  Mon Jun  2 17:09:21 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun  2 17:02:06 2008
Subject: [Haskell-cafe] Vancouver Haskell users meeting
In-Reply-To: <48445BE6.4090108@moonloop.net>
References: <48445BE6.4090108@moonloop.net>
Message-ID: <20080602210921.GC7820@scytale.galois.com>

jstrait:
> Anyone else here from Vancouver (Canada)?  I thought it would be great 
> to have a little informal get-together at a local cafe and share how 
> we're currently using Haskell, or really anything (problems,  
> comparisons, useful software tools, etc.) in relation to Haskell.
> 
> I'm scheduling a meeting for this Thursday, June 5th. for 7PM at 
> <http://www.waazubee.com/content/directions.php> Waazubee Cafe - 
> http://www.waazubee.com/content/directions.php  (at Commercial Dr. and 
> 1st Ave.) 
> 
> They have wireless internet access.  I'll get a table near the back, 
> bring my laptop, and will have a copy of Hudak's SOE book (the front 
> cover is impossible to miss) out on the table.
> 
> If anyone wants to meet, but this Thursday is not a good day for you, 
> let me know what days are better and we'll move the meeting.  If anyone 
> is sure that they will come this Thursday, you might let me know, so I 
> can have an idea about the resistance in changing the day, if needed.

Great! I've added these details to the events listing on http://haskell.org
From ndmitchell at gmail.com  Mon Jun  2 18:07:55 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Mon Jun  2 18:00:46 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
Message-ID: <404396ef0806021507r312db11ak8eefb6e4087afccf@mail.gmail.com>

Hi Krasimir,

> insert :: k -> v -> Chart k v -> Maybe (Chart k v)
>
> where the result is (Just _) if the (k,v) is actually added to the
> chart or Nothing if it was already there and nothing have to be done.

insertLookupWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k
a -> (Maybe a, Map k a)

This should provide the information you need, without the double
traversal of the data structure.

Thanks

Neil
From tphyahoo at gmail.com  Mon Jun  2 18:15:50 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Mon Jun  2 18:08:31 2008
Subject: [Haskell-cafe] hs-plugins compile error
In-Reply-To: <20080602192332.GB24905@netsoc.tcd.ie>
References: <20080602130511.GA24905@netsoc.tcd.ie>
	<20080602172401.GB7534@scytale.galois.com>
	<20080602192332.GB24905@netsoc.tcd.ie>
Message-ID: <910ddf450806021515x4864ec26obeb735f2a53ea9fe@mail.gmail.com>

after darcs record,

 darcs send -o file.patch

and then send file.patch via email to the maintainer.

2008/6/2 Edsko de Vries <devriese@cs.tcd.ie>:
> Hi Don,
>
> Is this the kind of thing you mean (I'm not really a darcs user; this is
> the patch created by darcs record):
>
> [Hide some names to remove ambiguity errors
> Edsko de Vries <edsko@edsko.net>**20080602202001] {
> hunk ./src/System/Plugins/Env.hs 76
> -import Distribution.Package
> +import Distribution.Package hiding (packageName)
> hunk ./src/System/Plugins/PackageAPI.hs 43
> -import Distribution.Package
> +import Distribution.Package hiding (depends, packageName)
> hunk ./src/System/Plugins/ParsePkgConfCabal.hs 9
> -import Distribution.Package
> +import Distribution.Package hiding (depends)
> }
>
> Edsko
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From duncan.coutts at worc.ox.ac.uk  Mon Jun  2 18:28:29 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Mon Jun  2 18:17:52 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
Message-ID: <1212445709.15010.144.camel@localhost>


On Mon, 2008-06-02 at 22:35 +0200, Krasimir Angelov wrote:

> The problem with this is that both the Map and the Set are traversed
> twice. The first time from lookup/member and the second time from
> insert. Does someone have an idea how to do this with the current
> libraries?


> The chart manipulation is in the tight loop of my application so I
> need fast code. Any other ideas?

I'm not sure if it helps your application but we had a discussion on
#haskell the other day about Data.Map and were talking about a general
insert/modify/delete operator like:

modify :: k -> Map k e -> (e, Maybe e -> Map k e)

so it's a lookup that returns the element at k and also a continuation
that lets you rebuild a new map with an altered element. I guess that
doesn't account for the element not existing. There's probably a
generalisation that does.

Duncan

From duncan.coutts at worc.ox.ac.uk  Mon Jun  2 18:32:21 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Mon Jun  2 18:21:41 2008
Subject: [Haskell-cafe] cabal install fail for happs-hsp-template
In-Reply-To: <910ddf450806020942n4bc2fac8kc454aeda446b77ee@mail.gmail.com>
References: <910ddf450806020942n4bc2fac8kc454aeda446b77ee@mail.gmail.com>
Message-ID: <1212445941.15010.148.camel@localhost>


On Mon, 2008-06-02 at 09:42 -0700, Thomas Hartman wrote:
> Can cabal install be made to work for this package?
> *****
> thartman@thartman-laptop:~>sudo cabal install happs-hsp-template
> [sudo] password for thartman:
> cabal: internal error: could not construct a valid install plan.
> The proposed (invalid) plan contained the following problems:
> Package Cabal is required by several packages, but they require
> inconsistent versions:
>   package ghc-6.8.2 requires Cabal-1.2.3.0
>   package plugins-1.2 requires Cabal-1.5.2

The package deps are not actually inconsistent, the problem is that the
current cabal-install dependency resolution algorithm is completely
naive and comes up with an invalid install plan.

I'll let people know when the new dep resolver for cabal-install is
ready (hopefully just a few days now). It should address this issue.

Duncan

From kr.angelov at gmail.com  Mon Jun  2 18:33:24 2008
From: kr.angelov at gmail.com (Krasimir Angelov)
Date: Mon Jun  2 18:26:04 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <404396ef0806021507r312db11ak8eefb6e4087afccf@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
	<404396ef0806021507r312db11ak8eefb6e4087afccf@mail.gmail.com>
Message-ID: <c97c08d20806021533p1cdc4f73g836b23d0cff96e40@mail.gmail.com>

Not completely! This is a possible implementation:

case insertLookupWithKey (\_ -> Set.union) k (Set.singleton v) chart of
  (Nothing, chart) -> Just chart
  (Just set, chart) | Set.member v set -> Nothing
                          | otherwise             -> Just chart

but notice that the set is still traversed twice.

On Tue, Jun 3, 2008 at 12:07 AM, Neil Mitchell <ndmitchell@gmail.com> wrote:
> Hi Krasimir,
>
>> insert :: k -> v -> Chart k v -> Maybe (Chart k v)
>>
>> where the result is (Just _) if the (k,v) is actually added to the
>> chart or Nothing if it was already there and nothing have to be done.
>
> insertLookupWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k
> a -> (Maybe a, Map k a)
>
> This should provide the information you need, without the double
> traversal of the data structure.
>
> Thanks
>
> Neil
>
From ndmitchell at gmail.com  Mon Jun  2 18:41:30 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Mon Jun  2 18:34:11 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <c97c08d20806021533p1cdc4f73g836b23d0cff96e40@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
	<404396ef0806021507r312db11ak8eefb6e4087afccf@mail.gmail.com>
	<c97c08d20806021533p1cdc4f73g836b23d0cff96e40@mail.gmail.com>
Message-ID: <404396ef0806021541v6d62f6ffgb198714f105100ff@mail.gmail.com>

Hi

> case insertLookupWithKey (\_ -> Set.union) k (Set.singleton v) chart of
>  (Nothing, chart) -> Just chart
>  (Just set, chart) | Set.member v set -> Nothing
>                          | otherwise             -> Just chart
>
> but notice that the set is still traversed twice.

Yes, I missed that bit. I don't see any way of reducing that, other
than using an unsafePerformIO and IORef to track the combining
function - which is probably a really bad idea.

Thanks

Neil
From ryani.spam at gmail.com  Mon Jun  2 18:52:29 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun  2 18:45:09 2008
Subject: [Haskell-cafe] [Newbie question] -- Looping stdin until condition
	is met
In-Reply-To: <1212192870.15596.1255975237@webmail.messagingengine.com>
References: <20080531002837.0F09A3C8001@banane.furius.ca>
	<bc36e24d0805301654x71d00170vcc042bd4cd42a107@mail.gmail.com>
	<1212192870.15596.1255975237@webmail.messagingengine.com>
Message-ID: <2f9b2d30806021552x36e5bcabw2727b04abfa9525f@mail.gmail.com>

On 5/30/08, Martin Blais <blais@furius.ca> wrote:
> Dear Philip, could you point your virtual finger towards a
> reference/paper/book/any-bleeping-thing that would help this simple
> beginner understand why it doesn't work in this case? I'm trying to
> picture why a "read" function that terminates the program would be
> useful anywhere. In fact, any library function other than something like
> UNIX's "exit" or "kill" which terminates my program is not really
> welcome in any of my computer programs, but then again, I haven't yet
> been illuminated by the genie of pure functional languages.  A reference
> would be awesome.

As others have pointed out, the reason why it doesn't work is due to
lazy evaluation; the exception is "hidden" in a pure value and isn't
triggered until some other bit of code causes the pure value to be
evaluated.  You can force the exception to be generated in your catch
block by using "seq" (or "$!", which is implemented using "seq").
This forces the evaluation to happen at that point, although there are
a lot of gotchas involved; for Int it works fine, though.

Your question, then, requires asking "why would you want to hide an
exception in a pure value"?  The answer to that is quite interesting,
but here's a simpler example that might enlighten you:

head :: [a] -> a
head (x:_) = x
head _ = error "head: empty list"

Just as you are required to prove before calling "head" that you
aren't passing an empty list, for your program to be total, you should
prove before calling "read" that the string parses properly.  If you
can't provide that proof (because, in this case, the string is
provided by the user), you should be using another function for
parsing.

Don suggested "reads" to implement "maybeRead", which seems like a
great idea to me.

  -- ryan
From ndmitchell at gmail.com  Mon Jun  2 19:07:32 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Mon Jun  2 19:00:13 2008
Subject: [Haskell-cafe] [Newbie question] -- Looping stdin until condition
	is met
In-Reply-To: <20080530235828.GI25572@scytale.galois.com>
References: <20080531002837.0F09A3C8001@banane.furius.ca>
	<20080530235828.GI25572@scytale.galois.com>
Message-ID: <404396ef0806021607x4b679180i8c3ec5255f2fe8e5@mail.gmail.com>

Hi

> The best thing to do is bypass read and use 'reads' to define your
> own safe read.
>
>    maybeRead :: Read a => String -> Maybe a
>    maybeRead s = case reads s of
>        [(x, "")] -> Just x
>        _         -> Nothing

Or just use the Safe package:
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/safe

http://hackage.haskell.org/packages/archive/safe/0.2/doc/html/Safe.html#v%3AreadMay

Thanks

Neil
From vigalchin at gmail.com  Tue Jun  3 00:11:54 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun  3 00:04:39 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <1212403100.15010.133.camel@localhost>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
	<1212403100.15010.133.camel@localhost>
Message-ID: <5ae4f2ba0806022111l33fecf27xfbd6ee5f7dabf35f@mail.gmail.com>

Hi Duncan,

     Not sure I agree the behavior is ok. E.g. here is a build of mmap:

vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell Setup.lhs
clean
cleaning...
vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell Setup.lhs
configure
Configuring bytestring-mmap-0.2.0...
vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell Setup.lhs
build
Preprocessing library bytestring-mmap-0.2.0...
Building bytestring-mmap-0.2.0...
[1 of 3] Compiling System.IO.Posix.MMap.Internal (
System/IO/Posix/MMap/Internal.hs, dist/build/System/IO/Posix/MMap/Internal.o
)
[2 of 3] Compiling System.IO.Posix.MMap.Lazy ( System/IO/Posix/MMap/Lazy.hs,
dist/build/System/IO/Posix/MMap/Lazy.o )
[3 of 3] Compiling System.IO.Posix.MMap ( System/IO/Posix/MMap.hs,
dist/build/System/IO/Posix/MMap.o )
/usr/bin/ar: creating dist/build/libHSbytestring-mmap-0.2.0.a

at this point rebuild and install the "unix" package ...

vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell Setup.lhs
clean
cleaning...
vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell Setup.lhs
configure
Configuring bytestring-mmap-0.2.0...
vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell Setup.lhs
build
Setup.lhs: error reading dist/setup-config; run "setup configure" command?

"dist/setup-config" is not being populated at the end. In your response
below, are you saying that teh segfaults occur because ghc itself relies on
the "unix" package?

Thanks, Vasili




On Mon, Jun 2, 2008 at 5:38 AM, Duncan Coutts <duncan.coutts@worc.ox.ac.uk>
wrote:

>
> On Mon, 2008-06-02 at 00:07 -0500, Galchin, Vasili wrote:
> > Hello,
> >
> >       I have been developing new code for the "unix" package. I have
> > run into what I think are ghc 6.8.2 anomalies but couldn't see a
> > pattern. Possibly now I do. I have been using the 32-bit x86 ghc
> > binary that I downloaded from http://www.haskell.org and running on
> > Ubuntu Linux. I am pretty I can repeat now. Everything is ok until I
> > do "sudo runhaskell Setup.hs install" which installs a new "unix"
> > package that I just built. Of course the "intall" installs
> > into /usr/local/lib/unix-2.3.0.0/ghc-6.8.2. The "install" seems to
> > destroy some ghc compiler state under /usr/local ...
>
> That sounds right. You're replacing the unix-2.3.0.0 library that comes
> with ghc-6.8.2 with your own version. It is highly unlikely to be ABI
> compatible with the one you are replacing and so all the other packages
> that already depends on the existing unix-2.3.0.0 library end up broken.
> You'd expect this kind of breakage to be exposed as link errors and
> segfaults.
>
> I suggest you do not replace any of the libraries that come with ghc. To
> be more precise, it is perfectly ok to *add new versions* but it is not
> ok to *replace existing versions* without rebuilding all the other libs
> that depend on it.
>
> Make sense?
>
> So if you really want to make changes to the unix lib, make sure you
> change the version number too. I also suggest not installing the
> packages as root, just install them locally. That way you can guarantee
> you never mess up your ghc install. You would be able to revert to a
> clean ghc install just by removing your
> ~/.ghc/$arch/ghc-6.8.2/package.conf file which will unregister *all*
> locally registered packages. To unregister individual packages use
> ghc-pkg --user unregister $pkgname
>
> Duncan
>
>
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From ajb at spamcop.net  Tue Jun  3 00:47:30 2008
From: ajb at spamcop.net (ajb@spamcop.net)
Date: Tue Jun  3 00:40:20 2008
Subject: [Haskell-cafe] Mutually Recursive Modules
In-Reply-To: <4843FBCD.8000001@charter.net>
References: <4843F81B.7060808@richardg.name> <4843FBCD.8000001@charter.net>
Message-ID: <20080603004730.dzo6cyduskgsgo0w-nwo@webmail.spamcop.net>

G'day all.

Quoting Isaac Dupree <isaacdupree@charter.net>:

> Luckily,
> it is very often the case that your code will be better off anyway if
> refactored to have less module recursion. (though not always.)

Nonetheless, I prefer not to leave the robustness of my code to luck.
Besides, if I liked structuring code around artificial language
restrictions, I'd be programming in C, not Haskell.

Cheers,
Andrew Bromage
From vigalchin at gmail.com  Tue Jun  3 01:04:26 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun  3 00:57:07 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <1212403100.15010.133.camel@localhost>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
	<1212403100.15010.133.camel@localhost>
Message-ID: <5ae4f2ba0806022204u51fb86dbs202783e73bb08573@mail.gmail.com>

Duncan,

     By installing localling, I "runhaskell Setup.hs configure
--prefix=$HOME" plus add local path to LD_LIBRARY_PATH and LD_RUN_PATH? On
Linux, does ghc use .so's or is it linked statically?

Vasili

On Mon, Jun 2, 2008 at 5:38 AM, Duncan Coutts <duncan.coutts@worc.ox.ac.uk>
wrote:

>
> On Mon, 2008-06-02 at 00:07 -0500, Galchin, Vasili wrote:
> > Hello,
> >
> >       I have been developing new code for the "unix" package. I have
> > run into what I think are ghc 6.8.2 anomalies but couldn't see a
> > pattern. Possibly now I do. I have been using the 32-bit x86 ghc
> > binary that I downloaded from http://www.haskell.org and running on
> > Ubuntu Linux. I am pretty I can repeat now. Everything is ok until I
> > do "sudo runhaskell Setup.hs install" which installs a new "unix"
> > package that I just built. Of course the "intall" installs
> > into /usr/local/lib/unix-2.3.0.0/ghc-6.8.2. The "install" seems to
> > destroy some ghc compiler state under /usr/local ...
>
> That sounds right. You're replacing the unix-2.3.0.0 library that comes
> with ghc-6.8.2 with your own version. It is highly unlikely to be ABI
> compatible with the one you are replacing and so all the other packages
> that already depends on the existing unix-2.3.0.0 library end up broken.
> You'd expect this kind of breakage to be exposed as link errors and
> segfaults.
>
> I suggest you do not replace any of the libraries that come with ghc. To
> be more precise, it is perfectly ok to *add new versions* but it is not
> ok to *replace existing versions* without rebuilding all the other libs
> that depend on it.
>
> Make sense?
>
> So if you really want to make changes to the unix lib, make sure you
> change the version number too. I also suggest not installing the
> packages as root, just install them locally. That way you can guarantee
> you never mess up your ghc install. You would be able to revert to a
> clean ghc install just by removing your
> ~/.ghc/$arch/ghc-6.8.2/package.conf file which will unregister *all*
> locally registered packages. To unregister individual packages use
> ghc-pkg --user unregister $pkgname
>
> Duncan
>
>
-------------- next part --------------
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From aruiz at um.es  Tue Jun  3 03:27:54 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Tue Jun  3 03:20:38 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>	
	<484277D3.9020604@um.es>	
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>	
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
Message-ID: <4844F27A.2080208@um.es>

Anatoly Yakovenko wrote:
>>> do you have any plans to provide an interface for inplace updates?
>> Yes, I will try to write a simple version of Data.Array.ST...
>>
> 
> I can try to help you, although I still dont quite grok monads.
> Wouldn't it be more efficient to use StorableArray, so you can cast
> from and to C?  I am not sure how vectors and matrixes are represented
> in C, but I imagine it should be possible to manipulate them without
> resorting to copying between haskell and C.
> 
That's right, the correspondence with StorableArray is direct, and 
efficient conversion can be easily added to the library. I mentioned the 
idea of Data.Array.ST to have also the possibility of writing pure code, 
without IO, internally implemented with inplace updates.

Alberto
From bulat.ziganshin at gmail.com  Tue Jun  3 03:37:21 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Tue Jun  3 03:32:52 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <4844F27A.2080208@um.es>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
	<4844F27A.2080208@um.es>
Message-ID: <731290342.20080603113721@gmail.com>

Hello Alberto,

Tuesday, June 3, 2008, 11:27:54 AM, you wrote:

>>> Yes, I will try to write a simple version of Data.Array.ST...
> That's right, the correspondence with StorableArray is direct, and
> efficient conversion can be easily added to the library. I mentioned the
> idea of Data.Array.ST to have also the possibility of writing pure code,
> without IO, internally implemented with inplace updates.

STRef/STArray operations are just IORef/IOArray operations imported in
some way/ you can easily import any other operations to ST monad as
far as you use rank-2 types to guarantee that impureness will not
escape the runST call. look into unsafeIOtoST function

providing unmovable STUArray variant may be a good idea


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From ketil at malde.org  Tue Jun  3 04:26:47 2008
From: ketil at malde.org (Ketil Malde)
Date: Tue Jun  3 04:19:12 2008
Subject: [Haskell-cafe] [ANN] bloomfilter 1.0 - Fast immutable and mutable
	Bloom filters
In-Reply-To: <910ddf450805310933l668697b6w5816c98c7305c6cd@mail.gmail.com>
	(Thomas Hartman's message of "Sat\, 31 May 2008 09\:33\:52 -0700")
References: <48408014.30401@serpentine.com>
	<910ddf450805310933l668697b6w5816c98c7305c6cd@mail.gmail.com>
Message-ID: <87tzgancu0.fsf@malde.org>

"Thomas Hartman" <tphyahoo@gmail.com> writes:

> What kind of speed do you get on your laptop for Data.Set? How much
> faster is the bloom filter?

I tried to modify examples/Words.hs to use Data.Set insted.  The
results look like this (first Bloom, second Data.Set, both compiled
with -O2):

    nmd9999:..filter/examples % ./Words   
    57025 words
    0.013326ss to count words
    Bloom { 4194304 bits } 
    0.050608ss to construct filter
    0.034806ss to query every element

    nmd9999:..filter/examples % ./WordsS                
    57025 words
    0.013291ss to count words
    False
    0.755115ss to construct filter
    0.423289ss to query every element

In order to avoid printing the entire set, while still evaluating it,
I replaced the printing of the set with printing the result of a
search for a non-existing element - I should really use a strict
insert, I guess.  Anyway, this hopefully gives an indication - looks
like a factor of 10 in this case, but it will depend on the size of
the data - more data, greater improvement.

BTW, Nice work, Bryan!  I have plans for this.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From aruiz at um.es  Tue Jun  3 04:56:50 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Tue Jun  3 04:52:49 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <731290342.20080603113721@gmail.com>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
	<4844F27A.2080208@um.es> <731290342.20080603113721@gmail.com>
Message-ID: <48450752.4080307@um.es>

Bulat Ziganshin wrote:
> Hello Alberto,
> 
> Tuesday, June 3, 2008, 11:27:54 AM, you wrote:
> 
>>>> Yes, I will try to write a simple version of Data.Array.ST...
>> That's right, the correspondence with StorableArray is direct, and
>> efficient conversion can be easily added to the library. I mentioned the
>> idea of Data.Array.ST to have also the possibility of writing pure code,
>> without IO, internally implemented with inplace updates.
> 
> STRef/STArray operations are just IORef/IOArray operations imported in
> some way/ you can easily import any other operations to ST monad as
> far as you use rank-2 types to guarantee that impureness will not
> escape the runST call. look into unsafeIOtoST function

Good! So you can easily "hide" the IO operations in the ST monad. I will 
definitely look into it.

> providing unmovable STUArray variant may be a good idea
> 
> 

Many thanks Bulat!
From duncan.coutts at worc.ox.ac.uk  Tue Jun  3 05:05:26 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Tue Jun  3 04:54:45 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <5ae4f2ba0806022111l33fecf27xfbd6ee5f7dabf35f@mail.gmail.com>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
	<1212403100.15010.133.camel@localhost>
	<5ae4f2ba0806022111l33fecf27xfbd6ee5f7dabf35f@mail.gmail.com>
Message-ID: <1212483926.15010.192.camel@localhost>


On Mon, 2008-06-02 at 23:11 -0500, Galchin, Vasili wrote:
> at this point rebuild and install the "unix" package ...
> 
> vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell
> Setup.lhs clean
> cleaning...
> vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell
> Setup.lhs configure
> Configuring bytestring-mmap-0.2.0...
> vigalchin@ubuntu:~/FTP/Haskell/bytestring-mmap-0.2.0$ runhaskell
> Setup.lhs build
> Setup.lhs: error reading dist/setup-config; run "setup configure"
> command?
> 
> "dist/setup-config" is not being populated at the end. In your
> response below, are you saying that teh segfaults occur because ghc
> itself relies on the "unix" package?

Something like that yes.

You're running runhaskell Setup.lhs and that loads and runs code from
the Cabal library. The Cabal library depends on the process library
which depends on the unix library. So by replacing the same version of
the unix package you're breaking everything else which depends on it,
including Cabal and thus runhaskell Setup.lhs.

So the solution is to not do that. Don't re-install the exact same
version of any of the core libs that come with ghc. Adding new versions
is fine, replacing existing versions is not fine because it breaks all
the other packages that were already built against that package.

Duncan

From duncan.coutts at worc.ox.ac.uk  Tue Jun  3 05:11:06 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Tue Jun  3 05:00:23 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <5ae4f2ba0806022204u51fb86dbs202783e73bb08573@mail.gmail.com>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
	<1212403100.15010.133.camel@localhost>
	<5ae4f2ba0806022204u51fb86dbs202783e73bb08573@mail.gmail.com>
Message-ID: <1212484266.15010.199.camel@localhost>


On Tue, 2008-06-03 at 00:04 -0500, Galchin, Vasili wrote:
> Duncan,
> 
>      By installing localling, I "runhaskell Setup.hs configure
> --prefix=$HOME" plus add local path to LD_LIBRARY_PATH and
> LD_RUN_PATH? On Linux, does ghc use .so's or is it linked statically?

ghc is linked statically but when you do things like runhaskell Setup.hs
you're asking ghc to dynamically load packages. runhaskell/runghc is
basically a form of ghci, and ghci does dynamic code loading. If you've
broken some of the packages that ghci loads and runs code from then
you'll run into problems, mysterious segfaults and the like.

As I understand it, in the next version of ghc it will track the ABI of
each package so we would be able to detect when people replace packages
with ones with the same version but with a different ABI (as you've been
doing) and refuse to link or run in those cases rather than running and
ending up with segfaults.

Duncan

From apfelmus at quantentunnel.de  Tue Jun  3 05:14:58 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Tue Jun  3 05:07:51 2008
Subject: [Haskell-cafe] Re: appending an element to a list
In-Reply-To: <3c4d5adf0806012204p25133bdaxbc22955b70f094ff@mail.gmail.com>
References: <483EE208.2010601@inf.fu-berlin.de>
	<483EF36B.5040100@daimi.au.dk>	<48404039.6030605@cisco.com>
	<48405717.20206@daimi.au.dk>	<87r6bja609.fsf@hbox.dyndns.org>	<3c4d5adf0805302159o23113ad2sb24754e02789bb06@mail.gmail.com>	<48414C2B.9010606@daimi.au.dk>
	<g1tjk4$c4i$1@ger.gmane.org>
	<3c4d5adf0806012204p25133bdaxbc22955b70f094ff@mail.gmail.com>
Message-ID: <g2322j$sig$1@ger.gmane.org>

Abhay Parvate wrote:
> I somehow thought it would be easy to talk about complexity of calculating
> individual elements in an infinite list should be sufficient, but that seems
> to be involved, and my over-generalization doesn't seem to work. Thanks for
> the link; particularly it has reference to Wadler's papers exactly on this
> problem.

Note however that Wadler's and similar formalisms are still a 
unsatisfactory in that they are quite clumsy to work with, it's quite 
tedious/impossible to analyze examples with a lot of lazy evaluation. 
But they are a good guideline.

In his book about purely functional data structures [1], Okasaki takes a 
different approach; each node of a data structure is given a debit, a 
cost to evaluate it. For instance, consider

   xs = x1 : x2 : x3 : ... : xn : []
           1    1    1 ... 1    1  0

   ys = y1 : y2 : y3 : ... : ym : []
           1    1    1 ... 1    1  0

The numbers below indicate the time it takes to evaluate the node to 
weak head normal form. For demonstration purposes, I arbitrarily chose 1 
for each (:) here.

The combined list will then have debits like

   xs ++ ys = x1 : x2 : x3 : ... : xn : y1 : y2 : y3 : ... : ym : []
                 2    2    2 ... 2    2    1    1    1 ... 1    1  0

In other words, the ys list is copied verbatim but each element of xs 
incurs an additional cost of 1, corresponding to one step in the 
evaluation of the concatenation with (++).

In order to force/inspect a constructor/node, you have to pay off its 
debits first. In the above example,  head (xs ++ ys)  would have to pay 
2 units of time (one unit for  head xs  and one for the (++)). Now, the 
thing about debits is that we can relocate them to the top and only 
overestimate the total running time if we do that. For instance, we 
could push all debits to the top

   xs ++ ys = x1   : x2 : x3 : ... : xn : y1 : y2 : y3 : ... : ym : []
                 2n+m   0    0 ... 0    0    0    0    0 ... 0    0  0

so that evaluating  head (xs ++ ys)  is now estimated to cost (2n+m) 
units of time while the rest is free/fully evaluated.

The above example is rather useless, but consider the case  n == m  and

   xs = x1 : x2 : x3 : ... : xn : []
           0    0    0 ... 0    0  0

   ys = y1 : y2 : y3 : ... : yn : []
           0    0    0 ... 0    0  0

i.e. two fully evaluated lists of the same length. Then, we have

   xs ++ reverse ys =
      x1 : x2 : x3 : ... : xn : yn : y{n-1} : ... : y1 : []
         1    1    1 ... 1    1    n        0 ... 0    0  0

because reversing the list ys is "monolithic", i.e. looking at its  head 
  already forces the tail of the list. But now, we can distribute the 
debits upwards

   xs ++ reverse ys =
      x1 : x2 : x3 : ... : xn : yn : y{n-1} : ... : y1 : []
         2    2    2 ... 2    2    0        0 ... 0    0  0

and thereby amortize the cost of reversing the second lists over the n 
elements of the first list. This is used in the implementation of purely 
functional queues, see also Okasaki's book.


[1]: Chris Okasaki. Purely Function Data Structures.
      http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf
      (This is the thesis on which the book is based.)


Regards,
apfelmus

From bulat.ziganshin at gmail.com  Tue Jun  3 05:42:11 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Tue Jun  3 05:37:59 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <48450752.4080307@um.es>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
	<4844F27A.2080208@um.es> <731290342.20080603113721@gmail.com>
	<48450752.4080307@um.es>
Message-ID: <483842413.20080603134211@gmail.com>

Hello Alberto,

Tuesday, June 3, 2008, 12:56:50 PM, you wrote:

> Good! So you can easily "hide" the IO operations in the ST monad. I will
> definitely look into it.

from implementation POV ST monad is nothing but renamed IO monad which
exports only subset of its operations which are guaranteed to safe.
or, saying in other words, it's just type hackery around IO monad that
provides safe operations

it's possible to define ST monad and its operations as following:

newtype ST s a = forall s. ST_Constructor (IO a)

unsafeIOtoSt action = ST_Constructor action

runST (ST_Constructor action) = unsafePerformIO action

newtype STRef s a = forall s. STRef (IORef a)

readSTRef (STRef ref)  =  unsafeIOtoSt (readIORef ref)

and so on. GHC uses technically (but not ideologically!) different
implementation where both monads are specializations of one generic
type. while Hugs afair uses exactly this approach. you may also look
at ArrayRef lib which reimplements arrays/refs for both compilers in
more unified way

anyway, because ST is just IO monad modulo type tricks, you can
execute any IO action inside ST by lifting it with unsafeIOtoSt

-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From yann at kierun.org  Tue Jun  3 06:30:26 2008
From: yann at kierun.org (Yann Golanski)
Date: Tue Jun  3 06:23:09 2008
Subject: [Haskell-cafe] Rotating backdrop (aka learning Haskell)
In-Reply-To: <20080520081557.GA18833@kierun.org>
References: <20080520081557.GA18833@kierun.org>
Message-ID: <20080603103026.GA10131@kierun.org>

First version is available at:
  http://www.kierun.org/backdropper-1.0.tbz2
It is minimal but does the trick of randomly rotating backgrounds.

Features to add are only rotate during work hours, making sure that all
images are shown within a day and a nice GUI. 

Criticism welcome.

-- 
yann@kierun.org             -= H+ =-             www.kierun.org
   PGP:   009D 7287 C4A7 FD4F 1680  06E4 F751 7006 9DE2 6318
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From gale at sefer.org  Tue Jun  3 07:45:11 2008
From: gale at sefer.org (Yitzchak Gale)
Date: Tue Jun  3 07:37:51 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <404396ef0806021541v6d62f6ffgb198714f105100ff@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
	<404396ef0806021507r312db11ak8eefb6e4087afccf@mail.gmail.com>
	<c97c08d20806021533p1cdc4f73g836b23d0cff96e40@mail.gmail.com>
	<404396ef0806021541v6d62f6ffgb198714f105100ff@mail.gmail.com>
Message-ID: <2608b8a80806030445x5272d3e2o78e3cb4aef6821ed@mail.gmail.com>

Krasimir Angelov wrote:
>> but notice that the set is still traversed twice.

Neil Mitchell wrote:
> I don't see any way of reducing that

Yeah, it looks like the Data.Set (and Data.IntSet) library
is missing the functions

insertMember :: Ord a => a -> Set a -> (Bool, Set a)
deleteMember :: Ord a => a -> Set a -> (Bool, Set a)

analagous to splitMember. It should be easy to write
those functions. If you do that for yourself, consider
making a patch of them and submitting the patch
as a library proposal.

But anyway, a set lookup is very cheap, even for a
set that is quite large. You may want to try just doing
the extra lookup, it might be good enough for you.
At least you eliminated the Map lookup.

Regards,
Yitz
From kr.angelov at gmail.com  Tue Jun  3 07:54:03 2008
From: kr.angelov at gmail.com (Krasimir Angelov)
Date: Tue Jun  3 07:46:43 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <2608b8a80806030445x5272d3e2o78e3cb4aef6821ed@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
	<404396ef0806021507r312db11ak8eefb6e4087afccf@mail.gmail.com>
	<c97c08d20806021533p1cdc4f73g836b23d0cff96e40@mail.gmail.com>
	<404396ef0806021541v6d62f6ffgb198714f105100ff@mail.gmail.com>
	<2608b8a80806030445x5272d3e2o78e3cb4aef6821ed@mail.gmail.com>
Message-ID: <c97c08d20806030454i2e3cb374x8cd30bc4378838a7@mail.gmail.com>

I actually made my own copy of Data.Map and added an extra:

alterLook?p :: Ord k => (Maybe a -> (b,Maybe a)) -> k -> Map k a -> (b,Map k a)

function. I also changed my data type to:

type ParseChart k v = Map k (Map v ())

so I don't have to copy the Data.Set module also. Unfortunately this
doesn't give much better performance - 5734 msec instead of 5828 msec.
Fortunately I found that there is a way to avoid to use Map at all in
one common case. This gave me time about 5024 msec.

Regards,
   Krasimir


On 6/3/08, Yitzchak Gale <gale@sefer.org> wrote:
> Krasimir Angelov wrote:
> >> but notice that the set is still traversed twice.
>
> Neil Mitchell wrote:
> > I don't see any way of reducing that
>
> Yeah, it looks like the Data.Set (and Data.IntSet) library
> is missing the functions
>
> insertMember :: Ord a => a -> Set a -> (Bool, Set a)
> deleteMember :: Ord a => a -> Set a -> (Bool, Set a)
>
> analagous to splitMember. It should be easy to write
> those functions. If you do that for yourself, consider
> making a patch of them and submitting the patch
> as a library proposal.
>
> But anyway, a set lookup is very cheap, even for a
> set that is quite large. You may want to try just doing
> the extra lookup, it might be good enough for you.
> At least you eliminated the Map lookup.
>
> Regards,
> Yitz
>
From ahey at iee.org  Tue Jun  3 09:28:29 2008
From: ahey at iee.org (Adrian Hey)
Date: Tue Jun  3 09:21:13 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
Message-ID: <484546FD.5050005@iee.org>

Hello Krasimir,

Krasimir Angelov wrote:
> Hi,
> 
> I have to write ParseChart implementation with Data.Map/Set. The chart
> is type like this:
> 
> type Chart k v = Map k (Set v)
> 
> now I need operation like:
> 
> insert :: k -> v -> Chart k v -> Maybe (Chart k v)
> 
> where the result is (Just _) if the (k,v) is actually added to the
> chart or Nothing if it was already there and nothing have to be done.
> The straight forward implementation is:
> 
> case Map.lookup k chart of
>   Nothing -> Just (Map.insert k (Set.singleton v) chart)
>   Just set | Set.member v set -> Nothing
>                | otherwise            -> Just (Map.insert k
> (Set.insert v set) chart)
> 

You can do this quite easily with the AVL library, something like this
(untested code)

import Data.Cordering
import Data.Tree.AVL

type Chart k v = AVL (k, AVL v)

insert :: (Ord k, Ord v) => k -> v -> Chart k v -> Maybe (Chart k v)
insert k v tk =
   case genOpenPathWith cmpk tk of
   EmptyBP pthk    -> Just $! insertPath pthk (k, singleton v) tk
   FullBP  pthk tv ->
    case genOpenPath (compare v) tv of
    EmptyBP pthv -> let tv' = insertPath pthv v tv
                    in tv' `seq` (Just $! writePath pthk (k, tv') tk)
    FullBP  _ _  -> Nothing
  where cmpk (k',tv) = case compare k k' of
                       LT -> Lt
                       EQ -> Eq tv
                       GT -> Gt

..or something like that (maybe you don't want all that strictness)

The insertPath & writePath functions do involve a second traversal
but do not repeat all the comparisons. Also, provided not too much
has happened in between, they should be very fast as the nodes on
the path are probably still in cache. The important thing is that
in the case where Nothing is returned you'll have burned very little
heap.

Regards
--
Adrian Hey
From jtod at dcs.gla.ac.uk  Tue Jun  3 10:07:33 2008
From: jtod at dcs.gla.ac.uk (John O'Donnell)
Date: Tue Jun  3 10:00:43 2008
Subject: [Haskell-cafe] hs-plugins compile error
References: <20080602130511.GA24905@netsoc.tcd.ie><20080602172401.GB7534@scytale.galois.com>
	<20080602192332.GB24905@netsoc.tcd.ie>
Message-ID: <BED9D15F73EDDE48BF480604236A45607556ED@ex1.ad.dcs.gla.ac.uk>

Hi,

What is the status of hs-plugins?  I recently tried to install the
version plugins-1.2 on hackage, using a Gnu/Linux box with Fedora 9
and ghc-6.8.2, but didn't get past the configure stage (see config.log
below).

The installation script is invoking gcc with a -V command line argument
but according to gcc documentation -V requires an argument.

Has anyone managed to get hs-plugins to work?  If so, what platform,
which version of ghc and gcc, and where did you find the hs-plugins
source?

Best wishes,
John O'Donnell


... from config.log...
gcc version 4.3.0 20080428 (Red Hat 4.3.0-8) (GCC) 
configure:1852: $? = 0
configure:1854: gcc -V </dev/null >&5
gcc: '-V' option must have argument
configure:1857: $? = 1
configure:1880: checking for C compiler default output file name
configure:1883: gcc    conftest.c  >&5
conftest.c:9:13: warning: missing terminating " character
conftest.c:10: error: stray '\33' in program
conftest.c:10: error: expected identifier or '(' before '[' token
conftest.c:10:4: error: invalid suffix "h" on integer constant
conftest.c:10:9: warning: missing terminating " character
conftest.c:10: error: missing terminating " character
configure:1886: $? = 1
configure: failed program was:
| /* confdefs.h.  */
| 
| #define PACKAGE_NAME ""
| #define PACKAGE_TARNAME ""
| #define PACKAGE_VERSION ""
| #define PACKAGE_STRING ""
| #define PACKAGE_BUGREPORT ""
| #define LEADING_UNDERSCORE 0
| #define TOP "/home/jtod/system/installs/hs-plugins/hs-plugins-1.2
| ESC[?1034h"
| #define WITH_GHC "ghc"
| #define GHC_LIB_PATH "/usr/local/lib/ghc-6.8.2"
| /* end confdefs.h.  */
| 
| int
| main ()
| {
| 
|   ;
|   return 0;
| }
configure:1925: error: C compiler cannot create executables




-----Original Message-----
From: haskell-cafe-bounces@haskell.org on behalf of Edsko de Vries
Sent: Mon 2008-06-02 20:23
To: Don Stewart
Cc: haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] hs-plugins compile error
 
Hi Don,

Is this the kind of thing you mean (I'm not really a darcs user; this is
the patch created by darcs record):

[Hide some names to remove ambiguity errors
Edsko de Vries <edsko@edsko.net>**20080602202001] {
hunk ./src/System/Plugins/Env.hs 76
-import Distribution.Package
+import Distribution.Package hiding (packageName)
hunk ./src/System/Plugins/PackageAPI.hs 43
-import Distribution.Package
+import Distribution.Package hiding (depends, packageName)
hunk ./src/System/Plugins/ParsePkgConfCabal.hs 9
-import Distribution.Package
+import Distribution.Package hiding (depends)
}

Edsko
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Haskell-Cafe mailing list
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From darrinth at gmail.com  Tue Jun  3 10:35:03 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Tue Jun  3 10:27:41 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
Message-ID: <a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>

On Sun, Jun 1, 2008 at 2:44 PM, Bertram Felgenhauer
<bertram.felgenhauer@googlemail.com> wrote:
> Hi,
>
> I'm pleased to announce yet another tool for importing darcs repositories
> to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in
> Haskell, on top of the darcs2 source code. The result is a much faster
> program - it can convert the complete ghc 6.9 branch (without libraries)
> in less than 15 minutes on my slightly dated machine (Athlon XP 2500+),
> which is quite fast [3]. Incremental updates work, too.
>

What's the appeal of this? I personally love git, but I thought all
the cool kids at this school used darcs and that was that.

--
Darrin
From devriese at cs.tcd.ie  Tue Jun  3 10:35:16 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Tue Jun  3 10:27:56 2008
Subject: [Haskell-cafe] hs-plugins compile error
In-Reply-To: <BED9D15F73EDDE48BF480604236A45607556ED@ex1.ad.dcs.gla.ac.uk>
References: <20080602192332.GB24905@netsoc.tcd.ie>
	<BED9D15F73EDDE48BF480604236A45607556ED@ex1.ad.dcs.gla.ac.uk>
Message-ID: <20080603143515.GB17501@netsoc.tcd.ie>

On Tue, Jun 03, 2008 at 03:07:33PM +0100, John O'Donnell wrote:
> Hi,
> 
> What is the status of hs-plugins?  I recently tried to install the
> version plugins-1.2 on hackage, using a Gnu/Linux box with Fedora 9
> and ghc-6.8.2, but didn't get past the configure stage (see config.log
> below).
> 
> The installation script is invoking gcc with a -V command line argument
> but according to gcc documentation -V requires an argument.
> 
> Has anyone managed to get hs-plugins to work?  If so, what platform,
> which version of ghc and gcc, and where did you find the hs-plugins
> source?

It's working fine for me (after applying the patch I submitted), on
Debian Lenny (which currently comes with ghc 6.8.2, gcc 4.2.4) and the
source from Hackage. Source from the darcs repository also works fine
(after applying the same patch).

I *am* getting an application crash sometimes when I close my
application, but I have not yet been able to track that down so I'm not
100% sure it's due to hs-plugins.

Edsko
From jtod at dcs.gla.ac.uk  Tue Jun  3 10:49:06 2008
From: jtod at dcs.gla.ac.uk (John O'Donnell)
Date: Tue Jun  3 10:41:45 2008
Subject: [Haskell-cafe] hs-plugins compile error
References: <20080602192332.GB24905@netsoc.tcd.ie>
	<BED9D15F73EDDE48BF480604236A45607556ED@ex1.ad.dcs.gla.ac.uk>
	<20080603143515.GB17501@netsoc.tcd.ie>
Message-ID: <BED9D15F73EDDE48BF480604236A45607556EE@ex1.ad.dcs.gla.ac.uk>

Thanks, Edsko.

My version of gcc is 4.3.0.  It may well be that some other piece of
software in the Fedora 9 distribution is incompatible with the hs-plugins
installation script.

Has anyone installed hs-plugins on Fedora?  I was able to get it to
compile on Fedora 4, using ghc-6.4, two or three years ago, but it's never
worked on any of my systems since then.

John


-----Original Message-----
From: Edsko de Vries [mailto:devriese@cs.tcd.ie]
Sent: Tue 2008-06-03 15:35
To: John O'Donnell
Cc: Edsko de Vries; Don Stewart; haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] hs-plugins compile error
 
On Tue, Jun 03, 2008 at 03:07:33PM +0100, John O'Donnell wrote:
> Hi,
> 
> What is the status of hs-plugins?  I recently tried to install the
> version plugins-1.2 on hackage, using a Gnu/Linux box with Fedora 9
> and ghc-6.8.2, but didn't get past the configure stage (see config.log
> below).
> 
> The installation script is invoking gcc with a -V command line argument
> but according to gcc documentation -V requires an argument.
> 
> Has anyone managed to get hs-plugins to work?  If so, what platform,
> which version of ghc and gcc, and where did you find the hs-plugins
> source?

It's working fine for me (after applying the patch I submitted), on
Debian Lenny (which currently comes with ghc 6.8.2, gcc 4.2.4) and the
source from Hackage. Source from the darcs repository also works fine
(after applying the same patch).

I *am* getting an application crash sometimes when I close my
application, but I have not yet been able to track that down so I'm not
100% sure it's due to hs-plugins.

Edsko

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From loup.vaillant at gmail.com  Tue Jun  3 10:57:02 2008
From: loup.vaillant at gmail.com (Loup Vaillant)
Date: Tue Jun  3 10:49:40 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
Message-ID: <6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>

2008/6/3 Darrin Thompson <darrinth@gmail.com>:
> On Sun, Jun 1, 2008 at 2:44 PM, Bertram Felgenhauer
> <bertram.felgenhauer@googlemail.com> wrote:
>> Hi,
>>
>> I'm pleased to announce yet another tool for importing darcs repositories
>> to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in
>> Haskell, on top of the darcs2 source code. The result is a much faster
>> program - it can convert the complete ghc 6.9 branch (without libraries)
>> in less than 15 minutes on my slightly dated machine (Athlon XP 2500+),
>> which is quite fast [3]. Incremental updates work, too.
>>
>
> What's the appeal of this? I personally love git, but I thought all
> the cool kids at this school used darcs and that was that.

Disclaimer: I'm no expert, this is what I've heard. Anyone please
confirm or deny the following?

Basically, git is waaay faster than Darcs on a number of use cases.
So, maybe the point of using this converter is when you just cannot
use Darcs any more (too old/big project, merging huge branch with
loads of conflicts, I don't know).

Another point may be "broadcast-ability": It is possible to expose two
repositories: one Darcs, one Git. If I use Git and not Darcs (please
don't sue me), it will be simpler for me to get the source from the
Git snapshot, provided there is one. Well, if I want to contribute
back... maybe I should switch.

I think the True Heresy (and most useful, if practical) would be to
convert back and forth between the two version control systems,
accepting patches from both :-)

Loup
From darrinth at gmail.com  Tue Jun  3 11:53:07 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Tue Jun  3 11:45:45 2008
Subject: [Haskell-cafe] Rewrite class with fundeps in pure h98?
Message-ID: <a2e649c70806030853h9bd015fr5c6c84c92603a796@mail.gmail.com>

I thought that I should be able to write something like the toHtml
function below with pure H98, but when I went to write it I ended up
needing fundeps. Is there a way to express this without using any
extensions?

The idea was to take a remotely Dom-like tree and flatten it into a
string, but not require any particular string type. Mostly I'm ripping
off HStringTemplate for the fun of it.

{-# OPTIONS -fglasgow-exts #-}
module Control.WebWidget where

import Data.Monoid
import Data.String

data (IsString s, Monoid s) => Dom s =
    Element s [Attr s] [Dom s] |
    Text s

data (IsString s, Monoid s) => Attr s = Attr s s

class (Monoid s, IsString s) => HTML d s | d -> s where
    toHtml :: d -> s

instance (Monoid s, IsString s) => HTML (Dom s) s where
    toHtml (Element name attrs children) =
        mconcat [
            fromString "<",
            name,
            mconcat $ map toHtml attrs,
            fromString ">",
            mconcat $ map toHtml children,
            fromString "</",
            name,
            fromString ">" ]
    toHtml (Text s) = s

instance (Monoid s, IsString s) => HTML (Attr s) s where
    toHtml (Attr key value) =
        mconcat [
            fromString " '",
            key,
            fromString "'='",
            value,
            fromString "' " ]


--
Darrin
From isaacdupree at charter.net  Tue Jun  3 11:56:55 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Tue Jun  3 11:49:43 2008
Subject: [Haskell-cafe] Implementing ParseChart with Data.Map
In-Reply-To: <1212445709.15010.144.camel@localhost>
References: <c97c08d20806021335w734106c4m436eea10b5b20ff3@mail.gmail.com>
	<1212445709.15010.144.camel@localhost>
Message-ID: <484569C7.7090602@charter.net>

Duncan Coutts wrote:
> modify :: k -> Map k e -> (e, Maybe e -> Map k e)
> 
> so it's a lookup that returns the element at k and also a continuation
> that lets you rebuild a new map with an altered element. I guess that
> doesn't account for the element not existing. There's probably a
> generalisation that does.

isn't it just adding the necessary Maybe?:
modify :: k -> Map k e -> (Maybe e, Maybe e -> Map k e)
?

-Isaac
From phercek at gmail.com  Tue Jun  3 12:42:44 2008
From: phercek at gmail.com (Peter Hercek)
Date: Tue Jun  3 12:35:33 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
Message-ID: <g23sa0$5u5$1@ger.gmane.org>

Loup Vaillant wrote:
> 2008/6/3 Darrin Thompson <darrinth@gmail.com>:
>> <--cut-->
>> What's the appeal of this? I personally love git, but I thought all
>> the cool kids at this school used darcs and that was that.
> 
> Disclaimer: I'm no expert, this is what I've heard. Anyone please
> confirm or deny the following?
> 
> Basically, git is waaay faster than Darcs on a number of use cases.

Other reason can be "git rebase". Of course there is a question
  how good practice it is ... but it is being used.

Peter.

From tphyahoo at gmail.com  Tue Jun  3 13:08:19 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Tue Jun  3 13:00:59 2008
Subject: [Haskell-cafe] ANN (2 Libs) -- hvac 0.1b,
	a lightweight web framework and HStringTemplate 0.3
In-Reply-To: <C389E474-BA69-4B02-AFB9-8AF70F16EC2E@gmail.com>
References: <C389E474-BA69-4B02-AFB9-8AF70F16EC2E@gmail.com>
Message-ID: <910ddf450806031008u4f3432b9hcaf26ca388fdad81@mail.gmail.com>

I just tried out hvac. I was trying to run the hvac examples
after following the readme in the samples directory.

sudo lighttpd -D -f lh.conf
[sudo] password for thartman:
2008-06-03 09:30:02: (log.c.75) server started

so that's okay, but

http://localhost:3000/hvac-board/board/1

in firefox attempted to open a binary file "1".

Same result for http://localhost:3000/hvac-board

I don't know if this is an hvac issue or a fastcgi issue (seems more
likely) but any
advice?

Thomas.

2008/3/22 Sterling Clover <s.clover@gmail.com>:
> 1) hvac 0.1b: transactional, declarative framework for lightweight web
> applications.
> 2) HStringTemplate 0.3
>
> 1) hvac 0.1b
>
> hvac (short for http view and controller) has been my project for the last
> little while, and is finally in a fairly usable state, so I'm opening up the
> repo (darcs get http://community.haskell.org/~sclv/hvac/) for folks to play
> with and to get some feedback. While not quite yet ready for hackage, the
> package as provided should be fully cabal installable. Documentation is
> available at http://community.haskell.org/~sclv/hvac/html_docs/hvac/
>
> The aim of hvac is to provide an environment that makes the creation of
> lightweight fastcgi based web applications as simple as possible, with an
> emphasis on concise, declarative style code, correct concurrent
> transactional logic, and transparency in adding caching combinators.
>
> There are two included example programs, naturally neither of which is
> feature complete. They share a common login module of about 50 lines of
> code, excluding imports, templates, and database schema.
>
> The first program is a classic, greenspun-style message board with basic
> login functionality. It totals roughly 40 lines and tends to use just under
> 4mb of resident memory on my system.
>
> The second is a wiki based on Pandoc and the PandocWiki code. The code
> totals roughly 30 lines (rendering borrowed from PandocWiki aside) and uses
> about 5mb of memory.
>
> hvac processes all requests in the STM monad, with some bells attached to
> properly interleave STM with session, database and filesystem operations
> such that they all conceptually occur together in a single transaction per
> request. Currently it is only fully tested with sqlite, but it should
> operate, modulo a few tweaks, with any database accessible via HDBC.
>
> hvac is particularly designed to use the HStringTemplate library as an
> output layer, in a simple declarative fashion. As the StringTemplate grammar
> is explicitly sub-turing, this ensures a clean separation of program logic
> from presentation, while providing a nonetheless fairly powerful language to
> express typical display tasks.
>
> The included cache combinators, still experimental, should allow a simple
> and fine-grained control over the level of caching of various disk-bound
> operations. Phantom types are used to ensure that no functions that modify
> state may be cached.
>
> To give a flavor of hvac code, the following is the complete (twenty lines!)
> source of the wiki controller (due to sql statements, some lines are rather
> long):
>
> wikiController tmpl =
>  h |/ "login" *> login_plug tmpl
>  <|>
>  (h |/ "wiki" |\\ \pageName ->    h |// "POST" *>
>          withValidation [ ("contents", return) ]
>          (\ [contents] -> do
>             pageId <- selectVal "id from pages where name=?" [toSql
> pageName]
>             maybe (addErrors [("Login","must be logged in.")] >> continue)
>                (\user -> case fromSql pageId of
>                            Just (_::Int) ->
>                              execStat "insert into
> page_hist(pageId,contents,author) values(?,?,?)" [pageId, toSql contents,
> toSql . userName $ user]
>                            Nothing -> do
>                              execStat "insert into pages(name,locked)
> values(?,?)" [toSql pageName, toSql (0::Int)]
>                              pid <- selectVal "max(id) from pages" []
>                              execStat "insert into
> page_hist(pageId,contents,author) values(?,?,?)" [pid, toSql contents, toSql
> . userName $ user]) =<< getSes
>             continue)
>       <|> do
>         pageId <- selectVal "id from pages where name=?" [toSql pageName]
>         (join $ renderf (tmpl "showPage") ("pageName", pageName)
>              <$> "pageContents" |= selectRow "* from page_hist where
> pageId=? order by time desc limit 1" [pageId] ))
>  <|> (redirect . ( ++ "/wiki/Index") =<< scriptName)
>
> Future directions for work on hvac include: Stress testing for correctness
> of transactional logic and benchmarks. Exploration of various efficiency
> tweaks. Unit tests. Further development of the cache combinator API.
> Improvement of the example apps and addition of a few others (a blog maybe).
> Expansion of the library of validator functions. Exploration of transferring
> hvac to the standard FastCGI bindings (currently it uses a custom modified
> version to work properly with STM). Improvement of the database layer,
> particularly with regards to common paging functions. Creation of a set of
> simple combinators for generating CRUD (create read update delete) pages.
> Creation of a minimal set of standard templates (maybe).
>
> 2) HStringTemplate 0.3.1
>
> This release of HStringTemplate (up now at Hackage) fixes a number of bugs
> pointed out to me by its small but growing user base (thanks, cinema,
> elliottt!) ranging from the minor (a particular two-level iteration pattern
> wasn't working properly) to the truly irritating (poor handling of file
> groups). It's still unfortunately skimpy on the docs, outside of the
> haddocks and the main StringTemplate grammar documentation at
> http://www.stringtemplate.org (although the examples from hvac should also
> prove helpful). However, it does have a set of very nice and handy new
> features for development.
>
> * renderf, a function similar in spirit to printf, that takes an arbitrary
> number of heterogeneous (String, value) tuples as arguments. This should cut
> down considerably on long setAttribute chains. Additionally, with custom
> instances (not, I'll grant, trivial to write) it can be used to
> declaratively chain together strings of attribute retrieval functions in
> arbitrary monads, as in the above code example from hvac.
>
> * dumpAttribs, a function/template that prints out the tree of the entire
> attribute environment a template is operating in -- extremely handy for
> development.
>
> * nullGroup, also for use in development, a simple way to display more
> information about templates that can't be found. Error messages in
> usafeVolatileDirectoryGroup have also been significantly improved.
>
> * getStringTemplate', a version of getStringTemplate guaranteed not to be
> inlined. While the optimizer will still sometimes rearrange code such that a
> volatile group is not updated properly, this at least helps remedy the
> situation (I think).
>
> * Some minor changes: For grammar reasons, dots have been removed from
> template names -- however, underscores and slashes are now available.
> Additionally, there's a much improved logic for which aspects of a local
> environment are overridden and preserved when a template is called from
> another.
>
> For both of these libraries, patches, comments, bug reports, requests, and
> of course contributions more than welcome!
>
> Regards,
> Sterl._______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From wnoise at ofb.net  Tue Jun  3 13:15:47 2008
From: wnoise at ofb.net (Aaron Denney)
Date: Tue Jun  3 13:08:32 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
	<g23sa0$5u5$1@ger.gmane.org>
Message-ID: <slrng4av27.ubl.wnoise@ofb.net>

On 2008-06-03, Peter Hercek <phercek@gmail.com> wrote:
> Loup Vaillant wrote:
>> 2008/6/3 Darrin Thompson <darrinth@gmail.com>:
>>> <--cut-->
>>> What's the appeal of this? I personally love git, but I thought all
>>> the cool kids at this school used darcs and that was that.
>> 
>> Disclaimer: I'm no expert, this is what I've heard. Anyone please
>> confirm or deny the following?
>> 
>> Basically, git is waaay faster than Darcs on a number of use cases.
>
> Other reason can be "git rebase". Of course there is a question
>   how good practice it is ... but it is being used.

Darcs patches are pretty much an implicit rebase.

-- 
Aaron Denney
-><-

From apfelmus at quantentunnel.de  Tue Jun  3 13:17:45 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Tue Jun  3 13:10:34 2008
Subject: [Haskell-cafe] Re: Rewrite class with fundeps in pure h98?
In-Reply-To: <a2e649c70806030853h9bd015fr5c6c84c92603a796@mail.gmail.com>
References: <a2e649c70806030853h9bd015fr5c6c84c92603a796@mail.gmail.com>
Message-ID: <g23ubp$dt8$1@ger.gmane.org>

Darrin Thompson wrote:
> I thought that I should be able to write something like the toHtml
> function below with pure H98, but when I went to write it I ended up
> needing fundeps. Is there a way to express this without using any
> extensions?
> 
> The idea was to take a remotely Dom-like tree and flatten it into a
> string, but not require any particular string type.
> 
> data (IsString s, Monoid s) => Dom s =
>     Element s [Attr s] [Dom s] |
>     Text s
> 
> data (IsString s, Monoid s) => Attr s = Attr s s
> 
> class (Monoid s, IsString s) => HTML d s | d -> s where
>     toHtml :: d -> s
> 
> instance (Monoid s, IsString s) => HTML (Dom s) s where
> 
> instance (Monoid s, IsString s) => HTML (Attr s) s where

The H98 way is to make a class for type constructors:

   class HTML d where
     toHTML :: (Monoid s, IsString s) => d s -> s

   instance HTML Dom where ...

   instance HTML Attr where ...


Btw, naming the class "HTML" is feels wrong, something like Serialize is 
probably a better fit.


Regards,
apfelmus

From tphyahoo at gmail.com  Tue Jun  3 13:20:56 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Tue Jun  3 13:13:42 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <20080602172131.GA7534@scytale.galois.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
Message-ID: <910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>

Note however that hpaste runs off an earlier version of HAppS, which
has changed radically from v8 to v9.

I seem to remember discussion of porting hpaste to the latest HAppS as
a demo app... are there still plans to do that?

Thomas.

2008/6/2 Don Stewart <dons@galois.com>:
> aditya_siram:
>>
>> I am building a web-app that, in broad strokes, allows a leader to
>> assign tasks to team members and allows team members to
>> accept/reject/pick tasks that they want to do.
>>
>> I really like Haskell and I would like to use it to implement the
>> solution. Are frameworks like Happs ready? Not so much in terms of
>> documentation, but in functionality and stability.
>
> HAppS is nice (see hpaste.org for example, which is nice and simple, and
> has been running for over a year).
>
> Another nice option in Haskell is using something like HStringTemplate
> or the xhtml combinators  with fastcgi hooked into GHC's concurrency
> mechanisms.
>
> You can find *many* more things here,
>
>    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Network
>    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Web
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From dons at galois.com  Tue Jun  3 13:23:03 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun  3 13:15:45 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>
Message-ID: <20080603172303.GA22053@scytale.galois.com>

A new version of happs was written on a Monday a couple of months ago,
using fastcgi and takusen. We're running it at galois, and you can
find the code on code.haskell.org/hpaste. So not quite what you wanted,
but another data point.

-- Don

tphyahoo:
> Note however that hpaste runs off an earlier version of HAppS, which
> has changed radically from v8 to v9.
> 
> I seem to remember discussion of porting hpaste to the latest HAppS as
> a demo app... are there still plans to do that?
> 
> Thomas.
> 
> 2008/6/2 Don Stewart <dons@galois.com>:
> > aditya_siram:
> >>
> >> I am building a web-app that, in broad strokes, allows a leader to
> >> assign tasks to team members and allows team members to
> >> accept/reject/pick tasks that they want to do.
> >>
> >> I really like Haskell and I would like to use it to implement the
> >> solution. Are frameworks like Happs ready? Not so much in terms of
> >> documentation, but in functionality and stability.
> >
> > HAppS is nice (see hpaste.org for example, which is nice and simple, and
> > has been running for over a year).
> >
> > Another nice option in Haskell is using something like HStringTemplate
> > or the xhtml combinators  with fastcgi hooked into GHC's concurrency
> > mechanisms.
> >
> > You can find *many* more things here,
> >
> >    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Network
> >    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Web
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe@haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From tphyahoo at gmail.com  Tue Jun  3 13:37:21 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Tue Jun  3 13:30:22 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <20080603172303.GA22053@scytale.galois.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>
	<20080603172303.GA22053@scytale.galois.com>
Message-ID: <910ddf450806031037n38f29034l4a4dcba81ef7269a@mail.gmail.com>

note to the curious that this is a git and not a darcs repo

git clone http://code.haskell.org/hpaste.git

thomas.

2008/6/3 Don Stewart <dons@galois.com>:
> A new version of happs was written on a Monday a couple of months ago,
> using fastcgi and takusen. We're running it at galois, and you can
> find the code on code.haskell.org/hpaste. So not quite what you wanted,
> but another data point.
>
> -- Don
>
> tphyahoo:
>> Note however that hpaste runs off an earlier version of HAppS, which
>> has changed radically from v8 to v9.
>>
>> I seem to remember discussion of porting hpaste to the latest HAppS as
>> a demo app... are there still plans to do that?
>>
>> Thomas.
>>
>> 2008/6/2 Don Stewart <dons@galois.com>:
>> > aditya_siram:
>> >>
>> >> I am building a web-app that, in broad strokes, allows a leader to
>> >> assign tasks to team members and allows team members to
>> >> accept/reject/pick tasks that they want to do.
>> >>
>> >> I really like Haskell and I would like to use it to implement the
>> >> solution. Are frameworks like Happs ready? Not so much in terms of
>> >> documentation, but in functionality and stability.
>> >
>> > HAppS is nice (see hpaste.org for example, which is nice and simple, and
>> > has been running for over a year).
>> >
>> > Another nice option in Haskell is using something like HStringTemplate
>> > or the xhtml combinators  with fastcgi hooked into GHC's concurrency
>> > mechanisms.
>> >
>> > You can find *many* more things here,
>> >
>> >    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Network
>> >    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Web
>> > _______________________________________________
>> > Haskell-Cafe mailing list
>> > Haskell-Cafe@haskell.org
>> > http://www.haskell.org/mailman/listinfo/haskell-cafe
>> >
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From dons at galois.com  Tue Jun  3 13:47:04 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun  3 13:39:43 2008
Subject: [Haskell-cafe] More on performance
Message-ID: <20080603174704.GB22053@scytale.galois.com>

I wrote up the second part of the tour of understanding low level
performance in GHC here,

    http://reddit.com/r/programming/info/6lx36/comments/

Follows on from the discussion last week about various performance
related things.

Enjoy.

-- Don
From dons at galois.com  Tue Jun  3 13:50:42 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun  3 13:43:23 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <910ddf450806031037n38f29034l4a4dcba81ef7269a@mail.gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>
	<20080603172303.GA22053@scytale.galois.com>
	<910ddf450806031037n38f29034l4a4dcba81ef7269a@mail.gmail.com>
Message-ID: <20080603175042.GC22053@scytale.galois.com>

Ah yes, the url was incorrect. Well spotted.

tphyahoo:
> note to the curious that this is a git and not a darcs repo
> 
> git clone http://code.haskell.org/hpaste.git
> 
> thomas.
> 
> 2008/6/3 Don Stewart <dons@galois.com>:
> > A new version of happs was written on a Monday a couple of months ago,
> > using fastcgi and takusen. We're running it at galois, and you can
> > find the code on code.haskell.org/hpaste. So not quite what you wanted,
> > but another data point.
> >
> > -- Don
> >
> > tphyahoo:
> >> Note however that hpaste runs off an earlier version of HAppS, which
> >> has changed radically from v8 to v9.
> >>
> >> I seem to remember discussion of porting hpaste to the latest HAppS as
> >> a demo app... are there still plans to do that?
> >>
> >> Thomas.
> >>
> >> 2008/6/2 Don Stewart <dons@galois.com>:
> >> > aditya_siram:
> >> >>
> >> >> I am building a web-app that, in broad strokes, allows a leader to
> >> >> assign tasks to team members and allows team members to
> >> >> accept/reject/pick tasks that they want to do.
> >> >>
> >> >> I really like Haskell and I would like to use it to implement the
> >> >> solution. Are frameworks like Happs ready? Not so much in terms of
> >> >> documentation, but in functionality and stability.
> >> >
> >> > HAppS is nice (see hpaste.org for example, which is nice and simple, and
> >> > has been running for over a year).
> >> >
> >> > Another nice option in Haskell is using something like HStringTemplate
> >> > or the xhtml combinators  with fastcgi hooked into GHC's concurrency
> >> > mechanisms.
> >> >
> >> > You can find *many* more things here,
> >> >
> >> >    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Network
> >> >    http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Web
> >> > _______________________________________________
> >> > Haskell-Cafe mailing list
> >> > Haskell-Cafe@haskell.org
> >> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >> >
> >> _______________________________________________
> >> Haskell-Cafe mailing list
> >> Haskell-Cafe@haskell.org
> >> http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
From phercek at gmail.com  Tue Jun  3 14:44:09 2008
From: phercek at gmail.com (Peter Hercek)
Date: Tue Jun  3 14:40:31 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <slrng4av27.ubl.wnoise@ofb.net>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>	<g23sa0$5u5$1@ger.gmane.org>
	<slrng4av27.ubl.wnoise@ofb.net>
Message-ID: <g243k9$19k$1@ger.gmane.org>

Aaron Denney wrote:
> On 2008-06-03, Peter Hercek <phercek@gmail.com> wrote:
>> Loup Vaillant wrote:
>>> 2008/6/3 Darrin Thompson <darrinth@gmail.com>:
>>>> <--cut-->
>>>> What's the appeal of this? I personally love git, but I thought all
>>>> the cool kids at this school used darcs and that was that.
>>> Disclaimer: I'm no expert, this is what I've heard. Anyone please
>>> confirm or deny the following?
>>>
>>> Basically, git is waaay faster than Darcs on a number of use cases.
>> Other reason can be "git rebase". Of course there is a question
>>   how good practice it is ... but it is being used.
> 
> Darcs patches are pretty much an implicit rebase.

You cannot push patch B if it depends on patch A without also
  pushing A. And darcs currently does not alow you to reorder
  B before A (which is what git rebase actually does). Git rebase
  works quite well even in cloned repositories.

See: http://bugs.darcs.net/issue891
Some discussin about it is also here:
http://lists.osuosl.org/pipermail/darcs-users/2008-February/011564.html

When the issue is fixed then darcs will be really patch based and
  will become the ultimate DSCM :-)

From alfonso.acosta at gmail.com  Tue Jun  3 14:55:05 2008
From: alfonso.acosta at gmail.com (Alfonso Acosta)
Date: Tue Jun  3 14:47:46 2008
Subject: [Haskell-cafe] Re: type-level integers using type families
In-Reply-To: <483E1FCF.9000101@gmail.com>
References: <483E1FCF.9000101@gmail.com>
Message-ID: <6a7c66fc0806031155s3562cbbag7990814a0aeeeb56@mail.gmail.com>

On Thu, May 29, 2008 at 5:15 AM, Peter Gavin <pgavin@gmail.com> wrote:
> Has anyone else tried implementing type-level integers using type families?

When I started to work on thetype-level and parameterized data
packages,  I considered using type-families and GADTs, but I found
quite a few problems which have been nicely summarized by Benedikt in
this thread.
From s.clover at gmail.com  Tue Jun  3 14:59:11 2008
From: s.clover at gmail.com (Sterling Clover)
Date: Tue Jun  3 14:51:53 2008
Subject: [Haskell-cafe] ANN (2 Libs) -- hvac 0.1b,
	a lightweight web framework and HStringTemplate 0.3
In-Reply-To: <910ddf450806031008u4f3432b9hcaf26ca388fdad81@mail.gmail.com>
References: <C389E474-BA69-4B02-AFB9-8AF70F16EC2E@gmail.com>
	<910ddf450806031008u4f3432b9hcaf26ca388fdad81@mail.gmail.com>
Message-ID: <B510CC63-F3E1-4D5F-8BFE-BEED933A4549@gmail.com>

Probably best not to keep this discussion in -cafe after this, as  
this is more of a debugging-type issue, but in my experience, I bet  
the lighttpd server is trying to serve the hvac-board fcgi file  
directly as a binary, rather than launching it as a fastcgi instance  
at all.  The configurations files I've built have worked fine for me,  
but your milage may vary -- getting fastcgi up and running can be a  
bit of a bear at times. At a minimum, you should make sure that the  
lh.conf file points correctly to your binary in the fastcgi.server  
variable, and that you have all the proper fastcgi libraries  
installed on your system.

Regards,
Sterl

On Jun 3, 2008, at 1:08 PM, Thomas Hartman wrote:

> I just tried out hvac. I was trying to run the hvac examples
> after following the readme in the samples directory.
>
> sudo lighttpd -D -f lh.conf
> [sudo] password for thartman:
> 2008-06-03 09:30:02: (log.c.75) server started
>
> so that's okay, but
>
> http://localhost:3000/hvac-board/board/1
>
> in firefox attempted to open a binary file "1".
>
> Same result for http://localhost:3000/hvac-board
>
> I don't know if this is an hvac issue or a fastcgi issue (seems more
> likely) but any
> advice?
>
> Thomas.
>
> 2008/3/22 Sterling Clover <s.clover@gmail.com>:
>> 1) hvac 0.1b: transactional, declarative framework for lightweight  
>> web
>> applications.
>> 2) HStringTemplate 0.3
>>
>> 1) hvac 0.1b
>>
>> hvac (short for http view and controller) has been my project for  
>> the last
>> little while, and is finally in a fairly usable state, so I'm  
>> opening up the
>> repo (darcs get http://community.haskell.org/~sclv/hvac/) for  
>> folks to play
>> with and to get some feedback. While not quite yet ready for  
>> hackage, the
>> package as provided should be fully cabal installable.  
>> Documentation is
>> available at http://community.haskell.org/~sclv/hvac/html_docs/hvac/
>>
>> The aim of hvac is to provide an environment that makes the  
>> creation of
>> lightweight fastcgi based web applications as simple as possible,  
>> with an
>> emphasis on concise, declarative style code, correct concurrent
>> transactional logic, and transparency in adding caching combinators.
>>
>> There are two included example programs, naturally neither of  
>> which is
>> feature complete. They share a common login module of about 50  
>> lines of
>> code, excluding imports, templates, and database schema.
>>
>> The first program is a classic, greenspun-style message board with  
>> basic
>> login functionality. It totals roughly 40 lines and tends to use  
>> just under
>> 4mb of resident memory on my system.
>>
>> The second is a wiki based on Pandoc and the PandocWiki code. The  
>> code
>> totals roughly 30 lines (rendering borrowed from PandocWiki aside)  
>> and uses
>> about 5mb of memory.
>>
>> hvac processes all requests in the STM monad, with some bells  
>> attached to
>> properly interleave STM with session, database and filesystem  
>> operations
>> such that they all conceptually occur together in a single  
>> transaction per
>> request. Currently it is only fully tested with sqlite, but it should
>> operate, modulo a few tweaks, with any database accessible via HDBC.
>>
>> hvac is particularly designed to use the HStringTemplate library  
>> as an
>> output layer, in a simple declarative fashion. As the  
>> StringTemplate grammar
>> is explicitly sub-turing, this ensures a clean separation of  
>> program logic
>> from presentation, while providing a nonetheless fairly powerful  
>> language to
>> express typical display tasks.
>>
>> The included cache combinators, still experimental, should allow a  
>> simple
>> and fine-grained control over the level of caching of various disk- 
>> bound
>> operations. Phantom types are used to ensure that no functions  
>> that modify
>> state may be cached.
>>
>> To give a flavor of hvac code, the following is the complete  
>> (twenty lines!)
>> source of the wiki controller (due to sql statements, some lines  
>> are rather
>> long):
>>
>> wikiController tmpl =
>>  h |/ "login" *> login_plug tmpl
>>  <|>
>>  (h |/ "wiki" |\\ \pageName ->    h |// "POST" *>
>>          withValidation [ ("contents", return) ]
>>          (\ [contents] -> do
>>             pageId <- selectVal "id from pages where name=?" [toSql
>> pageName]
>>             maybe (addErrors [("Login","must be logged in.")] >>  
>> continue)
>>                (\user -> case fromSql pageId of
>>                            Just (_::Int) ->
>>                              execStat "insert into
>> page_hist(pageId,contents,author) values(?,?,?)" [pageId, toSql  
>> contents,
>> toSql . userName $ user]
>>                            Nothing -> do
>>                              execStat "insert into pages(name,locked)
>> values(?,?)" [toSql pageName, toSql (0::Int)]
>>                              pid <- selectVal "max(id) from pages" []
>>                              execStat "insert into
>> page_hist(pageId,contents,author) values(?,?,?)" [pid, toSql  
>> contents, toSql
>> . userName $ user]) =<< getSes
>>             continue)
>>       <|> do
>>         pageId <- selectVal "id from pages where name=?" [toSql  
>> pageName]
>>         (join $ renderf (tmpl "showPage") ("pageName", pageName)
>>              <$> "pageContents" |= selectRow "* from page_hist where
>> pageId=? order by time desc limit 1" [pageId] ))
>>  <|> (redirect . ( ++ "/wiki/Index") =<< scriptName)
>>
>> Future directions for work on hvac include: Stress testing for  
>> correctness
>> of transactional logic and benchmarks. Exploration of various  
>> efficiency
>> tweaks. Unit tests. Further development of the cache combinator API.
>> Improvement of the example apps and addition of a few others (a  
>> blog maybe).
>> Expansion of the library of validator functions. Exploration of  
>> transferring
>> hvac to the standard FastCGI bindings (currently it uses a custom  
>> modified
>> version to work properly with STM). Improvement of the database  
>> layer,
>> particularly with regards to common paging functions. Creation of  
>> a set of
>> simple combinators for generating CRUD (create read update delete)  
>> pages.
>> Creation of a minimal set of standard templates (maybe).
>>
>> 2) HStringTemplate 0.3.1
>>
>> This release of HStringTemplate (up now at Hackage) fixes a number  
>> of bugs
>> pointed out to me by its small but growing user base (thanks, cinema,
>> elliottt!) ranging from the minor (a particular two-level  
>> iteration pattern
>> wasn't working properly) to the truly irritating (poor handling of  
>> file
>> groups). It's still unfortunately skimpy on the docs, outside of the
>> haddocks and the main StringTemplate grammar documentation at
>> http://www.stringtemplate.org (although the examples from hvac  
>> should also
>> prove helpful). However, it does have a set of very nice and handy  
>> new
>> features for development.
>>
>> * renderf, a function similar in spirit to printf, that takes an  
>> arbitrary
>> number of heterogeneous (String, value) tuples as arguments. This  
>> should cut
>> down considerably on long setAttribute chains. Additionally, with  
>> custom
>> instances (not, I'll grant, trivial to write) it can be used to
>> declaratively chain together strings of attribute retrieval  
>> functions in
>> arbitrary monads, as in the above code example from hvac.
>>
>> * dumpAttribs, a function/template that prints out the tree of the  
>> entire
>> attribute environment a template is operating in -- extremely  
>> handy for
>> development.
>>
>> * nullGroup, also for use in development, a simple way to display  
>> more
>> information about templates that can't be found. Error messages in
>> usafeVolatileDirectoryGroup have also been significantly improved.
>>
>> * getStringTemplate', a version of getStringTemplate guaranteed  
>> not to be
>> inlined. While the optimizer will still sometimes rearrange code  
>> such that a
>> volatile group is not updated properly, this at least helps remedy  
>> the
>> situation (I think).
>>
>> * Some minor changes: For grammar reasons, dots have been removed  
>> from
>> template names -- however, underscores and slashes are now available.
>> Additionally, there's a much improved logic for which aspects of a  
>> local
>> environment are overridden and preserved when a template is called  
>> from
>> another.
>>
>> For both of these libraries, patches, comments, bug reports,  
>> requests, and
>> of course contributions more than welcome!
>>
>> Regards,
>> Sterl._______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>

From s.clover at gmail.com  Tue Jun  3 15:02:49 2008
From: s.clover at gmail.com (Sterling Clover)
Date: Tue Jun  3 14:55:29 2008
Subject: [Haskell-cafe] Re: Rewrite class with fundeps in pure h98?
In-Reply-To: <g23ubp$dt8$1@ger.gmane.org>
References: <a2e649c70806030853h9bd015fr5c6c84c92603a796@mail.gmail.com>
	<g23ubp$dt8$1@ger.gmane.org>
Message-ID: <A95A1AC3-8322-4BC5-981B-B70916FD9E9E@gmail.com>

This was how it was originally done in HStringTemplate, as I recall.  
The mptcs were introduced in order to maintain lookup-maps of the  
correct type, and particularly to allow embedding of templates within  
one another. There may have been some other corner-cases involved as  
well. However, unless you run into them, the H98 way is certainly  
cleaner.

--Sterl

On Jun 3, 2008, at 1:17 PM, apfelmus wrote:

> Darrin Thompson wrote:
>> I thought that I should be able to write something like the toHtml
>> function below with pure H98, but when I went to write it I ended up
>> needing fundeps. Is there a way to express this without using any
>> extensions?
>> The idea was to take a remotely Dom-like tree and flatten it into a
>> string, but not require any particular string type.
>> data (IsString s, Monoid s) => Dom s =
>>     Element s [Attr s] [Dom s] |
>>     Text s
>> data (IsString s, Monoid s) => Attr s = Attr s s
>> class (Monoid s, IsString s) => HTML d s | d -> s where
>>     toHtml :: d -> s
>> instance (Monoid s, IsString s) => HTML (Dom s) s where
>> instance (Monoid s, IsString s) => HTML (Attr s) s where
>
> The H98 way is to make a class for type constructors:
>
>   class HTML d where
>     toHTML :: (Monoid s, IsString s) => d s -> s
>
>   instance HTML Dom where ...
>
>   instance HTML Attr where ...
>
>
> Btw, naming the class "HTML" is feels wrong, something like  
> Serialize is probably a better fit.
>
>
> Regards,
> apfelmus
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From jgoerzen at complete.org  Tue Jun  3 16:00:20 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Tue Jun  3 15:53:06 2008
Subject: [Haskell-cafe] HDBC-odbc 1.1.4.4 fixes Windows linking problems
Message-ID: <20080603200020.GA13041@complete.org>

Hi,

HDBC-odbc version 1.1.4.4 has been uploaded to Hackage.  It fixes the
problems some here have encountered regarding ODBC crashes or other
similar odd behavior on Windows.  Thanks to Andrew Appleyard for
tracking down the problem and sending me a patch.

The detailed explanation, if you're interested, is a ccall vs. stdcall
issue in FFI.  Details here:

http://git.complete.org/hdbc-odbc?a=commit;h=cca312d9891d227094494dcee518f436042e14b4

People that are not using HDBC-odbc on Windows will not find any
difference or other changes in this version.

-- 
John Goerzen
Author, Foundations of Python Network Programming
http://www.amazon.com/exec/obidos/tg/detail/-/1590593715
From vigalchin at gmail.com  Tue Jun  3 16:40:08 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun  3 16:32:50 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <1212483926.15010.192.camel@localhost>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
	<1212403100.15010.133.camel@localhost>
	<5ae4f2ba0806022111l33fecf27xfbd6ee5f7dabf35f@mail.gmail.com>
	<1212483926.15010.192.camel@localhost>
Message-ID: <5ae4f2ba0806031340h64bc888bs209f75e8eadb3545@mail.gmail.com>

> Something like that yes.
>
> You're running runhaskell Setup.lhs and that loads and runs code from
> the Cabal library. The Cabal library depends on the process library
> which depends on the unix library. So by replacing the same version of
> the unix package you're breaking everything else which depends on it,
> including Cabal and thus runhaskell Setup.lhs.
>
> So the solution is to not do that. Don't re-install the exact same
> version of any of the core libs that come with ghc. Adding new versions
> is fine, replacing existing versions is not fine because it breaks all
> the other packages that were already built against that package.
>

     But Duncan, let's suppose I build "unix" putting in a "local" directory
with a different version number than the released version of "unix".

     1) How do I get the "local" package.conf built and populated?

     2) How do I get a test case to link against this experimental local
version of "unix"? Is there a "--prefix" or something like that I pass on
runhaskell Setup.hs build?

Regards, Vasili


> Duncan
>
>
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From wnoise at ofb.net  Tue Jun  3 16:54:38 2008
From: wnoise at ofb.net (Aaron Denney)
Date: Tue Jun  3 16:47:25 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
	<g23sa0$5u5$1@ger.gmane.org> <slrng4av27.ubl.wnoise@ofb.net>
	<g243k9$19k$1@ger.gmane.org>
Message-ID: <slrng4bbsh.d0.wnoise@ofb.net>

This is drifting off-topic, but...
On 2008-06-03, Peter Hercek <phercek@gmail.com> wrote:
> Aaron Denney wrote:
>> On 2008-06-03, Peter Hercek <phercek@gmail.com> wrote:
>>> Loup Vaillant wrote:
>>>> 2008/6/3 Darrin Thompson <darrinth@gmail.com>:
>>>>> <--cut-->
>>>>> What's the appeal of this? I personally love git, but I thought all
>>>>> the cool kids at this school used darcs and that was that.
>>>> Disclaimer: I'm no expert, this is what I've heard. Anyone please
>>>> confirm or deny the following?
>>>>
>>>> Basically, git is waaay faster than Darcs on a number of use cases.
>>> Other reason can be "git rebase". Of course there is a question
>>>   how good practice it is ... but it is being used.
>> 
>> Darcs patches are pretty much an implicit rebase.
>
> You cannot push patch B if it depends on patch A without also
>   pushing A. And darcs currently does not alow you to reorder
>   B before A

True.  This is a *feature* not a bug.  You shouldn't be able to do this
automatically, because it can't be done right.  You need to do this sort
of thing manually.  If you don't, the heuristics used will bite you at
some point.  When they do commute, there is no problem.

> Git rebase works quite well even in cloned repositories.

Meh.  It can, if you're really really lucky.

> See: http://bugs.darcs.net/issue891
> Some discussin about it is also here:
> http://lists.osuosl.org/pipermail/darcs-users/2008-February/011564.html
>
> When the issue is fixed then darcs will be really patch based and
>   will become the ultimate DSCM :-)

Rebasing is doable in git as a one-repository operation because each
repository has multiple branches.  As darcs has one repo per branch,
it fundamentally needs to be done in multiple repos.

There are naturally two repos, upstream, and your-feature-development.

your-feature-development has a patch A that you want to rebase.

What you should do is pull upstream into new-tracking, then pull patch A
from your-feature-development into new-tracking.

If it applies with no problem, great: mv your-feature-development
your-feature-development-old; new-tracking your-feature-development.
Of course, in this case, you could have just pulled into
your-feature-development.  If there weren't any other patches to save in
the old your-feature-development, you can delete it instead of moving
it.

When there is a conflict, then you need to handle it somehow.  Neither
git nor darcs can do it automatically.  You can just record the merge
conflict and your resolution.  This keeps repos that pulled from you
valid, but this won't give you the "clean history" that you presumably
want.  So you need to combine the merger and cleanup into a new patch
with the same log message, etc.  It's true that git does make *this*
process very nice.

There is one thing that git rebase does easily (and correctly) that darcs
doesn't do nicely: rewriting history by merging commits "prior" to the
head.  I put prior in quotes, because darcs doesn't preserve history
in the first place.  I don't find that a compelling use, as opposed to
maintaing topic branches.

-- 
Aaron Denney
-><-

From oddron at gmail.com  Tue Jun  3 16:57:34 2008
From: oddron at gmail.com (Ronald Guida)
Date: Tue Jun  3 16:50:12 2008
Subject: [Haskell-cafe] Re: appending an element to a list
In-Reply-To: <g2322j$sig$1@ger.gmane.org>
References: <483EE208.2010601@inf.fu-berlin.de> <483EF36B.5040100@daimi.au.dk>
	<48404039.6030605@cisco.com> <48405717.20206@daimi.au.dk>
	<87r6bja609.fsf@hbox.dyndns.org>
	<3c4d5adf0805302159o23113ad2sb24754e02789bb06@mail.gmail.com>
	<48414C2B.9010606@daimi.au.dk> <g1tjk4$c4i$1@ger.gmane.org>
	<3c4d5adf0806012204p25133bdaxbc22955b70f094ff@mail.gmail.com>
	<g2322j$sig$1@ger.gmane.org>
Message-ID: <62728db30806031357k4eb64655w7af1371cc6fe974d@mail.gmail.com>

Thank you, apfelmus.  That was a wonderful explanation; the debit
method in [1] finally makes sense.

[1]: Chris Okasaki. Purely Function Data Structures.
     http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf
From oddron at gmail.com  Tue Jun  3 17:14:30 2008
From: oddron at gmail.com (Ronald Guida)
Date: Tue Jun  3 17:07:09 2008
Subject: [Haskell-cafe] Laziness leaks
Message-ID: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>

I was looking at the real time queues in [1] and I wanted to see what
would happen if I tried to write one in Haskell.  The easy part was
translating the real time queue from [1], p43 into Haskell.

The hard part is testing to see if the rotations really happen what
they should.  Basically, I decided to use Debug.Trace.trace to see
when rotations were actually occurring.

I pushed the numbers 1 to 10 into the queue, and then I popped the
queue ten times.  What I found is that none of the rotations would
actually take place until the first time I actually tried to /display
the value/ of a popped element.  What I realized is that my test
driver is lazy.  I figured out that I could put a bunch of 'seq'
functions in the test driver to get the rotations to happen.

My demonstration code is in:
http://hpaste.org/8080

This leads to two questions:

1. If I find a laziness leak, is 'seq' the appropriate way to plug it?

2. Is there any way to systematically search for or detect laziness
   leaks?
From dons at galois.com  Tue Jun  3 17:18:30 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun  3 17:11:10 2008
Subject: [Haskell-cafe] Laziness leaks
In-Reply-To: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
Message-ID: <20080603211830.GF22053@scytale.galois.com>

oddron:
> I was looking at the real time queues in [1] and I wanted to see what
> would happen if I tried to write one in Haskell.  The easy part was
> translating the real time queue from [1], p43 into Haskell.
> 
> The hard part is testing to see if the rotations really happen what
> they should.  Basically, I decided to use Debug.Trace.trace to see
> when rotations were actually occurring.
> 
> I pushed the numbers 1 to 10 into the queue, and then I popped the
> queue ten times.  What I found is that none of the rotations would
> actually take place until the first time I actually tried to /display
> the value/ of a popped element.  What I realized is that my test
> driver is lazy.  I figured out that I could put a bunch of 'seq'
> functions in the test driver to get the rotations to happen.
> 


Right, you have a requirement that things are evaluated earlier, but
you're representing this with a lazy list which will evaluate
them as late as possible.

Using something like weak strictness (seq) or deep strictness (rnf),
to enforce the requried level of evaluation prior to pushing things onto 
the queue is one way. Making the queue a stricter structure would also
work.

> My demonstration code is in:
> http://hpaste.org/8080
> 
> This leads to two questions:
> 
> 1. If I find a laziness leak, is 'seq' the appropriate way to plug it?

  * Strict data structures, for where you require stricness

    i.e. data Queue a = Nil | Node !a (Queue a)

  * Bang patterns on variables:

      foo !x = ... push x ....

  * Seq,

      foo x = x `seq` ... x ...

  * Deep seq:

      foo x = x `rnf` ... x ...

Are the main ways.
  
> 2. Is there any way to systematically search for or detect laziness
>    leaks?

Profiling, and looking at the Core. Being explicit about the evaluation
strategy you want is a fine idea though.

-- Don
From t.h at gmx.info  Tue Jun  3 17:25:28 2008
From: t.h at gmx.info (Timo B. =?utf-8?q?H=C3=BCbel?=)
Date: Tue Jun  3 17:18:08 2008
Subject: [Haskell-cafe] hs-plugins compile error
In-Reply-To: <BED9D15F73EDDE48BF480604236A45607556ED@ex1.ad.dcs.gla.ac.uk>
References: <20080602130511.GA24905@netsoc.tcd.ie>
	<20080602192332.GB24905@netsoc.tcd.ie>
	<BED9D15F73EDDE48BF480604236A45607556ED@ex1.ad.dcs.gla.ac.uk>
Message-ID: <200806032325.28694.t.h@gmx.info>

> What is the status of hs-plugins?  I recently tried to install the
> version plugins-1.2 on hackage, using a Gnu/Linux box with Fedora 9
> and ghc-6.8.2, but didn't get past the configure stage (see config.log
> below).

I am getting exactly the same error on a Gentoo box. I've tracked it down to 
some awkward escape character sequence in the TOP variable defined in 
config.h.

The following patch makes it work for me, but I've no idea if this is the 
right way to fix this problem:

hunk ./configure 1385
-TOP=`echo "Directory.getCurrentDirectory >>= putStrLn.init.tail.show " | 
ghc --interactive -ignore-dot-ghci -v0 | tr -d '\r'`
+TOP=`echo "Directory.getCurrentDirectory >>= putStr." | 
ghc --interactive -ignore-dot-ghci -v0`
hunk ./configure.ac 66
-TOP=`echo "Directory.getCurrentDirectory >>= putStrLn.init.tail.show " | 
ghc --interactive -ignore-dot-ghci -v0 | tr -d '\r'`
+TOP=`echo "Directory.getCurrentDirectory >>= putStr" | 
ghc --interactive -ignore-dot-ghci -v0`

Regards,
T.
From allbery at ece.cmu.edu  Tue Jun  3 18:12:16 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Tue Jun  3 18:04:59 2008
Subject: [Haskell-cafe] ghc 6.8.2 issue
In-Reply-To: <5ae4f2ba0806031340h64bc888bs209f75e8eadb3545@mail.gmail.com>
References: <5ae4f2ba0806012207i2797be95kf773d0cf75d6b39@mail.gmail.com>
	<1212403100.15010.133.camel@localhost>
	<5ae4f2ba0806022111l33fecf27xfbd6ee5f7dabf35f@mail.gmail.com>
	<1212483926.15010.192.camel@localhost>
	<5ae4f2ba0806031340h64bc888bs209f75e8eadb3545@mail.gmail.com>
Message-ID: <312D446F-B2AF-4A39-8F3E-5A1959A525DC@ece.cmu.edu>


On 2008 Jun 3, at 16:40, Galchin, Vasili wrote:

>      1) How do I get the "local" package.conf built and populated?
>
>      2) How do I get a test case to link against this experimental  
> local version of "unix"? Is there a "--prefix" or something like  
> that I pass on runhaskell Setup.hs build?

both cases the answer is the same:  --user --prefix=whatever

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


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From duncan.coutts at worc.ox.ac.uk  Tue Jun  3 19:06:22 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Tue Jun  3 18:55:35 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <20080603172303.GA22053@scytale.galois.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>
	<20080603172303.GA22053@scytale.galois.com>
Message-ID: <1212534382.15010.227.camel@localhost>


On Tue, 2008-06-03 at 10:23 -0700, Don Stewart wrote:
> A new version of happs was written on a Monday a couple of months ago,
> using fastcgi and takusen. We're running it at galois, and you can
> find the code on code.haskell.org/hpaste. So not quite what you wanted,
> but another data point.

That's very interesting. I hope we will also see a version with the same
feature set implemented with the latest HAppS. It would give an
interesting comparison of the web frameworks to see the same app
implemented in both.

Duncan

From sic at lerp.com  Tue Jun  3 19:03:33 2008
From: sic at lerp.com (Scott Cruzen)
Date: Tue Jun  3 18:56:11 2008
Subject: [Haskell-cafe] Re: [ANN] bloomfilter 1.0 - Fast immutable and
	mutable Bloom filters
In-Reply-To: <4841CFB2.1020203@cs.pdx.edu>
References: <48408014.30401@serpentine.com> <20080531005127.4b330ff7@solaris>
	<slrng433li.olb.wnoise@ofb.net> <20080531202904.45054b49@solaris>
	<sfid-H20080531-152306-+012.02-1@spamfilter.osbf.lua>
	<4841CFB2.1020203@cs.pdx.edu>
Message-ID: <20080603230333.GA14629@harlan.lerp.com>

* Jim Snow <jsnow@cs.pdx.edu> [080531 15:23]:
> Without looking at the code to verify that this is how it has really  
> been implemented, a bloom filter is like a series of hash tables, where  
> the hash table entries are one bit.  The bit is set if there is an item  
> that hashes to that value in the bloom filter.  So, assuming a single  
> hash table where half the bits are set, there's a 50% false positive  
> rate and no false negatives when you do a membership test.
>
> To reduce the false positives, we can add another hash table with a  
> different hash function.  Assuming it also is half full, we can check if  
> an item is in both tables, and our false positive rate drops to 25%.
>
> In practice, one might use something like 32 hash tables.  This yields a  
> false positive rate of 1/(2^32).  Their most obvious application is to  
> store the dictionary for a spell checker in a space-efficient way,  
> though I have a friend who wrote a paper on using them for router caches.
>
> There was a google tech talk on bloom filters awhile ago:  
> http://www.youtube.com/watch?v=947gWqwkhu0

One other use:

LOAF is a simple extension to email that lets you append your entire
address book to outgoing mail message without compromising your privacy.
Correspondents can use this information to prioritize their mail, and
learn more about their social networks. The LOAF home page is at
http://loaf.cantbedone.org.
From trebla at vex.net  Tue Jun  3 19:16:08 2008
From: trebla at vex.net (Albert Y. C. Lai)
Date: Tue Jun  3 19:08:46 2008
Subject: [Haskell-cafe] Laziness leaks
In-Reply-To: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
Message-ID: <4845D0B8.6040802@vex.net>

Ronald Guida wrote:
> I was looking at the real time queues in [1] and I wanted to see what
> would happen if I tried to write one in Haskell.  The easy part was
> translating the real time queue from [1], p43 into Haskell.
> 
> The hard part is testing to see if the rotations really happen what
> they should.  Basically, I decided to use Debug.Trace.trace to see
> when rotations were actually occurring.
> 
> I pushed the numbers 1 to 10 into the queue, and then I popped the
> queue ten times.  What I found is that none of the rotations would
> actually take place until the first time I actually tried to /display
> the value/ of a popped element.  What I realized is that my test
> driver is lazy.  I figured out that I could put a bunch of 'seq'
> functions in the test driver to get the rotations to happen.
> 
> My demonstration code is in:
> http://hpaste.org/8080
> 
> This leads to two questions:
> 
> 1. If I find a laziness leak, is 'seq' the appropriate way to plug it?
> 
> 2. Is there any way to systematically search for or detect laziness
>    leaks?
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 

I want to point out several non-causes of laziness. For a no-magic, 
no-surprise understanding, it is important to know both what causes 
laziness and what does not.

A. The lazy list at rtqRear, which is originally a strict list. It is an 
invariant that every thunk you put there is [] or x:y. (As a result, it 
is unnecessary to make RTQueue a strict record, since you want two of 
the fields to be lazy, and the remaining field rtqRear is de facto strict.)

B. rtqueue's thunked call to rotate, i.e.,

    rtqueue f r []    = let f' = rotate f r [] in RTQueue f' [] f'

Originally f' is forced before the record is returned (SML convention). 
In Haskell the rotate call is thunked as f' and the record is returned. 
But there will not be an accumulation of such rotate thunks. For example 
if you snoc twice in succession and the first instance builds a rotate 
thunk:

    snoc p (snoc q (RTQueue f r []))
-> snoc p (rtqueue f (q:r) [])
-> snoc p (RTQueue f' [] f')  where f' = thunk
-> rtqueue f' p:[] f'  where f' = thunk
-> f' is now forced by rtqueue's pattern matching on the 3rd param

So if one snoc builds a rotate thunk, the next snoc kills it. And 
similarly any interleaving of queue operations. (head and tail add their 
extra pattern matching.) Thus it can be proved that Haskell lags behind 
the original by just one step in this regard. This is ok unless you're 
done with reducing asymptotic cost and start looking at constant factor 
cost.

A true cause of laziness is in accumulating a chain of tail's and snocs 
without intermediate forcing, as observed.
From adam.smyczek at gmail.com  Tue Jun  3 20:11:33 2008
From: adam.smyczek at gmail.com (Adam Smyczek)
Date: Tue Jun  3 20:04:11 2008
Subject: [Haskell-cafe] A simple beginner question
Message-ID: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>

Example:

data SampleType = A | B Int | C String | D -- .... etc.

sampleTypes = [A, B 5, C "test"] :: [SampleType]

How do I find for example element A in the sampleTypes list?
Do I have to create e.g.:

isA :: SampleType -> Bool
isA A = True
isA _ = False

for every constructor and use find?
It feels like this is not the quicker method.

Thanks,
Adam


From oddron at gmail.com  Tue Jun  3 20:12:12 2008
From: oddron at gmail.com (Ronald Guida)
Date: Tue Jun  3 20:04:50 2008
Subject: [Haskell-cafe] Laziness leaks
In-Reply-To: <4845D0B8.6040802@vex.net>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
Message-ID: <62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>

Don Stewart wrote:
>> 2. Is there any way to systematically search for or detect laziness
>>    leaks?
>
> Profiling, and looking at the Core. Being explicit about the
> evaluation strategy you want is a fine idea though.

Albert Y. C. Lai wrote
> A true cause of laziness is in accumulating a chain of tail's and
> snocs without intermediate forcing, as observed.

So I just thought of something.  If laziness leads to laziness leaks,
then is there such a thing as a strictness leak?  I realized that the
answer is yes.

A lazy leak is a situation where I'm wasting resources to delay a
sequence of calculations instead of just doing them now.  But in a
strict language, I might waste resources to compute things that I'll
never need.  I would call that a strictness leak.

Now I could ask the dual question, "How do I detect strictness leaks,"
and I would probably get the same answers: profiling, looking at
object code, and being explicit about the evaluation strategy.

Both types of leaks share a lot in common.  In both cases, I'm wasting
resources.  If I have a real-time system, then either type of leak can
cause me to a miss a deadline.

With a strict evaluation strategy, I might miss a nearby deadline
because I'm busy calculating things that I don't need until the
distant future.

With a lazy evaluation strategy, I might miss a distant deadline
because I'm lazily putting off a calculation now.

If I were a college student, then this would be a laziness leak:

  Professor X assigns a report, due in a month.  Two days before the
  report is due, I'll head to the drugstore, load up on caffeine, and
  work for 48 hours straight to get it done.

And this would be a strictness leak:

  Professor X assigns a report, due in a month.  As soon as I leave
  the classroom, I'll head to the drugstore, load up on caffeine, and
  work for 48 hours straight to get it done.

And this would be an effective solution:

  Professor X assigns a report, due in a month.  I'll select 15 days,
  spaced out over the next month, and allocate four hours per day to
  work on the report.

By default, a lazy language will procrastinate.  By default, a strict
language will "anticrastinate".  Either way, I can waste resources by
blindly accepting the default time management plan.

So the real question is "How do I avoid laziness leaks or strictness
leaks" and apparently, the real answers are (1) learn how to
recognize when the default plan will waste resources, and (2) learn
how to express reasonable evaluation strategies in code.

I would ask, "how do I examine the evaluation order of my code", but
the answer is already available: use a debugger.  Haskell already has
debugging tools that do exactly what I need.
(http://www.haskell.org/haskellwiki/Debugging)

In particular, HOOD looks extremely interesting.
From ryani.spam at gmail.com  Tue Jun  3 20:33:33 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Tue Jun  3 20:26:11 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <20080603174704.GB22053@scytale.galois.com>
References: <20080603174704.GB22053@scytale.galois.com>
Message-ID: <2f9b2d30806031733p390c1590l9cedbfc5a405c704@mail.gmail.com>

I think it's hard to overstate how awesome the RULES pragma is.

Thanks for the example.

  -- ryan

On 6/3/08, Don Stewart <dons@galois.com> wrote:
> I wrote up the second part of the tour of understanding low level
> performance in GHC here,
>
>    http://reddit.com/r/programming/info/6lx36/comments/
>
> Follows on from the discussion last week about various performance
> related things.
>
> Enjoy.
>
> -- Don
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From philip.weaver at gmail.com  Tue Jun  3 20:48:24 2008
From: philip.weaver at gmail.com (Philip Weaver)
Date: Tue Jun  3 20:41:01 2008
Subject: [Haskell-cafe] A simple beginner question
In-Reply-To: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
Message-ID: <bc36e24d0806031748m632a9ecfg1f38544b65cebc57@mail.gmail.com>

On Tue, Jun 3, 2008 at 5:11 PM, Adam Smyczek <adam.smyczek@gmail.com> wrote:
> Example:
>
> data SampleType = A | B Int | C String | D -- .... etc.
>
> sampleTypes = [A, B 5, C "test"] :: [SampleType]
>
> How do I find for example element A in the sampleTypes list?
> Do I have to create e.g.:
>
> isA :: SampleType -> Bool
> isA A = True
> isA _ = False
>
> for every constructor and use find?

isA is already defined for every constructor, so all you have to do is
"find isA"

> It feels like this is not the quicker method.
>
> Thanks,
> Adam
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From oddron at gmail.com  Tue Jun  3 20:48:39 2008
From: oddron at gmail.com (Ronald Guida)
Date: Tue Jun  3 20:41:16 2008
Subject: [Haskell-cafe] A simple beginner question
In-Reply-To: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
Message-ID: <62728db30806031748qdf37398i8e725fee00700e87@mail.gmail.com>

Adam Smyczek wrote:
> data SampleType = A | B Int | C String | D -- .... etc.
>
> sampleTypes = [A, B 5, C "test"] :: [SampleType]
>
> How do I find for example element A in the sampleTypes list?

Here's one way to do it:

filter (\x -> case x of A -> True; otherwise -> False) sampleTypes
  ==> [A]

filter (\x -> case x of B _ -> True; otherwise -> False) sampleTypes
  ==> [B 5]

filter (\x -> case x of C _ -> True; otherwise -> False) sampleTypes
  ==> [C "test"]

Your idea works just as well:
> isA :: SampleType -> Bool
> isA A = True
> isA _ = False

filter isA sampleTypes
  ==> [A]

There is a third possibility:  Have you learned about the maybe
function or the either function yet?
  maybe :: b -> (a -> b) -> Maybe a -> b
  either :: (a -> c) -> (b -> c) -> Either a b -> c

I would call these "mediating morphisms", where "morphism" is techno-
babble for "function". You could write your own version of one of these
for SampleType.  Assuming you have:

  data SampleType = A | B Int | C String

You could write:

  sampletype :: t
            -> (Int -> t)
            -> (String -> t)
            -> SampleType -> t
  sampletype a bf cf s =
     case s of
       A -> a
       B n -> bf n
       C s -> cf s

  isA = sampletype True (const False) (const False)
  isB = sampletype False (const True) (const False)
  isC = sampletype False (const False) (const True)

filter isA sampleTypes
  ==> [A]

This (the mediating morphism) is probably overkill for what you want
to do, though.
From barsoap at web.de  Tue Jun  3 20:51:09 2008
From: barsoap at web.de (Achim Schneider)
Date: Tue Jun  3 20:44:03 2008
Subject: [Haskell-cafe] Re: A simple beginner question
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
Message-ID: <20080604025109.5a83976d@solaris>

Adam Smyczek <adam.smyczek@gmail.com> wrote:

> data SampleType = A | B Int | C String | D -- .... etc.
	deriving (Eq)

> sampleTypes = [A, B 5, C "test"] :: [SampleType]
> 

If you derive from Eq, you can do

isA = (==) A

filter isA sampleTypes

or ad-hoc:
filter ((==) A) sampleTypes

things like 
filter (\x -> case x of 
	{ A -> True
	; B b | b > 2 -> True
	; C c | c == "foo" -> True
	; _ -> False}) sampleTypes
work, too. Admittedly, I'm lambda-spoilt.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From barsoap at web.de  Tue Jun  3 21:02:43 2008
From: barsoap at web.de (Achim Schneider)
Date: Tue Jun  3 20:55:27 2008
Subject: [Haskell-cafe] Re: A simple beginner question
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
	<20080604025109.5a83976d@solaris>
Message-ID: <20080604030243.50c565d3@solaris>

Achim Schneider <barsoap@web.de> wrote:

> filter (\x -> case x of 
> 	{ A -> True
> 	; B b | b > 2 -> True
> 	; C c | c == "foo" -> True
> 	; _ -> False}) sampleTypes
 
coming to think of it: Why can't I write

filter (\A -> True
        \B b | b > 2 -> True
        \C c | c == "foo" -> True
        _ -> False 
       ) sampleTypes

? AFAICT it's syntactically unambiguous.

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From derek.a.elkins at gmail.com  Tue Jun  3 21:08:26 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Tue Jun  3 21:01:20 2008
Subject: [Haskell-cafe] Laziness leaks
In-Reply-To: <62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
Message-ID: <1212541707.7306.22.camel@derek-laptop>

On Tue, 2008-06-03 at 20:12 -0400, Ronald Guida wrote:
> Don Stewart wrote:
> >> 2. Is there any way to systematically search for or detect laziness
> >>    leaks?
> >
> > Profiling, and looking at the Core. Being explicit about the
> > evaluation strategy you want is a fine idea though.
> 
> Albert Y. C. Lai wrote
> > A true cause of laziness is in accumulating a chain of tail's and
> > snocs without intermediate forcing, as observed.
> 
> So I just thought of something.  If laziness leads to laziness leaks,
> then is there such a thing as a strictness leak?  I realized that the
> answer is yes.

I ask a similar question here albeit for a much narrower and more
technical notion:
http://lambda-the-ultimate.org/node/2273#comment-40156
and come to the same conclusion (at least for an even more narrow
notion).

From westondan at imageworks.com  Tue Jun  3 21:09:39 2008
From: westondan at imageworks.com (Dan Weston)
Date: Tue Jun  3 21:02:18 2008
Subject: [Haskell-cafe] A simple beginner question
In-Reply-To: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
Message-ID: <4845EB53.1070606@imageworks.com>

There's always one more way to do things in Haskell! :)

Here's yet another way to get at the payloads in a list. You don't have 
to know how this works to use it:

data SampleType = A | B Int | C String

unA :: SampleType -> [()]
unA A     = return ()
unA _     = fail "Not an A"

unB :: SampleType -> [Int]
unB (B b) = return b
unB _     = fail "Not a B"

unC :: SampleType -> [String]
unC (C c) = return c
unC _     = fail "Not a C"

-- I can check for more than one constructor...
-- Note that a single type must be returned,
-- so for C I return e.g. the length of the string
unBorC :: SampleType -> [Int]
unBorC (B b) = return b
unBorC (C c) = return (length c)
unBorC _     = fail "Not a B or C"

For lists, the >>= operator knows to ignore failure and collect anything 
else into a new list. The technobabble for this is that [] is a Monad.

*Main> let sampleTypes = [A, B 5, C "test", A, A, B 7, C "go"]
*Main> sampleTypes >>= unA
[(),(),()]
*Main> sampleTypes >>= unB
[5,7]
*Main> sampleTypes >>= unC
["test","go"]
*Main> sampleTypes >>= unBorC
[5,4,7,2]

Adam Smyczek wrote:
> Example:
> 
> data SampleType = A | B Int | C String | D -- .... etc.
> 
> sampleTypes = [A, B 5, C "test"] :: [SampleType]
> 
> How do I find for example element A in the sampleTypes list?
> Do I have to create e.g.:
> 
> isA :: SampleType -> Bool
> isA A = True
> isA _ = False
> 
> for every constructor and use find?
> It feels like this is not the quicker method.
> 
> Thanks,
> Adam
> 
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
> 


From barsoap at web.de  Tue Jun  3 21:50:36 2008
From: barsoap at web.de (Achim Schneider)
Date: Tue Jun  3 21:43:22 2008
Subject: [Haskell-cafe] Re: A simple beginner question
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
	<4845EB53.1070606@imageworks.com>
Message-ID: <20080604035036.5ae7861e@solaris>

Dan Weston <westondan@imageworks.com> wrote:

> There's always one more way to do things in Haskell! :)
> 
> Here's yet another way to get at the payloads in a list. You don't
> have to know how this works to use it:
> 
Bastard. He's going to try and find out how it works. 

To get back to the filters:

module Main where
import Control.Monad

data SampleType = A | B Int | C String deriving Show

noA :: SampleType -> [SampleType]
noA A = mzero
noA e = return e

noB :: SampleType -> [SampleType]
noB (B _) = mzero
noB e = return e

noAB :: SampleType -> [SampleType]
noAB m = [m] >>= noA >>= noB

sampleTypes = [A, B 5, C "test", A, A, B 7, C "go"]

*Main> sampleTypes >>= noA
[B 5,C "test",B 7,C "go"]
*Main> sampleTypes >>= noB
[A,C "test",A,A,C "go"]
*Main> sampleTypes >>= noAB
[C "test",C "go"]

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From greg at momotaro.chinmin.edu.tw  Tue Jun  3 23:05:41 2008
From: greg at momotaro.chinmin.edu.tw (Greg Matheson)
Date: Tue Jun  3 23:10:15 2008
Subject: [Haskell-cafe] HDBC-odbc 1.1.4.4 fixes Windows linking problems
In-Reply-To: <20080603200020.GA13041@complete.org>
References: <20080603200020.GA13041@complete.org>
Message-ID: <20080604030541.GA26462@momotaro.chinmin.edu.tw>

On Tue, 03 Jun 2008, John Goerzen wrote:

> Hi,

> HDBC-odbc version 1.1.4.4 has been uploaded to Hackage.  It fixes the
> problems some here have encountered regarding ODBC crashes or other
> similar odd behavior on Windows. 

I'm getting a 'Parse error in pattern' error.

C:\Documents and Settings\Administrator>ghci
GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> :m Database.HDBC.ODBC Database.HDBC
Prelude Database.HDBC Database.HDBC.ODBC> conn <- connectODBC "dictation"
Loading package array-0.1.0.0 ... linking ... done.
Loading package containers-0.1.0.1 ... linking ... done.
Loading package bytestring-0.9.0.1 ... linking ... done.
Loading package old-locale-1.0.0.0 ... linking ... done.
Loading package old-time-1.0.0.0 ... linking ... done.
Loading package mtl-1.1.0.0 ... linking ... done.
Loading package HDBC-1.1.4 ... linking ... done.
Loading package HDBC-odbc-1.1.4.4 ... linking ... done.
*** Exception: (unknown)
Prelude Database.HDBC Database.HDBC.ODBC> handleSqlError $ conn <- connectODBC "
dictation"
<interactive>:1:0: Parse error in pattern



-- 
Dr Bean                      If there is one thing we learn from the 
                             study of language learning, it is that
                             language learners learn more than we learn.  
From andrew.appleyard at gmail.com  Tue Jun  3 23:37:06 2008
From: andrew.appleyard at gmail.com (Andrew Appleyard)
Date: Tue Jun  3 23:31:49 2008
Subject: [Haskell-cafe] HDBC-odbc 1.1.4.4 fixes Windows linking problems
In-Reply-To: <20080604030541.GA26462@momotaro.chinmin.edu.tw>
References: <20080603200020.GA13041@complete.org>
	<20080604030541.GA26462@momotaro.chinmin.edu.tw>
Message-ID: <48460DE2.5080602@gmail.com>

On 4/06/2008 1:05 PM, Greg Matheson wrote:
> I'm getting a 'Parse error in pattern' error.
> 
> C:\Documents and Settings\Administrator>ghci
> GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
> Loading package base ... linking ... done.
> Prelude> :m Database.HDBC.ODBC Database.HDBC
> [...]
> Prelude Database.HDBC Database.HDBC.ODBC> handleSqlError $ conn <- connectODBC "
> dictation"
> <interactive>:1:0: Parse error in pattern

Try:

   conn <- handleSqlError $ connectODBC "dictation"

You can only use '<-' in a do expression, or at the GHCi prompt.

-- Andrew

From dons at galois.com  Tue Jun  3 23:56:32 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun  3 23:49:10 2008
Subject: [Haskell-cafe] A simple beginner question
In-Reply-To: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
Message-ID: <20080604035632.GA12175@scytale.galois.com>

adam.smyczek:
> Example:
> 
> data SampleType = A | B Int | C String | D -- .... etc.
> 
> sampleTypes = [A, B 5, C "test"] :: [SampleType]
> 
> How do I find for example element A in the sampleTypes list?
> Do I have to create e.g.:
> 
> isA :: SampleType -> Bool
> isA A = True
> isA _ = False
> 
> for every constructor and use find?
> It feels like this is not the quicker method.

This is where the implicit filtering in a list comprehension comes in
really handy,

    data T = A | B Int | C String | D
        deriving Show

    xs = [A, B 5, C "test", D]

    main = do print [ A | A       <- xs ] -- filter A's
              print [ x | x@(C _) <- xs ] -- filter C's

    {-

        *Main> main
        [A]
        [C "test"]

    -} 
From lrpalmer at gmail.com  Wed Jun  4 00:28:15 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun  4 00:20:52 2008
Subject: [Haskell-cafe] A simple beginner question
In-Reply-To: <62728db30806031748qdf37398i8e725fee00700e87@mail.gmail.com>
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
	<62728db30806031748qdf37398i8e725fee00700e87@mail.gmail.com>
Message-ID: <7ca3f0160806032128s44b03eeaw63242e20e8bd21ea@mail.gmail.com>

On Tue, Jun 3, 2008 at 6:48 PM, Ronald Guida <oddron@gmail.com> wrote:
> filter (\x -> case x of A -> True; otherwise -> False) sampleTypes
>  ==> [A]
>
> filter (\x -> case x of B _ -> True; otherwise -> False) sampleTypes
>  ==> [B 5]

There's a neat little mini-trick for these types of pattern matches:

filter (\x -> case x of B {} -> True; otherwise -> False) sampleTypes

Does the same thing, but works no matter how many arguments the
constructor B takes.

Luke
From bertram.felgenhauer at googlemail.com  Wed Jun  4 00:45:52 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Wed Jun  4 00:38:34 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
Message-ID: <20080604044552.GC4262@zombie.inf.tu-dresden.de>

Darrin Thompson wrote:
> On Sun, Jun 1, 2008 at 2:44 PM, Bertram Felgenhauer
> <bertram.felgenhauer@googlemail.com> wrote:
> > I'm pleased to announce yet another tool for importing darcs repositories
> > to git. [...]
>
> What's the appeal of this? I personally love git, but I thought all
> the cool kids at this school used darcs and that was that.

For myself, git-darcs-import itself is an opportunity to learn more
about both darcs and git. It wasn't meant to be argument in the git
vs. darcs discussion, although it was inevitable that it would be
seen as such.

I really like darcs' concepts, but in my opinion, darcs doesn't get
enough power out of the theory of patches to really shine so far.

This is a hard problem, and I can't offer solutions. Ideally, you'd have
semantic patches which just commute with virtually all other patches
because they "know" what they are about. The only thing that darcs
offers in that direction - besides handling conflicts, mergers and
undos gracefully, which is quite useful in itself - is a keyword
substitution patch type.

In the meantime, I prefer git to darcs, mainly because I'm sort of
attached to seeing the development history, i.e. I prefer to think of
patches as (partially) ordered instead of being a cloud of patches
that darcs uses as a model.

Bertram
From ronwalf at volus.net  Wed Jun  4 02:21:45 2008
From: ronwalf at volus.net (Ron Alford)
Date: Wed Jun  4 02:14:23 2008
Subject: [Haskell-cafe] Wouter-style expressions
Message-ID: <d9b7ed750806032321o6152eb91t70f5ed5361db9af8@mail.gmail.com>

Here's something that should be an easy extension of Wouter's approach
to extensible datatypes, but I'm failing (possibly since it's 2:20am).
 I several classes of expressions I'm trying to represent (thus,
Wouter's approach), and  my first operation to implement over them is
printing.

Attached is a simplified version of what I'm doing.  Expressions are
composed of conjunctives (and) and atoms.  Atoms are composed of a
predicate string and a list of fillers (taken from 'Const' and 'Var').
 For example (in a lisp like syntax):
(and (pred c ?var1) (pred ?var1 ?var2))

To do this, I defined a 'Printable' class:
class Functor f => Printable f where
    exprDoc :: f t -> Doc

I think the 't' here will get me into trouble later.

Combinations of printable types are also printable:
instance (Printable f, Printable g) => Printable (f :+: g) where
    exprDoc (Inr x) = exprDoc x
    exprDoc (Inl y) = exprDoc y


Constants, variables, and atoms are defined to be printable:
instance Printable Var where
    exprDoc (Var name) = text ('?':name)

instance Printable Const where
    exprDoc (Const name) = text name

instance Printable f => Printable (Atomic (Expr f)) where
    exprDoc (Atomic p tl) = parens $ hsep $
        (text p) : (map (\ (In t) -> exprDoc t) tl)

But the obvious definition for conjunction doesn't work:
instance Printable And where
    exprDoc (And el) = sep (map exprDoc el)

GHC barfs, throwing:
Couldn't match expected type `f t' against inferred type `t1'
      `t1' is a rigid type variable bound by
           the type signature for `exprDoc' at WouterTest.hs:62:17
      Expected type: [f t]
      Inferred type: [t1]
    In the second argument of `map', namely `el'
    In the first argument of `sep', namely `(map exprDoc el)'


I've attached the code.  Compile and inspect with:
$ ghci -fglasgow-exts -fallow-overlapping-instances WouterTest.hs

test1 works great (other than needing some redundant typing, any hints?).

test2 needs the definition of 'Printable And' to print, but I haven't
gotten that to work yet.  It also needs the redundant typing.


-Ron

However, I tried making more complex expression (conjunction, in this
case), but I can't get the types to align.  In particular, if I
uncomment the obvious definition
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From lemming at henning-thielemann.de  Wed Jun  4 03:32:04 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun  4 03:24:39 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <20080603174704.GB22053@scytale.galois.com>
References: <20080603174704.GB22053@scytale.galois.com>
Message-ID: <Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>


On Tue, 3 Jun 2008, Don Stewart wrote:

> I wrote up the second part of the tour of understanding low level
> performance in GHC here,
>
>     http://reddit.com/r/programming/info/6lx36/comments/
>
> Follows on from the discussion last week about various performance
> related things.

Now the difficult question: How to write the 'mean' function in terms of
'sum' and 'length' while getting the same performance?
From bjpop at csse.unimelb.edu.au  Wed Jun  4 03:57:50 2008
From: bjpop at csse.unimelb.edu.au (Bernie Pope)
Date: Wed Jun  4 03:43:05 2008
Subject: [Haskell-cafe] Laziness leaks
In-Reply-To: <62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
Message-ID: <68006573-98CC-44E8-97DC-B025DEA033E7@csse.unimelb.edu.au>


On 04/06/2008, at 10:12 AM, Ronald Guida wrote:
> I would ask, "how do I examine the evaluation order of my code", but
> the answer is already available: use a debugger.  Haskell already has
> debugging tools that do exactly what I need.
> (http://www.haskell.org/haskellwiki/Debugging)
>
> In particular, HOOD looks extremely interesting.

I would recommend the GHCi debugger for looking at the evaluation  
order of code.
Single stepping can be very illuminating.

Bernie.
From wss at Cs.Nott.AC.UK  Wed Jun  4 04:22:06 2008
From: wss at Cs.Nott.AC.UK (Wouter Swierstra)
Date: Wed Jun  4 04:15:38 2008
Subject: [Haskell-cafe] Wouter-style expressions
In-Reply-To: <d9b7ed750806032321o6152eb91t70f5ed5361db9af8@mail.gmail.com>
References: <d9b7ed750806032321o6152eb91t70f5ed5361db9af8@mail.gmail.com>
Message-ID: <06B81692-7391-420A-B476-F328FF743633@Cs.Nott.AC.UK>

Hi Ron,

I've attached a revised file that solves your problem.

The solution is actually quite subtle. If you define the class as:

class Functor f => Printable f where
  exprDoc :: f t -> Doc

you can't make recursive calls to sub-expressions. There is, after  
all, no reason to believe that "t" is Printable. The following choice  
of class is better:

class Functor f => Printable f where
   exprDoc :: Printable g => f (Expr g) -> Doc

Now when you define the instance for And, you can safely make  
recursive calls to the list of subchildren.

To define the function you want, just add a wrapper to exprDoc:

ppExpr : Printable f => Expr f -> Doc
ppExpr (In t) = exprDoc t

All the best,

Wouter

PS - You may want to add:

infixr 6 :+:

to you code. It'll save you a lot of parentheses!


This message has been checked for viruses but the contents of an attachment
may still contain software viruses, which could damage your computer system:
you are advised to perform your own checks. Email communications with the
University of Nottingham may be monitored as permitted by UK legislation.

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From gale at sefer.org  Wed Jun  4 04:24:22 2008
From: gale at sefer.org (Yitzchak Gale)
Date: Wed Jun  4 04:16:58 2008
Subject: [Haskell-cafe] A simple beginner question
In-Reply-To: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
References: <0F2FB381-056A-45E2-A046-ED80466F6608@gmail.com>
Message-ID: <2608b8a80806040124n2afb7cbcx931461a01d1e0e14@mail.gmail.com>

Adam Smyczek wrote:
> data SampleType = A | B Int | C String | D -- .... etc.
> sampleTypes = [A, B 5, C "test"] :: [SampleType]
> How do I find for example element A in the sampleTypes list?

There have been many useful replies. But since Adam
originally announced that this is a "beginner question", I think
some perspective is in order.

In Haskell, there is often no need at all for boolean-valued
functions to deconstruct a data structure. Usually pattern
matching does the job beautifully, and you structure your program
to exploit that. In the case that you do need them, though, the
previous responses are excellent suggestions.

In my experience, the ways that I get data out of an ADT,
from most common to most rare, are:

1. Just use pattern matching
2. Use record syntax to get selector functions
3. Define an Eq instance
4. Define per-constructor modifiers when the ADT is used as
  state in a state monad (this one is admittedly a pain in the neck)

I can't remember the last time I needed to write a function
like "isA" - it almost never comes up.

My opinion, YMMV.

Regards,
Yitz
From phercek at gmail.com  Wed Jun  4 04:37:10 2008
From: phercek at gmail.com (Peter Hercek)
Date: Wed Jun  4 04:29:54 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <slrng4bbsh.d0.wnoise@ofb.net>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>	<g23sa0$5u5$1@ger.gmane.org>
	<slrng4av27.ubl.wnoise@ofb.net>	<g243k9$19k$1@ger.gmane.org>
	<slrng4bbsh.d0.wnoise@ofb.net>
Message-ID: <g25k7i$c1s$1@ger.gmane.org>

Aaron Denney wrote:
> This is drifting off-topic, but...
> On 2008-06-03, Peter Hercek <phercek@gmail.com> wrote:
>> Aaron Denney wrote:
<--- cut --->
>>> Darcs patches are pretty much an implicit rebase.
>> You cannot push patch B if it depends on patch A without also
>>   pushing A. And darcs currently does not alow you to reorder
>>   B before A
> 
> True.  This is a *feature* not a bug.  You shouldn't be able to do this
> automatically, because it can't be done right.  You need to do this sort
> of thing manually.  If you don't, the heuristics used will bite you at
> some point.  When they do commute, there is no problem.

Sorry, I did not intend to indicate it should be done without doing the
  reordering first (by providing manual conflict resolution).

>> Git rebase works quite well even in cloned repositories.
> 
> Meh.  It can, if you're really really lucky.

Actually you are probably right, I needed to use a non-complicated
  workaround once (but I did it only about two times!). I might have
  been just lucky. I liked though that it did tell me what was wrong,
  in contrast to mercurial queues which just replicated both original
  branch and the rebased branch (so I finished with two copies on
  both sides at the end :-( ).

<--- cut --->

> Rebasing is doable in git as a one-repository operation because each
> repository has multiple branches.  As darcs has one repo per branch,
> it fundamentally needs to be done in multiple repos.
> 
> There are naturally two repos, upstream, and your-feature-development.
> 
> your-feature-development has a patch A that you want to rebase.
> 
> What you should do is pull upstream into new-tracking, then pull patch A
> from your-feature-development into new-tracking.
> 
> If it applies with no problem, great: mv your-feature-development
> your-feature-development-old; new-tracking your-feature-development.
> Of course, in this case, you could have just pulled into
> your-feature-development.  If there weren't any other patches to save in
> the old your-feature-development, you can delete it instead of moving
> it.
> 
> When there is a conflict, then you need to handle it somehow.  Neither
> git nor darcs can do it automatically.  You can just record the merge
> conflict and your resolution.  This keeps repos that pulled from you
> valid, but this won't give you the "clean history" that you presumably
> want.  So you need to combine the merger and cleanup into a new patch
> with the same log message, etc.  It's true that git does make *this*
> process very nice.

Ok, in such a simple case darcs can preserve the message too if the
  repository is not cloned (and you indicated that it does not really
  work with cloned repositories in git - I'm not an experienced git user).
  Just pull to the original repository and use amend-record to resolve
  the conflict and the message will be preserved. So I would tell that
  for *this* *simple* case darcs is better.

But what about this git rebasing option? How to do it more easily
  (than the solution I know and I described it later) in darcs?

using "git-rebase --onto master next topic" to get from:
     o---o---o---o---o  master
          \
           o---o---o---o---o  next
                            \
                             o---o---o  topic
to:

     o---o---o---o---o  master
         |            \
         |             o'--o'--o'  topic
          \
           o---o---o---o---o  next

This is the reason why I mentioned reordering depending patches AB
  to BA (with manual conflict resolution) would be needed in darcs
  to support (I believe a better) alternative to git rebase.
I do not know how to do this in darcs (without doing manual addition
  of "topic" changes with gnu patch utility in a new darcs repository
  clone which would not have "topic" changes (and "next" changes as
  well) pulled in and throwing avay the old one at the end).

> There is one thing that git rebase does easily (and correctly) that darcs
> doesn't do nicely: rewriting history by merging commits "prior" to the
> head.  I put prior in quotes, because darcs doesn't preserve history
> in the first place.  I don't find that a compelling use, as opposed to
> maintaing topic branches.

I do not know what you mean here. Can you point me to some example?

I hope that this is not too off-topic for haskell cafe ... and so far
  I believe this is not a flame war :-) I just like that Bertram's code
  exists and I think it (as well as git) should not be dismissed, since
  AFAIK there is more than performance to git as well as there is more
  to darcs than it not imposing patch order on us (which is the darcs
  feature I like).

Peter.

From jules at jellybean.co.uk  Wed Jun  4 04:39:58 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Wed Jun  4 04:32:35 2008
Subject: [Haskell-cafe] Laziness leaks
In-Reply-To: <62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
Message-ID: <484654DE.9090907@jellybean.co.uk>

Ronald Guida wrote:

[snip]

> By default, a lazy language will procrastinate.  By default, a strict
> language will "anticrastinate".  Either way, I can waste resources by
> blindly accepting the default time management plan.

Nice analysis.

Would you like to put that (the whole thing, not just that last para) on 
the wiki?

Jules
From simonpj at microsoft.com  Wed Jun  4 05:09:47 2008
From: simonpj at microsoft.com (Simon Peyton-Jones)
Date: Wed Jun  4 05:02:35 2008
Subject: [Haskell-cafe] problems with derive/TH
In-Reply-To: <910ddf450805230811v164ee48bp92544d433f086238@mail.gmail.com>
References: <910ddf450805230811v164ee48bp92544d433f086238@mail.gmail.com>
Message-ID: <638ABD0A29C8884A91BC5FB5C349B1C32AE5944FE8@EA-EXMSG-C334.europe.corp.microsoft.com>

| World.hs:42:0:
|    No instances for (Eq (a (M.Map String Player)),
|                      Eq (a (M.Map ItemId Item)),
|                      Eq (a (M.Map PlayerId Player)),
|                      Eq (a (M.Map RoomId Room)),
|                      Eq (a RoomId))
|      arising from the 'deriving' clause of a data type declaration
|                   at World.hs:(42,0)-(50,14)

Yes, automatic 'deriving' in GHC became a little more restrictive in GHC 6.8 (I think), for very good reasons.

I think that's what your problem is.  The darcs repo http://cdsmith.twu.net/demos/mud seems to be offline today, so I can't look, but I think that's highly likely.  The solution is invariably to add a manual instance declaration, as you have done in your subsequent message.

Simon
From greg at momotaro.chinmin.edu.tw  Wed Jun  4 05:03:17 2008
From: greg at momotaro.chinmin.edu.tw (Greg Matheson)
Date: Wed Jun  4 05:07:39 2008
Subject: [Haskell-cafe] HDBC-odbc 1.1.4.4 fixes Windows linking problems
In-Reply-To: <48460DE2.5080602@gmail.com>
References: <20080603200020.GA13041@complete.org>
	<20080604030541.GA26462@momotaro.chinmin.edu.tw>
	<48460DE2.5080602@gmail.com>
Message-ID: <20080604090317.GA26893@momotaro.chinmin.edu.tw>

On Wed, 04 Jun 2008, Andrew Appleyard wrote:

> >Prelude Database.HDBC Database.HDBC.ODBC> handleSqlError $ conn <- 
> >connectODBC "dictation"
> ><interactive>:1:0: Parse error in pattern

> Try:

>   conn <- handleSqlError $ connectODBC "dictation"

C:\cygwin\home\Administrator>dictation
dictation: user error (SQL error: SqlError {seState = "[\"IM002\",\"01S00\"]", s
eNativeError = -1, seErrorMsg = "connectODBC/sqlDriverConnect: [\"0: [Microsoft]
[ODBC \\197X\\176\\202\\181{\\166\\161\\186\\222\\178z\\173\\251] \\167\\228\\16
4\\163\\168\\236\\184\\234\\174\\198\\168\\211\\183\\189\\166W\\186\\217\\165B\\
165\\188\\171\\252\\169w\\185w\\179]\\170\\186\\197X\\176\\202\\181{\\166\\161\"
,\"0: [Microsoft][ODBC \\197X\\176\\202\\181{\\166\\161\\186\\222\\178z\\173\\25
1] \\181L\\174\\196\\170\\186\\179s\\189u\\166r\\166\\234\\196\\221\\169\\202\"]
"})

ghc can't handle Chinese Big5, it appears, but HDBC also does appear
to be talking ODBC.

--
Dr Bean                      If there is one thing we know after
                             studying experts, it is that
                             experts know more than we know.
From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 05:30:22 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 05:19:31 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
Message-ID: <1212571822.15010.266.camel@localhost>


On Wed, 2008-06-04 at 09:32 +0200, Henning Thielemann wrote:
> On Tue, 3 Jun 2008, Don Stewart wrote:
> 
> > I wrote up the second part of the tour of understanding low level
> > performance in GHC here,
> >
> >     http://reddit.com/r/programming/info/6lx36/comments/
> >
> > Follows on from the discussion last week about various performance
> > related things.
> 
> Now the difficult question: How to write the 'mean' function in terms of
> 'sum' and 'length' while getting the same performance?

There's another rather harder fusion transformation that notices when
two left folds are demanded in the same strictness context and they fold
over the same input list then they can be performed together.

sum    = foldl (\s x -> s + x) 0
length = foldl (\l x -> l + 1) 0

mean xs = sum xs / length xs

So we must note that sum and length are demanded at the same time and
since they are both foldl's will consume the whole of xs.

So we can merge the two foldl's into one just by tupling them up:

sumlength = foldl (\(s, l) x -> (s + x, l + 1)) (0, 0)

mean xs = s / l
  where (s, l) = sumlength xs

The Fortran people have been doing this kind of loop fusion for some
years. What makes it a bit harder for us is that we cannot do it with
rules because it's not a simple local transformation. It could probably
be done with a special compiler pass, though it'd need strictness
analysis to be done much earlier.

Duncan

From apfelmus at quantentunnel.de  Wed Jun  4 05:42:40 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Wed Jun  4 05:35:31 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
Message-ID: <g25o2h$p3p$1@ger.gmane.org>

Ronald Guida wrote:
> So I just thought of something.  If laziness leads to laziness leaks,
> then is there such a thing as a strictness leak?  I realized that the
> answer is yes.
> 
> A lazy leak is a situation where I'm wasting resources to delay a
> sequence of calculations instead of just doing them now.  But in a
> strict language, I might waste resources to compute things that I'll
> never need.  I would call that a strictness leak.
> 
> Now I could ask the dual question, "How do I detect strictness leaks,"
> and I would probably get the same answers: profiling, looking at
> object code, and being explicit about the evaluation strategy.
> 
> Both types of leaks share a lot in common.  In both cases, I'm wasting
> resources.  If I have a real-time system, then either type of leak can
> cause me to a miss a deadline.

I haven't heard the terms "laziness leak" and "strictness leak" before, 
imho they sound a bit spooky because it's not clear to me what the 
situation without leak would be. (Time vs Space? Is an O(n) algorithm a 
strictness leak compared to an O(log n) algorithm?)


Note that lazy evaluation never wastes time; evaluating a term with lazy 
evaluation will always take less reduction steps than doing so eagerly 
or partly eagerly. But it can waste space (-> "space leak"), for 
instance by accumulating a big expression like

   (..) -> ((..)+1) -> (((..) + 1) + 1) -> etc.

instead of evaluating  x+1  immediately

    5   -> 6        -> 7                -> etc.

However, this would be wasted time in case the whole expression will not 
be evaluated but just thrown away. So, it's a trade-off.

The effect you have in mind only appears in real-time systems, where 
lazy evaluation procrastinates everything by default. So, trying to 
implement a real-time system in a lazy language is more or less a 
paradox :) as Okasaki already points out in his book.


Eager evaluation may "waste" both time and space compared to alternative 
course of reduction.


Regards,
apfelmus

PS: The reduction strategies we compare to don't evaluate under lambdas.

From loup.vaillant at gmail.com  Wed Jun  4 05:48:18 2008
From: loup.vaillant at gmail.com (Loup Vaillant)
Date: Wed Jun  4 05:40:55 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <1212571822.15010.266.camel@localhost>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
Message-ID: <6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>

[Forgot to post to the list, sorry]

2008/6/4 Duncan Coutts <duncan.coutts@worc.ox.ac.uk>:
>
> On Wed, 2008-06-04 at 09:32 +0200, Henning Thielemann wrote:
>> On Tue, 3 Jun 2008, Don Stewart wrote:
>>
>> > I wrote up the second part of the tour of understanding low level
>> > performance in GHC here,
>> >
>> >     http://reddit.com/r/programming/info/6lx36/comments/
>> >
>> > Follows on from the discussion last week about various performance
>> > related things.
>>
>> Now the difficult question: How to write the 'mean' function in terms of
>> 'sum' and 'length' while getting the same performance?
>
> There's another rather harder fusion transformation that notices when
> two left folds are demanded in the same strictness context and they fold
> over the same input list then they can be performed together.
>
> sum    = foldl (\s x -> s + x) 0
> length = foldl (\l x -> l + 1) 0
>
> mean xs = sum xs / length xs
>
> So we must note that sum and length are demanded at the same time and
> since they are both foldl's will consume the whole of xs.
>
> So we can merge the two foldl's into one just by tupling them up:
>
> sumlength = foldl (\(s, l) x -> (s + x, l + 1)) (0, 0)
>
> mean xs = s / l
>  where (s, l) = sumlength xs

I see a problem with this particular fusion, though: It changes the
space complexity of the program, from linear to constant. Therefore,
with some programs, relying on this "optimization" can be a matter of
correctness, not just performance. Therefore, if it is not clear when
the compiler will optimize this, I'd rather not use it. (A counter
example is tail calls, which are rather easily deducible, at least in
a strict context)

At least, with more simple fusions, the difference was between
stressing the GC or not. The space and time complexities of the
problem didn't change at all. Only the constants did.

Loup
From ketil at malde.org  Wed Jun  4 05:49:49 2008
From: ketil at malde.org (Ketil Malde)
Date: Wed Jun  4 05:42:09 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	(Henning Thielemann's message of "Wed\,
	04 Jun 2008 09\:32\:04 +0200 \(MEST\)")
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
Message-ID: <87lk1l34xu.fsf@malde.org>


Henning Thielemann <lemming@henning-thielemann.de> writes:

> Now the difficult question: How to write the 'mean' function in terms of
> 'sum' and 'length' while getting the same performance?

Write a RULE pragma converting

 \xs -> (foldl' f y0 xs,foldl' g z0 xs) 

into

 \xs -> foldl' (\(y,z) x -> (f y x,g z x)) (y0,z0) xs

?

To actually work, it'd have to work for arbitrary top level function,
not just the (,) constructor.  No idea if it's feasible at all, of
course :-)

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From lemming at henning-thielemann.de  Wed Jun  4 05:51:42 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun  4 05:44:24 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <1212571822.15010.266.camel@localhost>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
Message-ID: <Pine.LNX.4.64.0806041144450.10155@poolpc16.informatik.uni-halle.de>


On Wed, 4 Jun 2008, Duncan Coutts wrote:

> On Wed, 2008-06-04 at 09:32 +0200, Henning Thielemann wrote:
>>
>> Now the difficult question: How to write the 'mean' function in terms of
>> 'sum' and 'length' while getting the same performance?
>
> There's another rather harder fusion transformation that notices when
> two left folds are demanded in the same strictness context and they fold
> over the same input list then they can be performed together.
>
> sum    = foldl (\s x -> s + x) 0
> length = foldl (\l x -> l + 1) 0
>
> mean xs = sum xs / length xs
>
> So we must note that sum and length are demanded at the same time and
> since they are both foldl's will consume the whole of xs.
>
> So we can merge the two foldl's into one just by tupling them up:
>
> sumlength = foldl (\(s, l) x -> (s + x, l + 1)) (0, 0)
>
> mean xs = s / l
>  where (s, l) = sumlength xs


How about assisting the compiler with a helper function named 'parallel' ?

parallel :: ([a] -> b, [a] -> c) -> [a] -> (b,c)
parallel (f,g) xs = (f xs, g xs)

mean xs =
   uncurry (/) $ parallel (sum,length) xs


? We could state RULES in terms of 'parallel'. By calling 'parallel', the 
user tells, that he wants fusion here.

Say
   "parallel/foldl/foldl" forall f, g, x0, y0.
       parallel (foldl f x0, foldl g y0) = foldl (\(x,y) z -> (f x z, g y z)) (x0,y0)
From apfelmus at quantentunnel.de  Wed Jun  4 06:00:34 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Wed Jun  4 05:53:25 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <g25k7i$c1s$1@ger.gmane.org>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>	<g23sa0$5u5$1@ger.gmane.org>	<slrng4av27.ubl.wnoise@ofb.net>	<g243k9$19k$1@ger.gmane.org>	<slrng4bbsh.d0.wnoise@ofb.net>
	<g25k7i$c1s$1@ger.gmane.org>
Message-ID: <g25p42$t66$1@ger.gmane.org>

Peter Hercek wrote:
> But what about this git rebasing option? How to do it more easily
>  (than the solution I know and I described it later) in darcs?
> 
> using "git-rebase --onto master next topic" to get from:
>     o---o---o---o---o  master
>          \
>           o---o---o---o---o  next
>                            \
>                             o---o---o  topic
> to:
> 
>     o---o---o---o---o  master
>         |            \
>         |             o'--o'--o'  topic
>          \
>           o---o---o---o---o  next
> 
> This is the reason why I mentioned reordering depending patches AB
>  to BA (with manual conflict resolution) would be needed in darcs
>  to support (I believe a better) alternative to git rebase.

I don't understand (probably because I haven't use either dvcs).

Either the changes in the  next->topic  path don't depend on the changes 
in the  fork->next  path. Then, the patches commute and it's no problem 
for darcs.

Or the  next->topic  path relies on features from  next  that are not 
present in  master . But then, you're screwed anyway and should merge 
some parts from  next  into  master  so as to advance the point where 
master  and  next  fork.

      o---o---o---o---o  master
                   \
            x---x---o---o---o  next
                             \
                              o---o---o  topic

(Of course, you don't actually advance the fork but rather add patches 
at the end of  master  . Hm, set of patches semantics seem to be a lot 
nicer here anyway. To me, the whole point of rebasing seems to be to 
somehow bring set semantics into the tree semantics.)


Regards,
apfelmus

From lrpalmer at gmail.com  Wed Jun  4 06:05:52 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun  4 05:58:29 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
	<6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>
Message-ID: <7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>

On Wed, Jun 4, 2008 at 9:48 AM, Loup Vaillant <loup.vaillant@gmail.com> wrote:
> I see a problem with this particular fusion, though: It changes the
> space complexity of the program, from linear to constant. Therefore,
> with some programs, relying on this "optimization" can be a matter of
> correctness, not just performance. Therefore, if it is not clear when
> the compiler will optimize this, I'd rather not use it. (A counter
> example is tail calls, which are rather easily deducible, at least in
> a strict context)

Haskell is not required to be lazy, only non-strict.  That is, Haskell
as a language is free to re-evaluate expressions bound in let clauses.
 This can change the time and space complexity of a program.

To me, time and space complexity is not about correctness but
performance.  Given unbounded time and space, you will still arrive at
the same result regardless of the complexity.  What makes the
asymptotic class more blessed than the associated constants?

However I still see your point.  If optimizations cannot be
guaranteed--the conditions under which they fire are brittle--then the
language can be yet harder to predict (which is not something Haskell
needs!).  It's hard to turn down an optimization which will
accidentally asymptotically improve your program, however.

I wonder what can be said about "stable" optimizations which are
insensitive to their environments in some sense.

Luke
From marlowsd at gmail.com  Wed Jun  4 06:33:35 2008
From: marlowsd at gmail.com (Simon Marlow)
Date: Wed Jun  4 06:26:17 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <008001c8bbf7$63753100$d0357ad5@cr3lt>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt>
Message-ID: <48466F7F.8090600@gmail.com>

Claus Reinke wrote:

> - i don't want to have to remove anything explicitly, because    that 
> would mean bypassing the haskell installation managers
> - i would want to see a single haskell installation manager
>    for each system,

I think that's fundamentally the wrong approach.  We shouldn't have to 
build a "Haskell installation manager".  Would you also want installation 
managers for Perl, Python, Ruby, C, C++, etc. each with their own different 
user interfaces and feature sets?  I think not - you want a single package 
manager for the whole system from which you can install/uninstall libraries 
for any language.

This is something that Windows gets completely wrong.  Why do I have twelve 
icons in my status bar all representing little programs that are running in 
the background checking for updates to their own bits of software?  Why on 
earth do I have a Printer Driver Update Manager?  And I'd be wondering the 
same thing about a "Haskell installation manager": installation and 
dependencies are not something specific to Haskell.

Cheers,
	Simon
From wnoise at ofb.net  Wed Jun  4 06:51:07 2008
From: wnoise at ofb.net (Aaron Denney)
Date: Wed Jun  4 06:44:01 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
	<g23sa0$5u5$1@ger.gmane.org> <slrng4av27.ubl.wnoise@ofb.net>
	<g243k9$19k$1@ger.gmane.org> <slrng4bbsh.d0.wnoise@ofb.net>
	<g25k7i$c1s$1@ger.gmane.org>
Message-ID: <slrng4cssv.4bu.wnoise@ofb.net>

On 2008-06-04, Peter Hercek <phercek@gmail.com> wrote:
> But what about this git rebasing option? How to do it more easily
>   (than the solution I know and I described it later) in darcs?
>
> using "git-rebase --onto master next topic" to get from:
>      o---o---o---o---o  master
>           \
>            o---o---o---o---o  next
>                             \
>                              o---o---o  topic
> to:
>
>      o---o---o---o---o  master
>          |            \
>          |             o'--o'--o'  topic
>           \
>            o---o---o---o---o  next

apfelmus answered this.  I might expand on his reply.

>> There is one thing that git rebase does easily (and correctly) that darcs
>> doesn't do nicely: rewriting history by merging commits "prior" to the
>> head.  I put prior in quotes, because darcs doesn't preserve history
>> in the first place.  I don't find that a compelling use, as opposed to
>> maintaing topic branches.
>
> I do not know what you mean here. Can you point me to some example?

Letting capitals be commits, and lowercase be trees at the point of
these commits.

Suppose your history is:

A -> B -> C -> D
|    |    |    |
a    b    c    d

And that B somehow doesn't make sense except with the additional changes
in C.  You don't want to deal with this, or have anyone see B.  All it
does is clutter up the history.  So you want to expunged it from the
history.

git rebase can rewrite this to

A ------> C' -> D'
|         |     |
a         c     d

Doing this in darcs would require unrecording B and C, and then
rerecording C'.  But, if D is in the repo, then it is likely that B and
C can't be commuted past it to be unrecorded.  (If they can, no
problem!)

Unrecording D (and possible E, F, G, etc.) lets you do this, but if you
then pull it back from another repo, it will depend on B and C, and pull
these in, which are now doppelgangers of C'.  Not having used darcs 2,
I'm not sure if that's still quite so fatal, but it remains bad news
AIUI.

The bottom line is that darcs is a tool for managing sets of always
existing patches. and ordering them lazily, as needed.  In particular,
no history generally exists, unless each patch depends on exactly one
previous.  It has a "differential" view of software development, in that
the changes, and not the sum at each point matter (though of course, the
current sum does matter.)

On the other hand, git is a tool for managing (and munging) histories
of development in many weird and wacky ways.  It has an "integral"
view of software development, the changes are lazily derived from the
saved state at each point, and are strictly ordered even when they're
independent.  It can, when needed, work with these changes to accomplish
fairly interesting history-altering tasks, but as soon as they're used
to construct a new history, they're discarded.  (Yes, git uses deltas,
but this is "merely" an optimization.)

The two models are dual to each other in many ways.

-- 
Aaron Denney
-><-

From wnoise at ofb.net  Wed Jun  4 07:11:56 2008
From: wnoise at ofb.net (Aaron Denney)
Date: Wed Jun  4 07:04:46 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>
	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
	<g23sa0$5u5$1@ger.gmane.org> <slrng4av27.ubl.wnoise@ofb.net>
	<g243k9$19k$1@ger.gmane.org> <slrng4bbsh.d0.wnoise@ofb.net>
	<g25k7i$c1s$1@ger.gmane.org> <g25p42$t66$1@ger.gmane.org>
Message-ID: <slrng4cu40.4bu.wnoise@ofb.net>

On 2008-06-04, apfelmus <apfelmus@quantentunnel.de> wrote:
> Peter Hercek wrote:
>> But what about this git rebasing option? How to do it more easily
>>  (than the solution I know and I described it later) in darcs?
>> 
>> using "git-rebase --onto master next topic" to get from:
>> to:
>>
>>     o---o---o---o---o  master
>>          \
>>           o---o---o---o---o  next
>>                            \
>>                             o---o---o  topic
>> 
>>     o---o---o---o---o  master
>>         |            \
>>         |             o'--o'--o'  topic
>>          \
>>           o---o---o---o---o  next
>> 
>> This is the reason why I mentioned reordering depending patches AB
>>  to BA (with manual conflict resolution) would be needed in darcs
>>  to support (I believe a better) alternative to git rebase.
>
> I don't understand (probably because I haven't use either dvcs).
>
> Either the changes in the  next->topic  path don't depend on the changes 
> in the  fork->next  path. Then, the patches commute and it's no problem 
> for darcs.

Right.  Then 

>>     o---o---o---o---o  master
>>          \
>>           o---o---o---o---o  next
>>                            \
>>                             o---o---o  topic

is not a good model for what darcs has.  What it has is more like

>>     o---o---o---o---o  master
>>         |\
>>         | o---o---o---o---o  next
>>         \                 |
>>          o---o---o--------+  topic

The patches in "topic" that are in "next" are indepent of the ones that
aren't in "next", so it's another (virtual) line-of-development, that
darcs can lazily construct as needed.  These lines-of-development are
similar to branches of git that have been merged, but you also have
access to the "unmerged" versions until a patch comes in that depends on
the merger.

If I commit three new features that don't interact, a darcs repo will
essentially look like:

       ---- topicA -
      /             \
history --- topicB --+--
      \             /
       ---- topicC -

Where the merger is "virtual".  Darcs will implicitly linearize this to
any of 
      
history --- topicA --- topicB --- topicC ---
history --- topicA --- topicC --- topicB ---
history --- topicB --- topicA --- topicC ---
history --- topicB --- topicC --- topicA ---
history --- topicC --- topicA --- topicB ---
history --- topicC --- topicB --- topicA ---

/as needed/. git constructs one of these, based on how you did the
commits, and gives you ways to alter it to the others.

> Or the  next->topic  path relies on features from  next  that are not 
> present in  master . But then, you're screwed anyway

Yep.

> and should merge some parts from next into master so as to advance the
> point where master and next fork.

That's one solution.  Of course, darcs doesn't have semantic dependency,
but syntactic dependency.  (You can add extra dependencies to
model semantic dependencies, but you can't take away the syntactic
dependencies.)  Another solution, if there's syntactic,
but not semantic dependencies, is to manually use patch and diff to get
90% there, and then cleanup and record.

-- 
Aaron Denney
-><-

From ganesh.sittampalam at credit-suisse.com  Wed Jun  4 07:13:28 2008
From: ganesh.sittampalam at credit-suisse.com (Sittampalam, Ganesh)
Date: Wed Jun  4 07:07:12 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
	<6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>
	<7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
Message-ID: <78A3C5650E28124399107F21A1FA41945B342E@ELON17P32002A.csfb.cs-group.com>

> I wonder what can be said about "stable" optimizations which are
insensitive to their environments in some sense.

http://citeseer.ist.psu.edu/veldhuizen02guaranteed.html

Ganesh

==============================================================================
Please access the attached hyperlink for an important electronic communications disclaimer: 

http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html
==============================================================================

From jon at ffconsultancy.com  Wed Jun  4 07:13:55 2008
From: jon at ffconsultancy.com (Jon Harrop)
Date: Wed Jun  4 07:10:46 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
References: <20080603174704.GB22053@scytale.galois.com>
	<6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>
	<7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
Message-ID: <200806041213.55484.jon@ffconsultancy.com>

On Wednesday 04 June 2008 11:05:52 Luke Palmer wrote:
> To me, time and space complexity is not about correctness but
> performance.

IRL the specification often dictates the complexity. If your code fails to 
satisfy the spec then it is wrong. Are you saying that Haskell code can never 
satisfy any such specification?

> Given unbounded time and space, you will still arrive at the same result
> regardless of the complexity. 

Given that the set of computers with unbounded time and space is empty, is it 
not fruitless to discuss its properties?

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/products/?e
From lemming at henning-thielemann.de  Wed Jun  4 08:14:08 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun  4 08:07:36 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
	<6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>
	<7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806041408290.30160@anubis.informatik.uni-halle.de>


On Wed, 4 Jun 2008, Luke Palmer wrote:

> On Wed, Jun 4, 2008 at 9:48 AM, Loup Vaillant <loup.vaillant@gmail.com> wrote:
>> I see a problem with this particular fusion, though: It changes the
>> space complexity of the program, from linear to constant. Therefore,
>> with some programs, relying on this "optimization" can be a matter of
>> correctness, not just performance. Therefore, if it is not clear when
>> the compiler will optimize this, I'd rather not use it. (A counter
>> example is tail calls, which are rather easily deducible, at least in
>> a strict context)
>
> Haskell is not required to be lazy, only non-strict.  That is, Haskell
> as a language is free to re-evaluate expressions bound in let clauses.
> This can change the time and space complexity of a program.
>
> To me, time and space complexity is not about correctness but
> performance.  Given unbounded time and space, you will still arrive at
> the same result regardless of the complexity.  What makes the
> asymptotic class more blessed than the associated constants?

Is it possible to extend the garbage collector that way, that it does not 
only check whether references to a piece of data exist, but that it also 
tries to eliminate these references by further evaluations. Consider again

mean xs = sum xs / fromIntegral (length xs)

If 'sum' forces construction of xs, unevaluated 'length' still points to 
the first element of xs. Could the garbage collector start counting for 
'length' in order to free the first elements of xs?
From barsoap at web.de  Wed Jun  4 08:36:50 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 08:29:37 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
Message-ID: <20080604143650.72978202@solaris>

Simon Marlow <marlowsd@gmail.com> wrote:

> Claus Reinke wrote:
> 
> > - i don't want to have to remove anything explicitly, because
> > that would mean bypassing the haskell installation managers
> > - i would want to see a single haskell installation manager
> >    for each system,
> 
> I think that's fundamentally the wrong approach.  We shouldn't have
> to build a "Haskell installation manager".  Would you also want
> installation managers for Perl, Python, Ruby, C, C++, etc. each with
> their own different user interfaces and feature sets?  I think not -
> you want a single package manager for the whole system from which you
> can install/uninstall libraries for any language.
> 
> This is something that Windows gets completely wrong.  Why do I have
> twelve icons in my status bar all representing little programs that
> are running in the background checking for updates to their own bits
> of software?  Why on earth do I have a Printer Driver Update
> Manager?  And I'd be wondering the same thing about a "Haskell
> installation manager": installation and dependencies are not
> something specific to Haskell.
> 
Well, then there are developers who don't want to do .ebuilds, .rpms
for 20 distributions, .debs for 20 distributions, .cabs... Meaning that
if you have a project with 5 developers using 3 1/2 distributions, you
will have a hard time installing.

Haskell code tends to be platform unspecific, one shouldn't have to
write platform-specific installation code just to make users happy.

You have a point, though, and I wouldn't mind at all cabal-install
being integrated into portage, that is, make portage
_understand_ .cabal files and introduce another field in them that
specifies non-haskell (e.g. gtk) dependencies.

That is: I'd like to see a cabal-install for every system, using native
package management where possible. Aren't there any usable
third-party package managers for windoze? Maybe we can hook properly
into cygwin, though it's surely not meant to support non-binary
packages.

Maybe gentoo should start to do binary releases, too, superseding
debian and any other distribution.

On another approach vector, I wouldn't want to update my Eve client
using portage. It has to check whether there's a patch available before
it connects to the server, anyway, so it can as well update.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From ketil at malde.org  Wed Jun  4 08:54:11 2008
From: ketil at malde.org (Ketil Malde)
Date: Wed Jun  4 08:46:31 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <20080604143650.72978202@solaris> (Achim Schneider's message of
	"Wed\, 4 Jun 2008 14\:36\:50 +0200")
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<20080604143650.72978202@solaris>
Message-ID: <87wsl5xswc.fsf@malde.org>

Achim Schneider <barsoap@web.de> writes:

Caveat: I have only a vague grasp on what exactly is being criticized
here - using a modern Linux distribution, tons of packages are
available, and almost all issues Claus point out seem to be taken care
of - at least as far as I can see.

> Well, then there are developers who don't want to do .ebuilds, .rpms
> for 20 distributions, .debs for 20 distributions, .cabs... Meaning that
> if you have a project with 5 developers using 3 1/2 distributions, you
> will have a hard time installing.

I think you should either require your developers to use the system
that is provided to them, or be able and willing to maintain their own
system.  Most large Linux distributions seem to come with lots of
Haskell-related stuff nowadays - 139 packages on my Ubuntu install
(divide by something close to 3, as most library stuff comes in -dev,
-doc and -prof variants).

> You have a point, though, and I wouldn't mind at all cabal-install
> being integrated into portage,

I'm not too familiar with portage, but I think a better solution is to
provide tools to automatically generate packages for the various
systems.  How would you specify dependencies on non-haskell components
in a portable way?

> Aren't there any usable third-party package managers for windoze?

The most usable one I've seen is Steam from Valve, IIRC.  It'd be cool
if Haskell packages were provided this way.

> Maybe gentoo should start to do binary releases, too, superseding
> debian and any other distribution.

Yeah, that'll happen. :-)

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 09:13:21 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 09:02:29 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <87wsl5xswc.fsf@malde.org>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<20080604143650.72978202@solaris>  <87wsl5xswc.fsf@malde.org>
Message-ID: <1212585201.15010.270.camel@localhost>


On Wed, 2008-06-04 at 14:54 +0200, Ketil Malde wrote:

> > You have a point, though, and I wouldn't mind at all cabal-install
> > being integrated into portage,
> 
> I'm not too familiar with portage, but I think a better solution is to
> provide tools to automatically generate packages for the various
> systems. 

Yeah, we've got one for gentoo/portage called hackport. That's why we
have so many packages in the haskell overlay. We didn't do them all
manually :-)

> How would you specify dependencies on non-haskell components in a
> portable way?

Unfortunately the same packages get named differently on different
package systems, eg "zlib", "libzlib", "libzlib-dev" etc. It's probably
possible to use reasonably standard names and map to the distro-names.
Doing that reliably is not going to be easy though.

Duncan



From Joseph.Re at MorganStanley.com  Wed Jun  4 09:13:34 2008
From: Joseph.Re at MorganStanley.com (Re, Joseph (IT))
Date: Wed Jun  4 09:07:51 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <87wsl5xswc.fsf@malde.org>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com><1211448821.5824.504.camel@localhost><008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com><20080604143650.72978202@solaris>
	<87wsl5xswc.fsf@malde.org>
Message-ID: <507725E31752A74CB00728FA6C17D99C09D4AEB1@NYWEXMB29.msad.ms.com>

Not sure about it's current state, but a friend was working on this
until he graduated recently: http://www.acm.uiuc.edu/projects/Wipt

-----Original Message-----
From: haskell-cafe-bounces@haskell.org
[mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Ketil Malde

> Aren't there any usable third-party package managers for windoze?

The most usable one I've seen is Steam from Valve, IIRC.  It'd be cool
if Haskell packages were provided this way.

-k
--------------------------------------------------------

NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.
From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 09:22:07 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 09:11:19 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <48466F7F.8090600@gmail.com>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt>  <48466F7F.8090600@gmail.com>
Message-ID: <1212585727.15010.281.camel@localhost>


On Wed, 2008-06-04 at 11:33 +0100, Simon Marlow wrote:
> Claus Reinke wrote:
> 
> > - i don't want to have to remove anything explicitly, because    that 
> > would mean bypassing the haskell installation managers
> > - i would want to see a single haskell installation manager
> >    for each system,
> 
> I think that's fundamentally the wrong approach.  We shouldn't have to 
> build a "Haskell installation manager".  Would you also want installation 
> managers for Perl, Python, Ruby, C, C++, etc. each with their own different 
> user interfaces and feature sets?  I think not - you want a single package 
> manager for the whole system from which you can install/uninstall libraries 
> for any language.

As I see it we need both. We need to make it easy to translate cabal
packages into distro packages. We do have tools to do that at the moment
for Gentoo, Debian and Fedora. I'm sure they could be improved.

However we cannot expect all distros (esp Windows) to have all packages
that are on hackage at all times. That's where it makes sense to have a
tool like cabal-install as a secondary package manager. There's also the
fact that most distro package managers do not handle unprivileged
per-user installations very well.

A further issue is that the dependencies that Haskell packages have are
pretty complex and more so than can actually be expressed in some distro
package systems. In particular Gentoo portage. Binary distros are better
off in that respect since the deps of binary haskell packages are
considerably simpler.

Duncan

From barsoap at web.de  Wed Jun  4 09:25:52 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 09:18:35 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<20080604143650.72978202@solaris> <87wsl5xswc.fsf@malde.org>
Message-ID: <20080604152552.56c2cc1d@solaris>

Ketil Malde <ketil@malde.org> wrote:

> Achim Schneider <barsoap@web.de> writes:
> 
> Caveat: I have only a vague grasp on what exactly is being criticized
> here - using a modern Linux distribution, tons of packages are
> available, and almost all issues Claus point out seem to be taken care
> of - at least as far as I can see.
> 
> > Well, then there are developers who don't want to do .ebuilds, .rpms
> > for 20 distributions, .debs for 20 distributions, .cabs... Meaning
> > that if you have a project with 5 developers using 3 1/2
> > distributions, you will have a hard time installing.
> 
> I think you should either require your developers to use the system
> that is provided to them, or be able and willing to maintain their own
> system.  Most large Linux distributions seem to come with lots of
> Haskell-related stuff nowadays - 139 packages on my Ubuntu install
> (divide by something close to 3, as most library stuff comes in -dev,
> -doc and -prof variants).
> 
Well, you have a point but still don't have one. Many of gentoo's
haskell .ebuilds are seriously outdated, eg. wxhaskell still depends on
ghc 6.4. See "Damnit, we need a CPAN"

The haskell overlay features about 240 packages from alex to yi,
hackage currently lists 596 packages.

There are always things that a distribution doesn't include, especially
sparsely used special purpose software. Compiling a LADSPA plugin by
hand isn't that much of an issue, but you'll get into problems as soon
as you want your programs to find it without touching paths that only
your system's package manager should touch. I'm proud to say that my
current gentoo installation is still the first one, surviving several
world updates and at least 4 years of hacking around, using a lot of
unstable and masked packages.


> > You have a point, though, and I wouldn't mind at all cabal-install
> > being integrated into portage,
> 
> I'm not too familiar with portage, but I think a better solution is to
> provide tools to automatically generate packages for the various
> systems.  How would you specify dependencies on non-haskell components
> in a portable way?
> 
By using portage ;)

Seriously: Gentoo isn't a distribution, but a meta-distribution. It
wouldn't make much sense to support the generation of alien binary
packages, though, as dependency names will surely differ, and if you
have to generate the whole distribution, you can equally well just use
portage to install it.

Regarding non-haskell dependencies: It's already a problem from
distribution to distribution. In portage, you would have to depend on
e.g. either gtk+ or emul-linux-x86-gtklibs (if you want to build 32bit
software...), in debian on gtk-dev. Each distribution would have to make
a list on how cabal's non-haskell dependencies map to their own package
names, which is seriously less work than figuring these out by hand.


-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From dfkettle at gmail.com  Wed Jun  4 09:38:34 2008
From: dfkettle at gmail.com (David)
Date: Wed Jun  4 09:31:10 2008
Subject: [Haskell-cafe] Installing Haskore under Windows
Message-ID: <ca74b7060806040638j13815a7bmf1dd670217980308@mail.gmail.com>

Hi!

I'm currently running ghc under Windows XP and want to play around
with Haskore, but I'm a little confused about how to install it, or if
it's even possible to use it with ghc. The 'readme' file contains this
note:

"Note that the file ghc_add/IOExtensions.hs is a partial replacement of
a library file of the same name under Hugs.  It does not work yet on
Windows/GHC (where one has to distinguish between binary and text IO)."

Does this mean I have to use Hugs rather than ghc? I have both Hugs
and ghc installed, but I'd prefer to use ghc if possible.

In either case, I find the install instructions (for Haskore, that is)
a little confusing, probably because I'm also new to Haskell. Any help
would be greatly appreciated.

Thanks.
From phercek at gmail.com  Wed Jun  4 09:39:40 2008
From: phercek at gmail.com (Peter Hercek)
Date: Wed Jun  4 09:32:20 2008
Subject: [Haskell-cafe] Re: [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <slrng4cu40.4bu.wnoise@ofb.net>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>	<g23sa0$5u5$1@ger.gmane.org>
	<slrng4av27.ubl.wnoise@ofb.net>	<g243k9$19k$1@ger.gmane.org>
	<slrng4bbsh.d0.wnoise@ofb.net>	<g25k7i$c1s$1@ger.gmane.org>
	<g25p42$t66$1@ger.gmane.org> <slrng4cu40.4bu.wnoise@ofb.net>
Message-ID: <g265uo$ckn$1@ger.gmane.org>

Aaron Denney wrote:
> On 2008-06-04, apfelmus <apfelmus@quantentunnel.de> wrote:
<-- cut -->
>> Or the  next->topic  path relies on features from  next  that are not 
>> present in  master . But then, you're screwed anyway
> 
> Yep.

Well not really, depends what kind the dependency is, this kind of rebase
  is useful when "topic" depends only syntactically (as you pointed later)
  on "next" or when the semantic dependency is only on a small part of "next".
  Git rebase allows you get the syntax or the small part of semantics to the
  rebased "topic" by asking you for (manual) conflict resolution. This would
  correspond to commuting darcs patches which depend on each other (again
  possible by providing manual conflict resolution).
Of course this happens only when it was anticipated that upstream merge
  of "next" happens before "topic", but then the upstream maintainers
  decided that "topic" should go upstream first. So, not often.


>> and should merge some parts from next into master so as to advance the
>> point where master and next fork.
> 
> That's one solution.  Of course, darcs doesn't have semantic dependency,
> but syntactic dependency.  (You can add extra dependencies to
> model semantic dependencies, but you can't take away the syntactic
> dependencies.)  Another solution, if there's syntactic,
> but not semantic dependencies, is to manually use patch and diff to get
> 90% there, and then cleanup and record.

OK, so I think this is what I expected for such a case.

Thanks for the explanation of the meaning of "merging patches prior head".

Peter.

From wqeqweuqy at hotmail.com  Wed Jun  4 09:40:55 2008
From: wqeqweuqy at hotmail.com (Neal Alexander)
Date: Wed Jun  4 09:33:55 2008
Subject: [Haskell-cafe] Re: library for drawing charts
In-Reply-To: <12204.203.185.215.144.1211767776.squirrel@dockerz.net>
References: <82B3919B-BE28-4D65-9A3B-957B5EC51D27@gmail.com>
	<12204.203.185.215.144.1211767776.squirrel@dockerz.net>
Message-ID: <g2661b$cvj$1@ger.gmane.org>

Tim Docker wrote:
> Peter wrote:
>> Has anyone got some code for drawing charts? I don't mean
>> graphs of functions, ala
>>
>> http://dockerz.net/twd/HaskellCharts
>> ...
>> I would like something that can generate PNGs in memory, i.e. not
>> directly to a file.
> 
> The library at the above URL supports a range of backends through the
> (nice to use) cairo graphics API. In memory images are supported. Also,
> it's by no means just graphs of functions - that just happens to be
> several of the demos.
> 
>> I'd like 2D pie charts, bar charts and something like a google-o-meter.
> 
> An the moment it does line charts and a few variants of these. I'll add
> pie and bar charts when I need them - patches in the meantime gratefully
> accepted.
> 
> Tim

I was using the HaskellCharts library and needed the same two things; so 
i rolled a quick and dirty pie chart generator (Barchart is on the TODO 
list).


http://72.167.145.184:8000/Screenshot.png
http://72.167.145.184:8000/PieChart.hs

----

x <- widgetGetDrawWindow canvas
y <- widgetGetSize canvas

renderWithDrawable x (f y)

where f = PieChart.graph "title" 0x548B54 [(50.0,"A"), (50.0,"B")]

From lemming at henning-thielemann.de  Wed Jun  4 09:46:22 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun  4 09:38:58 2008
Subject: [Haskell-cafe] Installing Haskore under Windows
In-Reply-To: <ca74b7060806040638j13815a7bmf1dd670217980308@mail.gmail.com>
References: <ca74b7060806040638j13815a7bmf1dd670217980308@mail.gmail.com>
Message-ID: <Pine.GSO.4.56.0806041544410.22012@haydn.informatik.uni-halle.de>


On Wed, 4 Jun 2008, David wrote:

> I'm currently running ghc under Windows XP and want to play around
> with Haskore, but I'm a little confused about how to install it, or if
> it's even possible to use it with ghc. The 'readme' file contains this
> note:

You can also use Haskore with GHC. For an extended version using Cabal
see:
   http://darcs.haskell.org/haskore/
From ross at soi.city.ac.uk  Wed Jun  4 09:56:14 2008
From: ross at soi.city.ac.uk (Ross Paterson)
Date: Wed Jun  4 09:48:52 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <1212585727.15010.281.camel@localhost>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<1212585727.15010.281.camel@localhost>
Message-ID: <20080604135614.GA11968@soi.city.ac.uk>

On Wed, Jun 04, 2008 at 02:22:07PM +0100, Duncan Coutts wrote:
> As I see it we need both. We need to make it easy to translate cabal
> packages into distro packages. We do have tools to do that at the moment
> for Gentoo, Debian and Fedora. I'm sure they could be improved.
> 
> However we cannot expect all distros (esp Windows) to have all packages
> that are on hackage at all times. That's where it makes sense to have a
> tool like cabal-install as a secondary package manager. There's also the
> fact that most distro package managers do not handle unprivileged
> per-user installations very well.

cabal-install probably needs extra features to work in this way.
If you ask it to install a package and its prerequisites, each of
those packages will either be
(1) already installed,
(2) absent but available from the native package manager,
(3) available from hackage.
In the second case you'd probably want to break out of cabal-install to
install the pre-packaged ones before building the new ones.
From claus.reinke at talk21.com  Wed Jun  4 10:14:22 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Wed Jun  4 10:07:04 2008
Subject: cabal and platform-independent haskell installation management
	(again) (Re: [Haskell-cafe] Re: Ubuntu and ghc)
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>	<1211448821.5824.504.camel@localhost><008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com>
Message-ID: <016d01c8c64d$4ac1dea0$73357ad5@cr3lt>

> I think that's fundamentally the wrong approach.  We shouldn't have to 
> build a "Haskell installation manager".  Would you also want installation 
> managers for Perl, Python, Ruby, C, C++, etc. each with their own different 
> user interfaces and feature sets?  I think not - you want a single package 
> manager for the whole system from which you can install/uninstall libraries 
> for any language.
> 
> This is something that Windows gets completely wrong.  Why do I have twelve 
> icons in my status bar all representing little programs that are running in 
> the background checking for updates to their own bits of software?  Why on 
> earth do I have a Printer Driver Update Manager?  And I'd be wondering the 
> same thing about a "Haskell installation manager": installation and 
> dependencies are not something specific to Haskell.

why then do we have ghc-pkg, or cabal? surely the native package
managers should handle all that?

there are (at least) two dimensions of uniformity: across different
kind of software on a single kind of system, and with a single kind 
of software across different kinds of system. platform-specific
package managers hide the software-specific notions of package
dependency maintainence, haskell-specific package managers
hide the platform-specific notions of package dependency 
maintainence. 

there is no need for platform- and haskell-specific tools to be 
entirely separate or in conflict with each other: where both exist, 
one can be a view on the other (if you are on linux-of-the-day, 
you can use its package manage, independent of whether your
packages are haskell or lisp; and if you are using haskell, you
should be able to use its package manager, independent of
whether you are on unix-variant-of-today or on 
unix-variant-of-yesterday).

there seems to be a lot of confusion here, some of us not 
understanding the issues because we happen to be using
systems where "everything just works", others among us
not understanding the issues because we happen to be
using systems where "such things would never work anyway",
and yet others insisting on "i'll do it my way, so i know what
works" (and then, of course, there are those who are
actively working on improving the situation who will see
my criticism as constructive, i hope!-).

1. there are no systems where "packages just work"!
    there are systems where a few people ensure that
    many people can live in such an illusion, though.

2. systems with native package manager software still
    need help from haskell-specific toolchains (unless
    you want the human package managers on those
    systems to code all haskell-specific dependencies
    by hand).

3. systems without native package managers (or perhaps
    i should say: systems on which users with unix background
    traditionally avoid getting acquainted with the details and 
    usage of whatever might pass as installation management 
    on those systems) are still in *very* wide-spread use, 
    and if haskell users on those systems are left out in the
    rain, haskell developers will not be able to support those
    systems. this limits the user and application base of haskell
    on those systems, making haskell less relevant than it could be.

4. haskell enables programming at a very high level of 
    abstraction, with fairly good support for mostly platform
    independent code. but that code needs to be installed, 
    and integrated with dependencies and dependents, and 
    the integrated haskell installations needs to be maintained.
    and that should "just work", even if the developer is on
    (1;2) and the user is on (3), or vice versa, or if developers
    and users are on different flavours of (1;2) or (3).

with these clarifications out of the way, my interpretation 
of cabal was that it set out to provide two things

(A) a uniform platform-independent interface to such a 
    haskell package installation manager.
(B) a uniform platform-independent toolchain to support
    such a haskell package installation manager.

on systems in the (1;2) class, human package managers 
would use (B) to integrate haskell packages into the native
package management software, so users might never even
encounter cabal. even so, (A) might offer a haskell-specific
view on the general platform package management (when 
you want to see the haskell gui libs rather than all gui libs).

on systems in the (3) class, users and developers would
interface with (A/B) directly, for lack of a better alternative.

and developers/users in the (4) class would simply use
(A/B), without having to check whether they are "real"
or just a view on the platform-specific software. it is this
cross platform view of software development that i'm
most interested in (i'm one of those who use bash, vim,
opera, and haskell, no matter whether i'm on windows,
solaris, or whatever, and the cross-platform availability
of those tools has saved me many a headache;-).

returning to my earlier message, it seems that my 
concerns were mainly these:

- it isn't sufficient to worry about installation management,
    one has to worry about integration, lifetime and uninstall
    management as well. in short, maintain the dependency
    graphs over any of "install"/"upgrade"/"uninstall".

- for this to work, cabal needs to maintain not only
    libraries as packages, but tools and compilers as
    well. without this, some dependencies are not
    recorded (this haddock depends on that ghc; to
    build this package i need that tool; that tool was 
    built with this ghc version, from those sources, etc). 
    
    and if the dependencies are not even recorded, they 
    are likely to be broken if one does install/upgrade or
    uninstall any haskell software, be it library, tool, or
    compiler.

i hope this clarifies things?-)
claus

ps. i'd cc to libraries or cabal, but i don't know which
    would be most appropriate (perhaps someone could
    point readers there to this thread if that sounds relevant?).


From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 10:31:40 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 10:20:48 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <20080604152552.56c2cc1d@solaris>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<20080604143650.72978202@solaris> <87wsl5xswc.fsf@malde.org>
	<20080604152552.56c2cc1d@solaris>
Message-ID: <1212589900.15010.302.camel@localhost>


On Wed, 2008-06-04 at 15:25 +0200, Achim Schneider wrote:

> Well, you have a point but still don't have one. Many of gentoo's
> haskell .ebuilds are seriously outdated, eg. wxhaskell still depends on
> ghc 6.4. See "Damnit, we need a CPAN"
> 
> The haskell overlay features about 240 packages from alex to yi,
> hackage currently lists 596 packages.

You may be interested to know I just tried to install 564 packages from
hackage using cabal-install (others excluded due to missing or
inconsistent dependencies). Of those, 156 failed to install (direct
failure or because they depended on another package that failed). I now
have 157 programs installed in ~/.cabal/bin and ghc-pkg take two and a
half seconds to tell me that I have 454 libraries installed (some were
installed previously via portage).

Duncan

From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 10:43:48 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 10:32:59 2008
Subject: cabal and platform-independent haskell installation management
	(again) (Re: [Haskell-cafe] Re: Ubuntu and ghc)
In-Reply-To: <016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost><008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com>  <016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
Message-ID: <1212590628.15010.312.camel@localhost>


On Wed, 2008-06-04 at 15:14 +0100, Claus Reinke wrote:
> > I think that's fundamentally the wrong approach.  We shouldn't have to 
> > build a "Haskell installation manager".  Would you also want installation 
> > managers for Perl, Python, Ruby, C, C++, etc. each with their own different 
> > user interfaces and feature sets?  I think not - you want a single package 
> > manager for the whole system from which you can install/uninstall libraries 
> > for any language.
> > 
> > This is something that Windows gets completely wrong.  Why do I have twelve 
> > icons in my status bar all representing little programs that are running in 
> > the background checking for updates to their own bits of software?  Why on 
> > earth do I have a Printer Driver Update Manager?  And I'd be wondering the 
> > same thing about a "Haskell installation manager": installation and 
> > dependencies are not something specific to Haskell.
> 
> why then do we have ghc-pkg, or cabal? surely the native package
> managers should handle all that?
> 
> there are (at least) two dimensions of uniformity: across different
> kind of software on a single kind of system, and with a single kind 
> of software across different kinds of system. platform-specific
> package managers hide the software-specific notions of package
> dependency maintainence, haskell-specific package managers
> hide the platform-specific notions of package dependency 
> maintainence. 
> 
> there is no need for platform- and haskell-specific tools to be 
> entirely separate or in conflict with each other: where both exist, 
> one can be a view on the other (if you are on linux-of-the-day, 
> you can use its package manage, independent of whether your
> packages are haskell or lisp; and if you are using haskell, you
> should be able to use its package manager, independent of
> whether you are on unix-variant-of-today or on 
> unix-variant-of-yesterday).
> 
> there seems to be a lot of confusion here, some of us not 
> understanding the issues because we happen to be using
> systems where "everything just works", others among us
> not understanding the issues because we happen to be
> using systems where "such things would never work anyway",
> and yet others insisting on "i'll do it my way, so i know what
> works" (and then, of course, there are those who are
> actively working on improving the situation who will see
> my criticism as constructive, i hope!-).
> 
> 1. there are no systems where "packages just work"!
>     there are systems where a few people ensure that
>     many people can live in such an illusion, though.

Yes indeed! :-)

> 2. systems with native package manager software still
>     need help from haskell-specific toolchains (unless
>     you want the human package managers on those
>     systems to code all haskell-specific dependencies
>     by hand).

Yes. As an illustration: gentoo has an "haskell-cabal.eclass" that
interfaces between ebuilds and cabal as the build manager and there is a
tool to generate ebuilds that use the haskell-cabal.eclass from .cabal
descriptions (so we get correct deps automatically).

> 3. systems without native package managers (or perhaps
>     i should say: systems on which users with unix background
>     traditionally avoid getting acquainted with the details and 
>     usage of whatever might pass as installation management 
>     on those systems) are still in *very* wide-spread use, 
>     and if haskell users on those systems are left out in the
>     rain, haskell developers will not be able to support those
>     systems. this limits the user and application base of haskell
>     on those systems, making haskell less relevant than it could be.

Eg Windows, OSX, Solaris.

> 4. haskell enables programming at a very high level of 
>     abstraction, with fairly good support for mostly platform
>     independent code. but that code needs to be installed, 
>     and integrated with dependencies and dependents, and 
>     the integrated haskell installations needs to be maintained.
>     and that should "just work", even if the developer is on
>     (1;2) and the user is on (3), or vice versa, or if developers
>     and users are on different flavours of (1;2) or (3).
> 
> with these clarifications out of the way, my interpretation 
> of cabal was that it set out to provide two things
> 
> (A) a uniform platform-independent interface to such a 
>     haskell package installation manager.
> (B) a uniform platform-independent toolchain to support
>     such a haskell package installation manager.

I guess so.

> on systems in the (1;2) class, human package managers 
> would use (B) to integrate haskell packages into the native
> package management software, so users might never even
> encounter cabal.

As in my example with the gentoo haskell packages above.

>  even so, (A) might offer a haskell-specific
> view on the general platform package management (when 
> you want to see the haskell gui libs rather than all gui libs).
> 
> on systems in the (3) class, users and developers would
> interface with (A/B) directly, for lack of a better alternative.
> 
> and developers/users in the (4) class would simply use
> (A/B), without having to check whether they are "real"
> or just a view on the platform-specific software. it is this
> cross platform view of software development that i'm
> most interested in (i'm one of those who use bash, vim,
> opera, and haskell, no matter whether i'm on windows,
> solaris, or whatever, and the cross-platform availability
> of those tools has saved me many a headache;-).
> 
> returning to my earlier message, it seems that my 
> concerns were mainly these:
> 
> - it isn't sufficient to worry about installation management,
>     one has to worry about integration, lifetime and uninstall
>     management as well. in short, maintain the dependency
>     graphs over any of "install"/"upgrade"/"uninstall".

For users in (1;2) class we would expect the native package manager to
do this.

> - for this to work, cabal needs to maintain not only
>     libraries as packages, but tools and compilers as
>     well. without this, some dependencies are not
>     recorded (this haddock depends on that ghc; to
>     build this package i need that tool; that tool was 
>     built with this ghc version, from those sources, etc). 
>     
>     and if the dependencies are not even recorded, they 
>     are likely to be broken if one does install/upgrade or
>     uninstall any haskell software, be it library, tool, or
>     compiler.

Right. Currently cabal-install in its roll as a secondary package
manager is very weak on that front. It does not record anything about
what it installs. There's clearly plenty of work to be done there.

> ps. i'd cc to libraries or cabal, but i don't know which
>     would be most appropriate (perhaps someone could
>     point readers there to this thread if that sounds relevant?).

You can cc both.

Duncan

From darrinth at gmail.com  Wed Jun  4 11:14:46 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Wed Jun  4 11:07:22 2008
Subject: cabal and platform-independent haskell installation management
	(again) (Re: [Haskell-cafe] Re: Ubuntu and ghc)
In-Reply-To: <016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
Message-ID: <a2e649c70806040814t2532bd75p684007ab04f635a6@mail.gmail.com>

On Wed, Jun 4, 2008 at 10:14 AM, Claus Reinke <claus.reinke@talk21.com> wrote:
> - it isn't sufficient to worry about installation management,
>   one has to worry about integration, lifetime and uninstall
>   management as well. in short, maintain the dependency
>   graphs over any of "install"/"upgrade"/"uninstall".
>

It's sufficient to worry about the problem at hand. Everything you've
mentioned can be done incrementally once the depsolver is happy.

After that it's quite likely that the set of people who care about
lifetimes and integration stuff will intersect with the people who
want to work on said stuff.

--
Darrin
From barsoap at web.de  Wed Jun  4 11:22:52 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 11:15:36 2008
Subject: [Haskell-cafe] Re: cabal and platform-independent haskell
 installation management (again) (Re: Re: Ubuntu and ghc)
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
	<1212590628.15010.312.camel@localhost>
Message-ID: <20080604172252.34df14f7@solaris>

Duncan Coutts <duncan.coutts@worc.ox.ac.uk> wrote:

> 
> On Wed, 2008-06-04 at 15:14 +0100, Claus Reinke wrote:
> > > I think that's fundamentally the wrong approach.  We shouldn't
> > > have to build a "Haskell installation manager".  Would you also
> > > want installation managers for Perl, Python, Ruby, C, C++, etc.
> > > each with their own different user interfaces and feature sets?
> > > I think not - you want a single package manager for the whole
> > > system from which you can install/uninstall libraries for any
> > > language.
> > > 
> > > This is something that Windows gets completely wrong.  Why do I
> > > have twelve icons in my status bar all representing little
> > > programs that are running in the background checking for updates
> > > to their own bits of software?  Why on earth do I have a Printer
> > > Driver Update Manager?  And I'd be wondering the same thing about
> > > a "Haskell installation manager": installation and dependencies
> > > are not something specific to Haskell.
> > 
> > why then do we have ghc-pkg, or cabal? surely the native package
> > managers should handle all that?
> > 
> > there are (at least) two dimensions of uniformity: across different
> > kind of software on a single kind of system, and with a single kind 
> > of software across different kinds of system. platform-specific
> > package managers hide the software-specific notions of package
> > dependency maintainence, haskell-specific package managers
> > hide the platform-specific notions of package dependency 
> > maintainence. 
> > 
> > there is no need for platform- and haskell-specific tools to be 
> > entirely separate or in conflict with each other: where both exist, 
> > one can be a view on the other (if you are on linux-of-the-day, 
> > you can use its package manage, independent of whether your
> > packages are haskell or lisp; and if you are using haskell, you
> > should be able to use its package manager, independent of
> > whether you are on unix-variant-of-today or on 
> > unix-variant-of-yesterday).
> > 
> > there seems to be a lot of confusion here, some of us not 
> > understanding the issues because we happen to be using
> > systems where "everything just works", others among us
> > not understanding the issues because we happen to be
> > using systems where "such things would never work anyway",
> > and yet others insisting on "i'll do it my way, so i know what
> > works" (and then, of course, there are those who are
> > actively working on improving the situation who will see
> > my criticism as constructive, i hope!-).
> > 
> > 1. there are no systems where "packages just work"!
> >     there are systems where a few people ensure that
> >     many people can live in such an illusion, though.
> 
> Yes indeed! :-)
> 
> > 2. systems with native package manager software still
> >     need help from haskell-specific toolchains (unless
> >     you want the human package managers on those
> >     systems to code all haskell-specific dependencies
> >     by hand).
> 
> Yes. As an illustration: gentoo has an "haskell-cabal.eclass" that
> interfaces between ebuilds and cabal as the build manager and there
> is a tool to generate ebuilds that use the haskell-cabal.eclass
> from .cabal descriptions (so we get correct deps automatically).
> 
> > 3. systems without native package managers (or perhaps
> >     i should say: systems on which users with unix background
> >     traditionally avoid getting acquainted with the details and 
> >     usage of whatever might pass as installation management 
> >     on those systems) are still in *very* wide-spread use, 
> >     and if haskell users on those systems are left out in the
> >     rain, haskell developers will not be able to support those
> >     systems. this limits the user and application base of haskell
> >     on those systems, making haskell less relevant than it could be.
> 
> Eg Windows, OSX, Solaris.
> 
> > 4. haskell enables programming at a very high level of 
> >     abstraction, with fairly good support for mostly platform
> >     independent code. but that code needs to be installed, 
> >     and integrated with dependencies and dependents, and 
> >     the integrated haskell installations needs to be maintained.
> >     and that should "just work", even if the developer is on
> >     (1;2) and the user is on (3), or vice versa, or if developers
> >     and users are on different flavours of (1;2) or (3).
> > 
> > with these clarifications out of the way, my interpretation 
> > of cabal was that it set out to provide two things
> > 
> > (A) a uniform platform-independent interface to such a 
> >     haskell package installation manager.
> > (B) a uniform platform-independent toolchain to support
> >     such a haskell package installation manager.
> 
> I guess so.
> 
> > on systems in the (1;2) class, human package managers 
> > would use (B) to integrate haskell packages into the native
> > package management software, so users might never even
> > encounter cabal.
> 
> As in my example with the gentoo haskell packages above.
> 
> >  even so, (A) might offer a haskell-specific
> > view on the general platform package management (when 
> > you want to see the haskell gui libs rather than all gui libs).
> > 
> > on systems in the (3) class, users and developers would
> > interface with (A/B) directly, for lack of a better alternative.
> > 
> > and developers/users in the (4) class would simply use
> > (A/B), without having to check whether they are "real"
> > or just a view on the platform-specific software. it is this
> > cross platform view of software development that i'm
> > most interested in (i'm one of those who use bash, vim,
> > opera, and haskell, no matter whether i'm on windows,
> > solaris, or whatever, and the cross-platform availability
> > of those tools has saved me many a headache;-).
> > 
> > returning to my earlier message, it seems that my 
> > concerns were mainly these:
> > 
> > - it isn't sufficient to worry about installation management,
> >     one has to worry about integration, lifetime and uninstall
> >     management as well. in short, maintain the dependency
> >     graphs over any of "install"/"upgrade"/"uninstall".
> 
> For users in (1;2) class we would expect the native package manager to
> do this.
> 
> > - for this to work, cabal needs to maintain not only
> >     libraries as packages, but tools and compilers as
> >     well. without this, some dependencies are not
> >     recorded (this haddock depends on that ghc; to
> >     build this package i need that tool; that tool was 
> >     built with this ghc version, from those sources, etc). 
> >     
> >     and if the dependencies are not even recorded, they 
> >     are likely to be broken if one does install/upgrade or
> >     uninstall any haskell software, be it library, tool, or
> >     compiler.
> 
> Right. Currently cabal-install in its roll as a secondary package
> manager is very weak on that front. It does not record anything about
> what it installs. There's clearly plenty of work to be done there.
> 
I'm wondering whether a hacked version of darcs could be used for
this. Together with sandboxing and support of alien packages,
it would already look like a full-fledged distribution... binary
packages could be a set of zipped darcs patches. Add USE-flag derived
dependencies and package and flag based stable/unstable marks and I'll
switch without hesition.

The question, IMHO, seems to be

"How would a package manager for a posix-compilant kinetic look like?"

I'd rather like a package manager to find them, rule them all and in
obsoletion bind them than attempting to hack around package managers *
packages incompatibilities.

PS: If you don't know why sandboxing is a MUST, read
http://myeve.eve-online.com/devblog.asp?a=blog&bid=526

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From jgoerzen at complete.org  Wed Jun  4 12:39:53 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Wed Jun  4 12:32:34 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <1212534382.15010.227.camel@localhost>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>	<20080602172131.GA7534@scytale.galois.com>	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>	<20080603172303.GA22053@scytale.galois.com>
	<1212534382.15010.227.camel@localhost>
Message-ID: <4846C559.9020201@complete.org>

Duncan Coutts wrote:
> On Tue, 2008-06-03 at 10:23 -0700, Don Stewart wrote:
>> A new version of happs was written on a Monday a couple of months ago,
>> using fastcgi and takusen. We're running it at galois, and you can
>> find the code on code.haskell.org/hpaste. So not quite what you wanted,
>> but another data point.
> 
> That's very interesting. I hope we will also see a version with the same
> feature set implemented with the latest HAppS. It would give an
> interesting comparison of the web frameworks to see the same app
> implemented in both.

I haven't looked at that particular version, but when I last looked at
web frameworks, I was somewhat disappointed.  HAppS seemed to have
little documentation on the current version anyhow, and especially
little coverage on what to do if your app revolved around serving data
from an existing SQL database or other data source rather than its own.

hvac sounds interesting but at that time at least it was not clear
whether it was stable or would continue to be maintained.

xhtml and HStringTemplate were overkill for what I wanted, so I wound up
just using the FastCGI and CGI toolkits themselves.  They are
surprisingly nice, and with a little bit of wrappers around them for
things like validating forms, have worked exceptionally well.

My needs for that project were not complex, the layout was not very
important, and the presentation never changes (only the business logic).
 So I understand that my needs may have been opposite from what most
people face.

-- John
From jgoerzen at complete.org  Wed Jun  4 12:43:23 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Wed Jun  4 12:36:00 2008
Subject: [Haskell-cafe] HDBC-odbc 1.1.4.4 fixes Windows linking problems
In-Reply-To: <20080604030541.GA26462@momotaro.chinmin.edu.tw>
References: <20080603200020.GA13041@complete.org>
	<20080604030541.GA26462@momotaro.chinmin.edu.tw>
Message-ID: <4846C62B.2050503@complete.org>

Greg Matheson wrote:
> On Tue, 03 Jun 2008, John Goerzen wrote:
> 
>> Hi,
> 
>> HDBC-odbc version 1.1.4.4 has been uploaded to Hackage.  It fixes the
>> problems some here have encountered regarding ODBC crashes or other
>> similar odd behavior on Windows. 
> 
> I'm getting a 'Parse error in pattern' error.
> 
> C:\Documents and Settings\Administrator>ghci
> GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
> Loading package base ... linking ... done.
> Prelude> :m Database.HDBC.ODBC Database.HDBC
> Prelude Database.HDBC Database.HDBC.ODBC> conn <- connectODBC "dictation"

Please note that this is not a valid connection string.

The HDBC-odbc API docs are available at
http://software.complete.org/static/hdbc-odbc/doc//HDBC-odbc/Database-HDBC-ODBC.html
and give the example string of:

"DSN=hdbctest1"

as well as a link to the Microsoft document that describes the string,
which lives at:

http://msdn.microsoft.com/en-us/library/ms715433(VS.85).aspx

That URL also contains error message descriptions.  For your state
01S00, it lists:

  Invalid connection string attribute
	
  An invalid attribute keyword was specified in the connection string
  (InConnectionString), but the driver was able to connect to the data
  source anyway. (Function returns SQL_SUCCESS_WITH_INFO.)

Your fix may be as simple as prepending the string with "DSN=".

-- John

From jgoerzen at complete.org  Wed Jun  4 12:51:05 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Wed Jun  4 12:43:40 2008
Subject: [Haskell-cafe] [ANNOUNCE] git-darcs-import 0.1
In-Reply-To: <6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
References: <20080601184446.GA27750@zombie.inf.tu-dresden.de>	<a2e649c70806030735o3df1882cj64f8f8c3e4a08d9d@mail.gmail.com>
	<6f9f8f4a0806030757y142f0710lb05754429e4b6515@mail.gmail.com>
Message-ID: <4846C7F9.4010006@complete.org>

Loup Vaillant wrote:
> 2008/6/3 Darrin Thompson <darrinth@gmail.com>:
>> On Sun, Jun 1, 2008 at 2:44 PM, Bertram Felgenhauer
>> <bertram.felgenhauer@googlemail.com> wrote:
>>> Hi,
>>>
>>> I'm pleased to announce yet another tool for importing darcs repositories
>>> to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in
>>> Haskell, on top of the darcs2 source code. The result is a much faster
>>> program - it can convert the complete ghc 6.9 branch (without libraries)
>>> in less than 15 minutes on my slightly dated machine (Athlon XP 2500+),
>>> which is quite fast [3]. Incremental updates work, too.
>>>
>> What's the appeal of this? I personally love git, but I thought all
>> the cool kids at this school used darcs and that was that.
> 
> Disclaimer: I'm no expert, this is what I've heard. Anyone please
> confirm or deny the following?

I've never been a cool kid at school, but I switched from Darcs to Git
recently.  I have not regretted it.  Git has quite a few features Darcs
doesn't by now, and there is a little bit (but not much) in the other
direction.  That and the lack of the indempotent merge bug.

Git's interface has really cleaned up in the last year, and it seems to
be well on the way to becoming the defacto DVCS of choice.  Maybe next
week, when it's picked up the last of the superdelegates, we can say for
sure, but of course bzr won't conceed anything at this point....

(OK, so we've had mind-numbing election coverage here in the US for too
long)

I've blogged about this.  http://changelog.complete.org/plugin/tag/git
will get you most of the relevant posts.

-- John
From icfp.publicity at googlemail.com  Wed Jun  4 12:53:13 2008
From: icfp.publicity at googlemail.com (Matthew Fluet (ICFP Publicity Chair))
Date: Wed Jun  4 12:45:52 2008
Subject: [Haskell-cafe] ICFP2008 Call for Poster proposals
Message-ID: <53ff55480806040953l730455cft7a8c4e89a0ded583@mail.gmail.com>

ICFP 2008 poster session
September 21, 2008
Call for presentation proposals

ICFP 2008 will feature a poster session for researchers and
practitioners, including students.  The session will provide friendly
feedback for work that is in gestation or ongoing, as well as
opportunities to meet each other and exchange ideas.  We welcome poster
submissions on all ICFP topics, especially presentations of

  - applications of and to functional programming;
  - recent work presented at more distant venues; and
  - ongoing work, whether or not submitted to ICFP.

There will be no formal proceedings, but presenters will be invited to
submit working notes, demo code, and other materials to supplement their
abstract and poster.  These materials will be released informally on a
Web page dedicated to the poster session.  An accepted submission is not
intended to replace conference or journal publication.

Persons interested in presenting a poster are invited to submit a
one-page abstract in SIGPLAN conference style
    http://www.acm.org/sigs/sigplan/authorInformation.htm
to the Web site
    https://www.softconf.com/s08/icfp08-posters/submit.html
by June 30, 2008.  The program committee will review the submissions
for relevance and interest, and notify the authors by July 14, 2008.
Accepted posters must be presented by the authors in person on Sunday,
September 21, 2008.

Important dates:
Submission: Monday, June 30, 2008
Notification: Monday, July 14, 2008
Presentation: Sunday, September 21, 2008

Program committee:
Benjamin Pierce (University of Pennsylvania)
Colin Runciman (University of York)
Chung-chieh Shan (Rutgers University)
From bertram.felgenhauer at googlemail.com  Wed Jun  4 13:15:36 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Wed Jun  4 13:08:19 2008
Subject: [Haskell-cafe] [ANN] hs-pgms 0.1 -- Programmer's Minesweeper in
	Haskell
Message-ID: <20080604171535.GA4265@zombie.inf.tu-dresden.de>

Hi,

I've just uploaded hs-pgms to hackage. It is a Haskell implementation
of Programmer's Minesweeper [1], which allows programmers to implement
minesweeper strategies and run them. (Note: ghc >= 6.8 is required.)

hs-pgms uses MonadPrompt to achieve a clean separation between
strategies, game logic, and presentation. There are two frontends,
one command line frontend which is mainly useful for collecting
statistics, and a GUI frontend, using gtk2hs, for watching the
strategies in action.

There's a git repo, see http://repo.or.cz/w/hs-pgms.git .

enjoy,

Bertram

[1] http://www.ccs.neu.edu/home/ramsdell/pgms/index.html
From trebla at vex.net  Wed Jun  4 14:37:07 2008
From: trebla at vex.net (Albert Y. C. Lai)
Date: Wed Jun  4 14:29:43 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <200806041213.55484.jon@ffconsultancy.com>
References: <20080603174704.GB22053@scytale.galois.com>	<6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>	<7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
	<200806041213.55484.jon@ffconsultancy.com>
Message-ID: <4846E0D3.4070608@vex.net>

Jon Harrop wrote:
> IRL the specification often dictates the complexity. If your code fails to 
> satisfy the spec then it is wrong. Are you saying that Haskell code can never 
> satisfy any such specification?

In addition to RL, it it should and it can in theory too:

http://www.cs.toronto.edu/~hehner/aPToP/  in particular chapter 4 
sections 4.2 and 4.3.

I also admire that Musser and Saini give asymptotic costs as an 
indispensible part of the STL specification. Everyone should at least do 
that much.
From trebla at vex.net  Wed Jun  4 14:52:12 2008
From: trebla at vex.net (Albert Y. C. Lai)
Date: Wed Jun  4 14:44:46 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <g25o2h$p3p$1@ger.gmane.org>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>	<4845D0B8.6040802@vex.net>	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org>
Message-ID: <4846E45C.3040402@vex.net>

apfelmus wrote:
> I haven't heard the terms "laziness leak" and "strictness leak" before, 
> imho they sound a bit spooky because it's not clear to me what the 
> situation without leak would be. (Time vs Space? Is an O(n) algorithm a 
> strictness leak compared to an O(log n) algorithm?)

"Leak" refers to a surprise. You didn't expect Firefox to use Omega(n) 
memory where n is the number of times you refresh a rather plain static 
HTML page, but it does, and you call it a memory "leak". You didn't 
expect foldl to lump a big thunk, but it does, and you call it a lazy 
"leak". Therefore "leak" refers to a program failing your expectation - 
even if you yourself wrote the program.

("Leak", "bug", "issue"... We surely are very creative in how to avoid 
calling a shovel a shovel, or an error an error.)

The solution is better education, better reasoning, and Intelligent 
Design. As you write every line of code, you should already know what to 
expect. No magic, no surprise, just science.

From s.clover at gmail.com  Wed Jun  4 15:00:08 2008
From: s.clover at gmail.com (Sterling Clover)
Date: Wed Jun  4 14:52:48 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <4846C559.9020201@complete.org>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>	<20080602172131.GA7534@scytale.galois.com>	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>	<20080603172303.GA22053@scytale.galois.com>
	<1212534382.15010.227.camel@localhost>
	<4846C559.9020201@complete.org>
Message-ID: <84455758-6AD3-4FE9-ABF8-C1FC739FE0ED@gmail.com>

>
> hvac sounds interesting but at that time at least it was not clear
> whether it was stable or would continue to be maintained.
>
> xhtml and HStringTemplate were overkill for what I wanted, so I  
> wound up
> just using the FastCGI and CGI toolkits themselves.  They are
> surprisingly nice, and with a little bit of wrappers around them for
> things like validating forms, have worked exceptionally well.
>

I'm in a position now where I can make a reasonable promise that hvac  
will not only be maintained but undergoing continued development. I  
just, for example, hooked in some basic postgresql support yesterday  
(although the changes are not tested/pushed to the repo yet).  
(Speaking of which, I noticed that the HDBC postgresql bindings don't  
set seState on an error -- is this intentional, or something that  
should be fixed up?)

As such though, I also can't promise that hvac as it stands is  
officially stable, although most work I imagine that will be done on  
it will consist of extensions rather than API-breaking changes.

I've also been working on a lightweight testing API for programs  
using the CGI monad, integrated with quickcheck. Although this  
project isn't "final" yet either, there's a working repo at http:// 
code.haskell.org/~sclv/cgicheck/ if anyone wants to play with it/use  
it. I plan to use this quite a bit to test hvac, and any applications  
produced using it.

Additionally, the hvac code now has a nice, though also incomplete  
orm/dsl-type library for database access (also built on top of HDBC).  
When I feel more confident/polished in the code there, I plan to  
split it out and hackage it as well.

Of course, folks with a little time/inclination who play with these  
things a bit and put them through the paces are a big help in working  
out the kinks such that I feel they're closer to "release- 
quality" (even if that "release" *is* only 0.1). :-)

Relatedly, I'd be very interested in developing a single common  
library for encoding/escaping/decoding/unescaping of common web  
formats (urls, javascript, basic xss escaping, rss-valid character  
escapes to html-valid ones, etc.) that uses a lightweight invertible  
combinator approach as described in Pierce's work on lenses (various  
papers at http://www.seas.upenn.edu/~harmony/) such that the encode/ 
decode methods are correct-by-construction bijections. There are  
various encoding bits scattered among the Haskell web libraries at  
the moment, each with varying degrees of correctness and conformance.  
It would be nice to direct energy here to a single centralized  
project, which would have some upfront architecture, and then,  
unfortunately, probably no small degree of spec-translation. If  
anyone else is interested in working on such a thing, I'd be  
delighted for ideas/collaboration (or better yet, if someone just  
picked up the idea and ran with it themselves!) (hmm... maybe galois  
has some internal libraries it wouldn't mind sharing as a partial  
basis?)

Regards,
Sterl.
From s.clover at gmail.com  Wed Jun  4 15:11:31 2008
From: s.clover at gmail.com (Sterling Clover)
Date: Wed Jun  4 15:04:10 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <Pine.LNX.4.64.0806041144450.10155@poolpc16.informatik.uni-halle.de>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
	<Pine.LNX.4.64.0806041144450.10155@poolpc16.informatik.uni-halle.de>
Message-ID: <C4E48333-7CAE-42A1-8EAD-FFAB9A31DE43@gmail.com>

> On Jun 4, 2008, at 5:51 AM, Henning Thielemann wrote:
> How about assisting the compiler with a helper function named  
> 'parallel' ?
>
> parallel :: ([a] -> b, [a] -> c) -> [a] -> (b,c)
> parallel (f,g) xs = (f xs, g xs)
>
> mean xs =
>   uncurry (/) $ parallel (sum,length) xs
>
>
> ? We could state RULES in terms of 'parallel'. By calling  
> 'parallel', the user tells, that he wants fusion here.
>
> Say
>   "parallel/foldl/foldl" forall f, g, x0, y0.
>       parallel (foldl f x0, foldl g y0) = foldl (\(x,y) z -> (f x  
> z, g y z)) (x0,y0)
>

Well, we already have &&&. Would a sufficiently specialized rule over  
that be a useful addition to Control.Arrow?

Regards,
Sterl.
From dons at galois.com  Wed Jun  4 16:11:53 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun  4 16:04:30 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <84455758-6AD3-4FE9-ABF8-C1FC739FE0ED@gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<20080602172131.GA7534@scytale.galois.com>
	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>
	<20080603172303.GA22053@scytale.galois.com>
	<1212534382.15010.227.camel@localhost>
	<4846C559.9020201@complete.org>
	<84455758-6AD3-4FE9-ABF8-C1FC739FE0ED@gmail.com>
Message-ID: <20080604201153.GG19197@scytale.galois.com>

s.clover:
> >
> >hvac sounds interesting but at that time at least it was not clear
> >whether it was stable or would continue to be maintained.
> >
> >xhtml and HStringTemplate were overkill for what I wanted, so I  
> >wound up
> >just using the FastCGI and CGI toolkits themselves.  They are
> >surprisingly nice, and with a little bit of wrappers around them for
> >things like validating forms, have worked exceptionally well.
> >
> 
> I'm in a position now where I can make a reasonable promise that hvac  
> will not only be maintained but undergoing continued development. I  
> just, for example, hooked in some basic postgresql support yesterday  
> (although the changes are not tested/pushed to the repo yet).  
> (Speaking of which, I noticed that the HDBC postgresql bindings don't  
> set seState on an error -- is this intentional, or something that  
> should be fixed up?)

Sterling,

Would you like to add some text on hvac and your other web libs
to our web programming wiki/faq,

    http://haskell.org/haskellwiki/Practical_web_programming_in_Haskell

Ideally, in a few months time, with enough additions, the full 
story will be covered on this wiki page, and it will be a great
boon to developers wanting to work in Haskell, in this hot area.

-- Don
From andrewcoppin at btinternet.com  Wed Jun  4 14:33:00 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun  4 16:05:06 2008
Subject: [Haskell-cafe] How would you hack it?
Message-ID: <4846DFDC.5020905@btinternet.com>

So anyway, today I found myself wanting to build a program that 
generates some test data. I managed to make it *work* without too much 
difficulty, but it wasn't exactly "elegant". I'm curios to know how 
higher-order minds would approach this problem. It's not an especially 
"hard" problem, and I'm sure there are several good solutions possible.

I have a file that contains several thousand words, seperated by white 
space. [I gather that on Unix there's a standard location for this 
file?] I want to end up with a file that contains a randomly-chosen 
selection of words. Actually, I'd like the end result to be a LaTeX 
file, containing sections, subsections, paragraphs and sentences. 
(Although obviously the actual sentences will be gibberish.) I'd like to 
be able to select how big the file should be, to within a few dozen 
characters anyway. Exact precision is not required.

How would you do this?

The approach I came up with is to slurp up the words like so:

  raw <- readFile "words.txt"
  let ws = words raw
  let n = length ws
  let wa = listArray (1,n) ws

(I actually used lazy ByteStrings of characters.) So now I have an array 
of packed ByteStrings, and I can pick array indexes at random and use 
"unwords" to build my gibberish "sentences".

The fun part is making a sentence come out the right size. There are two 
obvious possibilities:
- Assume that all words are approximately N characters long, and 
estimate how many words a sentence therefore needs to contain to have 
the required length.
- Start with an empty list and *actually count* the characters as you 
add each word. (You can prepend them rather than append them for extra 
efficiency.)
I ended up taking the latter approach - at least at the sentence level.

What I actually did was to write a function that builds lists of words. 
There is then another function that builds several sublists of 
approximately the prescribed lengths, inserts some commas, capitalises 
the first letter and appends a fullstop. This therefore generates a 
"sentence". After that, there's a function that builds several sentences 
of random size with random numbers of commas and makes a "paragraph" out 
of them. Next a function gathers several paragraphs and inserts a 
randomly-generated subsection heading. A similar function takes several 
subsections and adds a random section heading.

In my current implementation, all of this is in the IO monad (so I can 
pick things randomly). Also, the whole thing looks very repetative and 
really if I thought about it harder, it ought to be possible to factor 
it out into something smaller and more ellegant. The clause function 
builds clauses of "approximately" the right size, and each function 
above that (sentence, paragraph, subsection, section) becomes 
progressively less accurate in its sizing. On the other hand, the final 
generated text always for example has 4 subsections to each section, and 
they always look visually the same size. I'd like to make it more 
random, but all the code works by estimating "roughly" how big a 
particular construct is, and therefore how many of then are required to 
full N characters. For larger and larger N, actually counting this stuff 
would seem somewhat inefficient, so I'm estimating. But that makes it 
hard to add more randomness without losing overall size control.

The final file can end up being a fair way different in size to what I 
requested, and has an annoyingly regular internal structure. But 
essentially, it works.

It would be nice to modify the code to generate HTML - but since it's 
coded so simple-mindedly, that would be a copy & paste job.

Clearly, what I *should* have done is think more about a good 
abstraction before writing miles of code. ;-) So how would you guys do this?

From newsham at lava.net  Wed Jun  4 16:26:33 2008
From: newsham at lava.net (Tim Newsham)
Date: Wed Jun  4 16:19:09 2008
Subject: [Haskell-cafe] very hard to build darcs with win32 ghc-6.8.2!
Message-ID: <Pine.BSI.4.64.0806041026110.16752@malasada.lava.net>

I built darcs for win32 recently and it was much more difficult than
it should be.  Probably most of the blame goes to ghc-6.8.2 binary
release for win32.  Half of the effort is getting the zlib prereq
working.

Previously to build zlib for win32 ghc I did the following:
http://www.haskell.org/pipermail/haskell-cafe/2007-March/023059.html

However, now, the gcc binary for ghc-6.8.2 does not work as well as
I would like which requires a bit more effort:

- It did not automatically add mingw headers during compilation, and
   to fix this I had to force some extra flags.  I built a shell script
   "xcc":

   #!/bin/sh
   GHC=/ghc/ghc-6.8.2
   PATH=/c$GHC/gcc-lib:$PATH
   export PATH
   /c$GHC/gcc -I $GHC/include -I $GHC/include/mingw \
              -I $GHC/gcc-lib/include -L $GHC/gcc-lib "$@"

- During linking it did not find crt2.o and adding it to PATH and
   -L did not help, so I just copied wholesale all of
   /c/ghc/ghc-6.8.2/gcc-lib into my zlib source directory.

- At this point I was able to build with:
   CC=./xcc ./configure --prefix=/c/ghc/ghc-6.8.2 \
                        --libdir=/c/ghc/ghc-6.8.2
   make
   make install

Why is the gcc in ghc's directory so non-functional?

Ok, so with zlib (the C library) installed, the zlib haskell package
installs properly.  Dependency resolved.

Next, to build darcs I had to configure it without libcurl support
(or alternately spend time chasing down that dep, pass for now). 
Using cygwin I ran "./configure" which falsely uses the cygwin gcc
for configuration checks, but since gcc is never used directly during
the compilation process, that doesn't matter that much.  I could have
tried the "xcc" trick here again, but didn't bother.  I ran into
two problems during the build:

- -Werror is specified in the GNUMakefile and there are many warnings.
   I just removed -Werror for now.

- During linking it was not able to resolve "SleepEx" from
   src/win32/System/Posix.hs.  I could not figure out what is going
   on here.  I tried adding "-lkernel32" and "-L /ghc/ghc-6.8.2/gcc-lib
   -Lkernel32" to the Makefile and it still did not work even though
   /ghc/ghc-6.8.2/gcc-lib/libkernel32.a has SleepEx@8 defined(!)
   Finally I bit the bullet and hacked around this by noticing that
   mingw headers have _sleep() defined.  I replaced the code in Posix.hs
   with:

   foreign import ccall "_sleep" c_sleep :: CULong -> IO ()

   sleep :: Integer -> IO CInt
   sleep n = c_sleep (fromIntegral n) >> return (toEnum $ fromIntegral n)

At this point darcs builds and the binary seems to work (so far).
I don't know the implication of my sleep hack (which doesn't return
the actual time slept).

Here's a small test program which uses FFI to SleepEx which I was
not able to get working with win32 ghc-6.8.2.

------
{-# OPTIONS -fglasgow-exts -fffi #-}
module Main where
import Foreign.C.Types

foreign import ccall "SleepEx" c_SleepEx :: CUInt -> CInt -> IO CInt

main = do
     putStrLn "start"
     n <- c_SleepEx (2*1000) 1
     print n
-------

So, what is going on with ghc-6.8.2?  Why is the gcc so hard to use
now?  Why can't I get FFI working with standard win32 functions?
Why aren't there prebuilt win32 darcs binaries anymore?

Tim Newsham
http://www.thenewsh.com/~newsham/
From bulat.ziganshin at gmail.com  Wed Jun  4 16:21:18 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Wed Jun  4 16:21:08 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <4846DFDC.5020905@btinternet.com>
References: <4846DFDC.5020905@btinternet.com>
Message-ID: <908301814.20080605002118@gmail.com>

Hello Andrew,

Wednesday, June 4, 2008, 10:33:00 PM, you wrote:
> I have a file that contains several thousand words, seperated by white
> space. [I gather that on Unix there's a standard location for this 
> file?] I want to end up with a file that contains a randomly-chosen 
> selection of words.

does this letter was generated automatically? :)  good work! :)))


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From greg at maptuit.com  Wed Jun  4 16:18:12 2008
From: greg at maptuit.com (Gregory Collins)
Date: Wed Jun  4 16:25:12 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <4846DFDC.5020905@btinternet.com> (Andrew Coppin's message of
	"Wed, 04 Jun 2008 19:33:00 +0100")
References: <4846DFDC.5020905@btinternet.com>
Message-ID: <m1r6bdc5tn.fsf@subrosa.ca>

Andrew Coppin <andrewcoppin@btinternet.com> writes:

> Clearly, what I *should* have done is think more about a good
> abstraction before writing miles of code. ;-) So how would you guys do
> this?

If you want text that roughly resembles English, you're better off
getting a corpus of real English text and running it through a Markov
chain. Mark Dominus has written a few blog posts about this topic
recently, see http://blog.plover.com/lang/finnpar.html.

G.
From barsoap at web.de  Wed Jun  4 16:32:28 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 16:25:19 2008
Subject: [Haskell-cafe] Re: How would you hack it?
References: <4846DFDC.5020905@btinternet.com>
Message-ID: <20080604223228.284254b5@solaris>

Andrew Coppin <andrewcoppin@btinternet.com> wrote:

> I have a file that contains several thousand words, seperated by
> white space. [I gather that on Unix there's a standard location for
> this file?]
>
Looking at /usr/share/dict/words, I'm assured that the proper seperator
is \n.

> Clearly, what I *should* have done is think more about a good 
> abstraction before writing miles of code. ;-) So how would you guys
> do this?
>
Generate a Map Int [String] map, with the latter list being an infinite
list of words with that particular size.

Now assume that you want to have a 100 character sentence. You start by
looking if you got any 100 character word, if yes it's your sentence,
if not you divide it in half (maybe offset by a weighted random
factor [1]) and start over again.

You can then specify your whole document along the lines of

(capitalise $ words 100) ++ ". " ++ (capitalise $ words 10) ++ "?" ++
(capitalise $ words 20) ++ "oneone1!" 

[1] Random midpoint displacement is a very interesting topic by itself.

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From jgoerzen at complete.org  Wed Jun  4 16:51:15 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Wed Jun  4 16:43:53 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <84455758-6AD3-4FE9-ABF8-C1FC739FE0ED@gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>	<20080602172131.GA7534@scytale.galois.com>	<910ddf450806031020i2e09b83bo4cd13f395b612e1@mail.gmail.com>	<20080603172303.GA22053@scytale.galois.com>	<1212534382.15010.227.camel@localhost>	<4846C559.9020201@complete.org>
	<84455758-6AD3-4FE9-ABF8-C1FC739FE0ED@gmail.com>
Message-ID: <48470043.6020400@complete.org>

Sterling Clover wrote:
>> hvac sounds interesting but at that time at least it was not clear
>> whether it was stable or would continue to be maintained.
>>
>> xhtml and HStringTemplate were overkill for what I wanted, so I  
>> wound up
>> just using the FastCGI and CGI toolkits themselves.  They are
>> surprisingly nice, and with a little bit of wrappers around them for
>> things like validating forms, have worked exceptionally well.
>>
> 
> I'm in a position now where I can make a reasonable promise that hvac  
> will not only be maintained but undergoing continued development. I  
> just, for example, hooked in some basic postgresql support yesterday  
> (although the changes are not tested/pushed to the repo yet).  
> (Speaking of which, I noticed that the HDBC postgresql bindings don't  
> set seState on an error -- is this intentional, or something that  
> should be fixed up?)

That would be a bug, I think.  Could you submit it over at
software.complete.org, ideally with test code?  (Even more ideally, with
a patch <grin>)

-- John
From barsoap at web.de  Wed Jun  4 16:52:20 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 16:45:11 2008
Subject: [Haskell-cafe] Re: How would you hack it?
References: <4846DFDC.5020905@btinternet.com>
	<m1r6bdc5tn.fsf@subrosa.ca>
Message-ID: <20080604225220.40e0fa76@solaris>

Gregory Collins <greg@maptuit.com> wrote:

> Andrew Coppin <andrewcoppin@btinternet.com> writes:
> 
> > Clearly, what I *should* have done is think more about a good
> > abstraction before writing miles of code. ;-) So how would you guys
> > do this?
> 
> If you want text that roughly resembles English, you're better off
> getting a corpus of real English text and running it through a Markov
> chain. Mark Dominus has written a few blog posts about this topic
> recently, see http://blog.plover.com/lang/finnpar.html.
> 
If you run one over obscure academic papers, you can even generate
publishable results. I don't have a link ready, but there was a fun
incident involving this.

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past copyright information. All rights reserved. Unauthorised copying,
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signature prohibited. 

From lemming at henning-thielemann.de  Wed Jun  4 16:55:19 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun  4 16:47:52 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <4846DFDC.5020905@btinternet.com>
References: <4846DFDC.5020905@btinternet.com>
Message-ID: <Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>


On Wed, 4 Jun 2008, Andrew Coppin wrote:

> How would you do this?
>
> The approach I came up with is to slurp up the words like so:
>
>   raw <- readFile "words.txt"
>   let ws = words raw
>   let n = length ws
>   let wa = listArray (1,n) ws
>
> (I actually used lazy ByteStrings of characters.) So now I have an array
> of packed ByteStrings, and I can pick array indexes at random and use
> "unwords" to build my gibberish "sentences".

Sounds like a generator for scientific articles. :-)
Maybe
   http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain
 can be of help for you. It's also free of randomIO.

> In my current implementation, all of this is in the IO monad (so I can
> pick things randomly).

You know of
   http://www.haskell.org/pipermail/haskell-cafe/2006-December/020005.html
?

From lemming at henning-thielemann.de  Wed Jun  4 16:58:05 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun  4 16:50:37 2008
Subject: [Haskell-cafe] Re: How would you hack it?
In-Reply-To: <20080604225220.40e0fa76@solaris>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
	<20080604225220.40e0fa76@solaris>
Message-ID: <Pine.GSO.4.56.0806042255500.23485@haydn.informatik.uni-halle.de>


On Wed, 4 Jun 2008, Achim Schneider wrote:

> Gregory Collins <greg@maptuit.com> wrote:
>
> > Andrew Coppin <andrewcoppin@btinternet.com> writes:
> >
> > > Clearly, what I *should* have done is think more about a good
> > > abstraction before writing miles of code. ;-) So how would you guys
> > > do this?
> >
> > If you want text that roughly resembles English, you're better off
> > getting a corpus of real English text and running it through a Markov
> > chain. Mark Dominus has written a few blog posts about this topic
> > recently, see http://blog.plover.com/lang/finnpar.html.
> >
> If you run one over obscure academic papers, you can even generate
> publishable results. I don't have a link ready, but there was a fun
> incident involving this.

A famous paper generator is
   http://pdos.csail.mit.edu/scigen/
From andrewcoppin at btinternet.com  Wed Jun  4 16:50:28 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun  4 16:59:36 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <m1r6bdc5tn.fsf@subrosa.ca>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
Message-ID: <48470014.4000804@btinternet.com>

Gregory Collins wrote:
> Andrew Coppin <andrewcoppin@btinternet.com> writes:
>
>   
>> Clearly, what I *should* have done is think more about a good
>> abstraction before writing miles of code. ;-) So how would you guys do
>> this?
>>     
>
> If you want text that roughly resembles English, you're better off
> getting a corpus of real English text and running it through a Markov
> chain. Mark Dominus has written a few blog posts about this topic
> recently, see http://blog.plover.com/lang/finnpar.html.
>   

This is probably overkill for my purposes.

However, if you can find me a source that explains what a "Markov chain" 
actually *is*, I'd be quite interested.

[I've seen it mentioned several times in relation to data compression, 
but Wikipedia's article is too cryptic for me to comprehend. I think 
Wikipedia is just a poor way to learn completely new concepts; 
Wikipedia's description of digital filters is also utterly 
incomprehensible, but it turns out the subject isn't actually that hard.]

From andrewcoppin at btinternet.com  Wed Jun  4 16:54:57 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun  4 16:59:53 2008
Subject: [Haskell-cafe] Re: How would you hack it?
In-Reply-To: <20080604223228.284254b5@solaris>
References: <4846DFDC.5020905@btinternet.com> <20080604223228.284254b5@solaris>
Message-ID: <48470121.6090408@btinternet.com>

Achim Schneider wrote:
> Andrew Coppin <andrewcoppin@btinternet.com> wrote:
>
>   
>> I have a file that contains several thousand words, seperated by
>> white space. [I gather that on Unix there's a standard location for
>> this file?]
> Looking at /usr/share/dict/words, I'm assured that the proper seperator
> is \n.
>   

Thanks. I did look around trying to find this, but ultimately failed. 
(Is it a standard component, or is it installed as part of some specific 
application?)

As I understand it, Haskell's "words" function will work on any kind of 
white space - spaces, line feeds, caridge returns, tabs, etc. - so it 
should be fine. ;-) Since I'm developing on Windows, what I actually did 
was have Google find me a file online that I can download.

[Remember my post a while back? "GHC panic"? Apparently GHC doesn't like 
it if you try to represent the entire 400 KB file as a single [String]...]

> Generate a Map Int [String] map, with the latter list being an infinite
> list of words with that particular size.
>
> Now assume that you want to have a 100 character sentence. You start by
> looking if you got any 100 character word, if yes it's your sentence,
> if not you divide it in half (maybe offset by a weighted random
> factor [1]) and start over again.
>
> You can then specify your whole document along the lines of
>
> (capitalise $ words 100) ++ ". " ++ (capitalise $ words 10) ++ "?" ++
> (capitalise $ words 20) ++ "oneone1!" 
>
> [1] Random midpoint displacement is a very interesting topic by itself.
>   

I'm not following your logic, sorry...

From barsoap at web.de  Wed Jun  4 17:25:07 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 17:17:55 2008
Subject: [Haskell-cafe] Re: How would you hack it?
References: <4846DFDC.5020905@btinternet.com> <20080604223228.284254b5@solaris>
	<48470121.6090408@btinternet.com>
Message-ID: <20080604232507.7fd9fd81@solaris>

Andrew Coppin <andrewcoppin@btinternet.com> wrote:

> Achim Schneider wrote:
> > Andrew Coppin <andrewcoppin@btinternet.com> wrote:
> >
> >   
> >> I have a file that contains several thousand words, seperated by
> >> white space. [I gather that on Unix there's a standard location for
> >> this file?]
> > Looking at /usr/share/dict/words, I'm assured that the proper
> > seperator is \n.
> >   
> 
> Thanks. I did look around trying to find this, but ultimately failed. 
> (Is it a standard component, or is it installed as part of some
> specific application?)
> 
ksf@solaris ~ % equery b /usr/share/dict/words
[ Searching for file(s) /usr/share/dict/words in *... ]
sys-apps/miscfiles-1.4.2 (/usr/share/dict/words)
ksf@solaris ~ % eix miscfiles
[I] sys-apps/miscfiles
     Available versions:  1.4.2 {minimal}
     Installed versions:  1.4.2(18:27:27 02/14/07)(-minimal)
     Homepage:            http://www.gnu.org/directory/miscfiles.html
     Description:         Miscellaneous files

> > Generate a Map Int [String] map, with the latter list being an
> > infinite list of words with that particular size.
> >
> > Now assume that you want to have a 100 character sentence. You
> > start by looking if you got any 100 character word, if yes it's
> > your sentence, if not you divide it in half (maybe offset by a
> > weighted random factor [1]) and start over again.
> >
> > You can then specify your whole document along the lines of
> >
> > (capitalise $ words 100) ++ ". " ++ (capitalise $ words 10) ++ "?"
> > ++ (capitalise $ words 20) ++ "oneone1!" 
> >
> > [1] Random midpoint displacement is a very interesting topic by
> > itself. 
> 
> I'm not following your logic, sorry...
>
That's probably because I just described the points and not the rest
of the morphisms... imagine some plumbing and tape between my sentences.

Midpoint displacement is a great way to achieve randomness while still
keeping a uniform appearance. In the defining paper, that I don't have
ready right now, an example was shown where a realistic outline of
Australia was generated from ten or so data points: If you display it
next to the actual outline, only a geographer could tell which one's
the fake.

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From daniel.is.fischer at web.de  Wed Jun  4 17:28:52 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Wed Jun  4 17:19:32 2008
Subject: [Haskell-cafe] very hard to build darcs with win32 ghc-6.8.2!
In-Reply-To: <Pine.BSI.4.64.0806041026110.16752@malasada.lava.net>
References: <Pine.BSI.4.64.0806041026110.16752@malasada.lava.net>
Message-ID: <200806042328.52170.daniel.is.fischer@web.de>

Am Mittwoch, 4. Juni 2008 22:26 schrieb Tim Newsham:
>
> Here's a small test program which uses FFI to SleepEx which I was
> not able to get working with win32 ghc-6.8.2.
>
> ------
> {-# OPTIONS -fglasgow-exts -fffi #-}
> module Main where
> import Foreign.C.Types
>
> foreign import ccall "SleepEx" c_SleepEx :: CUInt -> CInt -> IO CInt

I seem to remember it should be "stdcall" on windows.
That might also have a role in not finding SleepEx@8.
>
> main = do
>      putStrLn "start"
>      n <- c_SleepEx (2*1000) 1
>      print n
> -------
>
> So, what is going on with ghc-6.8.2?  Why is the gcc so hard to use
> now?  Why can't I get FFI working with standard win32 functions?
> Why aren't there prebuilt win32 darcs binaries anymore?
>
> Tim Newsham
> http://www.thenewsh.com/~newsham/

From andrewcoppin at btinternet.com  Wed Jun  4 17:19:51 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun  4 17:25:40 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
References: <4846DFDC.5020905@btinternet.com>
	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
Message-ID: <484706F7.8000407@btinternet.com>

Henning Thielemann wrote:
> Sounds like a generator for scientific articles. :-)
> Maybe
>    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain
>  can be of help for you. It's also free of randomIO.
>   

That certainly looks interesting. Presumably if I train it right, it'll 
figure out that sentences need to start uppercase and end with a 
full-stop, and maybe have a few other punctuation marks thrown in. I'm 
not sure I trust it to generate valid LaTeX markup, but I can give it a 
try! ;-)

At any rate, thanks for the link - the possibilities for this look very 
interesting. (All sorts of data to be generated. And hey, maybe if I 
read the source I can even learn some of the theory behind it too...)

From list at phaedrusdeinus.org  Wed Jun  4 17:33:21 2008
From: list at phaedrusdeinus.org (John Melesky)
Date: Wed Jun  4 17:26:04 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <48470014.4000804@btinternet.com>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
	<48470014.4000804@btinternet.com>
Message-ID: <79F4406C-52CA-4467-9826-8819E3D8DEE3@phaedrusdeinus.org>

On Jun 4, 2008, at 3:50 PM, Andrew Coppin wrote:
> However, if you can find me a source that explains what a "Markov  
> chain" actually *is*, I'd be quite interested.

In a non-rigorous nutshell:

You have the word "star". You want to pick another word to follow it.  
It turns out that, based on analyzing a corpus ("corpus", here means  
"bunch of text you extract information from"), the following word  
pairs occur:

star wars (20% of the time)
star cluster (5% of the time)
star dust (10% of the time)
star system (25% of the time)
star -end-of-sentence- (5% of the time)
.
.
.

So you use those occurrence statistics to pick a feasible next word  
(let's choose "system", since it's the highest probability here -- in  
practice you'd probably choose one randomly based on a weighted  
likelihood). Then you look for all the word pairs which start with  
"system", and choose the next word in the same fashion. Repeat for as  
long as you want.

Those word-pair statistics, when you have them for all the words in  
your vocabulary, comprise the first-level Markov data for your corpus.

When you extend it to word triplets, it's second-level Markov data  
(and it will generate more reasonable fake text). You can build higher  
and higher Markov levels if you'd like.

And, ultimately, though the example is about text, you can use this  
method to generate "realistic" sequences of any sequential data.

Hope that helps.

-johnnnnnnn


From lanny at cisco.com  Wed Jun  4 18:23:20 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Wed Jun  4 18:15:44 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <484706F7.8000407@btinternet.com>
References: <4846DFDC.5020905@btinternet.com>	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
	<484706F7.8000407@btinternet.com>
Message-ID: <484715D8.8090803@cisco.com>

You might want to skim Shannon's 'A Mathematical Theory of
Communcations'.  Part 1, Section 2 and 3 are almost exactly your
topic.  (Or at least the direction you've headed in. :)

  http://plan9.bell-labs.com/cm/ms/what/shannonday/shannon1948.pdf

  -ljr

Andrew Coppin wrote:
> Henning Thielemann wrote:
>> Sounds like a generator for scientific articles. :-)
>> Maybe
>>   
>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain
>>  can be of help for you. It's also free of randomIO.
>>   
> 
> That certainly looks interesting. Presumably if I train it right, it'll
> figure out that sentences need to start uppercase and end with a
> full-stop, and maybe have a few other punctuation marks thrown in. I'm
> not sure I trust it to generate valid LaTeX markup, but I can give it a
> try! ;-)
> 
> At any rate, thanks for the link - the possibilities for this look very
> interesting. (All sorts of data to be generated. And hey, maybe if I
> read the source I can even learn some of the theory behind it too...)
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 19:48:50 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 19:37:53 2008
Subject: [Haskell-cafe] Re: cabal and platform-independent haskell
	installation management (again) (Re: Re: Ubuntu and ghc)
In-Reply-To: <20080604172252.34df14f7@solaris>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
	<1212590628.15010.312.camel@localhost>
	<20080604172252.34df14f7@solaris>
Message-ID: <1212623330.15010.318.camel@localhost>


On Wed, 2008-06-04 at 17:22 +0200, Achim Schneider wrote:

> The question, IMHO, seems to be
> 
> "How would a package manager for a posix-compilant kinetic look like?"

http://nixos.org/index.html


Duncan

From duncan.coutts at worc.ox.ac.uk  Wed Jun  4 19:53:13 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun  4 19:42:16 2008
Subject: [Haskell-cafe] very hard to build darcs with win32 ghc-6.8.2!
In-Reply-To: <Pine.BSI.4.64.0806041026110.16752@malasada.lava.net>
References: <Pine.BSI.4.64.0806041026110.16752@malasada.lava.net>
Message-ID: <1212623593.15010.322.camel@localhost>


On Wed, 2008-06-04 at 10:26 -1000, Tim Newsham wrote:
> I built darcs for win32 recently and it was much more difficult than
> it should be.  Probably most of the blame goes to ghc-6.8.2 binary
> release for win32.  Half of the effort is getting the zlib prereq
> working.
> 
> Previously to build zlib for win32 ghc I did the following:
> http://www.haskell.org/pipermail/haskell-cafe/2007-March/023059.html

The recent versions of the zlib package on hackage bundle a complete
copy of the zlib C library for the benefit of windows users (it uses the
system zlib on all other systems).

So it should "Just Work"tm.


Duncan


From ryani.spam at gmail.com  Wed Jun  4 22:16:59 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Wed Jun  4 22:09:33 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <g25o2h$p3p$1@ger.gmane.org>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org>
Message-ID: <2f9b2d30806041916x3e0088acw26e45033ee586b9a@mail.gmail.com>

On 6/4/08, apfelmus <apfelmus@quantentunnel.de> wrote:
> Note that lazy evaluation never wastes time; evaluating a term with lazy
> evaluation will always take less reduction steps than doing so eagerly or
> partly eagerly.

True, but you can still have a "time leak"; this is particularily
relevant in soft-real-time apps (like almost every app you use on a
regular basis, from your editor to games); a time leak is when a
computation that would take X time if evaluated every "time step" is
left for many timesteps without being evaluated, leading to a hitch in
responsiveness when it eventually is demanded N frames later taking
N*X time.

Eager applications almost never have this sort of "time leak", but
it's easy for it to happen with lazy evaluation.

A simple example: consider a variable that holds the number of
timesteps since the app launched, for example.  Every time step it
gets incremented by 1.  If the result is evaluated every time step, it
takes a constant amount of time per timestep.  But if you go a long
time without evaluating it, you end up with both a space leak (as the
+1 thunks build up) but a time leak as well--when you eventually
evaluate it, it takes O(n) time, where n is the number of frames since
the variable was last evaluated.

  -- ryan
From ninegua at gmail.com  Wed Jun  4 22:30:49 2008
From: ninegua at gmail.com (Paul L)
Date: Wed Jun  4 22:23:24 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
Message-ID: <856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>

Pardon me to hijack this thread, but I have an idea to build a
different kind of Web Framework and am not sure if somebody has
already done it.

The idea is to take REST further: every HTML page you see is a program
in its running state (as a continuation monad). Each click on its link
or form submission is seen as feeding data to resume its continuation.

So instead of writing a server-side program that responds to many CGI
calls, you write a single ordinary program that describe the
application logic, which during its execution gets represented as a
HTML page and interpreted by the server.

The server is then very much like a VM or an interpreter of an
embedded language, with execution stacks entirely encoded and stored
in each HTML page sent to the user and back from the user as an
encoded URL or form data. So the server is entirely stateless.

Besides providing scalability, the main advantage of this framework is
that web program can be written in a natural way which total ignores
stuffs like HTTP/CGI, protocol, session, client-server, etc, etc. Its
compiler or interpreter will figure out what part of the program data
(e.g. the code, the static environment) resides on the server side,
and what part is encoded into the HTML pages (e.g., the heap, the
dynamic environment).

Does such a beast exist or am I entirely day dreaming?
From donnie at darthik.com  Wed Jun  4 22:54:32 2008
From: donnie at darthik.com (Donnie Jones)
Date: Wed Jun  4 22:47:28 2008
Subject: [Haskell-cafe] Re: Having trouble with parallel Haskell
In-Reply-To: <4846FB27.1010105@serpentine.com>
References: <4846FB27.1010105@serpentine.com>
Message-ID: <fe05cbe50806041954p51ceb9dfq2784fe7e43cb6ead@mail.gmail.com>

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From barsoap at web.de  Wed Jun  4 23:05:15 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 22:58:05 2008
Subject: [Haskell-cafe] Re: What is the maturity of Haskell Web Frameworks
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
Message-ID: <20080605050515.2656b747@solaris>

"Paul L" <ninegua@gmail.com> wrote:

> Does such a beast exist or am I entirely day dreaming?
>
Daydreaming, at least partly: Just consider state that can't be stored
client-side at all, e.g. the contents of a wiki page.

Networking or HTML as interface isn't the real problem: It's the
multi-headedness of applications that make things complicated. As soon
as you have multiple programs or multiple instances of the same program
modify shared data, things get involved.

Traffic is another problem if state accumulates.

Thinking about REST, a nice feature to have would be session timeout
notifying: The server can keep the connection open and replace the
displayed page with one notifying the user that he's too slow for
current timeout settings.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From qdunkan at gmail.com  Wed Jun  4 23:14:41 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Wed Jun  4 23:07:16 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <484715D8.8090803@cisco.com>
References: <4846DFDC.5020905@btinternet.com>
	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
	<484706F7.8000407@btinternet.com> <484715D8.8090803@cisco.com>
Message-ID: <2518b95d0806042014m3b40937cj1ecf05011e6dae77@mail.gmail.com>

On Wed, Jun 4, 2008 at 3:23 PM, Lanny Ripple <lanny@cisco.com> wrote:
> You might want to skim Shannon's 'A Mathematical Theory of
> Communcations'.  Part 1, Section 2 and 3 are almost exactly your
> topic.  (Or at least the direction you've headed in. :)
>
>  http://plan9.bell-labs.com/cm/ms/what/shannonday/shannon1948.pdf

Rob Pike's "Practice of Programming" has a few chapters with a markov
generator in several different languages as a case study.  None of
them are functional, but it's a pretty clear description of the idea.

The "plan9" in the url reminded me :)
From barsoap at web.de  Wed Jun  4 23:28:25 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun  4 23:21:13 2008
Subject: [Haskell-cafe] Re: Laziness leaks
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org>
	<2f9b2d30806041916x3e0088acw26e45033ee586b9a@mail.gmail.com>
Message-ID: <20080605052825.7002ce4e@solaris>

"Ryan Ingram" <ryani.spam@gmail.com> wrote:

> On 6/4/08, apfelmus <apfelmus@quantentunnel.de> wrote:
> > Note that lazy evaluation never wastes time; evaluating a term with
> > lazy evaluation will always take less reduction steps than doing so
> > eagerly or partly eagerly.
> 
> True, but you can still have a "time leak"; this is particularily
> relevant in soft-real-time apps (like almost every app you use on a
> regular basis, from your editor to games); a time leak is when a
> computation that would take X time if evaluated every "time step" is
> left for many timesteps without being evaluated, leading to a hitch in
> responsiveness when it eventually is demanded N frames later taking
> N*X time.
> 
> Eager applications almost never have this sort of "time leak", but
> it's easy for it to happen with lazy evaluation.
> 
> A simple example: consider a variable that holds the number of
> timesteps since the app launched, for example.  Every time step it
> gets incremented by 1.  If the result is evaluated every time step, it
> takes a constant amount of time per timestep.  But if you go a long
> time without evaluating it, you end up with both a space leak (as the
> +1 thunks build up) but a time leak as well--when you eventually
> evaluate it, it takes O(n) time, where n is the number of frames since
> the variable was last evaluated.
> 
There won't ever be a space leak without a time leak nor a time leak
without a space leak. I'd just call it a leak.

You don't come across space-leaks in strict programs often because
data is usually allocated statically even if execution is non-strict.

Piping /dev/zero into a program that just sleeps does leak space,
though.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From allbery at ece.cmu.edu  Thu Jun  5 00:14:25 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Thu Jun  5 00:06:59 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
Message-ID: <388504A5-E615-478A-9D45-859FAAFE654F@ece.cmu.edu>


On 2008 Jun 4, at 22:30, Paul L wrote:

> The server is then very much like a VM or an interpreter of an
> embedded language, with execution stacks entirely encoded and stored
> in each HTML page sent to the user and back from the user as an
> encoded URL or form data. So the server is entirely stateless.


Mmm, if any of that HTML-stored state is sensitive server information,  
this becomes a problem. (E.g. can I trick your application into  
thinking I'm an admin and then go starting/stopping processes,  
changing passwords. etc.?)  You need to use extra care if anything  
sensitive is put where the client can munge it.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From bulat.ziganshin at gmail.com  Thu Jun  5 00:20:13 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Thu Jun  5 00:19:00 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
References: <4846DFDC.5020905@btinternet.com>
	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
Message-ID: <1444025595.20080605082013@gmail.com>

Hello Henning,

Thursday, June 5, 2008, 12:55:19 AM, you wrote:

> Sounds like a generator for scientific articles. :-)
> Maybe
>   
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain
>  can be of help for you. It's also free of randomIO.

once i've used something like this to generate this brilliant text:

can INR-s
        O, by thenion, Laertes,
        These at these haste is defeling and mornione.

KING CLAUDIUS   Heat killowers, and our vowst'

GUILDENSTERN    Ay, magamovinob vow;
        And lo leave they come, and he sole tobly all you,
        And, or spomir: So, wherefore hiacriful at ast, my lord, I have no orason; Frous stonbitter; at I'll I think himbers, seempended body jooke!
        That would be tracious arest, Rt: sor 'tis timeake or bifuchol
        gugnme:
        If thoughRqublest they are gave with this cercric if, for the no POLONIUS]

KING CLAUDIUS   I will violect of the queen with
        Dity.

ROSENCRANTZ     'Stive to came fat: the
        ne further then, which he his worldy, it is means me.



i've put a full copy to http://haskell.org/bz/not_exactly_hamlet.txt


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From bulat.ziganshin at gmail.com  Thu Jun  5 00:24:10 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Thu Jun  5 00:28:20 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <48470014.4000804@btinternet.com>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
	<48470014.4000804@btinternet.com>
Message-ID: <546528799.20080605082410@gmail.com>

Hello Andrew,

Thursday, June 5, 2008, 12:50:28 AM, you wrote:

> However, if you can find me a source that explains what a "Markov chain"
> actually *is*, I'd be quite interested.

*afaik*, the idea is simple: order-1 Markov chain is just text
generated with respect of probability of each char, and order-n is a
text generated using probability of each char in context of previous
n-1 chars. you just need to gather stats using previous papers :)

you can use this idea both to generate new naturally-looking words and
to gather stats about words itself and generate naturally-looking
sentences


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From twd2 at dockerz.net  Thu Jun  5 01:35:32 2008
From: twd2 at dockerz.net (Tim Docker)
Date: Thu Jun  5 01:28:07 2008
Subject: [Haskell-cafe] Re: library for drawing charts
In-Reply-To: <g2661b$cvj$1@ger.gmane.org>
References: <82B3919B-BE28-4D65-9A3B-957B5EC51D27@gmail.com>
	<12204.203.185.215.144.1211767776.squirrel@dockerz.net>
	<g2661b$cvj$1@ger.gmane.org>
Message-ID: <30547.203.185.215.144.1212644132.squirrel@dockerz.net>

Neal Alexander wrote:
> I was using the HaskellCharts library and needed the same two things; so
> i rolled a quick and dirty pie chart generator (Barchart is on the TODO
> list).
>
>
> http://72.167.145.184:8000/Screenshot.png
> http://72.167.145.184:8000/PieChart.hs

Nice! Do you mind if I refactor that a bit and add it to the HaskellCharts
library? The license is BSD.

Tim


From lemming at henning-thielemann.de  Thu Jun  5 01:43:01 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun  5 01:32:13 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <484706F7.8000407@btinternet.com>
References: <4846DFDC.5020905@btinternet.com>
	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
	<484706F7.8000407@btinternet.com>
Message-ID: <Pine.GSO.4.56.0806050737330.25369@haydn.informatik.uni-halle.de>


On Wed, 4 Jun 2008, Andrew Coppin wrote:

> Henning Thielemann wrote:
> > Sounds like a generator for scientific articles. :-)
> > Maybe
> >    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain
> >  can be of help for you. It's also free of randomIO.
>
> That certainly looks interesting. Presumably if I train it right, it'll
> figure out that sentences need to start uppercase and end with a
> full-stop, and maybe have a few other punctuation marks thrown in.

If you use different encodings for periods for abbreviations and sentence
ends, this is warranted.

> I'm not sure I trust it to generate valid LaTeX markup, but I can give
> it a try! ;-)

You may not want to construct a Markov Chain for characters but for larger
objects, say words and LaTeX commands. However when it comes to correct
parentheses, a Markov Chain might not be the appropriate tool, but a
grammar.
From lemming at henning-thielemann.de  Thu Jun  5 01:46:45 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun  5 01:36:21 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <79F4406C-52CA-4467-9826-8819E3D8DEE3@phaedrusdeinus.org>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
	<48470014.4000804@btinternet.com>
	<79F4406C-52CA-4467-9826-8819E3D8DEE3@phaedrusdeinus.org>
Message-ID: <Pine.GSO.4.56.0806050744090.25369@haydn.informatik.uni-halle.de>


On Wed, 4 Jun 2008, John Melesky wrote:

> So you use those occurrence statistics to pick a feasible next word
> (let's choose "system", since it's the highest probability here -- in
> practice you'd probably choose one randomly based on a weighted
> likelihood). Then you look for all the word pairs which start with
> "system", and choose the next word in the same fashion. Repeat for as
> long as you want.

"Markov chain" means, that you have a sequence of random experiments,
where the outcome of each experiment depends exclusively on a fixed number
(the level) of experiments immediately before the current one.

> Those word-pair statistics, when you have them for all the words in
> your vocabulary, comprise the first-level Markov data for your corpus.
>
> When you extend it to word triplets, it's second-level Markov data
> (and it will generate more reasonable fake text). You can build higher
> and higher Markov levels if you'd like.

If the level is too high, you will just reproduce the training text.
From martindemello at gmail.com  Thu Jun  5 02:07:05 2008
From: martindemello at gmail.com (Martin DeMello)
Date: Thu Jun  5 01:59:38 2008
Subject: [Haskell-cafe] getting set up in ubuntu
Message-ID: <f93a6bcc0806042307o27873fd0ha1595c9f336064cf@mail.gmail.com>

I finally ditched sabayon for ubuntu (one wireless problem too many),
and now I'm slowly getting stuff set up on it. Any Ubuntu people care
to share their experiences? I'm especially looking for guidelines on
what to install via apt-get and what to install independently.

Also, while I'm making Major Life Changes I might as well check out
xmonad :) If anyone has made the switch from fluxbox, do share how it
went.

martin
From jules at jellybean.co.uk  Thu Jun  5 02:26:32 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Thu Jun  5 02:19:04 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <20080605052825.7002ce4e@solaris>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>	<4845D0B8.6040802@vex.net>	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>	<g25o2h$p3p$1@ger.gmane.org>	<2f9b2d30806041916x3e0088acw26e45033ee586b9a@mail.gmail.com>
	<20080605052825.7002ce4e@solaris>
Message-ID: <48478718.7090102@jellybean.co.uk>

Achim Schneider wrote:
>  You don't come across space-leaks in strict programs often because
> data is usually allocated statically even if execution is non-strict.
> 
> Piping /dev/zero into a program that just sleeps does leak space,
> though.
> 

It only leaks 8K or whatever size your system buffers pipes until it 
suspends the writer though... or do I misunderstand your analogy?
From wqeqweuqy at hotmail.com  Thu Jun  5 02:39:43 2008
From: wqeqweuqy at hotmail.com (Neal Alexander)
Date: Thu Jun  5 02:32:35 2008
Subject: [Haskell-cafe] Re: library for drawing charts
In-Reply-To: <30547.203.185.215.144.1212644132.squirrel@dockerz.net>
References: <82B3919B-BE28-4D65-9A3B-957B5EC51D27@gmail.com>	<12204.203.185.215.144.1211767776.squirrel@dockerz.net>	<g2661b$cvj$1@ger.gmane.org>
	<30547.203.185.215.144.1212644132.squirrel@dockerz.net>
Message-ID: <g281nk$9sd$1@ger.gmane.org>

Tim Docker wrote:
> Neal Alexander wrote:
>> I was using the HaskellCharts library and needed the same two things; so
>> i rolled a quick and dirty pie chart generator (Barchart is on the TODO
>> list).
>>
>>
>> http://72.167.145.184:8000/Screenshot.png
>> http://72.167.145.184:8000/PieChart.hs
> 
> Nice! Do you mind if I refactor that a bit and add it to the HaskellCharts
> library? The license is BSD.
> 
> Tim

Yea whatever is cool, it needs some tweaks no doubt.

From ketil at malde.org  Thu Jun  5 03:25:43 2008
From: ketil at malde.org (Ketil Malde)
Date: Thu Jun  5 03:17:56 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <4846E45C.3040402@vex.net> (Albert Y. C. Lai's message of "Wed\,
	04 Jun 2008 14\:52\:12 -0400")
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org> <4846E45C.3040402@vex.net>
Message-ID: <87abi0l4w8.fsf@malde.org>

"Albert Y. C. Lai" <trebla@vex.net> writes:

>> I haven't heard the terms "laziness leak" and "strictness leak"
>> before

> "Leak" refers to a surprise.

I the meaning of "leak" is in a bit of flux.  Originally, I believe it
refers to a memory leak, where the programmer forgot to call free()
before losing the pointer, thus making the program consume memory it
can't recover, and can't use.

With automatic memory management, this doesn't happen, so "memory
leak" then started to mean retaining objects longer than necessary.

(Aside: am I the only one who is shocked by the memory consumption of
modern programs?  I use a simple time tracker (gnotime), a calendar
with a handful of entries (evolution), and they both typically consume
half to one gigabyte of memory.  In all fairness, it seems to be much
better under Ubuntu 8.04 than 7.10, but again, they haven't been
running for very long yet.)

I'm not sure I'll use terms like strictness and laziness leak, I think
it's hard to see what's being lost here, and if you have a laziness
leak, it is unclear if it's too much laziness or too little?

> ("Leak", "bug", "issue"... We surely are very creative in how to avoid
> calling a shovel a shovel, or an error an error.)

At least one text insisted on "defect".

Too much laziness or strictness may be harmful to performance, but
it's only a defect if it means the program fails to meet its
requirements. 

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From vigalchin at gmail.com  Thu Jun  5 03:38:26 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Thu Jun  5 03:31:01 2008
Subject: [Haskell-cafe] example of FFI FunPtr
Message-ID: <5ae4f2ba0806050038k1e0aea1exe6d81b22b1151eeb@mail.gmail.com>

Hello,

       I want to model a Haskell function that is a callback from C. I have
only found one example in the unix package's Semaphore.hsc, which apparently
is not used. I want to be able to marshall a Haskell function that is a
first class citizen residing in a Haskell data type and pass to a C function
via FFI. Are there examples of this?

Thanks, Vasili
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From ketil at malde.org  Thu Jun  5 03:40:50 2008
From: ketil at malde.org (Ketil Malde)
Date: Thu Jun  5 03:33:02 2008
Subject: cabal and platform-independent haskell installation management
	(again) (Re: [Haskell-cafe] Re: Ubuntu and ghc)
In-Reply-To: <016d01c8c64d$4ac1dea0$73357ad5@cr3lt> (Claus Reinke's message of
	"Wed\, 4 Jun 2008 15\:14\:22 +0100")
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
Message-ID: <878wxkl471.fsf@malde.org>

"Claus Reinke" <claus.reinke@talk21.com> writes:

> 1. there are no systems where "packages just work"!
>    there are systems where a few people ensure that
>    many people can live in such an illusion, though.

Exactly.  Integrating Cabal packages into the system package manager
is still non-trivial, and a package maintainer is necessary for this
to work.

Which is why it's rather utopian to hope that all of Hackage can be
found in even the most widely used distributions, since many of those
are way to narrow in scope for somebody to take on the work of
providing package management.  I bet some aren't even maintained, and
possibly don't work with current GHC or Cabal.

But I digress.

> - it isn't sufficient to worry about installation management,
>    one has to worry about integration, lifetime and uninstall
>    management as well. in short, maintain the dependency
>    graphs over any of "install"/"upgrade"/"uninstall".

There is an important difference between Hackage and, say, Ubuntu, and
that is that the latter does releases.  If I use a particular Ubuntu
version, I get a particular GHC version, and a particular version of
some dozens of libraries and applications.  They are all compiled with
that GHC version, tested, and can to a reasonable degree, be expected
to work together.  Sometimes they don't, but the good news is that a
zillion other users are in the same boat (well, even for Haskell, it's
probably dozens, at least), and chances are the bug will be fixed.

If I upgrade to the next version of Ubuntu, I can reasonably expect
all packages to be updated to current versions, and some to be
replaced. 

In contrast, for my packages on Hackage, I'm reasonably
certain it worked on my particular system at the time I uploaded
it.  And dependencies are none too specific - the package might work
with different versions than I compiled with or not.

I think for Cabal to provide the convenience currently afforded by
system package managers, you'd need to do Hackage-wide releases, and
test everything together.  This is a lot of work, but not impossible,
it's what Gnome and KDE does, for instance.  It would probably make
things easier for system package maintainers, too.

Alternatives, like pessimistic dependencies: only exact versions in
cabal files, will probably make you end up with installing every
version of every  package, and still suffer dependency hell.
Exhaustive testing of all version combinations, which will
require a lot of computational resources, even if it could be done
automatically.

--

I generally install most libraries from the distribution's repository,
and let the system worry about updates etc.  I think it's also an
advantage if my programs avoid depending on stuff that's not in the
repo, since it's likely to be is less widely used and maintained.

I install manually the stuff I need the distribution doesn't provide,
and also when I want to look at the code, or just have the latest and
greatest.  I tend to get the darcs version, rather than the Hackage
one, though.  The downside is that I need to reinstall these when I do
a system upgrade, but it's rare enough that it doesn't bother me much,
and chances are that more libraries are provided with my distribution
for every release, so a cleanup is probably a good idea anyway.

Anyway, this works pretty well for me - if I'm living on an illusion,
it's at least a good one. :-)

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From ketil at malde.org  Thu Jun  5 03:47:38 2008
From: ketil at malde.org (Ketil Malde)
Date: Thu Jun  5 03:39:50 2008
Subject: [Haskell-cafe] getting set up in ubuntu
In-Reply-To: <f93a6bcc0806042307o27873fd0ha1595c9f336064cf@mail.gmail.com>
	(Martin DeMello's message of "Wed\, 4 Jun 2008 23\:07\:05 -0700")
References: <f93a6bcc0806042307o27873fd0ha1595c9f336064cf@mail.gmail.com>
Message-ID: <874p88l3vp.fsf@malde.org>


"Martin DeMello" <martindemello@gmail.com> writes:


> Any Ubuntu people care to share their experiences? 

Ask, and ye shall receive..at least some kind of answer.

> I'm especially looking for guidelines on what to install via apt-get
> and what to install independently. 

I'd get as much as possible via apt-get, and only install manually
when that fails.

Libraries - which is probably what you will need most often, have
names that start with 'libghc6'.  For the whole list:

  apt-cache search libghc6

To see what the package is about, use e.g.: 

  apt-cache show libghc6-quickcheck-dev


There are (usually?) three packages for each library, -dev, -doc, and
-prof. Unless you have very little diskspace or a thin network
connection, get them all, e.g:

  sudo apt-get install libghc6-quickcheck-\*

You are then set up to unit-test your code.

> Also, while I'm making Major Life Changes I might as well check out
> xmonad :) If anyone has made the switch from fluxbox, do share how it
> went.

You're basically leaving it all (window management, icons, trays,
whatever) behind, so it doesn't matter much what you switch from.
Just:

  sudo apt-get install xmonad

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From marlowsd at gmail.com  Thu Jun  5 04:01:39 2008
From: marlowsd at gmail.com (Simon Marlow)
Date: Thu Jun  5 03:54:17 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <87wsl5xswc.fsf@malde.org>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>	<1211448821.5824.504.camel@localhost>	<008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com>	<20080604143650.72978202@solaris>
	<87wsl5xswc.fsf@malde.org>
Message-ID: <48479D63.1010004@gmail.com>

Ketil Malde wrote:

> The most usable one I've seen is Steam from Valve, IIRC.  It'd be cool
> if Haskell packages were provided this way.

Cygwin's installer seems to work pretty well, too.

Cheers,
	Simon
From cetin.sert at gmail.com  Thu Jun  5 04:03:22 2008
From: cetin.sert at gmail.com (Cetin Sert)
Date: Thu Jun  5 03:55:56 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
Message-ID: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>

Hi ^_^,

Let's say we have the following data type and functions:

data Tab a =      (:?:)
           |     a :?:   Tab a
           | Tab a :??: (Tab a,Tab a)
           deriving (Eq, Show, Read)

map f (:?:)          = (:?:)
map f (a :?: t)      = f a :?: map f t
map f (h :??: (l,r)) = map f h :??: (map f l, map f r)

filter p (:?:)          = (:?:)
filter p (a :?: t)      | p a       = filter p t
                        | otherwise = a :?: filter p t
filter p (h :??: (l,r)) = filter p h :??: (filter p l, filter p r)

is it possible to automatically derive map and filter?

data Tab a =      (:?:)
           |     a :?:   Tab a
           | Tab a :??: (Tab a,Tab a)
           deriving (Eq, Show, Read, Map, Filter)

If not, do you think it might be nice to have something like this in the
future?

Best Regards,
Cetin Sert
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From marlowsd at gmail.com  Thu Jun  5 04:05:05 2008
From: marlowsd at gmail.com (Simon Marlow)
Date: Thu Jun  5 03:57:42 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <20080604143650.72978202@solaris>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>	<1211448821.5824.504.camel@localhost>	<008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com> <20080604143650.72978202@solaris>
Message-ID: <48479E31.9050909@gmail.com>

Achim Schneider wrote:
> Simon Marlow <marlowsd@gmail.com> wrote:
> 
>> Claus Reinke wrote:
>>
>>> - i don't want to have to remove anything explicitly, because
>>> that would mean bypassing the haskell installation managers
>>> - i would want to see a single haskell installation manager
>>>    for each system,
>> I think that's fundamentally the wrong approach.  We shouldn't have
>> to build a "Haskell installation manager".  Would you also want
>> installation managers for Perl, Python, Ruby, C, C++, etc. each with
>> their own different user interfaces and feature sets?  I think not -
>> you want a single package manager for the whole system from which you
>> can install/uninstall libraries for any language.
>>
>> This is something that Windows gets completely wrong.  Why do I have
>> twelve icons in my status bar all representing little programs that
>> are running in the background checking for updates to their own bits
>> of software?  Why on earth do I have a Printer Driver Update
>> Manager?  And I'd be wondering the same thing about a "Haskell
>> installation manager": installation and dependencies are not
>> something specific to Haskell.
>>
> Well, then there are developers who don't want to do .ebuilds, .rpms
> for 20 distributions, .debs for 20 distributions, .cabs... Meaning that
> if you have a project with 5 developers using 3 1/2 distributions, you
> will have a hard time installing.

But the whole point is that the Haskell library developer doesn't have to 
make all these packages: they just make a Cabal package, and the distro 
maintainers have tools that turn a Cabal package into a .ebuild, .deb, .rpm 
etc.  There was also a tool to make Windows installers from Cabal packages 
in the works, but I haven't heard anything on that front for a while.

Cheers,
	Simon
From marlowsd at gmail.com  Thu Jun  5 04:16:17 2008
From: marlowsd at gmail.com (Simon Marlow)
Date: Thu Jun  5 04:08:55 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <1212585727.15010.281.camel@localhost>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>	<1211448821.5824.504.camel@localhost>	<008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com> <1212585727.15010.281.camel@localhost>
Message-ID: <4847A0D1.3040306@gmail.com>

Duncan Coutts wrote:
> On Wed, 2008-06-04 at 11:33 +0100, Simon Marlow wrote:
>> Claus Reinke wrote:
>>
>>> - i don't want to have to remove anything explicitly, because    that 
>>> would mean bypassing the haskell installation managers
>>> - i would want to see a single haskell installation manager
>>>    for each system,
>> I think that's fundamentally the wrong approach.  We shouldn't have to 
>> build a "Haskell installation manager".  Would you also want installation 
>> managers for Perl, Python, Ruby, C, C++, etc. each with their own different 
>> user interfaces and feature sets?  I think not - you want a single package 
>> manager for the whole system from which you can install/uninstall libraries 
>> for any language.
> 
> As I see it we need both. We need to make it easy to translate cabal
> packages into distro packages. We do have tools to do that at the moment
> for Gentoo, Debian and Fedora. I'm sure they could be improved.
> 
> However we cannot expect all distros (esp Windows) to have all packages
> that are on hackage at all times. That's where it makes sense to have a
> tool like cabal-install as a secondary package manager. There's also the
> fact that most distro package managers do not handle unprivileged
> per-user installations very well.

Well, that's true.  I guess what I'm really objecting to in Claus's message 
is the implication that we should always use a Haskell Installation 
Manager, even on systems with good built-in package management.

Yes, I agree we need good support for managing packages for the other 
scenarios: no system package manager, home-directory installs, no 
pre-prepared system package.  I just don't want whatever provision we make 
for these cases to replace the system package manager for global package 
installs on systems where that is well supported.

Cheers,
	Simon
From miguelimo38 at yandex.ru  Thu Jun  5 04:28:02 2008
From: miguelimo38 at yandex.ru (Miguel Mitrofanov)
Date: Thu Jun  5 04:20:51 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
Message-ID: <0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>

Well, it's certainly not possible for "filter", at least, not without  
additional hints to the compiler. For example, consider this type:

data Weird a = A | B a (Weird a) (Weird a)

filter p A = A
filter p (B x w1 w2) | p x = B x (filter p w1) (filter p w2)
                      | otherwise = ?????

On 5 Jun 2008, at 12:03, Cetin Sert wrote:

> Hi ^_^,
>
> Let's say we have the following data type and functions:
> data Tab a =      (:?:)
>
>            |     a :?:   Tab a
>            | Tab a :??: (Tab a,Tab a)
>            deriving (Eq, Show, Read)
>
> map f (:?:)          = (:?:)
> map f (a :?: t)      = f a :?: map f t
> map f (h :??: (l,r)) = map f h :??: (map f l, map f r)
>
>
> filter p (:?:)          = (:?:)
> filter p (a :?: t)      | p a       = filter p t
>                         | otherwise = a :?: filter p t
> filter p (h :??: (l,r)) = filter p h :??: (filter p l, filter  
> p r)
>
> is it possible to automatically derive map and filter?
> data Tab a =      (:?:)
>            |     a :?:   Tab a
>            | Tab a :??: (Tab a,Tab a)
>            deriving (Eq, Show, Read, Map, Filter)
>
> If not, do you think it might be nice to have something like this in  
> the future?
>
> Best Regards,
> Cetin Sert
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From tom.davie at gmail.com  Thu Jun  5 04:39:16 2008
From: tom.davie at gmail.com (Thomas Davie)
Date: Thu Jun  5 04:31:51 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
Message-ID: <2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>

Even deriving an instance of Functor seems rather implausable, what  
should it do for

data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)

Should fmap's function argument operate on 'a's, 'b's, or both?

Bob

On 5 Jun 2008, at 10:28, Miguel Mitrofanov wrote:

> Well, it's certainly not possible for "filter", at least, not  
> without additional hints to the compiler. For example, consider this  
> type:
>
> data Weird a = A | B a (Weird a) (Weird a)
>
> filter p A = A
> filter p (B x w1 w2) | p x = B x (filter p w1) (filter p w2)
>                     | otherwise = ?????
>
> On 5 Jun 2008, at 12:03, Cetin Sert wrote:
>
>> Hi ^_^,
>>
>> Let's say we have the following data type and functions:
>> data Tab a =      (:?:)
>>
>>           |     a :?:   Tab a
>>           | Tab a :??: (Tab a,Tab a)
>>           deriving (Eq, Show, Read)
>>
>> map f (:?:)          = (:?:)
>> map f (a :?: t)      = f a :?: map f t
>> map f (h :??: (l,r)) = map f h :??: (map f l, map f r)
>>
>>
>> filter p (:?:)          = (:?:)
>> filter p (a :?: t)      | p a       = filter p t
>>                        | otherwise = a :?: filter p t
>> filter p (h :??: (l,r)) = filter p h :??: (filter p l,  
>> filter p r)
>>
>> is it possible to automatically derive map and filter?
>> data Tab a =      (:?:)
>>           |     a :?:   Tab a
>>           | Tab a :??: (Tab a,Tab a)
>>           deriving (Eq, Show, Read, Map, Filter)
>>
>> If not, do you think it might be nice to have something like this  
>> in the future?
>>
>> Best Regards,
>> Cetin Sert
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From voigt at tcs.inf.tu-dresden.de  Thu Jun  5 04:49:33 2008
From: voigt at tcs.inf.tu-dresden.de (Janis Voigtlaender)
Date: Thu Jun  5 04:38:04 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
	<2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
Message-ID: <4847A89D.8010004@tcs.inf.tu-dresden.de>

Thomas Davie wrote:
> Even deriving an instance of Functor seems rather implausable, what  
> should it do for
> 
> data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)
> 
> Should fmap's function argument operate on 'a's, 'b's, or both?

But for many datatypes it is quite natural. Just google for "theory of
containers".

Ciao, Janis.

-- 
Dr. Janis Voigtlaender
http://wwwtcs.inf.tu-dresden.de/~voigt/
mailto:voigt@tcs.inf.tu-dresden.de


From loup.vaillant at gmail.com  Thu Jun  5 04:49:09 2008
From: loup.vaillant at gmail.com (Loup Vaillant)
Date: Thu Jun  5 04:41:42 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <g25o2h$p3p$1@ger.gmane.org>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org>
Message-ID: <6f9f8f4a0806050149j3d320413n9b376cae010dc377@mail.gmail.com>

2008/6/4 apfelmus <apfelmus@quantentunnel.de>:
> [...]
> But it can waste space (-> "space leak"), for instance by
> accumulating a big expression like
>
>  (..) -> ((..)+1) -> (((..) + 1) + 1) -> etc.
>
> instead of evaluating  x+1  immediately
>
>   5   -> 6        -> 7                -> etc.

So, it is called a "space leak" because the asymptotic space required
is greater in a lazy setting compared to a strict setting. Then, what
about:

sum . map (\x -> 2 * x + 42) $ [1..9999999]

Provided sum works in constant space (needs proper tail calls and the
right level of stricness), this runs in constant space in Haskell,
deforestation or not. However, the equivalent code in, say, Ocaml,
will work in linear space in the absence of deforestation. So, in this
case, I find legitimate to talk about a "strictness space leak". Well,
is it? Of course it uses linear space, there is no "leak"! hummm.

It feels like only lazy evaluation can be accused of space leak, while
strict evaluation cannot. Are we biased in favour of strict
evaluation? I mean, if we take strict evaluation as the default
(because it's mainstream), it is easy to think that lazy evaluation is
cool when better, but unacceptable when worse. Hence the word "leak".

Just my two cents,
Loup
From miguelimo38 at yandex.ru  Thu Jun  5 04:49:06 2008
From: miguelimo38 at yandex.ru (Miguel Mitrofanov)
Date: Thu Jun  5 04:41:57 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
	<2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
Message-ID: <45A93A68-A76A-4C35-B748-FD0CF1022E98@yandex.ru>

It can be even worse:

data X a b = X (X b a -> b)

Here (X a) is certainly a functor, but the implementation must also  
act on "a" contravariantly:

mapX :: (a -> a') -> X a' b -> X a b
mapX f (X h) = X $ h . fmap f
instance Functor (X a) where fmap f (X h) = X $ f . h . mapX f

On 5 Jun 2008, at 12:39, Thomas Davie wrote:

> Even deriving an instance of Functor seems rather implausable, what  
> should it do for
>
> data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)
>
> Should fmap's function argument operate on 'a's, 'b's, or both?
>
> Bob
>
> On 5 Jun 2008, at 10:28, Miguel Mitrofanov wrote:
>
>> Well, it's certainly not possible for "filter", at least, not  
>> without additional hints to the compiler. For example, consider  
>> this type:
>>
>> data Weird a = A | B a (Weird a) (Weird a)
>>
>> filter p A = A
>> filter p (B x w1 w2) | p x = B x (filter p w1) (filter p w2)
>>                    | otherwise = ?????
>>
>> On 5 Jun 2008, at 12:03, Cetin Sert wrote:
>>
>>> Hi ^_^,
>>>
>>> Let's say we have the following data type and functions:
>>> data Tab a =      (:?:)
>>>
>>>          |     a :?:   Tab a
>>>          | Tab a :??: (Tab a,Tab a)
>>>          deriving (Eq, Show, Read)
>>>
>>> map f (:?:)          = (:?:)
>>> map f (a :?: t)      = f a :?: map f t
>>> map f (h :??: (l,r)) = map f h :??: (map f l, map f r)
>>>
>>>
>>> filter p (:?:)          = (:?:)
>>> filter p (a :?: t)      | p a       = filter p t
>>>                       | otherwise = a :?: filter p t
>>> filter p (h :??: (l,r)) = filter p h :??: (filter p l,  
>>> filter p r)
>>>
>>> is it possible to automatically derive map and filter?
>>> data Tab a =      (:?:)
>>>          |     a :?:   Tab a
>>>          | Tab a :??: (Tab a,Tab a)
>>>          deriving (Eq, Show, Read, Map, Filter)
>>>
>>> If not, do you think it might be nice to have something like this  
>>> in the future?
>>>
>>> Best Regards,
>>> Cetin Sert
>>> _______________________________________________
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe@haskell.org
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From duncan.coutts at worc.ox.ac.uk  Thu Jun  5 05:11:57 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Thu Jun  5 05:00:59 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
In-Reply-To: <4847A0D1.3040306@gmail.com>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt>  <48466F7F.8090600@gmail.com>
	<1212585727.15010.281.camel@localhost>  <4847A0D1.3040306@gmail.com>
Message-ID: <1212657117.15010.327.camel@localhost>


On Thu, 2008-06-05 at 09:16 +0100, Simon Marlow wrote:

> > As I see it we need both. We need to make it easy to translate cabal
> > packages into distro packages. We do have tools to do that at the moment
> > for Gentoo, Debian and Fedora. I'm sure they could be improved.
> > 
> > However we cannot expect all distros (esp Windows) to have all packages
> > that are on hackage at all times. That's where it makes sense to have a
> > tool like cabal-install as a secondary package manager. There's also the
> > fact that most distro package managers do not handle unprivileged
> > per-user installations very well.
> 
> Well, that's true.  I guess what I'm really objecting to in Claus's message 
> is the implication that we should always use a Haskell Installation 
> Manager, even on systems with good built-in package management.
> 
> Yes, I agree we need good support for managing packages for the other 
> scenarios: no system package manager, home-directory installs, no 
> pre-prepared system package.  I just don't want whatever provision we make 
> for these cases to replace the system package manager for global package 
> installs on systems where that is well supported.

Indeed. I wholly agree.

Duncan

From greg at momotaro.chinmin.edu.tw  Thu Jun  5 05:03:27 2008
From: greg at momotaro.chinmin.edu.tw (Greg Matheson)
Date: Thu Jun  5 05:07:56 2008
Subject: [Haskell-cafe] HDBC-odbc 1.1.4.4 fixes Windows linking problems
In-Reply-To: <4846C62B.2050503@complete.org>
References: <20080603200020.GA13041@complete.org>
	<20080604030541.GA26462@momotaro.chinmin.edu.tw>
	<4846C62B.2050503@complete.org>
Message-ID: <20080605090327.GA28588@momotaro.chinmin.edu.tw>

On Wed, 04 Jun 2008, John Goerzen wrote:

> > Prelude Database.HDBC Database.HDBC.ODBC> conn <- connectODBC "dictation"

> Please note that this is not a valid connection string.

I need to remember the connection functions are specific to the 
drivers and there are differences between connectODBC and 
connectSqlite3.

> The HDBC-odbc API docs ...  give the example string of: "DSN=hdbctest1"
> as well as a link to the Microsoft document that describes the string:
> http://msdn.microsoft.com/en-us/library/ms715433(VS.85).aspx
> That URL also contains error message descriptions.  For your state
> 01S00, it lists:

>   Invalid connection string attribute

> Your fix may be as simple as prepending the string with "DSN=".

That did the trick. And I can insert and query the database. So 
HDBC-odbc-1.1.4.4 is good here.

-- 
Dr Bean                          Make a mistake.
                                 Try it, you'll like it.
                                 --Dr Bean
From devriese at cs.tcd.ie  Thu Jun  5 05:16:09 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Thu Jun  5 05:08:45 2008
Subject: [Haskell-cafe] What is the maturity of Haskell Web Frameworks
In-Reply-To: <856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
Message-ID: <20080605091609.GA8533@netsoc.tcd.ie>

On Wed, Jun 04, 2008 at 10:30:49PM -0400, Paul L wrote:
> Pardon me to hijack this thread, but I have an idea to build a
> different kind of Web Framework and am not sure if somebody has
> already done it.

Have a look at iTasks, written in Clean. Not *quite* Haskell, I know,
but close enough. I does what you suggest, it does what the OP suggested
(assigning tasks to people etc) and much more. For example, read the
following ICFP paper:

http://www.st.cs.ru.nl/papers/2007/plar2007-ICFP07-iTasks.pdf

Edsko
From devriese at cs.tcd.ie  Thu Jun  5 05:20:21 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Thu Jun  5 05:12:55 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
	<2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
Message-ID: <20080605092021.GA6483@netsoc.tcd.ie>

On Thu, Jun 05, 2008 at 10:39:16AM +0200, Thomas Davie wrote:
> Even deriving an instance of Functor seems rather implausable, what  
> should it do for
> 
> data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)
> 
> Should fmap's function argument operate on 'a's, 'b's, or both?

Generic Haskell can do all that. Read Ralf Hinze's "Generic Programs and
Proofs" for the theory:

http://www.informatik.uni-bonn.de/~ralf/publications/habilitation.pdf

Edsko
From claudiusmaximus at goto10.org  Thu Jun  5 05:21:41 2008
From: claudiusmaximus at goto10.org (Claude Heiland-Allen)
Date: Thu Jun  5 05:14:14 2008
Subject: [Haskell-cafe] example of FFI FunPtr
In-Reply-To: <5ae4f2ba0806050038k1e0aea1exe6d81b22b1151eeb@mail.gmail.com>
References: <5ae4f2ba0806050038k1e0aea1exe6d81b22b1151eeb@mail.gmail.com>
Message-ID: <4847B025.8030800@goto10.org>

Galchin, Vasili wrote:
> Hello,
> 
>        I want to model a Haskell function that is a callback from C. I have
> only found one example in the unix package's Semaphore.hsc, which apparently
> is not used. I want to be able to marshall a Haskell function that is a
> first class citizen residing in a Haskell data type and pass to a C function
> via FFI. Are there examples of this?

Attached is a simple example.

The main thing to note is 'foreign import ccall "wrapper"' which gives 
you a factory for turning Haskell functions into foreign function pointers.

More information:

http://www.cse.unsw.edu.au/~chak/haskell/ffi/


Claude
-- 
http://claudiusmaximus.goto10.org

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From vigalchin at gmail.com  Thu Jun  5 06:02:15 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Thu Jun  5 05:54:49 2008
Subject: [Haskell-cafe] example of FFI FunPtr
In-Reply-To: <4847B025.8030800@goto10.org>
References: <5ae4f2ba0806050038k1e0aea1exe6d81b22b1151eeb@mail.gmail.com>
	<4847B025.8030800@goto10.org>
Message-ID: <5ae4f2ba0806050302i61d5efadvfc18a6612dbdc5d8@mail.gmail.com>

thank you, Claude!

Vasili

On Th, Jun 5, 2008 at 4:21 AM, Claude Heiland-Allen <
claudiusmaximus@goto10.org> wrote:

> Galchin, Vasili wrote:
>
>> Hello,
>>
>>       I want to model a Haskell function that is a callback from C. I have
>> only found one example in the unix package's Semaphore.hsc, which
>> apparently
>> is not used. I want to be able to marshall a Haskell function that is a
>> first class citizen residing in a Haskell data type and pass to a C
>> function
>> via FFI. Are there examples of this?
>>
>
> Attached is a simple example.
>
> The main thing to note is 'foreign import ccall "wrapper"' which gives you
> a factory for turning Haskell functions into foreign function pointers.
>
> More information:
>
> http://www.cse.unsw.edu.au/~chak/haskell/ffi/<http://www.cse.unsw.edu.au/%7Echak/haskell/ffi/>
>
>
> Claude
> --
> http://claudiusmaximus.goto10.org
>
>
> CallBacker: CallBacker.hs callerback.c callerback.h
>        ghc -O2 -Wall -fffi -o CallBacker CallBacker.hs callerback.c
>
>
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From claus.reinke at talk21.com  Thu Jun  5 06:21:07 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Thu Jun  5 06:13:45 2008
Subject: [Haskell-cafe] Re: Ubuntu and ghc
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com><1211448821.5824.504.camel@localhost><008001c8bbf7$63753100$d0357ad5@cr3lt>
	<48466F7F.8090600@gmail.com><1212585727.15010.281.camel@localhost>
	<4847A0D1.3040306@gmail.com> <1212657117.15010.327.camel@localhost>
Message-ID: <013901c8c6f5$df826110$961a8351@cr3lt>

>> Well, that's true.  I guess what I'm really objecting to in Claus's message 
>> is the implication that we should always use a Haskell Installation 
>> Manager, even on systems with good built-in package management.

what was implied was that haskell installation manager (HIM) 
and native package managers (NPM) (where they exist) should 
collaborate, so that NPMs know how to extract dependencies 
from haskell packages, and HIM knows how to extract 
dependencies (haskell or otherwise) from NPMs.

for the NPM-calls-HIM direction, that could be dynamically
or, as in current practice, in a separate phase converting HIM
to NPM packages.

for the HIM-calls-NPM direction, that would simply present
a haskell view on the native software (ie, cabal install/list/..
negotiating with NPM). whereas, currently, if i understand
correctly, systems with NPM will have many haskell packages
under NPM control and some haskell packages under HIM
control and some haskell packages under no control whatsoever
(eg, installing tools or compilers leaves no record, necessitating
use of autoconf & co).

i'm not saying "reimplement and ignore NPMs", i'm saying
"NPMs and HIM should collaborate". if anything, that would
reduce the number of exceptions where haskell packages are 
installed without the NPM knowing about them. and i'd like
to see fewer cases where HIM forgets about what it or NPM have installed.

so, on systems with NPM, users have a choice of interface, 
but nothing bad will happen no matter whether they choose 
NPM directly or HIM as an interface to it. and haskell
book and tutorial authors only need to explain HIM, and
its commands will just work - independent of the variant 
or lack of NPM on the reader's system.
 
is that still objectionable?-)
claus

ps. it is a lot like using fmap, no matter what the Functor
    is, or using something like System.Process, no matter
    whether or not the OS supports that easily.

>> Yes, I agree we need good support for managing packages for the other 
>> scenarios: no system package manager, home-directory installs, no 
>> pre-prepared system package.  I just don't want whatever provision we make 
>> for these cases to replace the system package manager for global package 
>> installs on systems where that is well supported.
> 
> Indeed. I wholly agree.
> 
> Duncan
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From jules at jellybean.co.uk  Thu Jun  5 06:26:56 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Thu Jun  5 06:19:30 2008
Subject: [Haskell-cafe] Re: How would you hack it?
In-Reply-To: <20080604225220.40e0fa76@solaris>
References: <4846DFDC.5020905@btinternet.com>	<m1r6bdc5tn.fsf@subrosa.ca>
	<20080604225220.40e0fa76@solaris>
Message-ID: <4847BF70.9030205@jellybean.co.uk>

Achim Schneider wrote:
> If you run one over obscure academic papers, you can even generate
> publishable results. I don't have a link ready, but there was a fun
> incident involving this.

http://www.physics.nyu.edu/faculty/sokal/dawkins.html
From apfelmus at quantentunnel.de  Thu Jun  5 06:31:27 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Thu Jun  5 06:24:13 2008
Subject: [Haskell-cafe] Re: What is the maturity of Haskell Web Frameworks
In-Reply-To: <856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
Message-ID: <g28fa2$m16$1@ger.gmane.org>

Paul L wrote:
> Pardon me to hijack this thread, but I have an idea to build a
> different kind of Web Framework and am not sure if somebody has
> already done it.
> 
> The idea is to take REST further: every HTML page you see is a program
> in its running state (as a continuation monad). Each click on its link
> or form submission is seen as feeding data to resume its continuation.
> 
> So instead of writing a server-side program that responds to many CGI
> calls, you write a single ordinary program that describe the
> application logic, which during its execution gets represented as a
> HTML page and interpreted by the server.

WASH/CGI has something in that direction. I don't know a short 
introduction, but have a look at sections 4 and 8 of the implementation 
notes

   http://www.informatik.uni-freiburg.de/~thiemann/WASH/draft.pdf


The basic idea is that  displayForm  in a CGI-script like

   main = do
    password <- displayForm $ (label "Enter password" <-> editbox)
    ...

displays a HTML-page to the client, "waits" for a response and then 
resumes execution. It does not actually wait, but captures the 
continuation in the transmitted HTML page, for instance by saving a log 
of the previous events.

This is related to [MonadPrompt], which has a similar purpose, and to 
[Unimo], which is pretty much the same but from the slightly different 
viewpoint of implementing any monad directly from its operational semantics.

   [Unimo]: Chuan-Kai Lin. Programming Monads Operationally with Unimo.
            http://web.cecs.pdx.edu/~cklin/papers/unimo-143.pdf
   [MonadPrompt]: Ryan Ingram.
   http://hackage.haskell.org/cgi-bin/hackage-scripts/package/MonadPrompt


Regards,
apfelmus

From barsoap at web.de  Thu Jun  5 06:32:39 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 06:25:18 2008
Subject: [Haskell-cafe] Re: Laziness leaks
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org>
	<2f9b2d30806041916x3e0088acw26e45033ee586b9a@mail.gmail.com>
	<20080605052825.7002ce4e@solaris>
	<48478718.7090102@jellybean.co.uk>
Message-ID: <20080605123239.01b379b4@solaris>

Jules Bean <jules@jellybean.co.uk> wrote:

> Achim Schneider wrote:
> >  You don't come across space-leaks in strict programs often because
> > data is usually allocated statically even if execution is
> > non-strict.
> > 
> > Piping /dev/zero into a program that just sleeps does leak space,
> > though.
> > 
> 
> It only leaks 8K or whatever size your system buffers pipes until it 
> suspends the writer though... or do I misunderstand your analogy?
>
I don't think so. I would say that it leaks 8k memory and infinite
time. I did not intend the example to be implementation-dependent, but
then that kind of proves my point.

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From peteg42 at gmail.com  Thu Jun  5 06:50:18 2008
From: peteg42 at gmail.com (Peter Gammie)
Date: Thu Jun  5 06:43:35 2008
Subject: [Haskell-cafe] Re: What is the maturity of Haskell Web Frameworks
In-Reply-To: <g28fa2$m16$1@ger.gmane.org>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
	<g28fa2$m16$1@ger.gmane.org>
Message-ID: <F6BC7E00-122D-456A-AB09-3B10D2CCC628@gmail.com>

On 05/06/2008, at 5:31 PM, apfelmus wrote:

> WASH/CGI has something in that direction. I don't know a short  
> introduction, but have a look at sections 4 and 8 of the  
> implementation notes
>
>  http://www.informatik.uni-freiburg.de/~thiemann/WASH/draft.pdf

I think there is also some work done about using Arrows for this  
problem, cf John Hughes' original paper. (I hear the use of Arrows was  
inessential, see the followup by Thiemann.)

IMH-and-probably-offtopic-O, the continuation-based approach is  
semantically nice but I don't think anyone has reconciled it with the  
general desire for clean and tidy URIs. Going to:

http://example.com/continuations/45345345

is not anywhere near as aesthetic / phishing proof / ... as going to  
e.g.

http://example.com/comments/edit/16

(Though I grant that hpaste URIs are tantalisingly mysterious.)

The general problem is providing a way for the programmer to  
(schematically) specify the URIs and handlers without getting bogged  
down in state machine encodings.

If someone's got some good ideas here, I'd love to hear about it (on  
the web-devel mailing list, perhaps).

cheers
peter

-- 
http://peteg.org/

From barsoap at web.de  Thu Jun  5 06:51:42 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 06:44:31 2008
Subject: [Haskell-cafe] Re: How would you hack it?
References: <4846DFDC.5020905@btinternet.com>
	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>
Message-ID: <20080605125142.50de0fc6@solaris>

Henning Thielemann <lemming@henning-thielemann.de> wrote:

> Sounds like a generator for scientific articles. :-)
> Maybe
>    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain
>  can be of help for you. It's also free of randomIO.
> 
I once invented this, though ungeneralised, for a map generator of a
RTS... the river always went from the left to the right, at approximate
the middle of the map, its direction being dependant on its current
offset from that middle, its width (that is, a wide river can bend
upwards and downwards more than one tile) and a random factor. You can
also express this using a markoff chain.

-- 
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past copyright information. All rights reserved. Unauthorised copying,
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signature prohibited. 

From apfelmus at quantentunnel.de  Thu Jun  5 08:06:26 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Thu Jun  5 07:59:08 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <87abi0l4w8.fsf@malde.org>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>	<4845D0B8.6040802@vex.net>	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>	<g25o2h$p3p$1@ger.gmane.org>
	<4846E45C.3040402@vex.net> <87abi0l4w8.fsf@malde.org>
Message-ID: <g28ks3$9se$1@ger.gmane.org>

Ketil Malde wrote:
> I the meaning of "leak" is in a bit of flux.  Originally, I believe 
> it refers to a memory leak, where the programmer forgot to call 
> free() before losing the pointer, thus making the program consume 
> memory it can't recover, and can't use.
> 
> With automatic memory management, this doesn't happen, so "memory 
> leak" then started to mean retaining objects longer than necessary.

I agree. This definition fits the "space leak"

   foldl (+1) 0 [1..10000]   ->  (((...)+1)+1)

in the sense that the unevaluated expressions are retained in memory
longer than necessary; the difference being of course that it's not
garbage collection but beta-reduction that frees the memory in question.

On the other hand, I think that the situation of

   foldl (+1) 0 [1..10000]

in a strict language does not fit this definition of leak because
evaluating the list [1..10000] eagerly does not retain memory longer
than necessary, it consumes memory earlier than necessary.

So, this notion of leak is spot-on.

> I'm not sure I'll use terms like strictness and laziness leak, I 
> think it's hard to see what's being lost here, and if you have a 
> laziness leak, it is unclear if it's too much laziness or too little?

Me too, I don't see a reason to muddy the word with other meanings.
"Space leak" is a good word in the sense that "space" describes the
"leak"; it's the space that leaks and goes down the drain. Neither
laziness nor strictness can leak and be washed away with the rain.


> (Aside: am I the only one who is shocked by the memory consumption of
>  modern programs?  I use a simple time tracker (gnotime), a calendar
>  with a handful of entries (evolution), and they both typically 
> consume half to one gigabyte of memory.  In all fairness, it seems to
>  be much better under Ubuntu 8.04 than 7.10, but again, they haven't 
> been running for very long yet.)

Yeah :( When a piece of softwares wastes time and memory, they should
have written it in Haskell, so that at least the other bugs wouldn't
plague me as well.


Regards,
apfelmus

From jonathanccast at fastmail.fm  Thu Jun  5 10:40:53 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Thu Jun  5 10:33:28 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
	<2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
Message-ID: <28B5EEBB-7843-436D-9CFC-A01EEFDF1E9A@fastmail.fm>

On 5 Jun 2008, at 1:39 AM, Thomas Davie wrote:

> Even deriving an instance of Functor seems rather implausable, what  
> should it do for
>
> data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)
>
> Should fmap's function argument operate on 'a's, 'b's, or both?

class Functor (f :: * -> *) where ...

so, 'b's.

jcc

PS Why isn't Functor derivable?

From aruiz at um.es  Thu Jun  5 11:16:09 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Thu Jun  5 11:08:43 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <483842413.20080603134211@gmail.com>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
	<4844F27A.2080208@um.es> <731290342.20080603113721@gmail.com>
	<48450752.4080307@um.es> <483842413.20080603134211@gmail.com>
Message-ID: <48480339.6050900@um.es>

Hello Bulat and Anatoly,

I have written a first version of an interface to inplace updates in the 
ST monad for the hmatrix vectors and matrices. Many things must be
improved (range checking, documentation, etc.) but I hope that the 
general idea makes sense.

A few usage examples:

http://perception.inf.um.es/~aruiz/darcs/hmatrix/examples/inplace.hs

Code:

http://perception.inf.um.es/~aruiz/darcs/hmatrix/lib/Data/Packed/ST.hs

http://perception.inf.um.es/~aruiz/darcs/hmatrix/doc/html/Data-Packed-ST.html

Any suggestion will be welcome. I'm impressed by the power of the ST 
monad, it is extremely useful and elegant. Thank you again for your help!

In the future I will also try to include efficient conversions to/from 
standard Haskell arrays and those of other related libraries like Jed 
Brown's CArray.

Thanks,

Alberto


Bulat Ziganshin wrote:
> Hello Alberto,
> 
> Tuesday, June 3, 2008, 12:56:50 PM, you wrote:
> 
>> Good! So you can easily "hide" the IO operations in the ST monad. I will
>> definitely look into it.
> 
> from implementation POV ST monad is nothing but renamed IO monad which
> exports only subset of its operations which are guaranteed to safe.
> or, saying in other words, it's just type hackery around IO monad that
> provides safe operations
> 
> it's possible to define ST monad and its operations as following:
> 
> newtype ST s a = forall s. ST_Constructor (IO a)
> 
> unsafeIOtoSt action = ST_Constructor action
> 
> runST (ST_Constructor action) = unsafePerformIO action
> 
> newtype STRef s a = forall s. STRef (IORef a)
> 
> readSTRef (STRef ref)  =  unsafeIOtoSt (readIORef ref)
> 
> and so on. GHC uses technically (but not ideologically!) different
> implementation where both monads are specializations of one generic
> type. while Hugs afair uses exactly this approach. you may also look
> at ArrayRef lib which reimplements arrays/refs for both compilers in
> more unified way
> 
> anyway, because ST is just IO monad modulo type tricks, you can
> execute any IO action inside ST by lifting it with unsafeIOtoSt
> 
From johan.tibell at gmail.com  Thu Jun  5 11:19:28 2008
From: johan.tibell at gmail.com (Johan Tibell)
Date: Thu Jun  5 11:12:01 2008
Subject: [Haskell-cafe] Design your modules for qualified import
Message-ID: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>

Hi!

The last two weeks I've seen two new packages that add suffixes to
identifiers instead of relying on them being imported qualified to
distinguish them from identifiers in other modules. This is not a new
thing in Haskell community and there are examples of this practice in
libraries shipped with GHC. It is also common in papers (for good
reasons as we will see later). Atomic channels and variables under
Control.Concurrent.* are examples of using a prefix as a namespacing
tool. Let me reiterate the arguments [1,2] against this practice and
also speculate why this practice is more common in Haskell than in
e.g. Python, Java or Ruby.

* Cons of including a namespace prefix/suffix in identifiers

1. From experience these prefixes/suffixes tend to be short and
non-descriptive, typically just one letter e.g. foldU or elemB. Very
frequently used functions that every Haskell programmer is likely to
use often can have shorter name as the cost of memorizing them is
amortized over all their uses. Examples of short names that most
Haskell programmers know by heart is map, fold*, etc. Given that your
library won't see the same use as these functions your functions need
more descriptive names (or in this case use a qualified import that
makes them more descriptive e.g. Array.fold).

2. If your modules are imported qualified the suffix is redundant and
thus wastes space. Consider for example foldU imported qualified from
the module Data.Array as Array.foldU. Array.fold would have been
better in this case.

* Pros of using qualified imports

1. Your code will be more robust against additions to modules you
depend on. Consider this snippet:

import Some.Module

-- An utility function that the author of the above module forgot to include.
foo = ...

Now the author of Some.Module releases a new version of his or her
package which include `foo' and your code no longer compiles. If you
have no imports on the form

import Some.Module

your package can specify more relaxed version dependencies on other
packages [3].

2. It's easier to see from where an identifier is imported. Just check
the functions module prefix (e.g. Array in Array.foo). If you renamed
the import using import Foo as F you might have to check the import
list.

* Explicit, unqualified imports

An alternative to qualified imports that shares some of benefits is to
import names unqualified but explicitly enumerate the function names
e.g.

import Some.Module (foo, bar)

It is still not immediately obvious what module a name refers too when
using this style (point 2 under pros above) but it is at least easier
to find than when implicitly importing all names from a module. This
is my current preference for infix operators as they look quite ugly
qualified with a module name. It might also make sense if a few
functions (e.g. parser combinators) are used a lot in the same module
(e.g. an HTTP parser).

* Why is this practice common in Haskell

Here are some guesses:

1. It's common in papers. However, papers and libraries are quite
different. The former usually build up a small vocabulary and having
short names is a big win. Papers rarely make use of the module system
at all. The latter are included as pieces of large programs and their
names need to be adjusted accordingly.

2. It's the default. You have to add "qualified" to all your imports
to make them qualified. In most language imports are qualified by
default. I think the latter would have been a better choice but we
have to live with the current design so bite the bullet and add those
qualified keywords to your imports.

3. Lack of common interfaces. An example would be two different set
implementations that essentially have the same interface but since
there is no explicitly shared interface, defined using a type class,
you sometimes end up with different names. The lack of type families
might explain why e.g. collection classes don't share interfaces.

4. Haskell is a very expressive language. You can often write a whole
function definition on one line! Adding those module qualifications
makes your code slightly longer and it might just break your beautiful
one liner into two lines.

* Summary

Whenever you write a library design it so it works well with qualified
imports. That means leaving namespacing issues to the module system.
Try to think of how code using your functions will look like if it
uses them qualified.

* References

1. http://www.haskell.org/haskellwiki/Import_modules_properly
2. http://www.haskell.org/haskellwiki/Qualified_names
3. See section 2 Version numbers  -
http://www.haskell.org/haskellwiki/Library_versioning_policy

Cheers,

Johan
From mail at joachim-breitner.de  Thu Jun  5 11:22:44 2008
From: mail at joachim-breitner.de (Joachim Breitner)
Date: Thu Jun  5 11:15:29 2008
Subject: [Haskell-cafe] File locking wishlist
Message-ID: <1212679364.3483.14.camel@otto.ehbuehl.net>

Hi,

for a program of mine (darcswatch[1]), a rather long running process is
run at certain events (by cron, and by new emails). I want to achieve
that:
 * Only one instance of the program runs at a time.
 * If new events come in while the program runs, it should re-run itself
 * There is information attached to the events (only one Bool ATM)

So I?d like to implement something with this, or a similar, interface:

=======================================================================
module MyLocking where

-- | tries to get the lock. If it fails, notifies the running process
--   to re-start itself afterwards, with the given information
--   returns True if the lock was aquired
lockOrMark :: Show a => FilePath -> a -> IO Bool

-- | release the lock. If new events have come in, they are returned
--   in the list, and the lock is still kept. If the list is empty,
--   the lock was successfully released.
releaseLock :: Read a => FilePath -> IO [a]
?=======================================================================

I would use this module in this way:

realWork args = do
  someStuff args
  newArgs <- releaseLock "someDir/"
  unless (null newArgs) $ do
    -- we missed some events, so re-run and then try again.
    let newArg = combineInSomeWay newArgs
    realWork newArg 

main = do
  args <- getArgs
  l <- lockOrMark "someDir/" args
  when l $ do
    -- we got the lock, so lets work
    realWork args
    
I hope this makes the idea clear.


How could a possible implementation look like, when all operations
should be atomic? I was considering this, would it work fine?

lockOrMark would try to create a directory in the path. Whoever creates
the directory has the lock. If it works, create. If it fails, because
the directory already exists, then write the given args to a temporary
file with a unique name, and move it into that directory. If that fails
(because the directory has disappeared, i.e. the lock released), start
over with trying to create the directory. If it works, then you are
done.

releaseLock would try to rmdir the directory. If that succeeds, no files
have been in there, so no events were missed. If it does not succeed,
then there were files. Read and delete them and return the list of
arguments contained in them.


Greetings,
Joachim


[1] http://darcswatch.nomeata.de/

-- 
Joachim Breitner
  e-Mail: mail@joachim-breitner.de
  Homepage: http://www.joachim-breitner.de
  ICQ#: 74513189
  Jabber-ID: nomeata@joachim-breitner.de
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From darrinth at gmail.com  Thu Jun  5 12:30:45 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Thu Jun  5 12:23:18 2008
Subject: [Haskell-cafe] Re: cabal and platform-independent haskell
	installation management (again) (Re: Re: Ubuntu and ghc)
In-Reply-To: <1212623330.15010.318.camel@localhost>
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
	<1212590628.15010.312.camel@localhost>
	<20080604172252.34df14f7@solaris>
	<1212623330.15010.318.camel@localhost>
Message-ID: <a2e649c70806050930h3014296q1ed397e71177fd48@mail.gmail.com>

On Wed, Jun 4, 2008 at 7:48 PM, Duncan Coutts
<duncan.coutts@worc.ox.ac.uk> wrote:
>
> On Wed, 2008-06-04 at 17:22 +0200, Achim Schneider wrote:
>
>> The question, IMHO, seems to be
>>
>> "How would a package manager for a posix-compilant kinetic look like?"
>
> http://nixos.org/index.html
>

How well does that coexist with other OS's? Could I have it manage
only specific applications in it's store and trust the OS for the
rest?

--
Darrin
From my.bulk.mail.account at gmail.com  Thu Jun  5 12:31:16 2008
From: my.bulk.mail.account at gmail.com (A A)
Date: Thu Jun  5 12:23:53 2008
Subject: [Haskell-cafe] GHCi gives type signature that won't compile.
Message-ID: <6d5af6810806050931h104d31fcu77864609911acb05@mail.gmail.com>

Hi All

I can successfully compile the following code using ghci

import Data.Array.IArray

makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-
[lower..upper]
tridiagonal_solve (a, b, c, d, (lower, upper)) = x
    where
        gen_array f = (makeArray (lower, upper) f)
        x = gen_array x_f
            where
                x_f i
                    | i == upper     = (d_dash ! upper)
                    | otherwise         = (d_dash ! i) - (c_dash ! i) * (x !
(i + 1))
        d_dash = gen_array d_dash_f
            where
                d_dash_f i
                    | i == lower     = (d ! lower) / (b ! lower)
                    | otherwise        = ((d ! i) - (d_dash ! (i - 1)) * (a
! i)) /
                                          ((b ! i) - (c_dash ! (i - 1)) * (a
! i))
        c_dash = gen_array c_dash_f
            where
                c_dash_f i
                    | i == lower    = (c ! lower) / (b ! lower)
                    | otherwise     = (c ! i) /
                                          ((b ! i) - (c_dash ! (i - 1)) * (a
! i))

I then attempted to write a type signature for tridiagonal_solve. I didn't
succeed at this however, all of my type signatures gave compile errors when
attempting to load them in ghci. I asked in the #haskell channel, and they
suggested that I try the type signature from ghci :type function.

So I removed any type signatures, and reloaded the file in ghci, and typed
":type tridiagonal_solve" which produced the following output:

tridiagonal_solve :: (IArray a3 e,
                      IArray a6 e,
                      IArray a7 e,
                      Fractional e,
                      Ix a,
                      Num a,
                      IArray a4 e,
                      IArray a2 e,
                      IArray a5 e,
                      IArray a1 e,
                      Enum a) =>
                     (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7 a e

I then attempted to paste this into my code, the resulting code looking like
this:

import Data.Array.IArray

makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-
[lower..upper]]

tridiagonal_solve :: (IArray a3 e,
                      IArray a6 e,
                      IArray a7 e,
                      Fractional e,
                      Ix a,
                      Num a,
                      IArray a4 e,
                      IArray a2 e,
                      IArray a5 e,
                      IArray a1 e,
                      Enum a) =>
                     (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7 a e

tridiagonal_solve (a, b, c, d, (lower, upper)) = x
    where
        gen_array f = (makeArray (lower, upper) f)
        x = gen_array x_f
            where
                x_f i
                    | i == upper     = (d_dash ! upper)
                    | otherwise        = (d_dash ! i) - (c_dash ! i) * (x !
(i + 1))
        d_dash = gen_array d_dash_f
            where
                d_dash_f i
                    | i == lower     = (d ! lower) / (b ! lower)
                    | otherwise        = ((d ! i) - (d_dash ! (i - 1)) * (a
! i)) /
                                          ((b ! i) - (c_dash ! (i - 1)) * (a
! i))
        c_dash = gen_array c_dash_f
            where
                c_dash_f i
                    | i == lower    = (c ! lower) / (b ! lower)
                    | otherwise     = (c ! i) /
                                          ((b ! i) - (c_dash ! (i - 1)) * (a
! i))

When I attempt to load this into ghci, I recieve the following error:

[1 of 1] Compiling Main             ( main.lhs, interpreted )

main.lhs:29:11:
    Could not deduce (IArray a1 e)
      from the context (IArray a3 e,
                        IArray a6 e,
                        IArray a7 e,
                        Fractional e,
                        Ix a2,
                        Num a2,
                        IArray a4 e,
                        IArray a21 e,
                        IArray a5 e,
                        IArray a11 e,
                        Enum a2)
      arising from a use of `gen_array' at main.lhs:29:11-28
    Possible fix:
      add (IArray a1 e) to the context of
        the type signature for `tridiagonal_solve'
    In the expression: gen_array d_dash_f
    In the definition of `d_dash':
        d_dash = gen_array d_dash_f
               where
                   d_dash_f i | i == lower = (d ! lower) / (b ! lower)
                              | otherwise
                              = ((d ! i) - (d_dash ! (i - 1)) * (a ! i))
                              / ((b ! i) - (c_dash ! (i - 1)) * (a ! i))
    In the definition of `tridiagonal_solve':
        tridiagonal_solve (a, b, c, d, (lower, upper))
                            = x
                            where
                                gen_array f = (makeArray (lower, upper) f)
                                x = gen_array x_f
                                  where
                                      x_f i | i == upper = (d_dash ! upper)
                                            | otherwise
                                            = (d_dash ! i) - (c_dash ! i) *
(x ! (i + 1))
                                d_dash = gen_array d_dash_f
                                       where
                                           d_dash_f i | i == lower = (d !
lower) / (b ! lower)
                                                      | otherwise
                                                      = ((d ! i) - (d_dash !
(i - 1)) * (a ! i))
                                                      / ((b ! i) - (c_dash !
(i - 1)) * (a ! i))
                                c_dash = gen_array c_dash_f
                                       where
                                           c_dash_f i | i == lower = (c !
lower) / (b ! lower)
                                                      | otherwise
                                                      = (c ! i)
                                                      / ((b ! i) - (c_dash !
(i - 1)) * (a ! i))

main.lhs:35:11:
    Could not deduce (IArray a e)
      from the context (IArray a3 e,
                        IArray a6 e,
                        IArray a7 e,
                        Fractional e,
                        Ix a2,
                        Num a2,
                        IArray a4 e,
                        IArray a21 e,
                        IArray a5 e,
                        IArray a11 e,
                        Enum a2)
      arising from a use of `gen_array' at main.lhs:35:11-28
    Possible fix:
      add (IArray a e) to the context of
        the type signature for `tridiagonal_solve'
    In the expression: gen_array c_dash_f
    In the definition of `c_dash':
        c_dash = gen_array c_dash_f
               where
                   c_dash_f i | i == lower = (c ! lower) / (b ! lower)
                              | otherwise = (c ! i) / ((b ! i) - (c_dash !
(i - 1)) * (a ! i))
    In the definition of `tridiagonal_solve':
        tridiagonal_solve (a, b, c, d, (lower, upper))
                            = x
                            where
                                gen_array f = (makeArray (lower, upper) f)
                                x = gen_array x_f
                                  where
                                      x_f i | i == upper = (d_dash ! upper)
                                            | otherwise
                                            = (d_dash ! i) - (c_dash ! i) *
(x ! (i + 1))
                                d_dash = gen_array d_dash_f
                                       where
                                           d_dash_f i | i == lower = (d !
lower) / (b ! lower)
                                                      | otherwise
                                                      = ((d ! i) - (d_dash !
(i - 1)) * (a ! i))
                                                      / ((b ! i) - (c_dash !
(i - 1)) * (a ! i))
                                c_dash = gen_array c_dash_f
                                       where
                                           c_dash_f i | i == lower = (c !
lower) / (b ! lower)
                                                      | otherwise
                                                      = (c ! i)
                                                      / ((b ! i) - (c_dash !
(i - 1)) * (a ! i))

My question is, what should the type signature for tridiagonal_solve
actually be? I would like one that doesn't limit the generality of
tridiagonal_solve because I would like to pass different array types in the
one function invocation, as long as they have the same index and element
types. I'm happy if other functions need type signatures as well.

I'm using ghc 6.8.2 on windows, though I get a similar issue with ghc 6.4.1.

Thanks.

Clinton
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From miguelimo38 at yandex.ru  Thu Jun  5 12:36:21 2008
From: miguelimo38 at yandex.ru (Miguel Mitrofanov)
Date: Thu Jun  5 12:29:32 2008
Subject: [Haskell-cafe] GHCi gives type signature that won't compile.
In-Reply-To: <6d5af6810806050931h104d31fcu77864609911acb05@mail.gmail.com>
References: <6d5af6810806050931h104d31fcu77864609911acb05@mail.gmail.com>
Message-ID: <87849DF8-BF80-48D5-8FA3-5134328B88D3@yandex.ru>

Check your types for typos.

On 5 Jun 2008, at 20:31, A A wrote:

> Hi All
>
> I can successfully compile the following code using ghci
>
> import Data.Array.IArray
>
> makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-  
> [lower..upper]
> tridiagonal_solve (a, b, c, d, (lower, upper)) = x
>     where
>         gen_array f = (makeArray (lower, upper) f)
>         x = gen_array x_f
>             where
>                 x_f i
>                     | i == upper     = (d_dash ! upper)
>                     | otherwise         = (d_dash ! i) - (c_dash !  
> i) * (x ! (i + 1))
>         d_dash = gen_array d_dash_f
>             where
>                 d_dash_f i
>                     | i == lower     = (d ! lower) / (b ! lower)
>                     | otherwise        = ((d ! i) - (d_dash ! (i -  
> 1)) * (a ! i)) /
>                                           ((b ! i) - (c_dash ! (i -  
> 1)) * (a ! i))
>         c_dash = gen_array c_dash_f
>             where
>                 c_dash_f i
>                     | i == lower    = (c ! lower) / (b ! lower)
>                     | otherwise     = (c ! i) /
>                                           ((b ! i) - (c_dash ! (i -  
> 1)) * (a ! i))
>
> I then attempted to write a type signature for tridiagonal_solve. I  
> didn't succeed at this however, all of my type signatures gave  
> compile errors when attempting to load them in ghci. I asked in the  
> #haskell channel, and they suggested that I try the type signature  
> from ghci :type function.
>
> So I removed any type signatures, and reloaded the file in ghci, and  
> typed ":type tridiagonal_solve" which produced the following output:
>
> tridiagonal_solve :: (IArray a3 e,
>                       IArray a6 e,
>                       IArray a7 e,
>                       Fractional e,
>                       Ix a,
>                       Num a,
>                       IArray a4 e,
>                       IArray a2 e,
>                       IArray a5 e,
>                       IArray a1 e,
>                       Enum a) =>
>                      (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7  
> a e
>
> I then attempted to paste this into my code, the resulting code  
> looking like this:
>
> import Data.Array.IArray
>
> makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-  
> [lower..upper]]
>
> tridiagonal_solve :: (IArray a3 e,
>                       IArray a6 e,
>                       IArray a7 e,
>                       Fractional e,
>                       Ix a,
>                       Num a,
>                       IArray a4 e,
>                       IArray a2 e,
>                       IArray a5 e,
>                       IArray a1 e,
>                       Enum a) =>
>                      (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7  
> a e
>
> tridiagonal_solve (a, b, c, d, (lower, upper)) = x
>     where
>         gen_array f = (makeArray (lower, upper) f)
>         x = gen_array x_f
>             where
>                 x_f i
>                     | i == upper     = (d_dash ! upper)
>                     | otherwise        = (d_dash ! i) - (c_dash ! i)  
> * (x ! (i + 1))
>         d_dash = gen_array d_dash_f
>             where
>                 d_dash_f i
>                     | i == lower     = (d ! lower) / (b ! lower)
>                     | otherwise        = ((d ! i) - (d_dash ! (i -  
> 1)) * (a ! i)) /
>                                           ((b ! i) - (c_dash ! (i -  
> 1)) * (a ! i))
>         c_dash = gen_array c_dash_f
>             where
>                 c_dash_f i
>                     | i == lower    = (c ! lower) / (b ! lower)
>                     | otherwise     = (c ! i) /
>                                           ((b ! i) - (c_dash ! (i -  
> 1)) * (a ! i))
>
> When I attempt to load this into ghci, I recieve the following error:
>
> [1 of 1] Compiling Main             ( main.lhs, interpreted )
>
> main.lhs:29:11:
>     Could not deduce (IArray a1 e)
>       from the context (IArray a3 e,
>                         IArray a6 e,
>                         IArray a7 e,
>                         Fractional e,
>                         Ix a2,
>                         Num a2,
>                         IArray a4 e,
>                         IArray a21 e,
>                         IArray a5 e,
>                         IArray a11 e,
>                         Enum a2)
>       arising from a use of `gen_array' at main.lhs:29:11-28
>     Possible fix:
>       add (IArray a1 e) to the context of
>         the type signature for `tridiagonal_solve'
>     In the expression: gen_array d_dash_f
>     In the definition of `d_dash':
>         d_dash = gen_array d_dash_f
>                where
>                    d_dash_f i | i == lower = (d ! lower) / (b ! lower)
>                               | otherwise
>                               = ((d ! i) - (d_dash ! (i - 1)) * (a !  
> i))
>                               / ((b ! i) - (c_dash ! (i - 1)) * (a !  
> i))
>     In the definition of `tridiagonal_solve':
>         tridiagonal_solve (a, b, c, d, (lower, upper))
>                             = x
>                             where
>                                 gen_array f = (makeArray (lower,  
> upper) f)
>                                 x = gen_array x_f
>                                   where
>                                       x_f i | i == upper = (d_dash !  
> upper)
>                                             | otherwise
>                                             = (d_dash ! i) -  
> (c_dash ! i) * (x ! (i + 1))
>                                 d_dash = gen_array d_dash_f
>                                        where
>                                            d_dash_f i | i == lower =  
> (d ! lower) / (b ! lower)
>                                                       | otherwise
>                                                       = ((d ! i) -  
> (d_dash ! (i - 1)) * (a ! i))
>                                                       / ((b ! i) -  
> (c_dash ! (i - 1)) * (a ! i))
>                                 c_dash = gen_array c_dash_f
>                                        where
>                                            c_dash_f i | i == lower =  
> (c ! lower) / (b ! lower)
>                                                       | otherwise
>                                                       = (c ! i)
>                                                       / ((b ! i) -  
> (c_dash ! (i - 1)) * (a ! i))
>
> main.lhs:35:11:
>     Could not deduce (IArray a e)
>       from the context (IArray a3 e,
>                         IArray a6 e,
>                         IArray a7 e,
>                         Fractional e,
>                         Ix a2,
>                         Num a2,
>                         IArray a4 e,
>                         IArray a21 e,
>                         IArray a5 e,
>                         IArray a11 e,
>                         Enum a2)
>       arising from a use of `gen_array' at main.lhs:35:11-28
>     Possible fix:
>       add (IArray a e) to the context of
>         the type signature for `tridiagonal_solve'
>     In the expression: gen_array c_dash_f
>     In the definition of `c_dash':
>         c_dash = gen_array c_dash_f
>                where
>                    c_dash_f i | i == lower = (c ! lower) / (b ! lower)
>                               | otherwise = (c ! i) / ((b ! i) -  
> (c_dash ! (i - 1)) * (a ! i))
>     In the definition of `tridiagonal_solve':
>         tridiagonal_solve (a, b, c, d, (lower, upper))
>                             = x
>                             where
>                                 gen_array f = (makeArray (lower,  
> upper) f)
>                                 x = gen_array x_f
>                                   where
>                                       x_f i | i == upper = (d_dash !  
> upper)
>                                             | otherwise
>                                             = (d_dash ! i) -  
> (c_dash ! i) * (x ! (i + 1))
>                                 d_dash = gen_array d_dash_f
>                                        where
>                                            d_dash_f i | i == lower =  
> (d ! lower) / (b ! lower)
>                                                       | otherwise
>                                                       = ((d ! i) -  
> (d_dash ! (i - 1)) * (a ! i))
>                                                       / ((b ! i) -  
> (c_dash ! (i - 1)) * (a ! i))
>                                 c_dash = gen_array c_dash_f
>                                        where
>                                            c_dash_f i | i == lower =  
> (c ! lower) / (b ! lower)
>                                                       | otherwise
>                                                       = (c ! i)
>                                                       / ((b ! i) -  
> (c_dash ! (i - 1)) * (a ! i))
>
> My question is, what should the type signature for tridiagonal_solve  
> actually be? I would like one that doesn't limit the generality of  
> tridiagonal_solve because I would like to pass different array types  
> in the one function invocation, as long as they have the same index  
> and element types. I'm happy if other functions need type signatures  
> as well.
>
> I'm using ghc 6.8.2 on windows, though I get a similar issue with  
> ghc 6.4.1.
>
> Thanks.
>
> Clinton
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From philip.weaver at gmail.com  Thu Jun  5 12:51:23 2008
From: philip.weaver at gmail.com (Philip Weaver)
Date: Thu Jun  5 12:44:00 2008
Subject: [Haskell-cafe] GHCi gives type signature that won't compile.
In-Reply-To: <87849DF8-BF80-48D5-8FA3-5134328B88D3@yandex.ru>
References: <6d5af6810806050931h104d31fcu77864609911acb05@mail.gmail.com>
	<87849DF8-BF80-48D5-8FA3-5134328B88D3@yandex.ru>
Message-ID: <bc36e24d0806050951s60128ccfh890a71bf872b03eb@mail.gmail.com>

On Thu, Jun 5, 2008 at 9:36 AM, Miguel Mitrofanov <miguelimo38@yandex.ru> wrote:
> Check your types for typos.
>
> On 5 Jun 2008, at 20:31, A A wrote:
>
>> Hi All
>>
>> I can successfully compile the following code using ghci
>>
>> import Data.Array.IArray
>>
>> makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-
>> [lower..upper]
>> tridiagonal_solve (a, b, c, d, (lower, upper)) = x
>>    where
>>        gen_array f = (makeArray (lower, upper) f)
>>        x = gen_array x_f
>>            where
>>                x_f i
>>                    | i == upper     = (d_dash ! upper)
>>                    | otherwise         = (d_dash ! i) - (c_dash ! i) * (x
>> ! (i + 1))
>>        d_dash = gen_array d_dash_f
>>            where
>>                d_dash_f i
>>                    | i == lower     = (d ! lower) / (b ! lower)
>>                    | otherwise        = ((d ! i) - (d_dash ! (i - 1)) * (a
>> ! i)) /
>>                                          ((b ! i) - (c_dash ! (i - 1)) *
>> (a ! i))
>>        c_dash = gen_array c_dash_f
>>            where
>>                c_dash_f i
>>                    | i == lower    = (c ! lower) / (b ! lower)
>>                    | otherwise     = (c ! i) /
>>                                          ((b ! i) - (c_dash ! (i - 1)) *
>> (a ! i))
>>
>> I then attempted to write a type signature for tridiagonal_solve. I didn't
>> succeed at this however, all of my type signatures gave compile errors when
>> attempting to load them in ghci. I asked in the #haskell channel, and they
>> suggested that I try the type signature from ghci :type function.
>>
>> So I removed any type signatures, and reloaded the file in ghci, and typed
>> ":type tridiagonal_solve" which produced the following output:
>>
>> tridiagonal_solve :: (IArray a3 e,
>>                      IArray a6 e,
>>                      IArray a7 e,
>>                      Fractional e,
>>                      Ix a,
>>                      Num a,
>>                      IArray a4 e,
>>                      IArray a2 e,
>>                      IArray a5 e,
>>                      IArray a1 e,
>>                      Enum a) =>
>>                     (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7 a e
>>
>> I then attempted to paste this into my code, the resulting code looking
>> like this:
>>
>> import Data.Array.IArray
>>
>> makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <-
>> [lower..upper]]
>>
>> tridiagonal_solve :: (IArray a3 e,
>>                      IArray a6 e,
>>                      IArray a7 e,
>>                      Fractional e,
>>                      Ix a,
>>                      Num a,
>>                      IArray a4 e,
>>                      IArray a2 e,
>>                      IArray a5 e,
>>                      IArray a1 e,
>>                      Enum a) =>
>>                     (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7 a e
>>
>> tridiagonal_solve (a, b, c, d, (lower, upper)) = x
>>    where
>>        gen_array f = (makeArray (lower, upper) f)
>>        x = gen_array x_f
>>            where
>>                x_f i
>>                    | i == upper     = (d_dash ! upper)
>>                    | otherwise        = (d_dash ! i) - (c_dash ! i) * (x !
>> (i + 1))
>>        d_dash = gen_array d_dash_f
>>            where
>>                d_dash_f i
>>                    | i == lower     = (d ! lower) / (b ! lower)
>>                    | otherwise        = ((d ! i) - (d_dash ! (i - 1)) * (a
>> ! i)) /
>>                                          ((b ! i) - (c_dash ! (i - 1)) *
>> (a ! i))
>>        c_dash = gen_array c_dash_f
>>            where
>>                c_dash_f i
>>                    | i == lower    = (c ! lower) / (b ! lower)
>>                    | otherwise     = (c ! i) /
>>                                          ((b ! i) - (c_dash ! (i - 1)) *
>> (a ! i))
>>
>> When I attempt to load this into ghci, I recieve the following error:
>>
>> [1 of 1] Compiling Main             ( main.lhs, interpreted )
>>
>> main.lhs:29:11:
>>    Could not deduce (IArray a1 e)
>>      from the context (IArray a3 e,
>>                        IArray a6 e,
>>                        IArray a7 e,
>>                        Fractional e,
>>                        Ix a2,
>>                        Num a2,
>>                        IArray a4 e,
>>                        IArray a21 e,
>>                        IArray a5 e,
>>                        IArray a11 e,
>>                        Enum a2)
>>      arising from a use of `gen_array' at main.lhs:29:11-28
>>    Possible fix:
>>      add (IArray a1 e) to the context of
>>        the type signature for `tridiagonal_solve'
>>    In the expression: gen_array d_dash_f
>>    In the definition of `d_dash':
>>        d_dash = gen_array d_dash_f
>>               where
>>                   d_dash_f i | i == lower = (d ! lower) / (b ! lower)
>>                              | otherwise
>>                              = ((d ! i) - (d_dash ! (i - 1)) * (a ! i))
>>                              / ((b ! i) - (c_dash ! (i - 1)) * (a ! i))
>>    In the definition of `tridiagonal_solve':
>>        tridiagonal_solve (a, b, c, d, (lower, upper))
>>                            = x
>>                            where
>>                                gen_array f = (makeArray (lower, upper) f)
>>                                x = gen_array x_f
>>                                  where
>>                                      x_f i | i == upper = (d_dash ! upper)
>>                                            | otherwise
>>                                            = (d_dash ! i) - (c_dash ! i) *
>> (x ! (i + 1))
>>                                d_dash = gen_array d_dash_f
>>                                       where
>>                                           d_dash_f i | i == lower = (d !
>> lower) / (b ! lower)
>>                                                      | otherwise
>>                                                      = ((d ! i) - (d_dash
>> ! (i - 1)) * (a ! i))
>>                                                      / ((b ! i) - (c_dash
>> ! (i - 1)) * (a ! i))
>>                                c_dash = gen_array c_dash_f
>>                                       where
>>                                           c_dash_f i | i == lower = (c !
>> lower) / (b ! lower)
>>                                                      | otherwise
>>                                                      = (c ! i)
>>                                                      / ((b ! i) - (c_dash
>> ! (i - 1)) * (a ! i))
>>
>> main.lhs:35:11:
>>    Could not deduce (IArray a e)
>>      from the context (IArray a3 e,
>>                        IArray a6 e,
>>                        IArray a7 e,
>>                        Fractional e,
>>                        Ix a2,
>>                        Num a2,
>>                        IArray a4 e,
>>                        IArray a21 e,
>>                        IArray a5 e,
>>                        IArray a11 e,
>>                        Enum a2)
>>      arising from a use of `gen_array' at main.lhs:35:11-28
>>    Possible fix:
>>      add (IArray a e) to the context of
>>        the type signature for `tridiagonal_solve'
>>    In the expression: gen_array c_dash_f
>>    In the definition of `c_dash':
>>        c_dash = gen_array c_dash_f
>>               where
>>                   c_dash_f i | i == lower = (c ! lower) / (b ! lower)
>>                              | otherwise = (c ! i) / ((b ! i) - (c_dash !
>> (i - 1)) * (a ! i))
>>    In the definition of `tridiagonal_solve':
>>        tridiagonal_solve (a, b, c, d, (lower, upper))
>>                            = x
>>                            where
>>                                gen_array f = (makeArray (lower, upper) f)
>>                                x = gen_array x_f
>>                                  where
>>                                      x_f i | i == upper = (d_dash ! upper)
>>                                            | otherwise
>>                                            = (d_dash ! i) - (c_dash ! i) *
>> (x ! (i + 1))
>>                                d_dash = gen_array d_dash_f
>>                                       where
>>                                           d_dash_f i | i == lower = (d !
>> lower) / (b ! lower)
>>                                                      | otherwise
>>                                                      = ((d ! i) - (d_dash
>> ! (i - 1)) * (a ! i))
>>                                                      / ((b ! i) - (c_dash
>> ! (i - 1)) * (a ! i))
>>                                c_dash = gen_array c_dash_f
>>                                       where
>>                                           c_dash_f i | i == lower = (c !
>> lower) / (b ! lower)
>>                                                      | otherwise
>>                                                      = (c ! i)
>>                                                      / ((b ! i) - (c_dash
>> ! (i - 1)) * (a ! i))
>>
>> My question is, what should the type signature for tridiagonal_solve
>> actually be? I would like one that doesn't limit the generality of
>> tridiagonal_solve because I would like to pass different array types in the
>> one function invocation, as long as they have the same index and element
>> types. I'm happy if other functions need type signatures as well.
>>
>> I'm using ghc 6.8.2 on windows, though I get a similar issue with ghc
>> 6.4.1.

This sounds like a problem I've seen before.  GHCi would infer some
constraint like IArray a e, but when I put that into the type of the
function it would then complain that there's no instance of IArray a1
e, and when I put IArray a1 e in, it complains that there is no
instance for IArray a2 e.... and so on....

The problem was that there were terms of type "a" within the body of
the function (the same "a" from the type of the function), but it
wasn't figuring that out.  The solution was to litter my function body
with type ascriptions, and then in the type of the function introduce
all of the type variables with a "forall".  It also seems like all of
your "as" should be the same?  So... something like this might work:

  tridiagonal_solve :: forall a e . (IArray a e, Fractional e, Ix a, Num a....

Where you ascribe some of the terms in the body of your function to be
of type "a".

Hope that helps.  Sorry if I couldn't explain this problem very well.

>>
>> Thanks.
>>
>> Clinton
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From bulat.ziganshin at gmail.com  Thu Jun  5 12:45:48 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Thu Jun  5 12:44:40 2008
Subject: [Haskell-cafe] File locking wishlist
In-Reply-To: <1212679364.3483.14.camel@otto.ehbuehl.net>
References: <1212679364.3483.14.camel@otto.ehbuehl.net>
Message-ID: <693202115.20080605204548@gmail.com>

Hello Joachim,

Thursday, June 5, 2008, 7:22:44 PM, you wrote:

>  * Only one instance of the program runs at a time.
>  * If new events come in while the program runs, it should re-run itself
>  * There is information attached to the events (only one Bool ATM)

> So I?d like to implement something with this, or a similar, interface:

isn't it better to provide os-independent interface to semaphores?
named semaphores both on windows and unix may be used to implement
functionality you required and it's a more natural way

there is useful article [1] which describes both windows and unix way to
threads/events/semaphores/mutexes. how about implementing lightweight
library which abstracts over these differences?

OTOH, i've just recalled one C++ library which does exactly this job [2].
may be providing Haskell interface for it will be a better idea?


[1] http://www.ibm.com/developerworks/linux/library/l-ipc2lin1.html
[2] Abstraction of multitasking, file IO and socket IO for Unix and
    Windows systems http://www.garret.ru/~knizhnik/sal-108.zip

-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From ndmitchell at gmail.com  Thu Jun  5 12:54:51 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Thu Jun  5 12:47:25 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <28B5EEBB-7843-436D-9CFC-A01EEFDF1E9A@fastmail.fm>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
	<2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
	<28B5EEBB-7843-436D-9CFC-A01EEFDF1E9A@fastmail.fm>
Message-ID: <404396ef0806050954i5a9d6b1cw2cde7d6091650048@mail.gmail.com>

Hi

>  PS Why isn't Functor derivable?

Derive can do it: http://www.cs.york.ac.uk/~ndm/derive

I believe that Twan (the author of Functor deriving in Derive) is
trying to get this suggested for Haskell' as a proper deriving.

As for the original question, Uniplate will certainly do map, and will
probably help with filter - as the definition of Filter is not obvious
given the type. And you can have automatic deriving with Uniplate (see
PlateData in the paper or the module structure)
http://www.cs.york.ac.uk/~ndm/uniplate

Thanks

Neil
From lanny at cisco.com  Thu Jun  5 13:06:02 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Thu Jun  5 12:58:36 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <2518b95d0806042014m3b40937cj1ecf05011e6dae77@mail.gmail.com>
References: <4846DFDC.5020905@btinternet.com>	
	<Pine.GSO.4.56.0806042251560.23485@haydn.informatik.uni-halle.de>	
	<484706F7.8000407@btinternet.com> <484715D8.8090803@cisco.com>
	<2518b95d0806042014m3b40937cj1ecf05011e6dae77@mail.gmail.com>
Message-ID: <48481CFA.5070104@cisco.com>

Wow.  Did I really quote the article as "Communcations"?  (A new,
little known work by Shannon! :/  The link is correct anyway.

  -ljr

Evan Laforge wrote:
> On Wed, Jun 4, 2008 at 3:23 PM, Lanny Ripple <lanny@cisco.com> wrote:
>> You might want to skim Shannon's 'A Mathematical Theory of
>> Communcations'.  Part 1, Section 2 and 3 are almost exactly your
>> topic.  (Or at least the direction you've headed in. :)
>>
>>  http://plan9.bell-labs.com/cm/ms/what/shannonday/shannon1948.pdf
> 
> Rob Pike's "Practice of Programming" has a few chapters with a markov
> generator in several different languages as a case study.  None of
> them are functional, but it's a pretty clear description of the idea.
> 
> The "plan9" in the url reminded me :)
From paul at cogito.org.uk  Thu Jun  5 13:06:20 2008
From: paul at cogito.org.uk (Paul Johnson)
Date: Thu Jun  5 12:58:58 2008
Subject: [Haskell-cafe] Re: Laziness leaks
In-Reply-To: <20080605052825.7002ce4e@solaris>
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>	<4845D0B8.6040802@vex.net>	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>	<g25o2h$p3p$1@ger.gmane.org>	<2f9b2d30806041916x3e0088acw26e45033ee586b9a@mail.gmail.com>
	<20080605052825.7002ce4e@solaris>
Message-ID: <48481D0C.1070206@cogito.org.uk>

Achim Schneider wrote:
> There won't ever be a space leak without a time leak nor a time leak
> without a space leak. I'd just call it a leak.
>   
Actually I think you can have a space leak without a time leak.  For 
instance if every time around the main loop I cons data onto a linked 
list that never gets freed then I have a space leak.  If the list never 
gets used (or more realistically, if the program only ever uses the 
first N entries) then there is no time leak.

I agree that a time leak implies a space leak though.

Paul.
From barsoap at web.de  Thu Jun  5 13:14:31 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 13:07:11 2008
Subject: [Haskell-cafe] Re: Laziness leaks
References: <62728db30806031414p19593f40x5ad1bfd32e2dfc4b@mail.gmail.com>
	<4845D0B8.6040802@vex.net>
	<62728db30806031712w32421ae5scbf84920ecd71193@mail.gmail.com>
	<g25o2h$p3p$1@ger.gmane.org>
	<2f9b2d30806041916x3e0088acw26e45033ee586b9a@mail.gmail.com>
	<20080605052825.7002ce4e@solaris> <48481D0C.1070206@cogito.org.uk>
Message-ID: <20080605191431.5c6bd1d7@solaris>

Paul Johnson <paul@cogito.org.uk> wrote:

> Achim Schneider wrote:
> > There won't ever be a space leak without a time leak nor a time leak
> > without a space leak. I'd just call it a leak.
> >   
> Actually I think you can have a space leak without a time leak.  For 
> instance if every time around the main loop I cons data onto a linked 
> list that never gets freed then I have a space leak.  If the list
> never gets used (or more realistically, if the program only ever uses
> the first N entries) then there is no time leak.
> 
Sure there is: you leaked time while constructing the list.

The whole topic seems to degenerate into nit-picking for border cases.

One could define a leak as "a property of an error-free program
resulting in non-optimal performance", or much more concise,
"a trap no sufficiently smart programmer runs into".

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From newsham at lava.net  Thu Jun  5 13:28:07 2008
From: newsham at lava.net (Tim Newsham)
Date: Thu Jun  5 13:20:40 2008
Subject: [Haskell-cafe] re: very hard to build darcs with win32 ghc-6.8.2!
Message-ID: <Pine.BSI.4.64.0806050723410.16752@malasada.lava.net>

Here's the wrapup, thanks to those who replied:

   - the haskell zlib package on hackage no longer requires that zlib
     (the C library) be prebuilt.  It includes sources itself and
     builds and installs them using Cabal.
   - the haskell zlib package is not used by darcs.  It links against
     libz.a directly.  You do need to have libz.a somehow to build
     darcs.
   - the darcs link error with "SleepEx" is caused because it uses
     "foreign import ccall" when it should use "foreign import stdcall".
     Fixing the decl in src/win32/System/Posix.hs to stdcall fixes
     this issue.

I still think its odd that ghc's "gcc" is not very useable outside
of Cabal, but in this case it has no bearing on the zlib package.
If you choose to build "libz.a" (the C library) from sources using
this gcc it will be hard, but you could also get it from an external
source (such as the prebuilt libcurl library package).

Tim Newsham
http://www.thenewsh.com/~newsham/
From aeyakovenko at gmail.com  Thu Jun  5 13:28:50 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Thu Jun  5 13:21:22 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <48480339.6050900@um.es>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
	<4844F27A.2080208@um.es> <731290342.20080603113721@gmail.com>
	<48450752.4080307@um.es> <483842413.20080603134211@gmail.com>
	<48480339.6050900@um.es>
Message-ID: <e26d18e40806051028r303d050dp1d41f62b0721a0a1@mail.gmail.com>

Thanks, that's exactly what i was looking for.

On Thu, Jun 5, 2008 at 8:16 AM, Alberto Ruiz <aruiz@um.es> wrote:
> Hello Bulat and Anatoly,
>
> I have written a first version of an interface to inplace updates in the ST
> monad for the hmatrix vectors and matrices. Many things must be
> improved (range checking, documentation, etc.) but I hope that the general
> idea makes sense.
>
> A few usage examples:
>
> http://perception.inf.um.es/~aruiz/darcs/hmatrix/examples/inplace.hs
>
> Code:
>
> http://perception.inf.um.es/~aruiz/darcs/hmatrix/lib/Data/Packed/ST.hs
>
> http://perception.inf.um.es/~aruiz/darcs/hmatrix/doc/html/Data-Packed-ST.html
>
> Any suggestion will be welcome. I'm impressed by the power of the ST monad,
> it is extremely useful and elegant. Thank you again for your help!
>
> In the future I will also try to include efficient conversions to/from
> standard Haskell arrays and those of other related libraries like Jed
> Brown's CArray.
>
> Thanks,
>
> Alberto
>
>
> Bulat Ziganshin wrote:
>>
>> Hello Alberto,
>>
>> Tuesday, June 3, 2008, 12:56:50 PM, you wrote:
>>
>>> Good! So you can easily "hide" the IO operations in the ST monad. I will
>>> definitely look into it.
>>
>> from implementation POV ST monad is nothing but renamed IO monad which
>> exports only subset of its operations which are guaranteed to safe.
>> or, saying in other words, it's just type hackery around IO monad that
>> provides safe operations
>>
>> it's possible to define ST monad and its operations as following:
>>
>> newtype ST s a = forall s. ST_Constructor (IO a)
>>
>> unsafeIOtoSt action = ST_Constructor action
>>
>> runST (ST_Constructor action) = unsafePerformIO action
>>
>> newtype STRef s a = forall s. STRef (IORef a)
>>
>> readSTRef (STRef ref)  =  unsafeIOtoSt (readIORef ref)
>>
>> and so on. GHC uses technically (but not ideologically!) different
>> implementation where both monads are specializations of one generic
>> type. while Hugs afair uses exactly this approach. you may also look
>> at ArrayRef lib which reimplements arrays/refs for both compilers in
>> more unified way
>>
>> anyway, because ST is just IO monad modulo type tricks, you can
>> execute any IO action inside ST by lifting it with unsafeIOtoSt
>>
>
From martindemello at gmail.com  Thu Jun  5 14:04:35 2008
From: martindemello at gmail.com (Martin DeMello)
Date: Thu Jun  5 13:57:08 2008
Subject: [Haskell-cafe] getting set up in ubuntu
In-Reply-To: <874p88l3vp.fsf@malde.org>
References: <f93a6bcc0806042307o27873fd0ha1595c9f336064cf@mail.gmail.com>
	<874p88l3vp.fsf@malde.org>
Message-ID: <f93a6bcc0806051104v2822413fha2f48f4a0f7b1e1a@mail.gmail.com>

On Thu, Jun 5, 2008 at 12:47 AM, Ketil Malde <ketil@malde.org> wrote:
> "Martin DeMello" <martindemello@gmail.com> writes:

>> I'm especially looking for guidelines on what to install via apt-get
>> and what to install independently.
>
> I'd get as much as possible via apt-get, and only install manually
> when that fails.
>

Thanks! Did you have any conflicts between manual and apt-got stuff?
Is there any equivalent to gentoo's "package.provided" (which
basically says 'I have installed this manually; please don't try to
update it for me')?

martin
From barsoap at web.de  Thu Jun  5 14:27:53 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 14:20:35 2008
Subject: [Haskell-cafe] Analysing music
Message-ID: <20080605202753.139c8acc@solaris>

The recent discussion about Markoff chains inspired me to try to
train one with all the Bach midi's I have on my disk, collecting
statistics on what intervals tend to get played simultaneously,
which follow others and in which way the pitch offsets from its mean,
so that melodies fall and raise "naturally".

The rationale is that if it's Bach, it's harmonious but not respecting
any kind of usual chord progression.

So far, I got (a bit confused around the edges):

getMid mf = do
    mid <- MidiLoad.fromFile mf
    return $ MidiRead.retrieveTracks mid
    

toMelody :: MidiMusic.T -> StdMelody.T
toMelody = Music.mapNote f 
    where
        f note = 
            let body = MidiMusic.body note 
            in Melody.Note StdMelody.na (MidiMusic.pitch body)
    
main = do
    args <- Env.getArgs
    let mf:[] = args
    m <- getMid mf 
    putStr $ Format.prettyMelody $ Optimise.all 
        $ Music.chord $ map (\m -> Music.line $ map toMelody m) m


which results in
chord
  [e 3 bn na,
   chord
     [b 2 wn na,
      line
        [hnr, d 3 wn na, hnr, cs 3 hn na, a 2 hn na,
         chord [cs 3 hn na, line [b 2 hn na, c 3 hn na]]]]]

, for a set of random clicks in rosegarden's matrix editor.

Right now, I'm desperately searching for functions that can help me
analyse this beast, which afaict right now works best by having a
multitude of transformations (e.g. one big top-level chord with maximum
polyphony and a hell a lot of rests) that provide easy access to
whatever information is needed.

Does anyone of you know about previous work in this area? I don't want
to break cultural imperatives by not being as lazy as possible.

-- 
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past copyright information. All rights reserved. Unauthorised copying,
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signature prohibited. 

From dipankar at jfet.net  Thu Jun  5 14:32:59 2008
From: dipankar at jfet.net (Dipankar Ray)
Date: Thu Jun  5 14:25:38 2008
Subject: [Haskell-cafe] Analysing music
In-Reply-To: <20080605202753.139c8acc@solaris>
References: <20080605202753.139c8acc@solaris>
Message-ID: <Pine.LNX.4.64.0806051832050.2495@miles.jfet.net>


a somewhat random sample of work done in this direction:

http://arts.ucsc.edu/faculty/cope/experiments.htm

On Thu, 5 Jun 2008, Achim Schneider wrote:

> The recent discussion about Markoff chains inspired me to try to
> train one with all the Bach midi's I have on my disk, collecting
> statistics on what intervals tend to get played simultaneously,
> which follow others and in which way the pitch offsets from its mean,
> so that melodies fall and raise "naturally".
>
> The rationale is that if it's Bach, it's harmonious but not respecting
> any kind of usual chord progression.
>
> So far, I got (a bit confused around the edges):
>
> getMid mf = do
>    mid <- MidiLoad.fromFile mf
>    return $ MidiRead.retrieveTracks mid
>
>
> toMelody :: MidiMusic.T -> StdMelody.T
> toMelody = Music.mapNote f
>    where
>        f note =
>            let body = MidiMusic.body note
>            in Melody.Note StdMelody.na (MidiMusic.pitch body)
>
> main = do
>    args <- Env.getArgs
>    let mf:[] = args
>    m <- getMid mf
>    putStr $ Format.prettyMelody $ Optimise.all
>        $ Music.chord $ map (\m -> Music.line $ map toMelody m) m
>
>
> which results in
> chord
>  [e 3 bn na,
>   chord
>     [b 2 wn na,
>      line
>        [hnr, d 3 wn na, hnr, cs 3 hn na, a 2 hn na,
>         chord [cs 3 hn na, line [b 2 hn na, c 3 hn na]]]]]
>
> , for a set of random clicks in rosegarden's matrix editor.
>
> Right now, I'm desperately searching for functions that can help me
> analyse this beast, which afaict right now works best by having a
> multitude of transformations (e.g. one big top-level chord with maximum
> polyphony and a hell a lot of rests) that provide easy access to
> whatever information is needed.
>
> Does anyone of you know about previous work in this area? I don't want
> to break cultural imperatives by not being as lazy as possible.
>
> -- 
> (c) this sig last receiving data processing entity. Inspect headers for
> past copyright information. All rights reserved. Unauthorised copying,
> hiring, renting, public performance and/or broadcasting of this
> signature prohibited.
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From ben.franksen at online.de  Thu Jun  5 14:33:42 2008
From: ben.franksen at online.de (Ben Franksen)
Date: Thu Jun  5 14:26:28 2008
Subject: [Haskell-cafe] Re: Re: cabal and platform-independent haskell
	installation management (again) (Re: Re: Ubuntu and ghc)
References: <5ae4f2ba0805211532l35bef8eas9a10ff6df3e0f843@mail.gmail.com>
	<1211448821.5824.504.camel@localhost>
	<008001c8bbf7$63753100$d0357ad5@cr3lt> <48466F7F.8090600@gmail.com>
	<016d01c8c64d$4ac1dea0$73357ad5@cr3lt>
	<1212590628.15010.312.camel@localhost>
	<20080604172252.34df14f7@solaris>
	<1212623330.15010.318.camel@localhost>
	<a2e649c70806050930h3014296q1ed397e71177fd48@mail.gmail.com>
Message-ID: <g29bi6$1vh$1@ger.gmane.org>

Darrin Thompson wrote:
> On Wed, Jun 4, 2008 at 7:48 PM, Duncan Coutts
> <duncan.coutts@worc.ox.ac.uk> wrote:
>> On Wed, 2008-06-04 at 17:22 +0200, Achim Schneider wrote:
>>
>>> The question, IMHO, seems to be
>>>
>>> "How would a package manager for a posix-compilant kinetic look like?"
>>
>> http://nixos.org/index.html
> 
> How well does that coexist with other OS's? Could I have it manage
> only specific applications in it's store and trust the OS for the
> rest?

Yes. You can install nix (the package manager) under linux (and, I think,
other posix-compiant OS) and use it in parallel with native packages
(.deb, .rpm, whatever). This means you'll get some duplication, since the
nix store contains everything needed to build and run the installed
packages. The nix /package database/ contains not only nix package
descriptions but relies essentially on build-scripts, which are mostly
written in shell. So to use that, you'd have to have a posix-shell on your
system, too.

Cheers
Ben

From barsoap at web.de  Thu Jun  5 14:32:01 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 14:27:33 2008
Subject: [Haskell-cafe] Re: getting set up in ubuntu
References: <f93a6bcc0806042307o27873fd0ha1595c9f336064cf@mail.gmail.com>
	<874p88l3vp.fsf@malde.org>
	<f93a6bcc0806051104v2822413fha2f48f4a0f7b1e1a@mail.gmail.com>
Message-ID: <20080605203201.3dfccc7b@solaris>

"Martin DeMello" <martindemello@gmail.com> wrote:

> Thanks! Did you have any conflicts between manual and apt-got stuff?
> Is there any equivalent to gentoo's "package.provided" (which
> basically says 'I have installed this manually; please don't try to
> update it for me')?
> 
package.provided is bad, mkay?

It basically says "I messed up my system, try to continue anyway."

Don't use it for anything else than kernel sources, you should write
ebuilds for the rest and let portage do the managing.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From a.biurvOir4 at asuhan.com  Thu Jun  5 14:36:04 2008
From: a.biurvOir4 at asuhan.com (Kim-Ee Yeoh)
Date: Thu Jun  5 14:28:37 2008
Subject: [Haskell-cafe] More on performance
In-Reply-To: <200806041213.55484.jon@ffconsultancy.com>
References: <20080603174704.GB22053@scytale.galois.com>
	<Pine.GSO.4.56.0806040930420.19356@haydn.informatik.uni-halle.de>
	<1212571822.15010.266.camel@localhost>
	<6f9f8f4a0806040248x5f502f6eoae2a95dc8dc83778@mail.gmail.com>
	<7ca3f0160806040305x4bc0dd27tf8621b88acdf8c1e@mail.gmail.com>
	<200806041213.55484.jon@ffconsultancy.com>
Message-ID: <17676772.post@talk.nabble.com>



Jon Harrop wrote:
> 
> On Wednesday 04 June 2008 11:05:52 Luke Palmer wrote:
>> Given unbounded time and space, you will still arrive at the same result
>> regardless of the complexity. 
> 
> Given that the set of computers with unbounded time and space is empty, is
> it 
> not fruitless to discuss its properties?
> 

The set of omnipotent people is also empty. That has not stopped 
homo sapiens from discussing /its/ properties. All history is ever 
only such a discussion for nothing fires up the imagination nor 
provokes acts of brilliant foolhardiness like the unattainable.


-- Kim-Ee

-- 
View this message in context: http://www.nabble.com/More-on-performance-tp17629453p17676772.html
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From kenn at kenn.frap.net  Thu Jun  5 14:46:56 2008
From: kenn at kenn.frap.net (Kenn Knowles)
Date: Thu Jun  5 14:39:40 2008
Subject: [Haskell-cafe] Analysing music
In-Reply-To: <20080605202753.139c8acc@solaris>
References: <20080605202753.139c8acc@solaris>
Message-ID: <476d7e8c0806051146i4b6129bfx8202e85c7056bcd@mail.gmail.com>

David Cope's early research seems relevant.  Some LISP code to train a
Markov chain on Bach is available from the web page for his current
class.

http://arts.ucsc.edu/faculty/cope/music206b.html

He eschews higher-order functions; using them, you should be able to
port it to very concise and readable Haskell.  For the musical side of
things, the powerpoint presentations hint at additional data you can
put into your states and transitions to get better results for e.g.
cadences, characteristic embellishments, and melodic arcs.

Hope this is helpful,

- Kenn

On Thu, Jun 5, 2008 at 11:27 AM, Achim Schneider <barsoap@web.de> wrote:
> The recent discussion about Markoff chains inspired me to try to
> train one with all the Bach midi's I have on my disk, collecting
> statistics on what intervals tend to get played simultaneously,
> which follow others and in which way the pitch offsets from its mean,
> so that melodies fall and raise "naturally".
>
> The rationale is that if it's Bach, it's harmonious but not respecting
> any kind of usual chord progression.
>
> So far, I got (a bit confused around the edges):
>
> getMid mf = do
>    mid <- MidiLoad.fromFile mf
>    return $ MidiRead.retrieveTracks mid
>
>
> toMelody :: MidiMusic.T -> StdMelody.T
> toMelody = Music.mapNote f
>    where
>        f note =
>            let body = MidiMusic.body note
>            in Melody.Note StdMelody.na (MidiMusic.pitch body)
>
> main = do
>    args <- Env.getArgs
>    let mf:[] = args
>    m <- getMid mf
>    putStr $ Format.prettyMelody $ Optimise.all
>        $ Music.chord $ map (\m -> Music.line $ map toMelody m) m
>
>
> which results in
> chord
>  [e 3 bn na,
>   chord
>     [b 2 wn na,
>      line
>        [hnr, d 3 wn na, hnr, cs 3 hn na, a 2 hn na,
>         chord [cs 3 hn na, line [b 2 hn na, c 3 hn na]]]]]
>
> , for a set of random clicks in rosegarden's matrix editor.
>
> Right now, I'm desperately searching for functions that can help me
> analyse this beast, which afaict right now works best by having a
> multitude of transformations (e.g. one big top-level chord with maximum
> polyphony and a hell a lot of rests) that provide easy access to
> whatever information is needed.
>
> Does anyone of you know about previous work in this area? I don't want
> to break cultural imperatives by not being as lazy as possible.
>
> --
> (c) this sig last receiving data processing entity. Inspect headers for
> past copyright information. All rights reserved. Unauthorised copying,
> hiring, renting, public performance and/or broadcasting of this
> signature prohibited.
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From s.clover at gmail.com  Thu Jun  5 15:14:26 2008
From: s.clover at gmail.com (Sterling Clover)
Date: Thu Jun  5 15:07:02 2008
Subject: [Haskell-cafe] Analysing music
In-Reply-To: <476d7e8c0806051146i4b6129bfx8202e85c7056bcd@mail.gmail.com>
References: <20080605202753.139c8acc@solaris>
	<476d7e8c0806051146i4b6129bfx8202e85c7056bcd@mail.gmail.com>
Message-ID: <8C2F3E93-9B2B-4694-BD4F-CB2C0CAB9516@gmail.com>

Hofstadter (he of Godel Escher Bach) naturally has a lovely essay on  
Chopin reproduced in Metamagical Themas, which might be helpful as well.

Regards,
Sterl.

On Jun 5, 2008, at 2:46 PM, Kenn Knowles wrote:


> David Cope's early research seems relevant.  Some LISP code to train a
> Markov chain on Bach is available from the web page for his current
> class.
>
> http://arts.ucsc.edu/faculty/cope/music206b.html
>
> He eschews higher-order functions; using them, you should be able to
> port it to very concise and readable Haskell.  For the musical side of
> things, the powerpoint presentations hint at additional data you can
> put into your states and transitions to get better results for e.g.
> cadences, characteristic embellishments, and melodic arcs.
>
> Hope this is helpful,
>
> - Kenn
>
> On Thu, Jun 5, 2008 at 11:27 AM, Achim Schneider <barsoap@web.de>  
> wrote:
>
>> The recent discussion about Markoff chains inspired me to try to
>> train one with all the Bach midi's I have on my disk, collecting
>> statistics on what intervals tend to get played simultaneously,
>> which follow others and in which way the pitch offsets from its mean,
>> so that melodies fall and raise "naturally".
>>
>> The rationale is that if it's Bach, it's harmonious but not  
>> respecting
>> any kind of usual chord progression.
>>
>> So far, I got (a bit confused around the edges):
>>
>> getMid mf = do
>>    mid <- MidiLoad.fromFile mf
>>    return $ MidiRead.retrieveTracks mid
>>
>>
>> toMelody :: MidiMusic.T -> StdMelody.T
>> toMelody = Music.mapNote f
>>    where
>>        f note =
>>            let body = MidiMusic.body note
>>            in Melody.Note StdMelody.na (MidiMusic.pitch body)
>>
>> main = do
>>    args <- Env.getArgs
>>    let mf:[] = args
>>    m <- getMid mf
>>    putStr $ Format.prettyMelody $ Optimise.all
>>        $ Music.chord $ map (\m -> Music.line $ map toMelody m) m
>>
>>
>> which results in
>> chord
>>  [e 3 bn na,
>>   chord
>>     [b 2 wn na,
>>      line
>>        [hnr, d 3 wn na, hnr, cs 3 hn na, a 2 hn na,
>>         chord [cs 3 hn na, line [b 2 hn na, c 3 hn na]]]]]
>>
>> , for a set of random clicks in rosegarden's matrix editor.
>>
>> Right now, I'm desperately searching for functions that can help me
>> analyse this beast, which afaict right now works best by having a
>> multitude of transformations (e.g. one big top-level chord with  
>> maximum
>> polyphony and a hell a lot of rests) that provide easy access to
>> whatever information is needed.
>>
>> Does anyone of you know about previous work in this area? I don't  
>> want
>> to break cultural imperatives by not being as lazy as possible.
>>
>> --
>> (c) this sig last receiving data processing entity. Inspect  
>> headers for
>> past copyright information. All rights reserved. Unauthorised  
>> copying,
>> hiring, renting, public performance and/or broadcasting of this
>> signature prohibited.
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>

From ben.franksen at online.de  Thu Jun  5 15:36:20 2008
From: ben.franksen at online.de (Ben Franksen)
Date: Thu Jun  5 15:29:07 2008
Subject: [Haskell-cafe] Re: How would you hack it?
References: <4846DFDC.5020905@btinternet.com> <20080604223228.284254b5@solaris>
	<48470121.6090408@btinternet.com> <20080604232507.7fd9fd81@solaris>
Message-ID: <g29f7k$emq$1@ger.gmane.org>

Achim Schneider wrote:
> Andrew Coppin <andrewcoppin@btinternet.com> wrote:
>> Achim Schneider wrote:
>> > Andrew Coppin <andrewcoppin@btinternet.com> wrote:
>> >   
>> >> I have a file that contains several thousand words, seperated by
>> >> white space. [I gather that on Unix there's a standard location for
>> >> this file?]
>> > Looking at /usr/share/dict/words, I'm assured that the proper
>> > seperator is \n.
>> >   
>> 
>> Thanks. I did look around trying to find this, but ultimately failed.
>> (Is it a standard component, or is it installed as part of some
>> specific application?)
>> 
> ksf@solaris ~ % equery b /usr/share/dict/words
> [ Searching for file(s) /usr/share/dict/words in *... ]
> sys-apps/miscfiles-1.4.2 (/usr/share/dict/words)
> ksf@solaris ~ % eix miscfiles
> [I] sys-apps/miscfiles
>      Available versions:  1.4.2 {minimal}
>      Installed versions:  1.4.2(18:27:27 02/14/07)(-minimal)
>      Homepage:            http://www.gnu.org/directory/miscfiles.html
>      Description:         Miscellaneous files

On Ubuntu (and supposedly debian):

ben@sarun[1]: ~ > dpkg -S /usr/share/dict/words
dictionaries-common: /usr/share/dict/words

Cheers
Ben

From andrewcoppin at btinternet.com  Thu Jun  5 15:35:15 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Thu Jun  5 15:44:53 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <Pine.GSO.4.56.0806050744090.25369@haydn.informatik.uni-halle.de>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
	<48470014.4000804@btinternet.com>
	<79F4406C-52CA-4467-9826-8819E3D8DEE3@phaedrusdeinus.org>
	<Pine.GSO.4.56.0806050744090.25369@haydn.informatik.uni-halle.de>
Message-ID: <48483FF3.4070908@btinternet.com>

Henning Thielemann wrote:
> "Markov chain" means, that you have a sequence of random experiments,
> where the outcome of each experiment depends exclusively on a fixed number
> (the level) of experiments immediately before the current one.
>   

Right. So a "Markov chain" is actually a technical way of describing 
something that's intuitively pretty obvious? (E.g., PPM compression 
works by assuming that the input data is some sort of Markov chain with 
as-yet unknown transition probabilities.)

> If the level is too high, you will just reproduce the training text.
>   

Yeah, I can see that happening! ;-)

The key, I think, is for the training set to be much larger than what 
you want to produce...

From dons at galois.com  Thu Jun  5 16:11:47 2008
From: dons at galois.com (Don Stewart)
Date: Thu Jun  5 16:04:21 2008
Subject: [Haskell-cafe] Re: hmatrix
In-Reply-To: <48480339.6050900@um.es>
References: <e26d18e40805311209h4cd37689u30fe65e2ebd6c21e@mail.gmail.com>
	<484277D3.9020604@um.es>
	<e26d18e40806011145y4200e294yf8ffe08a426636b7@mail.gmail.com>
	<4843BF4A.2080800@um.es>
	<e26d18e40806021006y7277edcbn556971a87380bad0@mail.gmail.com>
	<4844F27A.2080208@um.es> <731290342.20080603113721@gmail.com>
	<48450752.4080307@um.es> <483842413.20080603134211@gmail.com>
	<48480339.6050900@um.es>
Message-ID: <20080605201147.GE19896@scytale.galois.com>

Good work, Alberto.

hmatrix looks like a good solution answer to some of the nested
arrays questions we have in Haskell

aruiz:
> Hello Bulat and Anatoly,
> 
> I have written a first version of an interface to inplace updates in the 
> ST monad for the hmatrix vectors and matrices. Many things must be
> improved (range checking, documentation, etc.) but I hope that the 
> general idea makes sense.
> 
> A few usage examples:
> 
> http://perception.inf.um.es/~aruiz/darcs/hmatrix/examples/inplace.hs
> 
> Code:
> 
> http://perception.inf.um.es/~aruiz/darcs/hmatrix/lib/Data/Packed/ST.hs
> 
> http://perception.inf.um.es/~aruiz/darcs/hmatrix/doc/html/Data-Packed-ST.html
> 
> Any suggestion will be welcome. I'm impressed by the power of the ST 
> monad, it is extremely useful and elegant. Thank you again for your help!
> 
> In the future I will also try to include efficient conversions to/from 
> standard Haskell arrays and those of other related libraries like Jed 
> Brown's CArray.
> 
> Thanks,
> 
> Alberto
> 
> 
> Bulat Ziganshin wrote:
> >Hello Alberto,
> >
> >Tuesday, June 3, 2008, 12:56:50 PM, you wrote:
> >
> >>Good! So you can easily "hide" the IO operations in the ST monad. I will
> >>definitely look into it.
> >
> >from implementation POV ST monad is nothing but renamed IO monad which
> >exports only subset of its operations which are guaranteed to safe.
> >or, saying in other words, it's just type hackery around IO monad that
> >provides safe operations
> >
> >it's possible to define ST monad and its operations as following:
> >
> >newtype ST s a = forall s. ST_Constructor (IO a)
> >
> >unsafeIOtoSt action = ST_Constructor action
> >
> >runST (ST_Constructor action) = unsafePerformIO action
> >
> >newtype STRef s a = forall s. STRef (IORef a)
> >
> >readSTRef (STRef ref)  =  unsafeIOtoSt (readIORef ref)
> >
> >and so on. GHC uses technically (but not ideologically!) different
> >implementation where both monads are specializations of one generic
> >type. while Hugs afair uses exactly this approach. you may also look
> >at ArrayRef lib which reimplements arrays/refs for both compilers in
> >more unified way
> >
> >anyway, because ST is just IO monad modulo type tricks, you can
> >execute any IO action inside ST by lifting it with unsafeIOtoSt
> >
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From lemming at henning-thielemann.de  Thu Jun  5 17:10:54 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun  5 17:00:36 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
Message-ID: <Pine.GSO.4.56.0806052310150.29590@haydn.informatik.uni-halle.de>


On Thu, 5 Jun 2008, Johan Tibell wrote:

> Hi!
>
> The last two weeks I've seen two new packages that add suffixes to
> identifiers instead of relying on them being imported qualified to
> distinguish them from identifiers in other modules. This is not a new
> thing in Haskell community and there are examples of this practice in
> libraries shipped with GHC. It is also common in papers (for good
> reasons as we will see later). Atomic channels and variables under
> Control.Concurrent.* are examples of using a prefix as a namespacing
> tool. Let me reiterate the arguments [1,2] against this practice and
> also speculate why this practice is more common in Haskell than in
> e.g. Python, Java or Ruby.

Thank you for emphasising these points, again!
From conor at strictlypositive.org  Thu Jun  5 17:17:09 2008
From: conor at strictlypositive.org (Conor McBride)
Date: Thu Jun  5 17:09:11 2008
Subject: [Haskell-cafe] automatically deriving Map and Filter on datatypes
	etc.
In-Reply-To: <28B5EEBB-7843-436D-9CFC-A01EEFDF1E9A@fastmail.fm>
References: <1ff5dedc0806050103h1639d907r7ac731de016787bc@mail.gmail.com>
	<0D31F43A-4404-40EA-8628-45A033FB6493@yandex.ru>
	<2638D507-4427-4A04-96E5-C8208F3F0D2F@gmail.com>
	<28B5EEBB-7843-436D-9CFC-A01EEFDF1E9A@fastmail.fm>
Message-ID: <460D5EB7-CF7F-4E33-963B-C0DEAC29A836@strictlypositive.org>

Hi

Statutory mathematics warning: lots.

On 5 Jun 2008, at 15:40, Jonathan Cast wrote:

> On 5 Jun 2008, at 1:39 AM, Thomas Davie wrote:
>
>> Even deriving an instance of Functor seems rather implausable,  
>> what should it do for
>>
>> data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)
>>
>> Should fmap's function argument operate on 'a's, 'b's, or both?
>
> class Functor (f :: * -> *) where ...
>
> so, 'b's.

While application remains injective, that seems
appropriate. But wouldn't we want more, eg,
that Wierd is a bifunctor (and, moreover,
bitraversable, bihalfzippable,...)?

Of course, there's a whole ghastly family of
these things for type constructors of varying
arities, together with stuff like "the fixpoint
of a bifunctor is a functor".

> jcc
>
> PS Why isn't Functor derivable?

It would be very handy, but it's the tip of the
iceberg. Being an Ulsterman, I get nervous
about engineering for machinery-iceberg collisions.
Perhaps it's worth looking for a systematic approach
to the more general situation (not necessarily kind
polymorphism; a systematic library treatment of
n-functors for n in {0,..,pickamax} would be a good
start).

An alterative, perhaps, is to replace arity by
indexing. This may get hairy. Untested stuff...

data Rewired f n where
   Nil :: Rewired f Zero
   A :: f Zero -> Rewired f Zero -> Rewired f Zero
   B :: f One -> Rewired f Zero -> Rewired f Zero

data Pick a b n where -- clearly a bit specific
   PickA :: a -> Pick a b Zero
   PickB :: b -> Pick a b One

type Wierd a b = Rewired (Pick a b) Zero

Here Rewired :: (* -> *) -> (* -> *), but
(* -> *) means "*-indexed type" not "container".
I'd rather be more precise and work with
(i -> *) -> (o -> *), but we have to take
i = o = * for now. The idea is to transform
a bunch of "input" datatypes indexed by i
to a bunch of output datatypes indexed by o.

In this example, we collect Bob's two element
types into a single GADT which specializes
differently at two distinct input indices.
There's no variation in the output index, so
I just made them all Zero. But here's another
old friend

data Vec f n where
   Nil  :: Vec f Zero
   Cons :: f Zero -> Vec f n -> Vec f (Suc n)

which has no input variation, but uses the
output index to specify length.

Anyhow, the point is that for these indexed
structures, you get to define much of the
generic kit once and for all, and you get
one obvious notion of "map".

type f :->: g = forall x. f x -> g x

class IxMap c where
   ixMap :: (f :->: g) -> (c f :->: c g)

Painless! Well, er, probably not. (Masochists
may choose to generalize this notion by
relaxing the index-preservation requirement
to some sort of index-simulation, thus
heading for Hancock's notion of "container
driver". I digress.)

Anyhow, it would be nice if kit developed
once for indexed structures could be lifted
automatically to the indexed encoding of
the more specific types you'd actually
like to work with. Maybe that's a thing to
be deriving.

{----------
Exercises for masochists (especially myself):

(1) Show that simply-typed lambda-terms
have IxMap structure (aka type-safe renaming)
over notions of typed variable, just as untyped
(de Bruijn) lambda-terms are an instance of
Functor. It may help to think systematically
about "notions of typed variable".

(2) Define an indexed container transformer
  IxFix ::
  ((* -> *) -> (* -> *)) -> ((* -> *) -> (* -> *))
in such a way that
  instance IxMap c => IxMap (IxFix c)
and present Vec, etc, with IxFix as the only
source of recursive datatype definition. Hint,
the more refined kind should be seen as
  (((i + o) -> *) -> (o -> *))
   ->
  ((i -> *) -> (o -> *))
so that c has places both for i-indexed inputs
and for o-indexed substructures.

(3) Grok and adapt the rest of Jeremy Gibbons'
"origami" apparatus.
----------}

Meanwhile, if you want to derive filtering,
think about what one-hole contexts for elements
need to look like, especially if you might want
to throw the element away. Fans of bifunctor
fixpoints and multivariate partial differentiation
may be amused to note that

   [x] = mu y. 1 + xy
   (d/dx) (1 + xy) = y

and that Cetin's

   Tab x = mu y. 1 + xy + y^3
   (d/dx) (1 + xy + y^3) = y

so perhaps a pattern is emerging...

It's been an interesting day: thanks to all for
the food for thought. It's clear that Haskell
(with recent extensions) can now express very
powerful abstractions such as "indexed
container", but not in a way which sits very
comfortably with normal usage. I think that's
a serious concern.

Cheers

Conor

From ketil at malde.org  Thu Jun  5 17:19:47 2008
From: ketil at malde.org (Ketil Malde)
Date: Thu Jun  5 17:12:02 2008
Subject: [Haskell-cafe] getting set up in ubuntu
In-Reply-To: <f93a6bcc0806051104v2822413fha2f48f4a0f7b1e1a@mail.gmail.com>
	(Martin DeMello's message of "Thu\, 5 Jun 2008 11\:04\:35 -0700")
References: <f93a6bcc0806042307o27873fd0ha1595c9f336064cf@mail.gmail.com>
	<874p88l3vp.fsf@malde.org>
	<f93a6bcc0806051104v2822413fha2f48f4a0f7b1e1a@mail.gmail.com>
Message-ID: <87lk1jk2a4.fsf@malde.org>

"Martin DeMello" <martindemello@gmail.com> writes:

> Thanks! Did you have any conflicts between manual and apt-got stuff?

Not yet, but I haven't really hammered my system with packages yet.

> Is there any equivalent to gentoo's "package.provided" (which
> basically says 'I have installed this manually; please don't try to
> update it for me')?

I'm not familar with Gentoo (anymore - I ran it briefly, but got tired
of all the compiling), but I think the answer is 'no'.  The native
packages go in /usr/{bin,lib,..}, while manual installs --
i.e. cabal -- puts stuff under /usr/local (or in your home dir).  

Native packages can of course only depend on and be built against
other native packages.  For "manually" installed packages, I believe
cabal will use the newest version wherever, as long as it's compatible
with the dependency specification in the .cabal file.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From lemming at henning-thielemann.de  Thu Jun  5 17:22:31 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun  5 17:12:08 2008
Subject: [Haskell-cafe] Analysing music
In-Reply-To: <20080605202753.139c8acc@solaris>
References: <20080605202753.139c8acc@solaris>
Message-ID: <Pine.GSO.4.56.0806052318410.29590@haydn.informatik.uni-halle.de>


On Thu, 5 Jun 2008, Achim Schneider wrote:

> The recent discussion about Markoff chains inspired me to try to
> train one with all the Bach midi's I have on my disk, collecting
> statistics on what intervals tend to get played simultaneously,
> which follow others and in which way the pitch offsets from its mean,
> so that melodies fall and raise "naturally".

I don't know, if you already found that one:
  http://darcs.haskell.org/haskore/src/Haskore/Example/Kantate147.hs

Surprisingly I also tried Markov Chain on a Bach song. But my approach was too
simplistic in order to produce a nice new song.
From dons at galois.com  Thu Jun  5 18:47:35 2008
From: dons at galois.com (Don Stewart)
Date: Thu Jun  5 18:40:11 2008
Subject: [Haskell-cafe] Package updates on haskell.org
Message-ID: <20080605224735.GD20317@scytale.galois.com>

The HWN, which I'm sadly too busy to maintain now, had a useful function
of generating recent package releases and getting them on the wiki, and
to people's inboxes.

This facility has been replaced by two processes:

    1) Users can subscribe to recent package updates via RSS:

        http://hackage.haskell.org/packages/archive/recent.rss

    2) The 'hackage2hwn' script now runs to keep the http://haskell.org
       'Recent Package Updates' section fresh, listing the latest
       updates. So you can always find the newest 20 packages by looking 
       at haskell.org

Cheers,
  Don
From barsoap at web.de  Thu Jun  5 18:50:03 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 18:42:49 2008
Subject: [Haskell-cafe] Analysing music
References: <20080605202753.139c8acc@solaris>
	<Pine.GSO.4.56.0806052318410.29590@haydn.informatik.uni-halle.de>
Message-ID: <20080606005003.295b5862@solaris>

Henning Thielemann <lemming@henning-thielemann.de> wrote:

> 
> On Thu, 5 Jun 2008, Achim Schneider wrote:
> 
> > The recent discussion about Markoff chains inspired me to try to
> > train one with all the Bach midi's I have on my disk, collecting
> > statistics on what intervals tend to get played simultaneously,
> > which follow others and in which way the pitch offsets from its
> > mean, so that melodies fall and raise "naturally".
> 
> I don't know, if you already found that one:
>   http://darcs.haskell.org/haskore/src/Haskore/Example/Kantate147.hs
> 
> Surprisingly I also tried Markov Chain on a Bach song. But my
> approach was too simplistic in order to produce a nice new song.
>
Yes, you need to take both dimension of music into account, that is
time and polyphony. Bach uses quite exceptional polyphony from time to
time, but it always stays harmonious: You have to have eg. a 0%
probability of ever playing a note and its minor second. The
probability of a note and its quint will most likely be at least 50%,
but then there are chords that sound atrocious if it's there. 

What I need is basically one view of the data as list of used chords,
and one graph of all possible time-linear progressions... that is,
voices, for a definition of "voice" that makes the guitarist in me
shudder.

Seems like I'm going to make close acquaintance with fgl, after all.

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From murray at sonology.net  Thu Jun  5 19:37:11 2008
From: murray at sonology.net (Murray)
Date: Thu Jun  5 19:30:02 2008
Subject: [Haskell-cafe] Analysing music 
In-Reply-To: <20080606005003.295b5862@solaris> 
References: <20080605202753.139c8acc@solaris>
	<Pine.GSO.4.56.0806052318410.29590@haydn.informatik.uni-halle.de>
	<20080606005003.295b5862@solaris>
Message-ID: <200806052337.m55NbLVg008663@fiennes-ds.lumison.net>

> What I need is basically one view of the data as list of used chords,
> and one graph of all possible time-linear progressions... that is,
> voices, for a definition of "voice" that makes the guitarist in me
> shudder.
> 
> Seems like I'm going to make close acquaintance with fgl, after all.

Sorry if this is too far off-topic but have you seen this?

     http://music.princeton.edu/~dmitri/

I?ve yet to dig into the paper but it looks kind of fun.

Clarence Barlow has an interesting algorithm for generating stochastic
musical data with ?harmonicity? being one of the parameters.  It is
implemented in an Atari ST (there?s *got* to be a better way!)
programme called Autobusk
<http://www.musikwissenschaft.uni-mainz.de/Autobusk/>.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~ Open your ears and your mind will follow. ~
~            - www.sonology.net -           ~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
From ajb at spamcop.net  Thu Jun  5 20:40:43 2008
From: ajb at spamcop.net (ajb@spamcop.net)
Date: Thu Jun  5 20:33:15 2008
Subject: [Haskell-cafe] How would you hack it?
In-Reply-To: <48483FF3.4070908@btinternet.com>
References: <4846DFDC.5020905@btinternet.com> <m1r6bdc5tn.fsf@subrosa.ca>
	<48470014.4000804@btinternet.com>
	<79F4406C-52CA-4467-9826-8819E3D8DEE3@phaedrusdeinus.org>
	<Pine.GSO.4.56.0806050744090.25369@haydn.informatik.uni-halle.de>
	<48483FF3.4070908@btinternet.com>
Message-ID: <20080605204043.h0ikeqi9s0s8s84o-nwo@webmail.spamcop.net>

G'day.

Quoting Andrew Coppin <andrewcoppin@btinternet.com>:

> Right. So a "Markov chain" is actually a technical way of describing
> something that's intuitively pretty obvious? (E.g., PPM compression
> works by assuming that the input data is some sort of Markov chain with
> as-yet unknown transition probabilities.)

Yes.  In fact, DMC compression (which has been proven to be the same thing
as PPM up to isomorphism) explicitly uses a Markov model.

If you're curious, I recently put some code for building dynamic Markov
models here.  It's not pretty, but you might find it useful:

     http://andrew.bromage.org/darcs/dynamicmarkov/

Cheers,
Andrew Bromage
From barsoap at web.de  Thu Jun  5 21:59:27 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun  5 21:52:12 2008
Subject: [Haskell-cafe] Re: Analysing music
References: <20080605202753.139c8acc@solaris>
	<Pine.GSO.4.56.0806052318410.29590@haydn.informatik.uni-halle.de>
	<20080606005003.295b5862@solaris>
	<200806052337.m55NbLVg008663@fiennes-ds.lumison.net>
Message-ID: <20080606035927.53b97951@solaris>

Murray <murray@sonology.net> wrote:

> > What I need is basically one view of the data as list of used
> > chords, and one graph of all possible time-linear progressions...
> > that is, voices, for a definition of "voice" that makes the
> > guitarist in me shudder.
> > 
> > Seems like I'm going to make close acquaintance with fgl, after all.
> 
> Sorry if this is too far off-topic but have you seen this?
> 
For the cafe, yes. Follow up to gmane.comp.lang.haskell.backstage,
please ;)

>      http://music.princeton.edu/~dmitri/
> 
> I?ve yet to dig into the paper but it looks kind of fun.
> 
It looks... mathematical. It also looks strikingly right, I just spend
a good quarter hour staring at the diagram and currently try to
convince my visualisation that the geometry is possible. The key points
to look out for are the diagonal lines featuring the same numbers,
vertical lines featuring series and where (_,n) changes into (n,_), to
get the mind accept the m?biusness.

I could show you why it's mirrored and twisted around the tritone using
a guitar and gnuplot, but I won't spoil the fun. Just observe that you
can easily play a flageolet on the 5th, 7th and 12th fret but not on the
6th. Western music is defined by fifth and fourths. It's all wave
mechanics, especially this darn problem of merging a linear scale to a
logarithmic one and trying to make sense while doing such an insane
thing.

> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ~ Open your ears and your mind will follow. ~
> ~            - www.sonology.net -           ~
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
You listen too much Stockhausen.

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signature prohibited. 

From ninegua at gmail.com  Thu Jun  5 22:40:51 2008
From: ninegua at gmail.com (Paul L)
Date: Thu Jun  5 22:33:21 2008
Subject: [Haskell-cafe] Re: What is the maturity of Haskell Web Frameworks
In-Reply-To: <F6BC7E00-122D-456A-AB09-3B10D2CCC628@gmail.com>
References: <BLU108-W49A501FFE2AC204EE805FDF4BB0@phx.gbl>
	<856033f20806041930t7499bda6n394938086ce38ecd@mail.gmail.com>
	<g28fa2$m16$1@ger.gmane.org>
	<F6BC7E00-122D-456A-AB09-3B10D2CCC628@gmail.com>
Message-ID: <856033f20806051940y5feee0c6lbf5ed1696f91d845@mail.gmail.com>

Thank you guys for all the good references!

To address a few concerns with this approach:

1. By stateless I don't mean to strip away any persistency. The
program can access file storage or DBMS just like any ordinary I/O
operation.

2. If we take it to the extreme side, the entire program including its
bytecode and all runtime data are in the page itself. The server is
really just a VM to execute it to the next step. Security is a
concern, but with proper cryptographic measures (e.g., a digitally
signed hash for integrity check) I don't think it's any less secure
(or insecure?) than existing web application frameworks.

3. The extreme scenario is perhaps not very practical, but still a
nice abstraction and a start point to optimize. For example, program
bytecode can just be its version number, which is matched against a
code repository on the server side to retrieve.

4. As for cryptic URIs, well, I don't think it's a real problem. URIs
meaningful to the users are often just starting point for a task flow.
URIs that refers to somewhere in the middle of a task flow are often
not meant to be readable anyway. Per-login-session data can be stuffed
into the cookies and remain invisible. Any sizeable chunk of data
should be handled as form data anyway. So what's left are the small
pieces that gets attached to URIs, they are  pretty harmless if you
ask me.

5. I for one do not think multi-user scenario is that much harder as I
was a MMOG developer. Sure, transactional behavior should be in place
to ensure correctness, but user to user interactions aren't very
complex for web applications to begin with. If they are, probably web
aren't the most suitable platform.

I took a quick look at the WASH paper, and the iData paper, and
visited Seaside's website. They are all very relevant, which at least
says something about a common vision. I'll just quote it from
Seaside's about page:

  "Unlike servlet models which require a separate handler
  for each page or request, Seaside models an entire user
  session as a continuous piece of code, with natural, linear
  control flow."

-- 
Regards,
Paul Liu

Yale Haskell Group
http://www.haskell.org/yale
From asumu at cyberberry.com  Fri Jun  6 00:33:30 2008
From: asumu at cyberberry.com (Asumu Takikawa)
Date: Fri Jun  6 00:26:14 2008
Subject: [Haskell-cafe] Vancouver Haskell users meeting
In-Reply-To: <48444E7C.7050602@moonloop.net>
References: <48444E7C.7050602@moonloop.net>
Message-ID: <20080606043330.GA3478@cyberberry.com>

Hi. I'd be interested in a meeting like this, but unfortunately since
UBC is done for winter term I'm out of Canada for the summer. If anyone
organizes a meet-up come fall I'd happily attend. 

Cheers,
AT

On 12:48 Mon 02 Jun     , Jon Strait wrote:
>    Anyone else here from Vancouver (Canada)?  I thought it would be great
>    to have a little informal get-together at a local cafe and share how
>    we're currently using Haskell, or really anything (problems,
>    comparisons, useful software tools, etc.) in relation to Haskell.
>    I'm scheduling a meeting for this Thursday, June 5th. for 7PM at
>    [1]Waazubee Cafe.  (At Commercial Dr. and 1st Ave.)
>    They have wireless internet access.  I'll get a table near the back,
>    bring my laptop, and will have a copy of Hudak's SOE book (the front
>    cover is impossible to miss) out on the table.
>    If anyone wants to meet, but this Thursday is not a good day for you,
>    let me know what days are better and we'll move the meeting.  If anyone
>    is sure that they will come this Thursday, you might let me know, so I
>    can have an idea about the resistance in changing the day, if needed.
>    Thanks,
>    Jon
> 
> References
> 
>    1. http://www.waazubee.com/content/directions.php

> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

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From vigalchin at gmail.com  Fri Jun  6 05:06:19 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Fri Jun  6 04:58:49 2008
Subject: [Haskell-cafe] example of FFI FunPtr
In-Reply-To: <5ae4f2ba0806060008i659a3e16yb179e94cf32ee8ab@mail.gmail.com>
References: <5ae4f2ba0806050038k1e0aea1exe6d81b22b1151eeb@mail.gmail.com>
	<4847B025.8030800@goto10.org>
	<5ae4f2ba0806060008i659a3e16yb179e94cf32ee8ab@mail.gmail.com>
Message-ID: <5ae4f2ba0806060206v6a1b2385vee642df8ccaa01de@mail.gmail.com>

Hi Claude,

     I want to do an incremental "experiment". I want just want  to pass a C
function to "callback" to a Haskell function. ???

Thanks, Vasili

On Thu, Jun 5, 2008 at 4:21 AM, Claude Heiland-Allen <
claudiusmaximus@goto10.org> wrote:

> Galchin, Vasili wrote:
>
>> Hello,
>>
>>       I want to model a Haskell function that is a callback from C. I have
>> only found one example in the unix package's Semaphore.hsc, which
>> apparently
>> is not used. I want to be able to marshall a Haskell function that is a
>> first class citizen residing in a Haskell data type and pass to a C
>> function
>> via FFI. Are there examples of this?
>>
>
> Attached is a simple example.
>
> The main thing to note is 'foreign import ccall "wrapper"' which gives you
> a factory for turning Haskell functions into foreign function pointers.
>
> More information:
>
> http://www.cse.unsw.edu.au/~chak/haskell/ffi/<http://www.cse.unsw.edu.au/%7Echak/haskell/ffi/>
>
>
> Claude
> --
> http://claudiusmaximus.goto10.org
>
>
> CallBacker: CallBacker.hs callerback.c callerback.h
>        ghc -O2 -Wall -fffi -o CallBacker CallBacker.hs callerback.c
>
>
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From g9ks157k at acme.softbase.org  Fri Jun  6 08:12:23 2008
From: g9ks157k at acme.softbase.org (Wolfgang Jeltsch)
Date: Fri Jun  6 08:04:59 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
Message-ID: <200806061412.23585.g9ks157k@acme.softbase.org>

Am Donnerstag, 5. Juni 2008 17:19 schrieb Johan Tibell:
> [?]

> 2. It's the default. You have to add "qualified" to all your imports
> to make them qualified. In most language imports are qualified by
> default. I think the latter would have been a better choice but we
> have to live with the current design so bite the bullet and add those
> qualified keywords to your imports.

If you leave out ?qualified?, you still get the qualified names imported.  And 
if you use conflicting identifiers always qualified then there?s no problem.  
For example, you can use

    import Data.Set as Set
    import Data.List as List

and then just say Set.null or List.null.

> [?]

> * Summary
>
> Whenever you write a library design it so it works well with qualified
> imports. That means leaving namespacing issues to the module system.
> Try to think of how code using your functions will look like if it
> uses them qualified.

I totally agree.

> [?]

Best wishes,
Wolfgang
From aruiz at um.es  Fri Jun  6 08:36:08 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Fri Jun  6 08:28:37 2008
Subject: [Haskell-cafe] Patrick Perry's BLAS package
Message-ID: <48492F38.3070107@um.es>

Hello all,

I have just noticed that yesterday this fantastic package has been 
uploaded to hackage:

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas-0.4

We finally have a high quality library for numeric linear algebra. This 
is very good news for the Haskell community.

Patrick, many thanks for your excellent work. Do you have similar plans 
for LAPACK?

Alberto
From jmaessen at alum.mit.edu  Fri Jun  6 08:47:02 2008
From: jmaessen at alum.mit.edu (Jan-Willem Maessen)
Date: Fri Jun  6 08:39:34 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <200806061412.23585.g9ks157k@acme.softbase.org>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
Message-ID: <A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>

On Jun 6, 2008, at 8:12 AM, Wolfgang Jeltsch wrote:

> Am Donnerstag, 5. Juni 2008 17:19 schrieb Johan Tibell:
>> [?]
>
>> 2. It's the default. You have to add "qualified" to all your imports
>> to make them qualified. In most language imports are qualified by
>> default. I think the latter would have been a better choice but we
>> have to live with the current design so bite the bullet and add those
>> qualified keywords to your imports.
>
> If you leave out ?qualified?, you still get the qualified names  
> imported.  And
> if you use conflicting identifiers always qualified then there?s no  
> problem.
> For example, you can use
>
>    import Data.Set as Set
>    import Data.List as List
>
> and then just say Set.null or List.null.

There's one caveat: Always choose descriptive names, even if you are  
assuming that you will usually use a qualified import.  The following  
are wonderful names, even though they conflict with the prelude:
   null
   filter
   map
   lookup

The following are terrible names:
   T
   C

What's a T?  What's a C?  There's no excuse to give something a lousy  
name just because the enclosing module is descriptively named.  I  
reject the naming conventions used by ML modules when writing Haskell  
code: Haskell modules are not ML modules.

-Jan-Willem Maessen

From barsoap at web.de  Fri Jun  6 10:57:07 2008
From: barsoap at web.de (Achim Schneider)
Date: Fri Jun  6 10:49:45 2008
Subject: [Haskell-cafe] Re: Design your modules for qualified import
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
Message-ID: <20080606165707.43133d30@solaris>

Jan-Willem Maessen <jmaessen@alum.mit.edu> wrote:

> On Jun 6, 2008, at 8:12 AM, Wolfgang Jeltsch wrote:
> 
> > Am Donnerstag, 5. Juni 2008 17:19 schrieb Johan Tibell:
> >> [?]
> >
> >> 2. It's the default. You have to add "qualified" to all your
> >> imports to make them qualified. In most language imports are
> >> qualified by default. I think the latter would have been a better
> >> choice but we have to live with the current design so bite the
> >> bullet and add those qualified keywords to your imports.
> >
> > If you leave out ?qualified?, you still get the qualified names  
> > imported.  And
> > if you use conflicting identifiers always qualified then there?s
> > no problem.
> > For example, you can use
> >
> >    import Data.Set as Set
> >    import Data.List as List
> >
> > and then just say Set.null or List.null.
> 
> There's one caveat: Always choose descriptive names, even if you are  
> assuming that you will usually use a qualified import.  The
> following are wonderful names, even though they conflict with the
> prelude: null
>    filter
>    map
>    lookup
> 
import Prelude as P

> The following are terrible names:
>    T
>    C
> 
Not to mention that this usage is hideously confusing while looking at
the haddock docs. While I don't mind Haskore having them, they should
just be different names for a type that has a clear name. It also
appears to generate an excessive amount of modules.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From lemming at henning-thielemann.de  Fri Jun  6 12:54:29 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Fri Jun  6 12:42:59 2008
Subject: [Haskell-cafe] Re: Design your modules for qualified import
In-Reply-To: <20080606165707.43133d30@solaris>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080606165707.43133d30@solaris>
Message-ID: <Pine.GSO.4.56.0806061850450.4093@haydn.informatik.uni-halle.de>


On Fri, 6 Jun 2008, Achim Schneider wrote:

> Jan-Willem Maessen <jmaessen@alum.mit.edu> wrote:
>
> > There's one caveat: Always choose descriptive names, even if you are
> > assuming that you will usually use a qualified import.  The
> > following are wonderful names, even though they conflict with the
> > prelude: null
> >    filter
> >    map
> >    lookup
> >
> import Prelude as P
>
> > The following are terrible names:
> >    T
> >    C
>
> Not to mention that this usage is hideously confusing while looking at
> the haddock docs.

But that will be resolved when Haddock can show identifiers with
qualifications.

> While I don't mind Haskore having them, they should just be different
> names for a type that has a clear name. It also appears to generate an
> excessive amount of modules.

It's good to have fine grained modules, because you can more easily
exchange the parts you want different from the standard way. For reducing
import lists for simple songs I think we could provide wrapper modules.
From duncan.coutts at worc.ox.ac.uk  Fri Jun  6 14:15:32 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Fri Jun  6 14:04:30 2008
Subject: [Haskell-cafe] ANNOUNCE: Cabal-1.4 release candidate
Message-ID: <1212776132.15010.383.camel@localhost>

Hi everyone,

== Cabal-1.4 release candidate ==

The second release candidate of Cabal-1.4 is out:
http://haskell.org/cabal/download.html

Please test and report bugs:
http://hackage.haskell.org/trac/hackage/

The aim for the Cabal-1.4 release is to get various fixes and
improvements into the hands of developers and to support a release of
cabal-install.

== cabal-install ==

A snapshot of cabal-install is also available:
http://haskell.org/cabal/download.html

It requires the zlib and HTTP packages (both are available from
hackage). Bug reports should go in the same trac as above.

cabal-install is intended to be the standard command line interface to
the whole Cabal/Hackage system. It replaces the "runhaskell Setup.hs"
interface and a few other tools you may or may not have heard of
(cabal-setup, cabal-upload, cabal-get). cabal-install is usable now and
we will be making a proper release some time after the Cabal-1.4
release.

== Testing ==

We are particularly interested in finding regressions from Cabal-1.2.x
or any important fixes that will require API changes since once we
release 1.4 we have to maintain API compatibility for the rest of the
1.4.x series.

This is also an excellent opportunity to make sure your favourite bug or
feature request is properly described in our bug tracker:
http://hackage.haskell.org/trac/hackage/

To help us guide development priorities please add yourself to the
ticket's cc list and describe why that bug or feature is important to
you.

== Compatibility ==

We have tried to preserve compatibility with all packages that worked
with the Cabal-1.2.x series. That is, packages that can be built using
Cabal (including custom Setup.hs scripts) but not packages that directly
import and use the Cabal API. Packages that directly import and use the
Cabal api will need updating. This affects packages that build distro
packages for example, rpm debs etc.

Currently we know of only one package on hackage which has a Setup.hs
script that compiles with 1.2 but fail to compile with 1.4. Takusen,
will require an update to be able to work with both Cabal-1.2.x and
1.4.x. A patch has been sent to the maintainers of Takusen.

== Credits ==

On behalf of the Cabal hackers and the community generally I'd like to
thank the large number of people who have contributed patches during
this development series. Previously I was rather worried that we were
not getting enough contributors to fix bugs and do new feature
development, but now I'm very pleased. :-)

== Get involved ==

Of course there's still a lot to do! We have big plans for Cabal-2.0,
cabal-install and the Hackage website. So if you're interested in
helping out with this core infrastructure project then:

 * subscribe to the cabal-devel mailing list:
     http://www.haskell.org/mailman/listinfo/cabal-devel

 * grab the source:
     http://haskell.org/cabal/code.html

 * read the guide to the source code:
     http://hackage.haskell.org/trac/hackage/wiki/SourceGuide

 * take a look at our list of bugs and feature requests:
     http://hackage.haskell.org/trac/hackage/report/12
   especially the easy tickets:
     http://hackage.haskell.org/trac/hackage/report/13

Duncan
(wearing his Cabal release manager hat)

From patperry at stanford.edu  Fri Jun  6 14:56:00 2008
From: patperry at stanford.edu (Patrick Perry)
Date: Fri Jun  6 14:48:43 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <48492F38.3070107@um.es>
References: <48492F38.3070107@um.es>
Message-ID: <D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>

Wow, thanks for noticing, Alberto!  For anyone interested, I put up a  
formal announcement describing the bindings a little bit here:

http://quantile95.com/

I just registered the domain yesterday, so it may take a few days to  
resolve the DNS magic.  Here's the text of the announcement:

I?m really happy that people seem to be interested in the library.  
Alberto, in particular, is the primary author of hmatrix, another  
haskell linear algebra library (which I stole a few ideas from), so if  
he endorses it, that means a lot to me.

So, Yet Another Linear Algebra Library? I?ve already mentioned  
hmatrix. There?s also another one called HBlas. Why would anyone want  
a third? Here are my reasons:

	* Support for both immutable and mutable types. Haskell tries to make  
you use immutable types as much as possible, and indeed there is a  
very good reason for this, but sometimes you have a 100MB matrix, and  
it just isn?t very practical to make a copy of it every time you  
modify it. hmatrix only supports immutable types, and HBlas only  
supports mutable ones. I wanted both.
	* Access control via phantom types. When you have immutable and  
mutable types, it?s very annoying to have separate functions for each  
type. Do I want to have to call ?numCols? for immutable matrices and  
?getNumCols? for mutable ones, even though both functions are pure,  
and both do exactly the same thing? No. If I want to add an immutable  
matrix to a mutable one, to I want to first call ?unsafeThaw? on the  
immutable one to cast it to be mutable? No. With the phantom type  
trick, you can get around this insanity. Jane Street Capital has a  
very good description of how this works.
	* Phantom types for matrix and vector shapes. This is a trick I  
learned from darcs. It means that the compiler can catch many  
dimension-mismatch mistakes. So, for instance, a function like
foo :: (BLAS1 e) =>
     Matrix (m,n) e -> Matrix (n,k) e -> Int -> Vector m e
foo a b i = let x = row b i in a <*> x
will not type-check. (?<*>? is the function to multiply a matrix by a  
vector. Everything is ok if you replace ?row? by ?col?.) This feature  
has caught a few bugs in my code.

	* Taking the conjugate transpose (?herm?) of a matrix is an O(1)  
operation. This is similar to hmatrix, where taking the transpose is  
O(1). As BLAS and LAPACK (mostly) support this, it makes no sense to  
copy a matrix just to work with the conjugate transpose. Why conjugate  
transpose instead of just transpose? Because the former is a far more  
common operation. This is why the ??? operator in MATLAB is conjugate  
transpose. The drawback for this feature is that BLAS and LAPACK do  
not support it everywhere. In particular, QR decomposition with  
pivoting is going to be a huge pain in the ass to support for herm-ed  
matrices.
	* Support for triangular and hermitian views of matrices. This is a  
feature of BLAS that no one seems to support (not even MATLAB). In  
addition to the ?Matrix? type, there are ?Tri Matrix? and ?Herm  
Matrix? types that only refer to the upper- or lower-triangular part  
of the matrix.
Hopefully the features above are compelling enough to make people want  
to use the library. These bindings have been a lot of work. For me to  
come up with the feature list above, I?ve already gone through a few  
iterations of dramatic re-writes (hence the version number). Of  
course, I always welcome suggestions for how to make it better.

What?s next? In the immediate future, I plan to add banded matrices.  
I?ve already written a good chunk of code for this, but it isn?t very  
well tested, so I decided to leave it out of the release. I?m also  
going to add permutation matrices. I don?t have plans to add support  
for packed triangular matrices, but if someone else wanted to do that,  
I would be happy to include it. The same goes for symmetric complex  
matrices.

LAPACK support is on the horizon, but that may take awhile. Also, I  
probably won?t do more than SVD, QR, and Cholesky, since those are all  
I need. Expect a preliminary announcement by the end of the summer.

This work would not have been possible without looking at the other  
excellent linear algebra libraries out there. In particular the GNU  
Scientific Library was the basis for much of the design. I also drew  
inspiration from hmatrix and the haskell array libraries.

Please let me know if you have any success in using the library, and  
if you have any suggestions for how to make it better.


Patrick

On Jun 6, 2008, at 5:36 AM, Alberto Ruiz wrote:

> Hello all,
>
> I have just noticed that yesterday this fantastic package has been  
> uploaded to hackage:
>
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas-0.4
>
> We finally have a high quality library for numeric linear algebra.  
> This is very good news for the Haskell community.
>
> Patrick, many thanks for your excellent work. Do you have similar  
> plans for LAPACK?
>
> Alberto

From xj2106 at columbia.edu  Fri Jun  6 16:22:31 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Fri Jun  6 16:19:02 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu> (Patrick
	Perry's message of "Fri, 6 Jun 2008 11:56:00 -0700")
References: <48492F38.3070107@um.es>
	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>
Message-ID: <87prquxqig.fsf@columbia.edu>

(Sorry, Patrick.  I forgot to CC haskell-cafe.)

Salute!  Excellent!

Patrick Perry <patperry@stanford.edu> writes:

> Wow, thanks for noticing, Alberto!  For anyone interested, I put up a
> formal announcement describing the bindings a little bit here:
>
> http://quantile95.com/
>
> I just registered the domain yesterday, so it may take a few days to
> resolve the DNS magic.  Here's the text of the announcement:
>

The magic is working, now.

>
> I?m really happy that people seem to be interested in the
> library. Alberto, in particular, is the primary author of hmatrix,
> another  haskell linear algebra library (which I stole a few ideas
> from), so if  he endorses it, that means a lot to me.
>
> So, Yet Another Linear Algebra Library? I?ve already mentioned
> hmatrix. There?s also another one called HBlas. Why would anyone want
> a third? Here are my reasons:
>
> 	* Support for both immutable and mutable types. Haskell tries
> to make you use immutable types as much as possible, and indeed there
> is a  very good reason for this, but sometimes you have a 100MB
> matrix, and  it just isn?t very practical to make a copy of it every
> time you  modify it. hmatrix only supports immutable types, and HBlas
> only  supports mutable ones. I wanted both.

I didn't use hmatrix a lot, because I wrote some STUArray
things and I wasn't sure what to do with that.  However, I
just noticed that there is a bunch of ST growing under
Data.Packed in hmatrix.  Guess things is going to change,
soon.  And perhaps with your work, Alberto doesn't need to
reinvent the wheel anymore.

> 
> 	* Access control via phantom types. When you have
> immutable and mutable types, it?s very annoying to have
> separate functions for each type. Do I want to have to
> call ?numCols? for immutable matrices and ?getNumCols? for
> mutable ones, even though both functions are pure, and
> both do exactly the same thing? No. If I want to add an
> immutable matrix to a mutable one, to I want to first call
> ?unsafeThaw? on the immutable one to cast it to be
> mutable? No. With the phantom type trick, you can get
> around this insanity. Jane Street Capital has a very good
> description of how this works.  

Lovely!

> * Phantom types for matrix and vector shapes. This is a
> trick I learned from darcs. It means that the compiler can
> catch many dimension-mismatch mistakes. So, for instance,
> a function like foo :: (BLAS1 e) => Matrix (m,n) e ->
> Matrix (n,k) e -> Int -> Vector m e foo a b i = let x =
> row b i in a <*> x will not type-check. (?<*>? is the
> function to multiply a matrix by a vector. Everything is
> ok if you replace ?row? by ?col?.) This feature has caught
> a few bugs in my code.

If I understand this correctly, the compiler can catch
dimension mismatches so that using `col' will result in a
compilation error when m and k are different, is it so?

>
> LAPACK support is on the horizon, but that may take awhile. Also, I
> probably won?t do more than SVD, QR, and Cholesky, since those are all
> I need. Expect a preliminary announcement by the end of the summer.
>
> This work would not have been possible without looking at the other
> excellent linear algebra libraries out there. In particular the GNU
> Scientific Library was the basis for much of the design. I also drew
> inspiration from hmatrix and the haskell array libraries.
>
> Please let me know if you have any success in using the library, and
> if you have any suggestions for how to make it better.

I haven't look through the code, yet.  But it looks like
there are certain levels of similarities between blas and
hmatrix.  Is it possible for these two libraries to
cooperate well with each other?  (I didn't look at HBlas, so
can't say much about that.)

Apart from some warnings, the library compiles fine in my
system.  But there is a minor issue about the library it
links against when `./Setup test'.  I need to use `-lcblas'
instead of `-lblas' to get it to link to correct libraries.
I don't know other people's system.  But in my system,
Gentoo Linux, I use blas library provided by atlas, and
libblas.so is a fortran library and libcblas.so is for C.

All in all, good job.  Thanks.

Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From jmaessen at alum.mit.edu  Fri Jun  6 16:35:16 2008
From: jmaessen at alum.mit.edu (Jan-Willem Maessen)
Date: Fri Jun  6 16:27:49 2008
Subject: [Haskell-cafe] Re: Design your modules for qualified import
In-Reply-To: <Pine.GSO.4.56.0806061850450.4093@haydn.informatik.uni-halle.de>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080606165707.43133d30@solaris>
	<Pine.GSO.4.56.0806061850450.4093@haydn.informatik.uni-halle.de>
Message-ID: <243AABC8-0311-4C50-BC98-563440F96DB2@alum.mit.edu>


On Jun 6, 2008, at 12:54 PM, Henning Thielemann wrote:

>
> On Fri, 6 Jun 2008, Achim Schneider wrote:
>
>> Jan-Willem Maessen <jmaessen@alum.mit.edu> wrote:
>>
>>> There's one caveat: Always choose descriptive names, even if you are
>>> assuming that you will usually use a qualified import.  The
>>> following are wonderful names, even though they conflict with the
>>> prelude: null
>>>   filter
>>>   map
>>>   lookup
>>>
>> import Prelude as P

Precisely.  If I import the prelude qualified and your library  
unqualified, is my code readable?  I should hope it is.  And if the  
library used the overlapping names reasonably, you shouldn't be left  
wondering when you read my code.

>>> The following are terrible names:
>>>   T
>>>   C
>>
>> Not to mention that this usage is hideously confusing while looking  
>> at
>> the haddock docs.
>
> But that will be resolved when Haddock can show identifiers with
> qualifications.

I specifically *didn't* bring up the Haddock issue, because I think  
it's a side show.  Fundamentally, these types are neither clear nor  
descriptive.  Their treatment by one or another documentation tool is,  
at some level, beside the point.

> It's good to have fine grained modules, because you can more easily
> exchange the parts you want different from the standard way. For  
> reducing
> import lists for simple songs I think we could provide wrapper  
> modules.

Make your modules as small as you like; small modules are great.  But  
keep things readable, please!

-Jan

>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From himself at poczta.nom.pl  Fri Jun  6 17:48:29 2008
From: himself at poczta.nom.pl (Andrzej Jaworski)
Date: Fri Jun  6 16:44:42 2008
Subject: [Haskell-cafe] Patrick Perry's BLAS package
Message-ID: <002101c8c81f$6b3d9b00$e9d54c59@bzdryk>

Hi,

Indeed, this has been long awaited. Long live Patrick!!!
And continue the good work:-)

However, such essential work shouldn't be dependent on heroic effort of an
individual. If Haskell is to remain non-commercial a disciplined community
effort should be taken akin to Pythonian. Perhaps also thouse of you who teach
Haskell could better use cheap labour of students,
after all Haskell's module system is not all that weak;-)

Cheers,
-A.J.

From ko at daimi.au.dk  Fri Jun  6 18:41:07 2008
From: ko at daimi.au.dk (Klaus Ostermann)
Date: Fri Jun  6 18:33:36 2008
Subject: [Haskell-cafe] Question about kinds
Message-ID: <17701553.post@talk.nabble.com>


Why does the code below not pass the type checker?

If I could explictly parameterize y with the type constructor Id (as e.g. in
System F), then 'y Id' should have the type Int -> Int
and hence "y Id x" should be OK, but with Haskell's implicit type parameters
it does not work.

So, how can I make this work?

Klaus
------------

type Id a = a

x :: Id Int
x = undefined

y :: (a Int) -> (a Int)
y = undefined

test = y x

Error:
  Couldn't match expected type `a Int' against inferred type `Id Int'
  In the first argument of `y', namely `x'
  In the expression: y x
  In the definition of `test': test = y x


-- 
View this message in context: http://www.nabble.com/Question-about-kinds-tp17701553p17701553.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From patperry at stanford.edu  Fri Jun  6 18:45:47 2008
From: patperry at stanford.edu (Patrick Perry)
Date: Fri Jun  6 18:38:36 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <87prquxqig.fsf@columbia.edu>
References: <48492F38.3070107@um.es>
	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>
	<87prquxqig.fsf@columbia.edu>
Message-ID: <C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>

>
>>
>> a function like foo :: (BLAS1 e) => Matrix (m,n) e ->
>> Matrix (n,k) e -> Int -> Vector m e foo a b i = let x =
>> row b i in a <*> x will not type-check. (?<*>? is the
>> function to multiply a matrix by a vector. Everything is
>> ok if you replace ?row? by ?col?.) This feature has caught
>> a few bugs in my code.
>
> If I understand this correctly, the compiler can catch
> dimension mismatches so that using `col' will result in a
> compilation error when m and k are different, is it so?

Yes, the compiler infers the type of expression to be

Matrix(m,n) e -> Matrix (l,m) e -> Int -> Vector n e

which is different from the declared type.  The error will be  
something like "Expected type Vector m e, but got type Vector a1 e  
instead".

> I haven't look through the code, yet.  But it looks like
> there are certain levels of similarities between blas and
> hmatrix.  Is it possible for these two libraries to
> cooperate well with each other?  (I didn't look at HBlas, so
> can't say much about that.)

This is more work than you might think.  The data structures are  
different, many of the function names are different, and the module  
namespaces overlap.  I wouldn't recommend any switch from hmatrix to  
blas right now unless you really need mutable types-- hmatrix has a  
lot more linear algebra functionality.

> Apart from some warnings, the library compiles fine in my
> system.  But there is a minor issue about the library it
> links against when `./Setup test'.  I need to use `-lcblas'
> instead of `-lblas' to get it to link to correct libraries.
> I don't know other people's system.  But in my system,
> Gentoo Linux, I use blas library provided by atlas, and
> libblas.so is a fortran library and libcblas.so is for C.

I don't know of a good way to get around this.  It seems like every  
system has a different convention for the location and name of the  
cblas libraries.  So, everyone has to edit the "extra-libraries" and  
the "extra-lib-dirs" field in the blas.cabal file.  Does anyone know  
of a better way of doing this?


Patrick

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From dons at galois.com  Fri Jun  6 22:32:18 2008
From: dons at galois.com (Don Stewart)
Date: Fri Jun  6 22:24:50 2008
Subject: [Haskell-cafe] Patrick Perry's BLAS package
In-Reply-To: <002101c8c81f$6b3d9b00$e9d54c59@bzdryk>
References: <002101c8c81f$6b3d9b00$e9d54c59@bzdryk>
Message-ID: <20080607023218.GA11462@scytale.galois.com>

himself:
> Hi,
> 
> Indeed, this has been long awaited. Long live Patrick!!!
> And continue the good work:-)
> 
> However, such essential work shouldn't be dependent on heroic effort of an
> individual. If Haskell is to remain non-commercial a disciplined community
> effort should be taken akin to Pythonian. Perhaps also thouse of you who teach
> Haskell could better use cheap labour of students,
> after all Haskell's module system is not all that weak;-)
> 

Yes, more libraries! 500 is not enough!

The best thing anyone here can do for haskell is contribute a library.

Latest packages:
    http://hackage.haskell.org/packages/archive/recent.html

How to upload a package:
    http://www.haskell.org/haskellwiki/How_to_write_a_Haskell_program

Join in!

The more areas we cover with Haskell code, the easier the path is to
ongoing development, and a viable, sustainable Haskell world.

-- Don
From derek.a.elkins at gmail.com  Fri Jun  6 22:43:25 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Fri Jun  6 22:35:58 2008
Subject: [Haskell-cafe] Question about kinds
In-Reply-To: <17701553.post@talk.nabble.com>
References: <17701553.post@talk.nabble.com>
Message-ID: <1212806605.7306.31.camel@derek-laptop>

On Fri, 2008-06-06 at 15:41 -0700, Klaus Ostermann wrote:
> Why does the code below not pass the type checker?
> 
> If I could explictly parameterize y with the type constructor Id (as e.g. in
> System F), then 'y Id' should have the type Int -> Int
> and hence "y Id x" should be OK, but with Haskell's implicit type parameters
> it does not work.
> 
> So, how can I make this work?
> 
> Klaus
> ------------
> 
> type Id a = a
> 
> x :: Id Int
> x = undefined
> 
> y :: (a Int) -> (a Int)
> y = undefined
> 
> test = y x
> 
> Error:
>   Couldn't match expected type `a Int' against inferred type `Id Int'
>   In the first argument of `y', namely `x'
>   In the expression: y x
>   In the definition of `test': test = y x

Down this path is higher-order unification which is undecidable.

You can use a newtype.

From oddron at gmail.com  Sat Jun  7 00:05:48 2008
From: oddron at gmail.com (Ronald Guida)
Date: Fri Jun  6 23:58:16 2008
Subject: [Haskell-cafe] Teaching Monads
Message-ID: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>

Monads in Haskell are a topic that I, like most beginners, find
difficult and "mind-twisting".  Now that I think I understand monads,
they seem to be very simple; I've read that this is a common
experience.

So I wonder, what would it take to help beginners catch on with a
minimum of fuss or frustration?  The plethora of monad tutorials out
there is clear evidence that plenty of others have wondered the same
thing.

What made monads "click" for me is when I understood the following
things:

1. When monads are being used, closures are almost always involved.

2. These closures naturally arise when desugaring do-syntax.

 do x1 <- m1               m1 >>= (\x1 ->
    x2 <- m2               m2 >>= (\x2 ->          [Eq1]
    x3 <- m3               m3 >>= (\x3 ->
    return (f x1 x2 x3)    return (f x1 x2 x3))))

3. These closures are extremely similar to the closures that arise
   when desugaring let-syntax.

 let x1 = f1 in            f1 -$ (\x1 ->      Where:
   let x2 = f2 in          f2 -$ (\x2 ->      (-$) :: a -> (a -> b) -> b
     let x3 = f3 in        f3 -$ (\x3 ->      x -$ f = f x
       f x1 x2 x3          f x1 x2 x3)))

4. While I can think of a monad as a fancy container that holds an
   element of type "t", it might be more accurate to think of a monad
   as a container that merely displays the type "t" as a label for its
   contents. The container might hold one object of type "t", or it
   might hold several.  It might not be holding any at all.  Perhaps
   the container /never/ holds an object of type "t", but instead it
   holds a set of instructions to produce such an object.
   (e.g. Reader, State).

Naturally, it's hard to illustrate nested closures, higher-order
functions, and objects that aren't really there.  It's easy to
illustrate a sequential scheme where a single "thing" passes through a
series of operations, while some related data travels in parallel.

                   m1 >>= f1 >>= f2 >>= f3        [Eq2]

In any case, the extreme similarity between desugared "do" and
desugared "let" leads me to think of the concepts of a manual
plumbing system and a monadic plumbing system.

Basically, a manual plumbing system is what I have if I'm threading
information down through a series of nested function calls in a
certain stereotypical way.  A monadic plumbing system is what I get
when I introduce the appropriate monad to encapsulate my threading.

In fact, if I look at Wadler [*], there are three examples of an
evaluator that use what I'm calling "manual plumbing".  In section
2.5, the operations required of a monad (return, bind) pretty much
just drop right out.  Wadler even points out the similarity between
"bind" and "let".

Now that I finally "get it", I feel that the Wadler paper, section 2.5
in particular, is probably a better introduction than many of the
monad tutorials out there.  Moreover, I feel that for /some/ of
the tutorials out there, they spend too much time and too many
illustrations explaining things like [Eq2], and then they quickly
present do-notation and gloss over [Eq1].

For me, I found that that the concepts of "manual plumbing" and
"monadic plumbing" were key to actually grasping the Wadler paper and
understanding what monads are.  In particular, I feel that these two
concepts might be a way to help other beginners catch on as well.

OK, so before I attempt to write a monad tutorial based on "manual
plumbing" and "monadic plumbing", I would like to know, does anyone
else think this is a good idea?

[*] "Monads for Functional Programming".
(http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf)
From jstrait at moonloop.net  Sat Jun  7 00:15:35 2008
From: jstrait at moonloop.net (Jon Strait)
Date: Sat Jun  7 00:18:53 2008
Subject: [Haskell-cafe] Vancouver Haskell users meeting
In-Reply-To: <20080606043330.GA3478@cyberberry.com>
References: <48444E7C.7050602@moonloop.net>
	<20080606043330.GA3478@cyberberry.com>
Message-ID: <484A0B67.9070108@moonloop.net>

I'll try to keep this going.  I think it's a good idea.

See you in the fall!

Jon

Asumu Takikawa wrote:
> Hi. I'd be interested in a meeting like this, but unfortunately since
> UBC is done for winter term I'm out of Canada for the summer. If anyone
> organizes a meet-up come fall I'd happily attend. 
>
> Cheers,
> AT
>
> On 12:48 Mon 02 Jun     , Jon Strait wrote:
>   
>>    Anyone else here from Vancouver (Canada)?  I thought it would be great
>>    to have a little informal get-together at a local cafe and share how
>>    we're currently using Haskell, or really anything (problems,
>>    comparisons, useful software tools, etc.) in relation to Haskell.
>>    I'm scheduling a meeting for this Thursday, June 5th. for 7PM at
>>    [1]Waazubee Cafe.  (At Commercial Dr. and 1st Ave.)
>>    They have wireless internet access.  I'll get a table near the back,
>>    bring my laptop, and will have a copy of Hudak's SOE book (the front
>>    cover is impossible to miss) out on the table.
>>    If anyone wants to meet, but this Thursday is not a good day for you,
>>    let me know what days are better and we'll move the meeting.  If anyone
>>    is sure that they will come this Thursday, you might let me know, so I
>>    can have an idea about the resistance in changing the day, if needed.
>>    Thanks,
>>    Jon
>>
>> References
>>
>>    1. http://www.waazubee.com/content/directions.php
>>     
>
>   
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>     
>
>   

From andrewcoppin at btinternet.com  Fri Jun  6 14:35:00 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Sat Jun  7 01:33:13 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
Message-ID: <48498354.5030506@btinternet.com>

Johan Tibell wrote:
> * Why is this practice common in Haskell
>
> Here are some guesses:
>
> 1. It's common in papers.

Maybe.
> 2. It's the default.
>   

Probably not.

> 3. Lack of common interfaces.
>   

Yes.

It's really quite frustrating that it is 100% impossible to write a 
single function that will process lists, arrays, sets, maps, byte 
strings, etc. You have to write several different versions. OK, so some 
functions really don't make sense for a set because it's unordered, and 
some functions don't make sense for a map, and so forth. But for 
example, if I write some complicated algorithm that uses a list to store 
data and I change that to a set instead, I now have to wade through the 
function changing every operation from a list-op into a set-op. It's 
really very annoying!

The problem - as I'm sure everybody is well aware - is that it's rather 
hard to come up with a type system formulation that works even though 
lists and arrays can store everything, unboxed arrays can only store 
types X, Y and Z, sets and maps require ordered data, byte strings only 
store bytes, and so on and so forth.

> 4. Haskell is a very expressive language. You can often write a whole
> function definition on one line! Adding those module qualifications
> makes your code slightly longer and it might just break your beautiful
> one liner into two lines.
>   

5. Writing "Hello" Prelude.++ "World" is just ugly. ;-)

In addition, I feel I should point out that only *very* recently did I 
discover that it is in fact possible to import a module qualified and 
still be able to refer to it easily. What do I mean by that? Well, 
suppose I do

  import Text.ParserCombinators.Parsec

I do *not* want to have to write "Text.ParserCombinators.Parsec.runParser"!!

Until very recently, it was not at all clear to me that there is 
actually a very simple solution to this problem:

  import Text.ParserCombinators.Parsec as P

Now I only have to write "P.runPaser", which is much shorter.

This fact probably needs to be mentioned more loudly - I'm sure I'm not 
the only person to have overlooked it...

From ajb at spamcop.net  Sat Jun  7 02:45:43 2008
From: ajb at spamcop.net (ajb@spamcop.net)
Date: Sat Jun  7 02:38:11 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
Message-ID: <20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>

G'day all.

Quoting Jan-Willem Maessen <jmaessen@alum.mit.edu>:

> There's one caveat: Always choose descriptive names, even if you are
> assuming that you will usually use a qualified import.  The following
> are wonderful names, even though they conflict with the prelude:
>   null
>   filter
>   map
>   lookup

On the contrary, these are terrible names _because_ they conflict
with the Prelude.  Especially "map", for which there's no excuse.
If it does the obvious thing, it's far better to define a real
Functor instance.

It's okay if you highly encourage or effectively mandate qualified
import, like Data.Map does.  However, unlike Data.Map, if you do
that then please don't define any operators.  Requiring someone to
type m M.! k is just wrong.

Cheers,
Andrew Bromage
From lrpalmer at gmail.com  Sat Jun  7 02:50:42 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Sat Jun  7 02:43:13 2008
Subject: [Haskell-cafe] Question about kinds
In-Reply-To: <17701553.post@talk.nabble.com>
References: <17701553.post@talk.nabble.com>
Message-ID: <7ca3f0160806062350w2893d5f6p580cbf0d167a0c85@mail.gmail.com>

On Fri, Jun 6, 2008 at 4:41 PM, Klaus Ostermann <ko@daimi.au.dk> wrote:
> type Id a = a
>
> x :: Id Int
> x = undefined
>
> y :: (a Int) -> (a Int)
> y = undefined

In "a Int", "a" refers to any type constructor, not any type function.
 So the best you can do is:

newtype Id a = Id a
-- rest as before

Luke
From devriese at cs.tcd.ie  Sat Jun  7 04:41:46 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Sat Jun  7 04:34:17 2008
Subject: [Haskell-cafe] Question about kinds
In-Reply-To: <17701553.post@talk.nabble.com>
References: <17701553.post@talk.nabble.com>
Message-ID: <20080607084146.GA17111@netsoc.tcd.ie>

On Fri, Jun 06, 2008 at 03:41:07PM -0700, Klaus Ostermann wrote:
> 
> Why does the code below not pass the type checker?
> 
> If I could explictly parameterize y with the type constructor Id (as e.g. in
> System F), then 'y Id' should have the type Int -> Int
> and hence "y Id x" should be OK, but with Haskell's implicit type parameters
> it does not work.

The type of 'Id' is expanded to simply 'Int', and 'Int' does not unify
with 'm a' for any type constructor 'm': Haskell's type level functions
are always unevaluated (type synonyms don't count: they are always
expanded).

So, if you wanted to to this, you'd need to do

  newtype Id a = Id a

Of course, now your values need to be tagged as well.

Edsko
From ryani.spam at gmail.com  Sat Jun  7 04:50:37 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Sat Jun  7 04:43:06 2008
Subject: [Haskell-cafe] Question about kinds
In-Reply-To: <17701553.post@talk.nabble.com>
References: <17701553.post@talk.nabble.com>
Message-ID: <2f9b2d30806070150s373fe21w421460aad3c6c1e0@mail.gmail.com>

"type" declarations are not first-class; treat them more like macro
expansions.  In particular, you cannot make a function polymorphic
over a type declaration.

You can make this typecheck using a "data" or "newtype" declaration for Id:

newtype Id x = Identity x
(or)
data Id x = Identity x

You do need to wrap/unwrap the "Identity" constructor then.

  -- ryan

On Fri, Jun 6, 2008 at 3:41 PM, Klaus Ostermann <ko@daimi.au.dk> wrote:
>
> Why does the code below not pass the type checker?
>
> If I could explictly parameterize y with the type constructor Id (as e.g. in
> System F), then 'y Id' should have the type Int -> Int
> and hence "y Id x" should be OK, but with Haskell's implicit type parameters
> it does not work.
>
> So, how can I make this work?
>
> Klaus
> ------------
>
> type Id a = a
>
> x :: Id Int
> x = undefined
>
> y :: (a Int) -> (a Int)
> y = undefined
>
> test = y x
>
> Error:
>  Couldn't match expected type `a Int' against inferred type `Id Int'
>  In the first argument of `y', namely `x'
>  In the expression: y x
>  In the definition of `test': test = y x
From slavomir.kaslev at gmail.com  Sat Jun  7 05:26:17 2008
From: slavomir.kaslev at gmail.com (Slavomir Kaslev)
Date: Sat Jun  7 05:18:48 2008
Subject: [Haskell-Cafe] Quick question for a slow program
Message-ID: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>

Hello,

I was just brushing my haskell-fu skills writing a solution for Google
Treasure Hunt Problem 4. Hers is what it looks like:

> primes = sieve [2..]
>     where
>       sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
>
> sumOf n l = sum (take n l) : sumOf n (tail l)
>
> find l = foldl1 aux l
>     where
>       aux (x:xs) (y:ys) | x == y = x : aux xs ys
>                         | x < y  = aux xs (y:ys)
>                         | x > y  = aux (x:xs) ys
>
> puzzle = find (reverse [primes, p7, p17, p41, p541])
>     where
>       p7 = sumOf 7 primes
>       p17 = sumOf 17 primes
>       p41 = sumOf 41 primes
>       p541 = sumOf 541 primes
>
> main = do mapM (\x -> putStrLn $ show x) puzzle

While the code is quite readable and straight forward it is as slow as
tortoise with four legs broken. What optimizations would you suggest,
while still keeping the code clear and highlevel?

Thank you in advance.

Cheers.

-- 
Slavomir Kaslev
From claus.reinke at talk21.com  Sat Jun  7 05:38:10 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Sat Jun  7 05:30:45 2008
Subject: [Haskell-cafe] Question about kinds
References: <17701553.post@talk.nabble.com>
Message-ID: <007101c8c882$349ce3e0$f20a8351@cr3lt>

short answer: use newtype instead of type (and check the
language spec for the difference between the two).

> Why does the code below not pass the type checker?

because of the type error?-) seriously, though, it is useful to
accompany such questions with some indication of what you're
trying to do, to put a cap on the wide variety of possible answers
(depending on what it is you're trying to achieve, there are many
different techniques or tricks that might apply), and to have 
something to compare the non-working code against (also in
case the intention needs to be edited before working code
can be suggested).
 
> If I could explictly parameterize y with the type constructor Id (as e.g. in
> System F), then 'y Id' should have the type Int -> Int
> and hence "y Id x" should be OK, but with Haskell's implicit type parameters
> it does not work.

schemes that rely on implicit 'Id' tend to be doomed to failure
in haskell and often suggest a need to get better acquainted
with the limitations of haskell's type system (such schemes 
often arise from invalid generalisations of promising features,
and many of us, myself included, have fallen into that trap at 
one point or other, often while working with type constructor
classes):

- type synonyms are syntactic macros, not part of the
    type system proper; the error message is a bit 
    confusing by trying to be helpful (giving type synonym
    applications instead of their expansion: the type system
    has seen 'Int', not 'Id Int')
- things of kind (* -> *) are type _constructors_, not
    arbitrary type functions
- type families are a restricted kind of type function, but
    can only be applied forwards (F t1 ~> t2), not be
    inferred or abstracted over

simplified, if the type system had to _infer_ 'Id' (or the
composition of type constructors, a related favourite;-),
it could do so anywhere, any number of times. in haskell's
approach to this, programmers have to indicate where
such things are meant to occur (eg, by using newtypes).

hth,
claus

> So, how can I make this work?
> 
> Klaus
> ------------
> 
> type Id a = a
> 
> x :: Id Int
> x = undefined
> 
> y :: (a Int) -> (a Int)
> y = undefined
> 
> test = y x
> 
> Error:
>  Couldn't match expected type `a Int' against inferred type `Id Int'
>  In the first argument of `y', namely `x'
>  In the expression: y x
>  In the definition of `test': test = y x
> 
> 
> -- 
> View this message in context: http://www.nabble.com/Question-about-kinds-tp17701553p17701553.html
> Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From aruiz at um.es  Sat Jun  7 06:19:28 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Sat Jun  7 06:12:09 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
References: <48492F38.3070107@um.es>	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>	<87prquxqig.fsf@columbia.edu>
	<C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
Message-ID: <484A60B0.2090307@um.es>

Patrick Perry wrote:

 > Xiao-Yong Jin wrote:
>> Apart from some warnings, the library compiles fine in my
>> system.  But there is a minor issue about the library it
>> links against when `./Setup test'.  I need to use `-lcblas'
>> instead of `-lblas' to get it to link to correct libraries.
>> I don't know other people's system.  But in my system,
>> Gentoo Linux, I use blas library provided by atlas, and
>> libblas.so is a fortran library and libcblas.so is for C.
> 
> I don't know of a good way to get around this.  It seems like every 
> system has a different convention for the location and name of the cblas 
> libraries.  So, everyone has to edit the "extra-libraries" and the 
> "extra-lib-dirs" field in the blas.cabal file.  Does anyone know of a 
> better way of doing this?
> 

A possible solution is using flags in the cabal configuration file. For 
instance, I have this in hmatrix.cabal:

if flag(mkl)
  if arch(x86_64)
   extra-libraries: gsl mkl_lapack mkl_intel_lp64 mkl_sequential mkl_core
  else
    extra-libraries: gsl mkl_lapack mkl_intel mkl_sequential mkl_core
else
  extra-libraries: gsl blas lapack

so if I want to link with Intel's MKL optimized blas/lapack instead of 
ATLAS I simply add the -fmkl flag:

runhaskell Setup.lhs configure -fmkl etc.

or even

cabal install hmatrix -fmkl

Other flags can be added to support different distributions. We could 
have something like

cabal install package -ffedora

or

cabal install package -fcblas

etc.

Alberto
From johan.tibell at gmail.com  Sat Jun  7 06:31:46 2008
From: johan.tibell at gmail.com (Johan Tibell)
Date: Sat Jun  7 06:24:14 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <48498354.5030506@btinternet.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
Message-ID: <90889fe70806070331rdf4165bk440f4cf9f59084@mail.gmail.com>

On Fri, Jun 6, 2008 at 8:35 PM, Andrew Coppin
<andrewcoppin@btinternet.com> wrote:
>  import Text.ParserCombinators.Parsec as P
>
> Now I only have to write "P.runPaser", which is much shorter.

Or maybe even

> import Text.ParserCombinators.Parsec as Parser

and then `Parser.run'.

Having the module hierarchy be shallower so you don't have to add a
`as' to every import might also help. I think Python does this better
for common modules which have short and sweet name lite `system'.

Cheers,

Johan
From dominic.steinitz at blueyonder.co.uk  Sat Jun  7 06:59:20 2008
From: dominic.steinitz at blueyonder.co.uk (Dominic Steinitz)
Date: Sat Jun  7 06:50:56 2008
Subject: [Haskell-cafe] Mersenne Build Problem
Message-ID: <484A6A08.4020600@blueyonder.co.uk>

I'm getting errors (see below) trying to build the tests in

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mersenne-random-0.1.1

I built the package itself using

./Setup configure -f use_sse2

I thought I had an intel core duo (also see below). I think I may be
missing a library but I'm not sure which one.

Thanks, Dominic.

> dom@lagrange:~/mersenne-random-0.1.1> cat /proc/cpuinfo
> processor       : 0
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 15
> model name      : Intel(R) Core(TM)2 Duo CPU     E4500  @ 2.20GHz
> stepping        : 13
> cpu MHz         : 1200.000
> cache size      : 2048 KB
> physical id     : 0
> siblings        : 2
> core id         : 0
> cpu cores       : 2
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 10
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pni monitor ds_cpl est tm2 ssse3 cx16 xtpr lahf_lm
> bogomips        : 4392.14
> clflush size    : 64
> 
> processor       : 1
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 15
> model name      : Intel(R) Core(TM)2 Duo CPU     E4500  @ 2.20GHz
> stepping        : 13
> cpu MHz         : 1200.000
> cache size      : 2048 KB
> physical id     : 0
> siblings        : 2
> core id         : 1
> cpu cores       : 2
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 10
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pni monitor ds_cpl est tm2 ssse3 cx16 xtpr lahf_lm
> bogomips        : 4388.99
> clflush size    : 64


> dom@lagrange:~/mersenne-random-0.1.1/tests> make
> ghc -O2 -ddump-simpl-stats -no-recomp Unit.hs --make
> [1 of 1] Compiling Main             ( Unit.hs, Unit.o )
> 
> ==================== FloatOut stats: ====================
> 154 Lets floated to top level; 35 Lets floated elsewhere; from 40 Lambda groups
> 
> 
> 
> ==================== FloatOut stats: ====================
> 133 Lets floated to top level; 14 Lets floated elsewhere; from 34 Lambda groups
> 
> 
> 
> ==================== Grand total simplifier statistics ====================
> Total ticks:     8378
> 
> 2022 PreInlineUnconditionally
> 1760 PostInlineUnconditionally
> 991 UnfoldingDone
> 132 RuleFired
>     1 *#
>     15 +#
>     25 ++
>     1 <#
>     3 ==#->case
>     2 SC:a0
>     1 SC:a_s2sW0
>     1 SPEC GHC.Num.-
>     2 SPEC GHC.Real.$p1Integral
>     2 SPEC GHC.Real.$p1Real
>     2 SPEC GHC.Real.$p2Real
>     3 SPEC Main.speed
>     3 SPEC System.Random.random
>     1 eftInt
>     9 fold/build
>     14 foldr/app
>     1 fromIntegral/Word->Int
>     1 int2Double#
>     1 int2Word#
>     3 map
>     2 mapList
>     1 minimumInt
>     2 remInt#
>     2 take
>     2 takeList
>     17 unpack
>     6 unpack-append
>     9 unpack-list
> 212 LetFloatFromLet
> 1 EtaReduction
> 2874 BetaReduction
> 27 CaseOfCase
> 341 KnownBranch
> 3 CaseElim
> 2 CaseIdentity
> 13 FillInCaseDefault
> 22 SimplifierDone
> 
> 
> Linking Unit ...
> Unit.o: In function `s4Da_info':
> (.text+0x1b21): undefined reference to `genrand_real2'
> Unit.o: In function `s4RA_info':
> (.text+0x3e75): undefined reference to `genrand_real2'
> Unit.o: In function `s4S4_info':
> (.text+0x3f61): undefined reference to `genrand_real2'
> Unit.o: In function `s5su_info':
> (.text+0x40bc): undefined reference to `genrand_real2'
> /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `mersennezmrandomzm0zi1zi1_SystemziRandomziMersenne_zdwa2_info':
> ghc13223_0.hc:(.text+0x1a3): undefined reference to `gen_rand64_mix'
> /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2J1_info':
> ghc13223_0.hc:(.text+0x91d): undefined reference to `gen_rand64_mix'
> /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2JZ_info':
> ghc13223_0.hc:(.text+0xb3d): undefined reference to `genrand_real2'
> /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2LJ_info':
> ghc13223_0.hc:(.text+0xf8d): undefined reference to `gen_rand64_mix'
> /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s35i_info':
> ghc13223_0.hc:(.text+0x1397): undefined reference to `genrand_real2'
> /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s36A_info':
> ghc13223_0.hc:(.text+0x1517): undefined reference to `gen_rand64_mix'
> collect2: ld returned 1 exit status
> make: *** [all] Error 1

From apfelmus at quantentunnel.de  Sat Jun  7 07:00:42 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Sat Jun  7 06:53:26 2008
Subject: [Haskell-cafe] Re: appending an element to a list
In-Reply-To: <62728db30806031357k4eb64655w7af1371cc6fe974d@mail.gmail.com>
References: <483EE208.2010601@inf.fu-berlin.de>
	<483EF36B.5040100@daimi.au.dk>	<48404039.6030605@cisco.com>
	<48405717.20206@daimi.au.dk>	<87r6bja609.fsf@hbox.dyndns.org>	<3c4d5adf0805302159o23113ad2sb24754e02789bb06@mail.gmail.com>	<48414C2B.9010606@daimi.au.dk>
	<g1tjk4$c4i$1@ger.gmane.org>	<3c4d5adf0806012204p25133bdaxbc22955b70f094ff@mail.gmail.com>	<g2322j$sig$1@ger.gmane.org>
	<62728db30806031357k4eb64655w7af1371cc6fe974d@mail.gmail.com>
Message-ID: <g2dpor$kf1$1@ger.gmane.org>

Ronald Guida wrote:
> Thank you, apfelmus.  That was a wonderful explanation; the debit
> method in [1] finally makes sense.

A diagram says more than a thousand words :)

My explanation is not entirely faithful to Okasaki, let me elaborate.


In his book, Okasaki calls the process of transferring the debits from
the input

>   xs = x1 : x2 : x3 : ... : xn : []
>           1    1    1 ... 1    1  0
> 
>   ys = y1 : y2 : y3 : ... : ym : []
>           1    1    1 ... 1    1  0 

to the output

>   xs ++ ys = x1 : x2 : x3 : ... : xn : y1 : y2 : y3 : ... : ym : []
>                 2    2    2 ... 2    2    1    1    1 ... 1    1  0 

"debit inheritance". In other words, the debits of xs and ys (here 1 at
each node) are carried over to xs ++ ys (in addition to the debits
created by ++ itself). In the thesis, he doesn't give it an explicit
name, but discusses this phenomenon in the very last paragraphs of
chapter 3.4 .


The act of relocating debits from child to parent nodes as exemplified with

>   xs ++ reverse ys =
>      x1 : x2 : x3 : ... : xn : yn : y{n-1} : ... : y1 : []
>         1    1    1 ... 1    1    n        0 ... 0    0  0 

>   xs ++ reverse ys =
>      x1 : x2 : x3 : ... : xn : yn : y{n-1} : ... : y1 : []
>         2    2    2 ... 2    2    0        0 ... 0    0  0

is called "debit passing", but Okasaki doesn't use it earlier than in 
the chapter "Implicit recursive slowdown". But the example I gave here 
is useful for understand the scheduled implementation of real time 
queues. The trick there is to not create a "big" suspension with  n 
debits but to really "physically" distribute them across the data structure

      x1 : x2 : x3 : ... : xn : yn : y{n-1} : ... : y1 : []
         2    2    2 ... 2    2    2        2 ... 2    2  2

and discharge them by forcing a node with every call to  snoc . I say
"physically" because this forcing performs actual work, it does not
simply "mentally" discharge a debit to amortize work that will be done
later. Note that the 2 debits added to each  yi  are an overestimation
here, but the real time queue implementation pays for them nonetheless.


My focus on debit passing in the original explanation might suggest that
debits can only be discharged when actually evaluating the node to which
the debit was assigned. This is not the case, an operation may discharge
any debits, even in parts of the data structure that it doesn't touch.
Of course, it must discharge debits of nodes it does touch.

For instance, in the proof of theorem 3.1 (thesis) for queues, Okasaki
writes "We can restore the invariant by discharging the first (two) 
debit(s) in  the queue" without bothering to analyze which node this 
will be. So, the front queue might look like

      f1 : f2 : f3 : ... : fn : f{n+1} : f{n+2} : ... : fm : []
         0    0    1 ... 1    1        n        0 ... 0    0  0

and it's one of the nodes that carries one debit, or it could look like

           f2 : f3 : ... : fn : f{n+1} : f{n+2} : ... : fm : []
              0    0 ... 0    0       n-3       0 ... 0    0  0

and it's the node with the large amount of debits. In fact, it's not 
even immediate that these two are the only possibilities.

However, with the debit passing from my previous post, it's easier to 
say which node will be discharged. But even then, only  tail  discharges 
exactly the debits of nodes it inspects while the  snoc  operation 
discharges debits in the untouched front list. Of course, as soon as 
identifying the nodes becomes tractable, chances are that you can turn 
it into a real-time data structure.

Another good example are skew heaps from

[2]:
   Chris Okasaki. Fun with binary heap trees.
   in  J. Gibbons, O. de Moor. The Fun of Programming.
   http://www.palgrave.com/PDFs/0333992857.Pdf

Here, the "good" nodes are annotated with one debit. Every  join 
operation discharges O(log n) of them and allocates new ones while 
walking down the tree, but the "time" to actually walk down the tree is 
not counted immediately. This is just like (++) walks down the first 
list and allocates debits without immediately using O(n) time to do that.


Regards,
apfelmus


PS: In a sense, discharging arbitrary debits can still be explained with 
debit passing: first pass those debits to the top and the discharge them 
because any operation has to inspect the top.

From dan.doel at gmail.com  Sat Jun  7 09:03:02 2008
From: dan.doel at gmail.com (Dan Doel)
Date: Sat Jun  7 08:55:31 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <48498354.5030506@btinternet.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
Message-ID: <200806070903.02682.dan.doel@gmail.com>

On Friday 06 June 2008, Andrew Coppin wrote:
> It's really quite frustrating that it is 100% impossible to write a
> single function that will process lists, arrays, sets, maps, byte
> strings, etc. You have to write several different versions. OK, so some
> functions really don't make sense for a set because it's unordered, and
> some functions don't make sense for a map, and so forth. But for
> example, if I write some complicated algorithm that uses a list to store
> data and I change that to a set instead, I now have to wade through the
> function changing every operation from a list-op into a set-op. It's
> really very annoying!

It's not 100% impossible, depending on what exactly you're doing. For 
instance...

  Set a, ByteStrings, Seq a, Map k a and [a] are Monoids
  Set, Array i, Map k, Tree, Seq and [] are Foldable functors
  Array i, Map k, Tree, Seq, Tree and [] are Traversable functors

Those can get you lots of operations (folds, maps, unions...) although there 
may be gaps that could be filled (Foldable is sufficient to define null, for 
instance, but it isn't in Data.Foldable).

There's also the collections library (or Edison, if that's more your style) on 
hackage that takes such things a lot further. It seems it needs to be tweaked 
a bit to run on 6.8 according to the log, though.

And there's also the issue of whether you can make all such generic operations 
perform well enough for every instance without making gigantic type classes 
that allow you to override every single operation (or if you can't, which way 
do you sacrifice).

Of course, the prelude isn't a very good example of this sort of thing, so if 
that's the only place one looks (or in any module specific to one particular 
data structure), there's not much to find.

-- Dan
From phercek at gmail.com  Sat Jun  7 09:18:03 2008
From: phercek at gmail.com (Peter Hercek)
Date: Sat Jun  7 09:14:49 2008
Subject: [Haskell-cafe] Re: Design your modules for qualified import
In-Reply-To: <48498354.5030506@btinternet.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
Message-ID: <g2e211$f25$1@ger.gmane.org>

Andrew Coppin wrote:
> Until very recently, it was not at all clear to me that there is 
> actually a very simple solution to this problem:
> 
>  import Text.ParserCombinators.Parsec as P
> 
> Now I only have to write "P.runPaser", which is much shorter.
> 
> This fact probably needs to be mentioned more loudly - I'm sure I'm not 
> the only person to have overlooked it...

I have one efficient way to find all the needed language
  features without reading the specification from the start to
  the end or waiting till my questions get answered. The point
  is that common sense will indicate you where the required
  features should be logically located in the language grammar.
  E.g. if you want something related to imported modules it is
  logical to check all the alternatives available in import
  declaration. Then I check the grammar how the production for
  import declaration (impdelc) looks like (where it can be used
  etc.). Mostly it is enough sometimes I need to check the
  language specification since it is not obvious from the
  grammar.

The result is that when I learn a new language the first thing
  I'm looking for is the formal grammar. Luckily most languages
  have it available. Some languages (like Haskell) are obsessed
  with shortcuts and the result is that their grammar is a bit
  cryptic; others (like VHDL) have it just great - production
  names clearly indicate what they actually do. On the other
  side haskell has nice online report :-)

Peter.

From s_zefirov at ipmce.ru  Sat Jun  7 09:32:46 2008
From: s_zefirov at ipmce.ru (Serguey Zefirov)
Date: Sat Jun  7 09:22:38 2008
Subject: [Haskell-cafe] Data.Map traversal.
Message-ID: <484A8DFE.7030209@ipmce.ru>

I found that I often need predecessor and successor of some key in 
Data.Map.Map. Just like that:

predKey, succKey :: Ord k => Data.Map.Map k a -> k -> Maybe k
predKeyElem, succKeyElem :: Ord k => Data.Map.Map k a -> k -> Maybe (k,a)

Data.Map has operations like that on key indexes, but it is slightly 
unnatural to work with three entities (index, key and element) where two 
suffices.

So I propose to include those operations into next version of Data.Map.
 
If anyone could point me in the right direction I could do any necessary 
modifications myself (just because I need it).

From miguelimo38 at yandex.ru  Sat Jun  7 09:35:21 2008
From: miguelimo38 at yandex.ru (Miguel Mitrofanov)
Date: Sat Jun  7 09:28:05 2008
Subject: [Haskell-cafe] Teaching Monads
In-Reply-To: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>
References: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>
Message-ID: <0A68E976-C842-4049-B17C-F3F6F33032FD@yandex.ru>


On 7 Jun 2008, at 08:05, Ronald Guida wrote:

> What made monads "click" for me is when I understood the following
> things:

Well, in case anybody's interested, I didn't know anything about  
monads before I tried to read the book "Toposes theory" (not sure  
about the exact name, I've read it in Russian) by P.T. Johnstone. It's  
Chapter 0 contained some facts about monads without proofs or even  
definitions. I've looked for some definitions in Mathematical  
Encyclopedia, asked one of my professors about other ones, tried to  
prove all results in this chapter by myself (successfully), and,  
suddenly, found out that I understand what monads are.

Then, while reading YAHT, I've thought a bit, then realized, that  
Haskell monads are the same beast I already know (I didn't know about  
Kleisli triples before), and everything was clear.
From dan.doel at gmail.com  Sat Jun  7 09:49:45 2008
From: dan.doel at gmail.com (Dan Doel)
Date: Sat Jun  7 09:42:21 2008
Subject: [Haskell-cafe] Teaching Monads
In-Reply-To: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>
References: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>
Message-ID: <200806070949.46114.dan.doel@gmail.com>

On Saturday 07 June 2008, Ronald Guida wrote:
> 3. These closures are extremely similar to the closures that arise
>    when desugaring let-syntax.
>
>  let x1 = f1 in            f1 -$ (\x1 ->      Where:
>    let x2 = f2 in          f2 -$ (\x2 ->      (-$) :: a -> (a -> b) -> b
>      let x3 = f3 in        f3 -$ (\x3 ->      x -$ f = f x
>        f x1 x2 x3          f x1 x2 x3)))

In fact, this is the identity monad (this is not valid Haskell, but we'll let 
that slide):

    type Id a = a

    instance Monad Id where
      return a = a
      a >>= f  = f a

    do x1 <- f1             f1 >>= \x1           (\x1 ->
       x2 <- f2             f2 >>= \x2            (\x2 ->
       x3 <- f3             f3 >>= \x3              (\x3 -> f x1 x2 x3) f3)
       return (f x1 x2 x3)  return (f x1 x2 x3)    f2) f1

Which is the same as the lets modulo let-polymorphism and recursive bindings.

(In Haskell, you need a newtype wrapper but it's otherwise the same.)

> OK, so before I attempt to write a monad tutorial based on "manual
> plumbing" and "monadic plumbing", I would like to know, does anyone
> else think this is a good idea?

I think the general consensus is "don't write yet more monad tutorials." If 
you think Wadler's original paper is good, then it doesn't hurt to recommend 
it (you could instead write a "don't be afraid of reading academic papers" 
tutorial :)).

But don't let me stop you, of course. :)

-- Dan
From xj2106 at columbia.edu  Sat Jun  7 10:21:13 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sat Jun  7 10:17:55 2008
Subject: [Haskell-cafe] Issues of the "mailto" link on the list archive page
Message-ID: <873anpxr52.fsf@columbia.edu>

Hi,

I had private conversation with Andrzej Jaworski about the
fact that his reply to Alberto Ruiz's post is off thread.
What he did was clicking on the "mailto" link beside the
author's name on the list archive web page [1].

[1] http://www.haskell.org/pipermail/haskell-cafe/2008-June/044023.html

I am not quite sure about what this link is supposed to do.
But, if it is meant for people to click and reply to the
thread, it is not doing this correctly, as the "Subject" and
"In-Reply-To" fields in the link are obtained from these
fields in the head of current email.  It would be useful if
the link shows "Subject" with an added "Re: " if there is
not already one, and fill in the "in-Reply-To" field with
the value from the "Message-Id" field of current email
head.  An optional "Reference" field is informative for most
of the email client, too.

Sorry if this topic has the least connection to the glorious
Haskell.

Best,
Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From dbueno at gmail.com  Sat Jun  7 10:59:57 2008
From: dbueno at gmail.com (Denis Bueno)
Date: Sat Jun  7 10:52:25 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <48498354.5030506@btinternet.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
Message-ID: <6dbd4d000806070759x7355f70br5f992eeec1f363fd@mail.gmail.com>

On Fri, Jun 6, 2008 at 2:35 PM, Andrew Coppin
<andrewcoppin@btinternet.com> wrote:
> Johan Tibell wrote:
>> 3. Lack of common interfaces.
>>
>
> Yes.
>
> It's really quite frustrating that it is 100% impossible to write a single
> function that will process lists, arrays, sets, maps, byte strings, etc. You
> have to write several different versions. OK, so some functions really don't
> make sense for a set because it's unordered, and some functions don't make
> sense for a map, and so forth. But for example, if I write some complicated
> algorithm that uses a list to store data and I change that to a set instead,
> I now have to wade through the function changing every operation from a
> list-op into a set-op. It's really very annoying!

I can think of at least two ways I have been able to keep generic code
generic, in the way you describe:

1.  Use the Data.Foldable interface.  Lists, Sets, Sequences and Trees
are all foldable.  This doesn't help with your complaint about arrays
and bytestrings, but it's something.  You can do a lot with Foldable.

2. Factor out the operations *your app uses* into a typeclass.  For
some code I was writing I wrote the following interface

-- | Represents a container of type @t@ storing elements of type @a@ that
-- support membership, insertion, and deletion.
class Ord a => Setlike t a where
    -- | The set-like object with an element removed.
    without  :: t -> a -> t
    -- | The set-like object with an element included.
    with     :: t -> a -> t
    -- | Whether the set-like object contains a certain element.
    contains :: t -> a -> Bool

[Aside: This could be made H98 easily, but I didn't need it to be.]

By implementing this class for various types (sets and lists, as well
as a few others I used) I achieved the implementation-agnosticism you
described at fairly low cost.  If I needed to change out a list for an
array, I only changed the code that creates the initial data
structure, or the signature in the actual record containing the type
--- in other words, I only changed what needed to be changed, and the
rest was inferred.

The reason I think it makes sense for *me* to have created and
implemented this interface, instead of a library writer, is that for
each task that is data-structure agnostic in some respect, you will
need a *different* set of operations.  I know which ones I need, so I
should make only those generic.  The library writer, to be generic,
would have to write interfaces for all combinations of operations one
might care about (too many for this not to be a waste of time) and
that *still* wouldn't be good enough, because certain operations have
slightly differing semantics (or signatures) that make genericity
inadvisable (e.g. Set.map does not preserve the length of the input
list, but List.map does.  If your code relies on this rule about
"map", it is bad to use an interface with a "generic" map).

Perhaps there are certain, small, common interfaces --- like Setlike
--- that could be agreed upon.  But some people will always clamor
that it doesn't fit their application, or doesn't have the right
methods.  Which I think is okay, if we don't ask too much of standard
libs.

-- 
Denis
From loup.vaillant at gmail.com  Sat Jun  7 11:31:29 2008
From: loup.vaillant at gmail.com (Loup Vaillant)
Date: Sat Jun  7 11:23:57 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <48498354.5030506@btinternet.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
Message-ID: <6f9f8f4a0806070831p17045ed5x8983fcabf7ed4085@mail.gmail.com>

2008/6/6 Andrew Coppin <andrewcoppin@btinternet.com>:
> Until very recently, it was not at all clear to me that there is actually a
> very simple solution to this problem:
>
>  import Text.ParserCombinators.Parsec as P
>
> Now I only have to write "P.runPaser", which is much shorter.

Err, I have a beginner question, then:
Is there any difference between:

import Very.Long.Module.Name as M

and:

import qualified Very.Long.Module.Name as M

?
Loup
From tphyahoo at gmail.com  Sat Jun  7 12:13:18 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Sat Jun  7 12:05:45 2008
Subject: [Haskell-cafe] installing happy 1.17
Message-ID: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>

I had a problem installing happy 1.17 (same result with happy head).
This appears to be required for installing happs-hsp-template via
cabal install.

thanks for any advice!

Thomas.

*****

thartman@thartman-laptop:~/haskellInstalls/smallInstalls>darcs get
--partial http://darcs.haskell.org/happy/
**********************
Copying patch 87 of 87... done.
Applying patch 86 of 86... done.
Finished getting.

thartman@thartman-laptop:~/haskellInstalls/smallInstalls>cd happy

thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>runghc
Setup.lhs configure

Setup.lhs:30:43: Not in scope: `buildVerbose'
thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>cabal --version
cabal-install version 0.4.9
using version 1.3.12 of the Cabal library
thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>ghc-pkg
list | grep -i cabal
    Cabal-1.2.3.0, Cabal-1.3.11, Cabal-1.3.12, Cabal-1.5.2,
From tphyahoo at gmail.com  Sat Jun  7 12:37:57 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Sat Jun  7 12:30:25 2008
Subject: [Haskell-cafe] ANNOUNCE: Cabal-1.4 release candidate
In-Reply-To: <1212776132.15010.383.camel@localhost>
References: <1212776132.15010.383.camel@localhost>
Message-ID: <910ddf450806070937o4f636f24ua6f3821598037024@mail.gmail.com>

as promised,

sudo cabal install plugins

works out of the box now. that's nice :)

thomas.

2008/6/6 Duncan Coutts <duncan.coutts@worc.ox.ac.uk>:
> Hi everyone,
>
> == Cabal-1.4 release candidate ==
>
> The second release candidate of Cabal-1.4 is out:
> http://haskell.org/cabal/download.html
>
> Please test and report bugs:
> http://hackage.haskell.org/trac/hackage/
>
> The aim for the Cabal-1.4 release is to get various fixes and
> improvements into the hands of developers and to support a release of
> cabal-install.
>
> == cabal-install ==
>
> A snapshot of cabal-install is also available:
> http://haskell.org/cabal/download.html
>
> It requires the zlib and HTTP packages (both are available from
> hackage). Bug reports should go in the same trac as above.
>
> cabal-install is intended to be the standard command line interface to
> the whole Cabal/Hackage system. It replaces the "runhaskell Setup.hs"
> interface and a few other tools you may or may not have heard of
> (cabal-setup, cabal-upload, cabal-get). cabal-install is usable now and
> we will be making a proper release some time after the Cabal-1.4
> release.
>
> == Testing ==
>
> We are particularly interested in finding regressions from Cabal-1.2.x
> or any important fixes that will require API changes since once we
> release 1.4 we have to maintain API compatibility for the rest of the
> 1.4.x series.
>
> This is also an excellent opportunity to make sure your favourite bug or
> feature request is properly described in our bug tracker:
> http://hackage.haskell.org/trac/hackage/
>
> To help us guide development priorities please add yourself to the
> ticket's cc list and describe why that bug or feature is important to
> you.
>
> == Compatibility ==
>
> We have tried to preserve compatibility with all packages that worked
> with the Cabal-1.2.x series. That is, packages that can be built using
> Cabal (including custom Setup.hs scripts) but not packages that directly
> import and use the Cabal API. Packages that directly import and use the
> Cabal api will need updating. This affects packages that build distro
> packages for example, rpm debs etc.
>
> Currently we know of only one package on hackage which has a Setup.hs
> script that compiles with 1.2 but fail to compile with 1.4. Takusen,
> will require an update to be able to work with both Cabal-1.2.x and
> 1.4.x. A patch has been sent to the maintainers of Takusen.
>
> == Credits ==
>
> On behalf of the Cabal hackers and the community generally I'd like to
> thank the large number of people who have contributed patches during
> this development series. Previously I was rather worried that we were
> not getting enough contributors to fix bugs and do new feature
> development, but now I'm very pleased. :-)
>
> == Get involved ==
>
> Of course there's still a lot to do! We have big plans for Cabal-2.0,
> cabal-install and the Hackage website. So if you're interested in
> helping out with this core infrastructure project then:
>
>  * subscribe to the cabal-devel mailing list:
>     http://www.haskell.org/mailman/listinfo/cabal-devel
>
>  * grab the source:
>     http://haskell.org/cabal/code.html
>
>  * read the guide to the source code:
>     http://hackage.haskell.org/trac/hackage/wiki/SourceGuide
>
>  * take a look at our list of bugs and feature requests:
>     http://hackage.haskell.org/trac/hackage/report/12
>   especially the easy tickets:
>     http://hackage.haskell.org/trac/hackage/report/13
>
> Duncan
> (wearing his Cabal release manager hat)
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From dokondr at gmail.com  Sat Jun  7 12:44:35 2008
From: dokondr at gmail.com (Dmitri O.Kondratiev)
Date: Sat Jun  7 12:37:03 2008
Subject: [Haskell-cafe] Newbie Q: Overloading and type classes
Message-ID: <53396d9e0806070944r1c728f37rc2c88bd49eb69475@mail.gmail.com>

{--

I try to define class Store that will group types implmenting different
storage mechanisms .
All types should support two functions:
1) put (key, value) pair into storage
2) get value from storage corresponding to the given key

As an example I start with the following storage types:
--}

-- simple memory cell
data OneCell k v = Cell(k, v)

-- list of cells
data CellList k v = CLst [(k, v)]

{--
First, without grouping these types into any class, just to illustrate what
these types should do, I define the following functions:
--}
{--
put::(k, v) -> OneCell k v -> OneCell k v
put (k1, v1) (Cell(k, v)) = Cell(k1, v1)

get :: Eq k => k -> OneCell k v -> Maybe v
get k (Cell (_, v)) = Just v

c1 ::OneCell String Int
c1 = Cell("one", 1)

putLst :: (k,v) ->  CellList k v -> CellList k v
putLst (k,v) (CLst xs) = CLst ((k,v) : xs)

getLst :: Eq k => k -> CellList k v -> Maybe v
getLst k (CLst xs) = lookup k xs

cl1 = CLst [("one",1),("two",2),("three",3)]
--}

{--
These work as expected.
Now I try to define Store class that should allow me to overload put & get
functions:
--}

class Store s where
    put :: Eq k => (k, v) -> s  -> s
    get :: k s -> Maybe v
{--
instance Store OneCell where
    put (k1, v1) (Cell(k, v)) = Cell(k1, v1)
    get k (Cell (_, v)) = Just v
--}

{--

I get the following error:

 `OneCell' is not applied to enough type arguments
 Expected kind `*', but `OneCell' has kind `* -> * -> *'
 In the instance declaration for `Store OneCell'
--}

instance Store CellList where
    put (k,v) (CLst xs) = CLst ((k,v) : xs)
    get k (CLst xs) = lookup k xs

{--

I get the following error:

`CellList' is not applied to enough type arguments
Expected kind `*', but `CellList' has kind `* -> * -> *'
In the instance declaration for `Store CellList'
--}

What should I do to create Store class?
Thanks!

-- 
Dmitri O. Kondratiev
dokondr@gmail.com
http://www.geocities.com/dkondr
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From derek.a.elkins at gmail.com  Sat Jun  7 12:54:18 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Sat Jun  7 12:46:54 2008
Subject: [Haskell-cafe] Teaching Monads
In-Reply-To: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>
References: <62728db30806062105t455382c4h503651d8427d6da0@mail.gmail.com>
Message-ID: <1212857658.7306.35.camel@derek-laptop>

On Sat, 2008-06-07 at 00:05 -0400, Ronald Guida wrote:
> Monads in Haskell are a topic that I, like most beginners, find
> difficult and "mind-twisting".  Now that I think I understand monads,
> they seem to be very simple; I've read that this is a common
> experience.
> 
> So I wonder, what would it take to help beginners catch on with a
> minimum of fuss or frustration?  The plethora of monad tutorials out
> there is clear evidence that plenty of others have wondered the same
> thing.
> 
> What made monads "click" for me is when I understood the following
> things:
> 
> 1. When monads are being used, closures are almost always involved.
> 
> 2. These closures naturally arise when desugaring do-syntax.
> 
>  do x1 <- m1               m1 >>= (\x1 ->
>     x2 <- m2               m2 >>= (\x2 ->          [Eq1]
>     x3 <- m3               m3 >>= (\x3 ->
>     return (f x1 x2 x3)    return (f x1 x2 x3))))
> 
> 3. These closures are extremely similar to the closures that arise
>    when desugaring let-syntax.
> 
>  let x1 = f1 in            f1 -$ (\x1 ->      Where:
>    let x2 = f2 in          f2 -$ (\x2 ->      (-$) :: a -> (a -> b) -> b
>      let x3 = f3 in        f3 -$ (\x3 ->      x -$ f = f x
>        f x1 x2 x3          f x1 x2 x3)))
> 
> 4. While I can think of a monad as a fancy container that holds an
>    element of type "t", it might be more accurate to think of a monad
>    as a container that merely displays the type "t" as a label for its
>    contents. The container might hold one object of type "t", or it
>    might hold several.  It might not be holding any at all.  Perhaps
>    the container /never/ holds an object of type "t", but instead it
>    holds a set of instructions to produce such an object.
>    (e.g. Reader, State).
> 
> Naturally, it's hard to illustrate nested closures, higher-order
> functions, and objects that aren't really there.  It's easy to
> illustrate a sequential scheme where a single "thing" passes through a
> series of operations, while some related data travels in parallel.
> 
>                    m1 >>= f1 >>= f2 >>= f3        [Eq2]
> 
> In any case, the extreme similarity between desugared "do" and
> desugared "let" leads me to think of the concepts of a manual
> plumbing system and a monadic plumbing system.
> 
> Basically, a manual plumbing system is what I have if I'm threading
> information down through a series of nested function calls in a
> certain stereotypical way.  A monadic plumbing system is what I get
> when I introduce the appropriate monad to encapsulate my threading.
> 
> In fact, if I look at Wadler [*], there are three examples of an
> evaluator that use what I'm calling "manual plumbing".  In section
> 2.5, the operations required of a monad (return, bind) pretty much
> just drop right out.  Wadler even points out the similarity between
> "bind" and "let".
> 
> Now that I finally "get it", I feel that the Wadler paper, section 2.5
> in particular, is probably a better introduction than many of the
> monad tutorials out there.  Moreover, I feel that for /some/ of
> the tutorials out there, they spend too much time and too many
> illustrations explaining things like [Eq2], and then they quickly
> present do-notation and gloss over [Eq1].
> 
> For me, I found that that the concepts of "manual plumbing" and
> "monadic plumbing" were key to actually grasping the Wadler paper and
> understanding what monads are.  In particular, I feel that these two
> concepts might be a way to help other beginners catch on as well.
> 
> OK, so before I attempt to write a monad tutorial based on "manual
> plumbing" and "monadic plumbing", I would like to know, does anyone
> else think this is a good idea?

Why should I recommend a beginner to this tutorial rather than one of
the dozens of others online or, better yet, to Wadler's papers directly
(which is what I do)?

From david.maciver at gmail.com  Sat Jun  7 13:18:15 2008
From: david.maciver at gmail.com (David MacIver)
Date: Sat Jun  7 13:10:45 2008
Subject: [Haskell-Cafe] Quick question for a slow program
In-Reply-To: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
Message-ID: <a1a662200806071018v56254525gf13b6716596f79c3@mail.gmail.com>

On Sat, Jun 7, 2008 at 10:26 AM, Slavomir Kaslev
<slavomir.kaslev@gmail.com> wrote:
> Hello,
>
> I was just brushing my haskell-fu skills writing a solution for Google
> Treasure Hunt Problem 4. Hers is what it looks like:
>
>> primes = sieve [2..]
>>     where
>>       sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]

Read this: www.cs.hmc.edu/~oneill/papers/Sieve-JFP.pdf

This is probably the biggest culprit in your code. :-)
From aruiz at um.es  Sat Jun  7 13:24:54 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Sat Jun  7 13:17:31 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
References: <48492F38.3070107@um.es>	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>	<87prquxqig.fsf@columbia.edu>
	<C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
Message-ID: <484AC466.7030908@um.es>

Xiao-Yong Jin wrote:
 > Salute!  Excellent!
 >
 > Patrick Perry <patperry@stanford.edu> writes:
 >
 >>
 >> 	* Support for both immutable and mutable types. Haskell tries
 >> to make you use immutable types as much as possible, and indeed there
 >> is a  very good reason for this, but sometimes you have a 100MB
 >> matrix, and  it just isn?t very practical to make a copy of it every
 >> time you  modify it. hmatrix only supports immutable types, and HBlas
 >> only  supports mutable ones. I wanted both.
 >
 > I didn't use hmatrix a lot, because I wrote some STUArray
 > things and I wasn't sure what to do with that.  However, I
 > just noticed that there is a bunch of ST growing under
 > Data.Packed in hmatrix.  Guess things is going to change,
 > soon.  And perhaps with your work, Alberto doesn't need to
 > reinvent the wheel anymore.
 >

Sure, in the future the internal modules of hmatrix (if not all of them) 
can be replaced by Patrick's blas and the future lapack. And several 
alternative high level interfaces may coexist as thin layers on the 
underlying computational engine with different goals: from very simple 
interfaces for causal usage to advanced ones for more complex applications.

>>>
>>> a function like foo :: (BLAS1 e) => Matrix (m,n) e ->
>>> Matrix (n,k) e -> Int -> Vector m e foo a b i = let x =
>>> row b i in a <*> x will not type-check. (?<*>? is the
>>> function to multiply a matrix by a vector. Everything is
>>> ok if you replace ?row? by ?col?.) This feature has caught
>>> a few bugs in my code.
>>
>> If I understand this correctly, the compiler can catch
>> dimension mismatches so that using `col' will result in a
>> compilation error when m and k are different, is it so?
> 
> Yes, the compiler infers the type of expression to be
> 
> Matrix(m,n) e -> Matrix (l,m) e -> Int -> Vector n e
> 
> which is different from the declared type.  The error will be something 
> like "Expected type Vector m e, but got type Vector a1 e instead".

And if I understand it correctly, usage is also very practical. You can 
define something like

listVector 3 [1,2,3::Double]

and the dimension type is "free". But if you give a signature you get 
static dimension checking:

listVector 3 [1,2,3] Vector TypeDim3 Double

I like this approach very much. Which types do you recommend for the 
dimensions?

User friendly static dimension checking must be available in any serious 
Haskell linear algebra library. Frederik Eaton also made very 
interesting work on this in his index aware library.

>> I haven't look through the code, yet.  But it looks like
>> there are certain levels of similarities between blas and
>> hmatrix.  Is it possible for these two libraries to
>> cooperate well with each other?  (I didn't look at HBlas, so
>> can't say much about that.)
> 
> This is more work than you might think.  The data structures are 
> different, many of the function names are different, and the module 
> namespaces overlap.  I wouldn't recommend any switch from hmatrix to 
> blas right now unless you really need mutable types-- hmatrix has a lot 
> more linear algebra functionality.

>> Apart from some warnings, the library compiles fine in my
>> system.  But there is a minor issue about the library it
>> links against when `./Setup test'.  I need to use `-lcblas'
>> instead of `-lblas' to get it to link to correct libraries.
>> I don't know other people's system.  But in my system,
>> Gentoo Linux, I use blas library provided by atlas, and
>> libblas.so is a fortran library and libcblas.so is for C.
> 
> I don't know of a good way to get around this.  It seems like every 
> system has a different convention for the location and name of the cblas 
> libraries.  So, everyone has to edit the "extra-libraries" and the 
> "extra-lib-dirs" field in the blas.cabal file.  Does anyone know of a 
> better way of doing this?
> 

(sorry if you receive this again, a previous message seems to be lost)

A possible solution is using flags in the cabal configuration file. For 
instance, I have this in hmatrix.cabal:

if flag(mkl)
  if arch(x86_64)
   extra-libraries: gsl mkl_lapack mkl_intel_lp64 mkl_sequential mkl_core
  else
    extra-libraries: gsl mkl_lapack mkl_intel mkl_sequential mkl_core
else
  extra-libraries: gsl blas lapack

so if I want to link with Intel's MKL optimized blas/lapack instead of 
ATLAS I simply add the -fmkl flag:

runhaskell Setup.lhs configure -fmkl etc.

or even

cabal install hmatrix -fmkl

Other flags can be added to support different distributions. We could 
have something like

cabal install package -ffedora

or

cabal install package -fcblas

etc.

Alberto


From duncan.coutts at worc.ox.ac.uk  Sat Jun  7 13:44:48 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sat Jun  7 13:33:32 2008
Subject: [Haskell-cafe] Re: Fwd: installing happy 1.17
In-Reply-To: <910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
References: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>
	<910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
Message-ID: <1212860688.15010.412.camel@localhost>


On Sat, 2008-06-07 at 09:36 -0700, Thomas Hartman wrote:
> cabal issue?

Yes and no.

What is happening is that there are several versions of the Cabal
library installed. In particular Cabal-1.3.12 and Cabal-1.5.2. The happy
package uses build-type Custom so cabal-install compiles the Setup.lhs
script. The question is what version of the Cabal library should it use?
The happy.cabal file specifies cabal-version: >= 1.2 so we'd better
respect that. But even then we have several choices. Currently it just
picks the highest one of the remaining choices. In this case that meant
Cabal-1.5.2 -- the latest development version. This version turns out to
have API changes that means that we get a type error when compiling
Setup.lhs. As it happens, if cabal-install had picked one of the other
choices then it would have compiled ok because the 1.2.x and upcoming
1.4.x series do not have those api changes.

The immediate workarounds are:
      * unregister Cabal-1.5.2
      * cabal install happy --cabal-lib-version 1.3.12

Perhaps a better solution is for cabal-install to choose the version of
the Cabal library differently. Of course it has to be within the hard
constraints specified in the .cabal file and on the command line. But
after that perhaps it should prefer the version of the Cabal library
that it itself was built with and at second preference the latest
version in the same major series. The last preference would be as now,
the latest version available.

Sound sensible?

Duncan

> ---------- Forwarded message ----------
> From: Thomas Hartman <tphyahoo@gmail.com>
> Date: 2008/6/7
> Subject: installing happy 1.17
> To: haskell <haskell-cafe@haskell.org>
> 
> 
> I had a problem installing happy 1.17 (same result with happy head).
> This appears to be required for installing happs-hsp-template via
> cabal install.
> 
> thanks for any advice!
> 
> Thomas.
> 
> *****
> 
> thartman@thartman-laptop:~/haskellInstalls/smallInstalls>darcs get
> --partial http://darcs.haskell.org/happy/
> **********************
> Copying patch 87 of 87... done.
> Applying patch 86 of 86... done.
> Finished getting.
> 
> thartman@thartman-laptop:~/haskellInstalls/smallInstalls>cd happy
> 
> thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>runghc
> Setup.lhs configure
> 
> Setup.lhs:30:43: Not in scope: `buildVerbose'
> thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>cabal --version
> cabal-install version 0.4.9
> using version 1.3.12 of the Cabal library
> thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>ghc-pkg
> list | grep -i cabal
>    Cabal-1.2.3.0, Cabal-1.3.11, Cabal-1.3.12, Cabal-1.5.2,

From dries at harnie.be  Sat Jun  7 13:58:45 2008
From: dries at harnie.be (Dries Harnie)
Date: Sat Jun  7 13:51:24 2008
Subject: [Haskell-Cafe] Quick question for a slow program
In-Reply-To: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
Message-ID: <20080607195845.5e7ea7b2@kaabuntu.harnie>

On Sat, 7 Jun 2008 12:26:17 +0300
"Slavomir Kaslev" <slavomir.kaslev@gmail.com> wrote:

> I was just brushing my haskell-fu skills writing a solution for Google
> Treasure Hunt Problem 4. Hers is what it looks like:
> 
> > primes = sieve [2..]
> >     where
> >       sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
> >
> > sumOf n l = sum (take n l) : sumOf n (tail l)
> >
> > find l = foldl1 aux l
> >     where
> >       aux (x:xs) (y:ys) | x == y = x : aux xs ys
> >                         | x < y  = aux xs (y:ys)
> >                         | x > y  = aux (x:xs) ys
> >
> > puzzle = find (reverse [primes, p7, p17, p41, p541])
> >     where
> >       p7 = sumOf 7 primes
> >       p17 = sumOf 17 primes
> >       p41 = sumOf 41 primes
> >       p541 = sumOf 541 primes
> >
> > main = do mapM (\x -> putStrLn $ show x) puzzle
> 
> While the code is quite readable and straight forward it is as slow as
> tortoise with four legs broken. What optimizations would you suggest,
> while still keeping the code clear and highlevel?

While I can't quite prove it, I surmise find is wasting a lot of time
tracking down numbers which are sums of three or four of those lists before
continuing.

Here's mine:

> sliding n = map (sum . take n) $ tails primes
> 
> merge (x:xs) (y:ys) | x < y     = x:merge xs (y:ys)
> 	              | otherwise = y:merge (x:xs) ys
> 
> four = filter (\l -> length l == 5) $ group $ foldr1 merge $ map sliding [1,5,43,107,689]

In my original implementation I used an isPrime test at the end, but I like
your approach better (hence the 1 in map sliding).

Does this still count as "clear and highlevel"? :)

Dries Harnie
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From dons at galois.com  Sat Jun  7 14:07:26 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun  7 13:59:57 2008
Subject: [Haskell-cafe] Mersenne Build Problem
In-Reply-To: <484A6A08.4020600@blueyonder.co.uk>
References: <484A6A08.4020600@blueyonder.co.uk>
Message-ID: <20080607180726.GA13289@scytale.galois.com>

dominic.steinitz:
> I'm getting errors (see below) trying to build the tests in
> 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mersenne-random-0.1.1
> 
> I built the package itself using
> 
> ./Setup configure -f use_sse2
> 
> I thought I had an intel core duo (also see below). I think I may be
> missing a library but I'm not sure which one.
> 
> > Unit.o: In function `s4Da_info':
> > (.text+0x1b21): undefined reference to `genrand_real2'
> > Unit.o: In function `s4RA_info':
> > (.text+0x3e75): undefined reference to `genrand_real2'
> > Unit.o: In function `s4S4_info':
> > (.text+0x3f61): undefined reference to `genrand_real2'
> > Unit.o: In function `s5su_info':
> > (.text+0x40bc): undefined reference to `genrand_real2'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `mersennezmrandomzm0zi1zi1_SystemziRandomziMersenne_zdwa2_info':
> > ghc13223_0.hc:(.text+0x1a3): undefined reference to `gen_rand64_mix'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2J1_info':
> > ghc13223_0.hc:(.text+0x91d): undefined reference to `gen_rand64_mix'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2JZ_info':
> > ghc13223_0.hc:(.text+0xb3d): undefined reference to `genrand_real2'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2LJ_info':
> > ghc13223_0.hc:(.text+0xf8d): undefined reference to `gen_rand64_mix'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s35i_info':
> > ghc13223_0.hc:(.text+0x1397): undefined reference to `genrand_real2'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s36A_info':
> > ghc13223_0.hc:(.text+0x1517): undefined reference to `gen_rand64_mix'
> > collect2: ld returned 1 exit status
> > make: *** [all] Error 1
> 

Lookks like the C bits didn't install properly? Possibly your cabal is
very old?
From himself at poczta.nom.pl  Sat Jun  7 15:08:25 2008
From: himself at poczta.nom.pl (Andrzej Jaworski)
Date: Sat Jun  7 14:02:06 2008
Subject: [Haskell-cafe] Patrick Perry's BLAS package
References: <002101c8c81f$6b3d9b00$e9d54c59@bzdryk>
	<20080607023218.GA11462@scytale.galois.com>
Message-ID: <003101c8c8d1$e319ad50$e9d54c59@bzdryk>

On Jun 7, 11:21 am, Don Stewart <d...@galois.com> wrote: 
> The best thing anyone here can do for haskell is contribute a library. 
> The more areas we cover with Haskell code, the easier the path is to 
> ongoing development, and a viable, sustainable Haskell world. 

Hi Don, 
I cannot agree more but: 
(1) I doubt that your consistant contribution and sense of 
responsibility can be replaced by independent volunteers. 
(2) More important than the number of libraries is their maintenance 
and accessibility by which I mean not just sufficient documentation 
but also reviews with pragmatic suggestions and shared experience 
formated into some knoledge base. 
(3) Haskell attracts guys that like originality [ like me;-) ] which 
is dengerous since building viable programming environment should be a 
top down affair. Regular coders are easier to cooperate. 

Conclusion: Some coordination effort is inevitable. Complementary 
librairs should be chained and updated together like toolboxes in 
Matlab, which might encourage writers to dedicate domain specific 
articles or a book around them. 

Cheers, 
-Andrzej Jaworski 


From bertram.felgenhauer at googlemail.com  Sat Jun  7 14:22:36 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Sat Jun  7 14:15:10 2008
Subject: [Haskell-cafe] Mersenne Build Problem
In-Reply-To: <484A6A08.4020600@blueyonder.co.uk>
References: <484A6A08.4020600@blueyonder.co.uk>
Message-ID: <20080607182236.GB4258@zombie.inf.tu-dresden.de>

Dominic Steinitz wrote:
> I'm getting errors (see below) trying to build the tests in
> 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mersenne-random-0.1.1
> 
[snip]
> > Linking Unit ...
> > Unit.o: In function `s4Da_info':
> > (.text+0x1b21): undefined reference to `genrand_real2'
> > Unit.o: In function `s4RA_info':
> > (.text+0x3e75): undefined reference to `genrand_real2'
> > Unit.o: In function `s4S4_info':
> > (.text+0x3f61): undefined reference to `genrand_real2'
> > Unit.o: In function `s5su_info':
> > (.text+0x40bc): undefined reference to `genrand_real2'
> > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/[...]
                                         ^^^^^^^^^^^^^^^^
[snip]

The missing symbols are inlined functions. ghc 6.9 doesn't include the
header files anymore when compiling via C. (The solution is to create
C wrappers around those functions. I guess I'll whip up a patch.)

HTH,

Bertram
From daniel.is.fischer at web.de  Sat Jun  7 14:27:31 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Sat Jun  7 14:18:03 2008
Subject: [Haskell-Cafe] Quick question for a slow program
In-Reply-To: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
Message-ID: <200806072027.31395.daniel.is.fischer@web.de>

Am Samstag, 7. Juni 2008 11:26 schrieb Slavomir Kaslev:
> Hello,
>
> I was just brushing my haskell-fu skills writing a solution for Google
>
> Treasure Hunt Problem 4. Hers is what it looks like:
> > primes = sieve [2..]
> >     where
> >       sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]

That alone breaks at least three of the tortoise's legs.
Simple trial division:
primes = 2:3:filter isPrime [5,7 .. ]

isPrime n
    | n < 2	= False
    | n < 4 = True
    | even n = False
    | otherwise = go (tail primes)
      where
	r = floor $ sqrt (fromIntegral n + 0.5)
	go (p:ps) = (r < p) || (n `mod` p /= 0) && go ps

is orders of magnitude faster. A really good prime generator wins a lot.

> >
> > sumOf n l = sum (take n l) : sumOf n (tail l)

This is also not really good,

sumOf n l = zipWith (-) (drop n sms) sms
      where
	sms = scanl (+) 0 l

is a bit faster, specialising 

primeSums = scanl (+) 0 primes

sumOfPrimes n = zipWith (-) (drop n primeSums) primeSums

a bit more.
I don't see more improvements directly.

> >
> > find l = foldl1 aux l
> >     where
> >       aux (x:xs) (y:ys) | x == y = x : aux xs ys
> >
> >                         | x < y  = aux xs (y:ys)
> >                         | x > y  = aux (x:xs) ys
> >
> > puzzle = find (reverse [primes, p7, p17, p41, p541])
> >     where
> >       p7 = sumOf 7 primes
> >       p17 = sumOf 17 primes
> >       p41 = sumOf 41 primes
> >       p541 = sumOf 541 primes
> >
> > main = do mapM (\x -> putStrLn $ show x) puzzle
>
> While the code is quite readable and straight forward it is as slow as
> tortoise with four legs broken. What optimizations would you suggest,
> while still keeping the code clear and highlevel?
>
> Thank you in advance.
>
> Cheers.

From gsan at stillpsycho.net  Sat Jun  7 14:34:57 2008
From: gsan at stillpsycho.net (=?utf-8?q?G=C3=B6khan_San?=)
Date: Sat Jun  7 14:27:29 2008
Subject: [Haskell-cafe] Dynamic curiosity
Message-ID: <200806072034.57585.gsan@stillpsycho.net>

Hello All,

I've recently modified my existing project to support dynamic data 
(using 'Data.Dynamic'), and despite my earlier benchmarks on 'Dynamic', the 
program slowed down by a factor of 10. Profiler says that 'fromDynamic' is 
consuming 60% of the CPU time (with -O2).

Using the below function instead of 'fromDynamic' seems to make coercion 20 
times faster (thereby solving my problem):

> {-# OPTIONS -fglasgow-exts #-}

> import GHC.Prim

> data Dynamic' = Dynamic' TypeRep Any

> fromDynamic'   :: forall a. Typeable a => Dynamic -> Maybe a
> fromDynamic' d =
>     let Dynamic' t v = unsafeCoerce# d
>     in if t == typeOf (undefined :: a) 
>        then Just (unsafeCoerce# v) 
>        else Nothing  

I was able to reproduce the same result from scratch.

The only difference with the standard implementation (I put it below for 
reference), other than the first ugly unsafeCoerce#, seems to be existential 
quantification (i.e. When I replace "if t == typeOf (undefined :: a) ..." 
with the "case ..." below, performance goes down again.).

> fromDynamic :: Typeable a => Dynamic -> Maybe a
> fromDynamic (Dynamic t v) =
>     case unsafeCoerce v of 
>     r | t == typeOf r -> Just r
>       | otherwise     -> Nothing

So what is causing the improvement, or am I missing something?

Thanks.

-- Gokhan
From duncan.coutts at worc.ox.ac.uk  Sat Jun  7 14:39:20 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sat Jun  7 14:28:03 2008
Subject: [Haskell-cafe] Re: Fwd: installing happy 1.17
In-Reply-To: <1212860688.15010.412.camel@localhost>
References: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>
	<910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
	<1212860688.15010.412.camel@localhost>
Message-ID: <1212863960.15010.413.camel@localhost>


On Sat, 2008-06-07 at 18:44 +0100, Duncan Coutts wrote:

> Perhaps a better solution is for cabal-install to choose the version of
> the Cabal library differently. Of course it has to be within the hard
> constraints specified in the .cabal file and on the command line. But
> after that perhaps it should prefer the version of the Cabal library
> that it itself was built with and at second preference the latest
> version in the same major series. The last preference would be as now,
> the latest version available.
> 
> Sound sensible?

Done:

Sat Jun  7 19:26:00 BST 2008  Duncan Coutts <duncan@haskell.org>
  * Use a smarter preference when picking a Cabal lib to build Setup.hs
  Instead of just using the latest version we use the best version
  according to the following preferences in priority order:
  - the same version as cabal-install was itself built with
  - the same major version number as cabal-install was built with
  - a stable version of Cabal (even second digit of major number)
  - the latest version

Duncan

From daniel.is.fischer at web.de  Sat Jun  7 14:46:34 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Sat Jun  7 14:37:38 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <6f9f8f4a0806070831p17045ed5x8983fcabf7ed4085@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
	<6f9f8f4a0806070831p17045ed5x8983fcabf7ed4085@mail.gmail.com>
Message-ID: <200806072046.34715.daniel.is.fischer@web.de>

Am Samstag, 7. Juni 2008 17:31 schrieb Loup Vaillant:
> 2008/6/6 Andrew Coppin <andrewcoppin@btinternet.com>:
> > Until very recently, it was not at all clear to me that there is actually
> > a very simple solution to this problem:
> >
> >  import Text.ParserCombinators.Parsec as P
> >
> > Now I only have to write "P.runPaser", which is much shorter.
>
> Err, I have a beginner question, then:
> Is there any difference between:
>
> import Very.Long.Module.Name as M
>
> and:
>
> import qualified Very.Long.Module.Name as M

The former lets you access functions from Very.Long.Module.Name also 
unqualified.

>
> ?
> Loup

From bulat.ziganshin at gmail.com  Sat Jun  7 14:44:15 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Sat Jun  7 14:44:34 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <6f9f8f4a0806070831p17045ed5x8983fcabf7ed4085@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
	<6f9f8f4a0806070831p17045ed5x8983fcabf7ed4085@mail.gmail.com>
Message-ID: <1565966080.20080607224415@gmail.com>

Hello Loup,

Saturday, June 7, 2008, 7:31:29 PM, you wrote:
> Is there any difference between:

> import Very.Long.Module.Name as M

> and:

> import qualified Very.Long.Module.Name as M

with first you get *both* qualified and unqualified identifiers, with
second - only qualified


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From lrpalmer at gmail.com  Sat Jun  7 15:08:11 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Sat Jun  7 15:00:37 2008
Subject: [Haskell-cafe] Newbie Q: Overloading and type classes
In-Reply-To: <53396d9e0806070944r1c728f37rc2c88bd49eb69475@mail.gmail.com>
References: <53396d9e0806070944r1c728f37rc2c88bd49eb69475@mail.gmail.com>
Message-ID: <7ca3f0160806071208y3220e9c6r399396c31e0a7ead@mail.gmail.com>

2008/6/7 Dmitri O.Kondratiev <dokondr@gmail.com>:
> class Store s where
>     put :: Eq k => (k, v) -> s  -> s
>     get :: k s -> Maybe v

I suspect you want this to be a constructor class.  That is, you want
to make explicit the fact that the type s depends on k and v.

class Store s where
    put :: Eq k => (k,v) -> s k v -> s k v
    get :: s k v -> Maybe v

If instead you have cell types which are restricted in what they can
store in different ways, you might explore fundeps or associated
types:

-- fundeps
class Store s k v | s -> k v where
    put :: (k,v) -> s -> s
    get :: s -> Maybe v

-- associated types
class Store s where
    type Key s :: *
    type Value s :: *
    put :: (Key s, Value s) -> s -> s
    get :: s -> Maybe (Value s)

But if you can get away with the former, I would recommend that before
looking into these advanced extensions.

Luke
From lrpalmer at gmail.com  Sat Jun  7 15:11:12 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Sat Jun  7 15:03:40 2008
Subject: [Haskell-cafe] Newbie Q: Overloading and type classes
In-Reply-To: <7ca3f0160806071208y3220e9c6r399396c31e0a7ead@mail.gmail.com>
References: <53396d9e0806070944r1c728f37rc2c88bd49eb69475@mail.gmail.com>
	<7ca3f0160806071208y3220e9c6r399396c31e0a7ead@mail.gmail.com>
Message-ID: <7ca3f0160806071211u73a4e50dh4c80dd053f7e8aab@mail.gmail.com>

On Sat, Jun 7, 2008 at 1:08 PM, Luke Palmer <lrpalmer@gmail.com> wrote:
> 2008/6/7 Dmitri O.Kondratiev <dokondr@gmail.com>:
>> class Store s where
>>     put :: Eq k => (k, v) -> s  -> s
>>     get :: k s -> Maybe v
>
> I suspect you want this to be a constructor class.  That is, you want
> to make explicit the fact that the type s depends on k and v.
>
> class Store s where
>    put :: Eq k => (k,v) -> s k v -> s k v
>    get :: s k v -> Maybe v

Oops.  Should be:

    get :: k -> s k v -> Maybe v

And correspondingly for the later examples.  After actually using my
brain thinking about your problem, and reading the word "Newbie", I
would absolutely stay away from the fundeps/associated types business.
 :-)  Try to get this working with Cell and CellList first :-)

Luke

> If instead you have cell types which are restricted in what they can
> store in different ways, you might explore fundeps or associated
> types:
>
> -- fundeps
> class Store s k v | s -> k v where
>    put :: (k,v) -> s -> s
>    get :: s -> Maybe v
>
> -- associated types
> class Store s where
>    type Key s :: *
>    type Value s :: *
>    put :: (Key s, Value s) -> s -> s
>    get :: s -> Maybe (Value s)
>
> But if you can get away with the former, I would recommend that before
> looking into these advanced extensions.
>
> Luke
>
From bertram.felgenhauer at googlemail.com  Sat Jun  7 15:20:45 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Sat Jun  7 15:13:17 2008
Subject: [Haskell-cafe] Re: Fwd: installing happy 1.17
In-Reply-To: <1212860688.15010.412.camel@localhost>
References: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>
	<910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
	<1212860688.15010.412.camel@localhost>
Message-ID: <20080607192045.GF4258@zombie.inf.tu-dresden.de>

Duncan Coutts wrote:
> The immediate workarounds are:
>       * unregister Cabal-1.5.2

Better, hide it (that's reversible) - or does that not work with
cabal-install?

Bertram
From duncan.coutts at worc.ox.ac.uk  Sat Jun  7 15:42:04 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sat Jun  7 15:33:23 2008
Subject: [Haskell-cafe] Re: Fwd: installing happy 1.17
In-Reply-To: <20080607192045.GF4258@zombie.inf.tu-dresden.de>
References: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>
	<910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
	<1212860688.15010.412.camel@localhost>
	<20080607192045.GF4258@zombie.inf.tu-dresden.de>
Message-ID: <1212867724.15010.416.camel@localhost>


On Sat, 2008-06-07 at 21:20 +0200, Bertram Felgenhauer wrote:
> Duncan Coutts wrote:
> > The immediate workarounds are:
> >       * unregister Cabal-1.5.2
> 
> Better, hide it (that's reversible) - or does that not work with
> cabal-install?

If Cabal ignored hidden packages then you could never install packages
that depend on the ghc package since that's always hidden.

Though again we could use that as a preference rather than a hard
constraint.

Duncan

From ryani.spam at gmail.com  Sat Jun  7 16:20:03 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Sat Jun  7 16:15:24 2008
Subject: [Haskell-cafe] example of FFI FunPtr
In-Reply-To: <5ae4f2ba0806060206v6a1b2385vee642df8ccaa01de@mail.gmail.com>
References: <5ae4f2ba0806050038k1e0aea1exe6d81b22b1151eeb@mail.gmail.com>
	<4847B025.8030800@goto10.org>
	<5ae4f2ba0806060008i659a3e16yb179e94cf32ee8ab@mail.gmail.com>
	<5ae4f2ba0806060206v6a1b2385vee642df8ccaa01de@mail.gmail.com>
Message-ID: <2f9b2d30806071320u4fc852dne3e4f5b5784ae723@mail.gmail.com>

2008/6/6 Galchin, Vasili <vigalchin@gmail.com>:
>      I want to do an incremental "experiment". I want just want  to pass a C
> function to "callback" to a Haskell function. ???

This is easy; just declare the function via the FFI; here's an example
from my implementation for the 2006 ICFP contest
(http://www.boundvariable.org/); this interface is used to get access
to a fast C VM from the high-level haskell debugger.  The C VM can
call back into Haskell in order to get and fetch characters from the
console, and to notify the debugger of allocations and frees. The
haskell-side debugger can query the state of the VM via the "get"
functions exported by the VM.

In this example, get_program_size is a first class haskell IO action;
it can be passed around like any other action.  If you know the
function call is referentially transparent (pure), you can leave the
"IO" off of the return result of the function; be careful with this,
it's calling into whatever C-code you are giving and so you should
treat it as carefully as you treat unsafePerformIO.

The "unsafe" keyword allows GHC to optimize certain calls; in order to
use it you need to know that the function won't call back into Haskell
code.

foreign import ccall unsafe load_program :: Ptr Word32 -> Word32 -> IO ()
foreign import ccall execute :: Word32 {-numCycles-}
                                -> FunPtr GetChar
                                -> FunPtr PutChar
                                -> FunPtr Notify {-alloc-}
                                -> FunPtr Notify {-free-}
                                -> IO Word32 {-returnCode 0=success, 1=failure-}
foreign import ccall unsafe get_program :: IO (Ptr Word32)
foreign import ccall unsafe get_program_size :: IO Word32
foreign import ccall unsafe get_registers :: Ptr Word32
foreign import ccall unsafe get_pc :: IO Word32
foreign import ccall unsafe get_prev_pc :: IO Word32
foreign import ccall unsafe set_pc :: Word32 -> IO Bool

type GetChar = IO Word32
type PutChar = Word32 -> IO ()
type Notify = Ptr Word32 -> Word32 -> IO ()
foreign import ccall "wrapper" mkGetChar :: GetChar -> IO (FunPtr GetChar)
foreign import ccall "wrapper" mkPutChar :: PutChar -> IO (FunPtr PutChar)
foreign import ccall "wrapper" mkNotify :: Notify -> IO (FunPtr Notify)
From lanny at cisco.com  Sat Jun  7 17:34:37 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Sat Jun  7 17:27:42 2008
Subject: [Haskell-Cafe] Quick question for a slow program
In-Reply-To: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
Message-ID: <484AFEED.908@cisco.com>

The second prime generator on this page

   http://www.haskell.org/haskellwiki/Prime_numbers

is quick and easy.  I keep it nearby for all those sudden attacks of
needing to solve yet another projecteuler problem.

  -ljr

Slavomir Kaslev wrote:
> Hello,
> 
> I was just brushing my haskell-fu skills writing a solution for Google
> Treasure Hunt Problem 4. Hers is what it looks like:
> 
>> primes = sieve [2..]
>>     where
>>       sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
>>
>> sumOf n l = sum (take n l) : sumOf n (tail l)
>>
>> find l = foldl1 aux l
>>     where
>>       aux (x:xs) (y:ys) | x == y = x : aux xs ys
>>                         | x < y  = aux xs (y:ys)
>>                         | x > y  = aux (x:xs) ys
>>
>> puzzle = find (reverse [primes, p7, p17, p41, p541])
>>     where
>>       p7 = sumOf 7 primes
>>       p17 = sumOf 17 primes
>>       p41 = sumOf 41 primes
>>       p541 = sumOf 541 primes
>>
>> main = do mapM (\x -> putStrLn $ show x) puzzle
> 
> While the code is quite readable and straight forward it is as slow as
> tortoise with four legs broken. What optimizations would you suggest,
> while still keeping the code clear and highlevel?
> 
> Thank you in advance.
> 
> Cheers.
> 
From tphyahoo at gmail.com  Sat Jun  7 17:46:23 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Sat Jun  7 17:40:10 2008
Subject: [Haskell-cafe] Re: Fwd: installing happy 1.17
In-Reply-To: <1212867724.15010.416.camel@localhost>
References: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>
	<910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
	<1212860688.15010.412.camel@localhost>
	<20080607192045.GF4258@zombie.inf.tu-dresden.de>
	<1212867724.15010.416.camel@localhost>
Message-ID: <910ddf450806071446i154926f4ybee2478ea38635fb@mail.gmail.com>

great, sudo cabal install from inside 1.17 distribution dir now seems
to do the right thing.

however, after it's done installing (apparently without error) the
happy version is still 1.16 and the happy executable is from 2006.

This means that I still can't install other packages that rely on happy >=1.17

sudo cabal install haskell-src-exts
Resolving dependencies...
'haskell-src-exts-0.3.4' is cached.
Configuring haskell-src-exts-0.3.4...
cabal: happy version >=1.17 is required but the version found at
/usr/bin/happy is version 1.16
cabal: Error: some packages failed to install:
haskell-src-exts-0.3.4 failed during the configure step. The exception was:
exit: ExitFailure 1


happy-1.17>sudo cabal install
Resolving dependencies...
Warning: defaultUserHooks in Setup script is deprecated.
Configuring happy-1.17...
Warning: No 'build-type' specified. If you do not need a custom Setup.hs or
./configure script then use 'build-type: Simple'.
Preprocessing executables for happy-1.17...
Building happy-1.17...
[ 1 of 18] Compiling Paths_happy      (
dist/build/autogen/Paths_happy.hs,
dist/build/happy/happy-tmp/Paths_happy.o )
Linking dist/build/happy/happy ...
Installing: /home/thartman/.cabal/bin
thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy-1.17>happy
--version
Happy Version 1.16 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c)
1997-2005 Simon Marlow

Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY.
This program is free software; you can redistribute it and/or modify
it under the terms given in the file 'LICENSE' distributed with
the Happy sources.
thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy-1.17>ls
-l `which happy`
-rwxr-xr-x 1 root root 941968 2006-11-23 21:34 /usr/bin/happy
thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy-1.17>




2008/6/7 Duncan Coutts <duncan.coutts@worc.ox.ac.uk>:
>
> On Sat, 2008-06-07 at 21:20 +0200, Bertram Felgenhauer wrote:
>> Duncan Coutts wrote:
>> > The immediate workarounds are:
>> >       * unregister Cabal-1.5.2
>>
>> Better, hide it (that's reversible) - or does that not work with
>> cabal-install?
>
> If Cabal ignored hidden packages then you could never install packages
> that depend on the ghc package since that's always hidden.
>
> Though again we could use that as a preference rather than a hard
> constraint.
>
> Duncan
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From duncan.coutts at worc.ox.ac.uk  Sat Jun  7 18:07:00 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sat Jun  7 17:56:34 2008
Subject: [Haskell-cafe] Re: Fwd: installing happy 1.17
In-Reply-To: <910ddf450806071446i154926f4ybee2478ea38635fb@mail.gmail.com>
References: <910ddf450806070913x3bd5f69cia04724ad37c23eed@mail.gmail.com>
	<910ddf450806070936p44837a8cu4b9d12e386349953@mail.gmail.com>
	<1212860688.15010.412.camel@localhost>
	<20080607192045.GF4258@zombie.inf.tu-dresden.de>
	<1212867724.15010.416.camel@localhost>
	<910ddf450806071446i154926f4ybee2478ea38635fb@mail.gmail.com>
Message-ID: <1212876420.15010.421.camel@localhost>


On Sat, 2008-06-07 at 14:46 -0700, Thomas Hartman wrote:
> great, sudo cabal install from inside 1.17 distribution dir now seems
> to do the right thing.
> 
> however, after it's done installing (apparently without error) the
> happy version is still 1.16 and the happy executable is from 2006.
> 
> This means that I still can't install other packages that rely on happy >=1.17
> 
> sudo cabal install haskell-src-exts
> Resolving dependencies...
> 'haskell-src-exts-0.3.4' is cached.
> Configuring haskell-src-exts-0.3.4...
> cabal: happy version >=1.17 is required but the version found at
> /usr/bin/happy is version 1.16

At the moment by default cabal-install installs binaries to ~/.cabal/bin
which isn't on the $PATH unless you deliberately change your $PATH.

The reason we don't put things directly into ~/bin/ is because some
people worry about cabal-install "clobbering" programs that the user
already had in ~/bin/. One idea for resolving this is:

http://hackage.haskell.org/trac/hackage/ticket/289

We'd very much appreciate feedback on what the right thing to do is and
if the above spec is ok for someone to implement it.

Duncan

From xj2106 at columbia.edu  Sat Jun  7 18:45:01 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sat Jun  7 18:43:40 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
Message-ID: <87y75gx3te.fsf@columbia.edu>

Hi, probably I am just being dumb, but what is the most
efficient way to do a sum of every elements in a Vector of
either hmatrix or blas?  I know there is sum of absolute
values from BLAS.  So what about I want a plain "sum"?

I can only think of the following two ways.


1. Using Data.List.foldl', so it is

> sum' = foldl' (+) 0 . toList

in hmatrix or

> sum' = foldl' (+) 0 . elems

in blas.

2. Using <.>, so it is

> sum' v = constant 1 (dim v) <.> v

in hmatrix or

> sum' v = constant (dim v) 1 <.> v

in blas.


Which one is better?  I guess it probably depends on the
internal implementation of BLAS, but I am actually thinking
in some thing similar to

> t += *v++;

Any delightful idea to convert my mind from a C shaped one
to a Haskell shaped one?

Best,
Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From dokondr at gmail.com  Sat Jun  7 19:07:19 2008
From: dokondr at gmail.com (Dmitri O.Kondratiev)
Date: Sat Jun  7 19:00:46 2008
Subject: [Haskell-cafe] Newbie Q: Overloading and type classes
In-Reply-To: <7ca3f0160806071211u73a4e50dh4c80dd053f7e8aab@mail.gmail.com>
References: <53396d9e0806070944r1c728f37rc2c88bd49eb69475@mail.gmail.com>
	<7ca3f0160806071208y3220e9c6r399396c31e0a7ead@mail.gmail.com>
	<7ca3f0160806071211u73a4e50dh4c80dd053f7e8aab@mail.gmail.com>
Message-ID: <53396d9e0806071607r6f7c3bbepff259a80a923584f@mail.gmail.com>

{--
Thanks!
Yes, you got it right - I "want to make explicit the fact that the type s
depends on k and v.
So I followed your advice and used the most simple way to do what I need:
--}

class Store s where
    put :: Eq k => (k, v) -> s k v -> s k v
    get :: Eq k => k -> s k v -> Maybe v

instance Store OneCell where
    put (k1, v1) (Cell(k, v)) = Cell(k1, v1)
    get k (Cell (_, v)) = Just v

instance Store CellList where
    put (k,v) (CLst xs) = CLst ((k,v) : xs)
    get k (CLst xs) = lookup k xs


storePut :: (Store s, Eq k)  => s k v -> k -> v -> s k v
storePut store key value = put (key, value) store

storeGet :: (Store s, Eq k) => k -> s k v -> Maybe v
storeGet key store = get key store

aCell :: OneCell String Int
aCell = Cell("one", 1)
lst :: CellList Int String
lst = CLst [(1, "one"),(2, "two"),(3, "three")]

st1 = storePut aCell "two" 2
st2 = storePut lst 4 "four"

-- v1 = storeGet "one" st2 -- error
v2 = storeGet "one" st1 -- ok

{--
And what does the word "newbie" imply to you when answering my question?
In what case using 'fundeps' and 'associated types' will make sence for this
example?
--}

Thanks again for your great help!
Dima

On Sat, Jun 7, 2008 at 11:11 PM, Luke Palmer <lrpalmer@gmail.com> wrote:

>
> Oops.  Should be:
>
>    get :: k -> s k v -> Maybe v
>
> And correspondingly for the later examples.  After actually using my
> brain thinking about your problem, and reading the word "Newbie", I
> would absolutely stay away from the fundeps/associated types business.
>  :-)  Try to get this working with Cell and CellList first :-)
>
> Luke
>

> > If instead you have cell types which are restricted in what they can
> > store in different ways, you might explore fundeps or associated
> > types:
> >
> > -- fundeps
> > class Store s k v | s -> k v where
> >    put :: (k,v) -> s -> s
> >    get :: s -> Maybe v
> >
> > -- associated types
> > class Store s where
> >    type Key s :: *
> >    type Value s :: *
> >    put :: (Key s, Value s) -> s -> s
> >    get :: s -> Maybe (Value s)
> >
> > But if you can get away with the former, I would recommend that before
> > looking into these advanced extensions.
> >
> > Luke
> >
>



-- 
Dmitri O. Kondratiev
dokondr@gmail.com
http://www.geocities.com/dkondr
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From thomas.dubuisson at gmail.com  Sun Jun  8 01:11:49 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Sun Jun  8 00:59:33 2008
Subject: [Haskell-cafe] [ANN] Bindings to Xen Control (xenctrl.h)
In-Reply-To: <1212380364.2448.39.camel@Clunker>
References: <1212300682.2448.14.camel@Clunker>
	<20080601063140.GA1200@scytale.galois.com>
	<1212380364.2448.39.camel@Clunker>
Message-ID: <1212901910.2430.7.camel@Clunker>

Version 0.0.3 was release, which is nearly a complete (and completely
trivial) xenctrl.h binding.  Aside from unit tests and programs, the
main things missing are grant table operations.  There is now a quick
and dirty home page at the wiki [1] and a darcs repo on c.h.o [2].
Comments, requests, and contributions are all encouraged.

TomMD

P.S. I intend to finish the bindings then move onto
design/implementation of the higher level 'System.Xen' module when time
permits.

[1] http://haskell.org/haskellwiki/HsXenCtrl
[2] http://code.haskell.org/~tommd/hsXenCtrl

On Mon, 2008-06-02 at 00:19 -0400, Thomas M. DuBuisson wrote:
> Don,
> I'll throw future work ideas in the next releases cabal.  The most
> obvious doors opened are Haskell rewrites of the current Xen
> infrastructure (virt-install, xm, xend).  Slightly more interesting
> tasks could be (warning: random thoughts):
> 
> 1) HAPPS server that can manage Xen domains (without requiring python
> libs or System.cmd)
> 2) Network or BSD socket based remote management programs in Haskell.
> haxr or session-types might be of use here.
> 3) With the functions that can alter the CPUs availability, more complex
> rules or sharing arrangements could be implemented.  Same concept
> applies to other resources such as PCI and memory allocation.  Seeing as
> Xen doesn't over-commit memory, a guest VM program that detects low/high
> memory situations and reports to the host for policy controlled
> balloning (adjustment of VM allocated memory) would be kind of fun...
> but probably complete overkill for any user of Xen.
> 
> Right now I think the bindings are enough for an 'xm' replacement but
> nothing more.  I've over doubled the number of functions bound just now.
> There will probably be regular releases for the next few weeks as I find
> time.
> 
> Thomas
> 
> On Sat, 2008-05-31 at 23:31 -0700, Don Stewart wrote: 
> > thomas.dubuisson:
> > > All,
> > > I'm just getting started with hsXenCtrl [1] as both a fun way to play
> > > with Xen and become proficient with Haskell FFI.  Once I get my
> > > community.haskell.org account squared away I'll likely setup a public
> > > darcs repo (and a homepage somewhere).
> > > 
> > > As for modules: I intend to expand on the trival FFI bindings in
> > > System.Xen.CBindings and there'll be a higher level interface in
> > > System.Xen (functions will standardize on returning Either or throwing
> > > exceptions, hiding the xc_handle open/close, etc).
> > > 
> > > Typical Disclaimers:
> > > The _only_ thing I've actually done with this, just tonight, is pause /
> > > unpause domains.  API is subject to change!  Only my exact build of Xen
> > > is sure to work, and no promise even then.
> > > 
> > > TomMD
> > > 
> > > [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl
> > 
> > Good stuff. Perhaps the synopsis should include a link or description of
> > the typical use cases/ thinks we might achieve?
> > 
> > -- Don

From lrpalmer at gmail.com  Sun Jun  8 02:18:38 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Sun Jun  8 02:11:06 2008
Subject: [Haskell-cafe] Newbie Q: Overloading and type classes
In-Reply-To: <53396d9e0806071607r6f7c3bbepff259a80a923584f@mail.gmail.com>
References: <53396d9e0806070944r1c728f37rc2c88bd49eb69475@mail.gmail.com>
	<7ca3f0160806071208y3220e9c6r399396c31e0a7ead@mail.gmail.com>
	<7ca3f0160806071211u73a4e50dh4c80dd053f7e8aab@mail.gmail.com>
	<53396d9e0806071607r6f7c3bbepff259a80a923584f@mail.gmail.com>
Message-ID: <7ca3f0160806072318t369cfc54gb9eb50d884459a74@mail.gmail.com>

On Sat, Jun 7, 2008 at 5:07 PM, Dmitri O.Kondratiev <dokondr@gmail.com> wrote:
> {--
> And what does the word "newbie" imply to you when answering my question?
> In what case using 'fundeps' and 'associated types' will make sence for this
> example?
> --}

Well, functional dependencies ("fundeps") and associated types are
"advanced" extensions to the language (not Haskell98), and I
personally would not consider it a good idea to approach them until
you have a good handle on typeclasses.  Actually, associated types are
not that bad, save for the peculiar restrictions on what is possible
to define (because of decidability issues).  Fundeps are a bit
stranger, IMO..

However, since you asked, I'll here try to expound a situation in
which you might need associated types.

Let's say you have a CellHash type that very efficiently stores
key-value pairs, but only if the key is a string.  So you have:

data CellHash v = ...

In the simple case, there is no way to make this an instance of Store,
since Store requires a constructor with two parameters.  And we can't
really hack around it, because an instance of Store must support *any*
key type by definition.

Instead, we can use associated types, which associate *types* to
instances in a class.  These associated types will tell us about the
acceptable keys and values of a particular instance:

class Store s where
    type Key s :: *
    type Value s :: *
    put :: (Key s, Value s) -> s -> s
    get :: Key s -> s -> Value s

The ":: *" annotates the kind of the result; for 'normal' value types
it is *, for constructors with one parameter it is "* -> *", etc.

It is straightforward to implement Store for your Cell and CellList.

instance Store (Cell k v) where  -- note that this is not "instance
Store Cell" anymore
    type Key (Cell k v) = k
    type Value (Cell k v) = v
    -- as before

But now we can make an instance for CellHash too:

instance Store (CellHash v) where
    type Key (CellHash v) = String
    type Value (CellHash v) = v
    -- straightforward

There's a situation where you would want to use associated types.  But
they are quite new, and can be hard to work with because of all the
restrictions on their creation.  For example, IIRC something like this
would be illegal in the above instance:

    type Key (CellHash v) = HashKey String StringHashPolicy

Because the right hand side is larger in terms of number of symbols
than the left.  This is untested, and I'm unsure of my knowledge here,
so take the former with a grain of salt.

Fundeps could be used to achieve the same thing, but are not without
their caveats.

Luke
From dominic.steinitz at blueyonder.co.uk  Sun Jun  8 03:51:24 2008
From: dominic.steinitz at blueyonder.co.uk (Dominic Steinitz)
Date: Sun Jun  8 03:44:02 2008
Subject: [Haskell-cafe] Re: Mersenne Build Problem
References: <484A6A08.4020600@blueyonder.co.uk>
	<20080607182236.GB4258@zombie.inf.tu-dresden.de>
Message-ID: <loom.20080608T074544-409@post.gmane.org>

Bertram Felgenhauer <bertram.felgenhauer <at> googlemail.com> writes:

> 
> The missing symbols are inlined functions. ghc 6.9 doesn't include the
> header files anymore when compiling via C. (The solution is to create
> C wrappers around those functions. I guess I'll whip up a patch.)
> 

Bertram,

Thanks. That's done the trick. I tried 0.1.1 and it works with 6.8 and 0.1.2 
works with 6.9.

It certainly is a lot faster than system.random.

Dominic.

From johan.tibell at gmail.com  Sun Jun  8 04:55:36 2008
From: johan.tibell at gmail.com (Johan Tibell)
Date: Sun Jun  8 04:48:01 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <200806070903.02682.dan.doel@gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<48498354.5030506@btinternet.com>
	<200806070903.02682.dan.doel@gmail.com>
Message-ID: <90889fe70806080155r62ce1fc2v300d6667ef45c70f@mail.gmail.com>

On Sat, Jun 7, 2008 at 3:03 PM, Dan Doel <dan.doel@gmail.com> wrote:
> On Friday 06 June 2008, Andrew Coppin wrote:
>> It's really quite frustrating that it is 100% impossible to write a
>> single function that will process lists, arrays, sets, maps, byte
>> strings, etc. You have to write several different versions. OK, so some
>> functions really don't make sense for a set because it's unordered, and
>> some functions don't make sense for a map, and so forth. But for
>> example, if I write some complicated algorithm that uses a list to store
>> data and I change that to a set instead, I now have to wade through the
>> function changing every operation from a list-op into a set-op. It's
>> really very annoying!
>
> It's not 100% impossible, depending on what exactly you're doing. For
> instance...
>
>  Set a, ByteStrings, Seq a, Map k a and [a] are Monoids
>  Set, Array i, Map k, Tree, Seq and [] are Foldable functors
>  Array i, Map k, Tree, Seq, Tree and [] are Traversable functors
>
> Those can get you lots of operations (folds, maps, unions...) although there
> may be gaps that could be filled (Foldable is sufficient to define null, for
> instance, but it isn't in Data.Foldable).

These do help in the case you want to traverse data structures that
share a set of properties (e.g. are Functors). However, it doesn't
address the problem of sharing an interface among Set, IntSet,
ByteSet, etc. In other words there's a need for a Set type class.
Hopefully type families will help us write such an interface and keep
it efficient.

Cheers,

Johan
From toman144 at student.liu.se  Sun Jun  8 08:54:17 2008
From: toman144 at student.liu.se (Tomas Andersson)
Date: Sun Jun  8 08:46:51 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <87y75gx3te.fsf@columbia.edu>
References: <87y75gx3te.fsf@columbia.edu>
Message-ID: <200806081454.18467.toman144@student.liu.se>

Den Sunday 08 June 2008 00.45.01 skrev Xiao-Yong Jin:

> Any delightful idea to convert my mind from a C shaped one
> to a Haskell shaped one?
>

 You can never go wrong with a good old fashioned hand written tail recursion 
when you're in doubt, they are pretty much the closest thing to for-loops 
there is in haskell and should be easy to grok for Imperative programmers and 
usually produce really fast code.

sum vect = let d = dim vect
           in sum' (d - 1) 0
  where sum' 0 s = s + (vect @> 0)
        sum' index s = sum' (index - 1) (s + (vect @> index))


 I don't know the hmatrix api very well, but if there is a function for 
computing the inner product between two vectors you could always do something 
like the following meta code:

sum v = innerProduct v <1,1,1,1,1,1>


> Best,
> Xiao-Yong


From igloo at earth.li  Sun Jun  8 09:38:11 2008
From: igloo at earth.li (Ian Lynagh)
Date: Sun Jun  8 09:30:37 2008
Subject: [Haskell-cafe] Data.Map traversal.
In-Reply-To: <484A8DFE.7030209@ipmce.ru>
References: <484A8DFE.7030209@ipmce.ru>
Message-ID: <20080608133811.GA8068@matrix.chaos.earth.li>


Hi Serguey,

On Sat, Jun 07, 2008 at 05:32:46PM +0400, Serguey Zefirov wrote:
> 
> So I propose to include those operations into next version of Data.Map.
> 
> If anyone could point me in the right direction I could do any necessary 
> modifications myself (just because I need it).

Please see http://www.haskell.org/haskellwiki/Library_submissions for
how to propose changes to the libraries.


Thanks
Ian

From igloo at earth.li  Sun Jun  8 09:41:38 2008
From: igloo at earth.li (Ian Lynagh)
Date: Sun Jun  8 09:34:01 2008
Subject: [Haskell-cafe] Issues of the "mailto" link on the list archive
	page
In-Reply-To: <873anpxr52.fsf@columbia.edu>
References: <873anpxr52.fsf@columbia.edu>
Message-ID: <20080608134138.GB8068@matrix.chaos.earth.li>

On Sat, Jun 07, 2008 at 10:21:13AM -0400, Xiao-Yong Jin wrote:
> 
> I had private conversation with Andrzej Jaworski about the
> fact that his reply to Alberto Ruiz's post is off thread.
> What he did was clicking on the "mailto" link beside the
> author's name on the list archive web page [1].
> 
> [1] http://www.haskell.org/pipermail/haskell-cafe/2008-June/044023.html
> 
> I am not quite sure about what this link is supposed to do.
> But, if it is meant for people to click and reply to the
> thread, it is not doing this correctly, as the "Subject" and
> "In-Reply-To" fields in the link are obtained from these
> fields in the head of current email.  It would be useful if
> the link shows "Subject" with an added "Re: " if there is
> not already one, and fill in the "in-Reply-To" field with
> the value from the "Message-Id" field of current email
> head.  An optional "Reference" field is informative for most
> of the email client, too.

If anyone knows how we can make mailman do this better, please let us
know.


Thanks
Ian

From apfelmus at quantentunnel.de  Sun Jun  8 09:44:58 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Sun Jun  8 09:37:40 2008
Subject: [Haskell-cafe] Re: Quick question for a slow program
In-Reply-To: <484AFEED.908@cisco.com>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>
	<484AFEED.908@cisco.com>
Message-ID: <g2gnoq$ncq$1@ger.gmane.org>

Lanny Ripple wrote:
> The second prime generator on this page
> 
>    http://www.haskell.org/haskellwiki/Prime_numbers
> 
> is quick and easy.  I keep it nearby for all those sudden attacks of
> needing to solve yet another projecteuler problem.

The second prime sieve did not create an implicit heap as advertised. 
I've fixed that and also cleaned up the page a bit, moving this sieve to 
the section "Implicit Heap".


Regards,
apfelmus

From xj2106 at columbia.edu  Sun Jun  8 10:15:01 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sun Jun  8 10:11:53 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <200806081454.18467.toman144@student.liu.se> (Tomas Andersson's
	message of "Sun, 8 Jun 2008 14:54:17 +0200")
References: <87y75gx3te.fsf@columbia.edu>
	<200806081454.18467.toman144@student.liu.se>
Message-ID: <87r6b8vwre.fsf@columbia.edu>

Tomas Andersson <toman144@student.liu.se> writes:

>  You can never go wrong with a good old fashioned hand written tail recursion 
> when you're in doubt, they are pretty much the closest thing to for-loops 
> there is in haskell and should be easy to grok for Imperative programmers and 
> usually produce really fast code.
>
> sum vect = let d = dim vect
>            in sum' (d - 1) 0
>   where sum' 0 s = s + (vect @> 0)
>         sum' index s = sum' (index - 1) (s + (vect @> index))
>

Do I need the strict version of sum'?  Put something like

sum' a b | a `seq` b `seq` False = undefined

Or ghc will optimize it automatically?  I always don't know
when such optimization is useful.

>
>
>  I don't know the hmatrix api very well, but if there is a function for 
> computing the inner product between two vectors you could always do something 
> like the following meta code:
>
> sum v = innerProduct v <1,1,1,1,1,1>

I just doubt the efficiency here.  If v is a very large
vector, I guess the allocation time of that intermediate
vector [1,1..] is not small.  But it is just my guess.

Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From judah.jacobson at gmail.com  Sun Jun  8 14:01:45 2008
From: judah.jacobson at gmail.com (Judah Jacobson)
Date: Sun Jun  8 13:54:08 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
References: <48492F38.3070107@um.es>
	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>
	<87prquxqig.fsf@columbia.edu>
	<C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
Message-ID: <6d74b0d20806081101n34e1d99l567c551f82b156ec@mail.gmail.com>

2008/6/6 Patrick Perry <patperry@stanford.edu>:
>
> Apart from some warnings, the library compiles fine in my
> system.  But there is a minor issue about the library it
> links against when `./Setup test'.  I need to use `-lcblas'
> instead of `-lblas' to get it to link to correct libraries.
> I don't know other people's system.  But in my system,
> Gentoo Linux, I use blas library provided by atlas, and
> libblas.so is a fortran library and libcblas.so is for C.
>
> I don't know of a good way to get around this.  It seems like every system
> has a different convention for the location and name of the cblas libraries.
>  So, everyone has to edit the "extra-libraries" and the "extra-lib-dirs"
> field in the blas.cabal file.  Does anyone know of a better way of doing
> this?
>

My preference is to use an autoconf script to solve that problem.
("build-type: Configure" in the cabal file.)

For example, the editline and readline C libraries require termcap,
which may be linked using one of -lcurses, -ltermcap, etc.  The
Haskell packages have a configure script which checks which of
curses/termcap is available and outputs an editline.buildinfo file
with the extra-libraries field filled in.  That file is then used
automatically by cabal in the build and install phases.

See for example:
http://code.haskell.org/editline/editline.cabal
http://code.haskell.org/editline/configure.ac
http://code.haskell.org/editline/editline.buildinfo.in

There's also more information is in the Cabal manual:
http://haskell.org/cabal/release/latest/doc/users-guide/x30.html#system-dependent

Best,
-Judah
From dons at galois.com  Sun Jun  8 14:33:35 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  8 14:25:59 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <87r6b8vwre.fsf@columbia.edu>
References: <87y75gx3te.fsf@columbia.edu>
	<200806081454.18467.toman144@student.liu.se>
	<87r6b8vwre.fsf@columbia.edu>
Message-ID: <20080608183335.GA18015@scytale.galois.com>

xj2106:
> Tomas Andersson <toman144@student.liu.se> writes:
> 
> >  You can never go wrong with a good old fashioned hand written tail recursion 
> > when you're in doubt, they are pretty much the closest thing to for-loops 
> > there is in haskell and should be easy to grok for Imperative programmers and 
> > usually produce really fast code.
> >
> > sum vect = let d = dim vect
> >            in sum' (d - 1) 0
> >   where sum' 0 s = s + (vect @> 0)
> >         sum' index s = sum' (index - 1) (s + (vect @> index))
> >
> 
> Do I need the strict version of sum'?  Put something like
> 
> sum' a b | a `seq` b `seq` False = undefined
> 
> Or ghc will optimize it automatically?  I always don't know
> when such optimization is useful.

If you give a type annotation, so GHC can tell its an atomic type, like
Int or Double, 's' will be inferred as strict. But if in doubt, use bang
patterns:

    {-# LANGUAGE BangPatterns #-}

    sum vect = sum' (d-1) 0
        where
            d = dim vect
            
            go :: Int -> Double -> Double           -- for example
            go 0 s = s + (vect @> 0)
            go !i !s = go (i-1) (s + (vect @> i))


See this recent post on understanding how these kind of loops are compiled,

    http://cgi.cse.unsw.edu.au/~dons/blog/2008/05/16

The core for your loop should look very good, assuming @> is efficient.

-- Don
From aruiz at um.es  Sun Jun  8 15:27:11 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Sun Jun  8 15:19:42 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <87r6b8vwre.fsf@columbia.edu>
References: <87y75gx3te.fsf@columbia.edu>	<200806081454.18467.toman144@student.liu.se>
	<87r6b8vwre.fsf@columbia.edu>
Message-ID: <484C328F.5080205@um.es>

Xiao-Yong Jin wrote:
> Tomas Andersson <toman144@student.liu.se> writes:
> 
>>  You can never go wrong with a good old fashioned hand written tail recursion 
>> when you're in doubt, they are pretty much the closest thing to for-loops 
>> there is in haskell and should be easy to grok for Imperative programmers and 
>> usually produce really fast code.
>>
>> sum vect = let d = dim vect
>>            in sum' (d - 1) 0
>>   where sum' 0 s = s + (vect @> 0)
>>         sum' index s = sum' (index - 1) (s + (vect @> index))
>>
> 
> Do I need the strict version of sum'?  Put something like
> 
> sum' a b | a `seq` b `seq` False = undefined
> 
> Or ghc will optimize it automatically?  I always don't know
> when such optimization is useful.
> 
>>
>>  I don't know the hmatrix api very well, but if there is a function for 
>> computing the inner product between two vectors you could always do something 
>> like the following meta code:
>>
>> sum v = innerProduct v <1,1,1,1,1,1>
> 
> I just doubt the efficiency here.  If v is a very large
> vector, I guess the allocation time of that intermediate
> vector [1,1..] is not small.  But it is just my guess.

My experience is that Haskell allocation time is very fast and usually 
negligible in most non trivial matrix computations.

A good thing about

sum v = constant 1 (dim v) <.> v

is that a constant vector is efficiently created internally (not from an 
intermediate Haskell list), and the inner product will be computed by 
the possibly optimized blas version available in your machine.

You can also write simple definitions like the next one for the average 
of the rows of a matrix as a simple vector-matrix product:

mean m = w <> m
     where w = constant k r
           r = rows m
           k = 1 / fromIntegral r

I prefer high level "index free" matrix operations to C-like code. 
Definitions are clearer, have less bugs, and are also more efficient if 
you use optimized numerical libs.

In any case, many algorithms can be solved by the recursive approach 
described by Tomas.

Alberto

> 
> Xiao-Yong
From lanny at cisco.com  Sun Jun  8 18:21:45 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Sun Jun  8 18:14:03 2008
Subject: [Haskell-cafe] Re: Quick question for a slow program
In-Reply-To: <g2gnoq$ncq$1@ger.gmane.org>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>	<484AFEED.908@cisco.com>
	<g2gnoq$ncq$1@ger.gmane.org>
Message-ID: <484C5B79.3060405@cisco.com>

At least when I teased apart why the first one worked it looked
heap-like.  Each step of the foldr pulled off the smallest nonprime
and merged the next two lists guaranteeing that the next smallest
nonprime would be at the head of the next step.

Can't argue with results though.  The version you have up is about
twice as fast as the old one (if a bit harder to read).

  -ljr

apfelmus wrote:
> Lanny Ripple wrote:
>> The second prime generator on this page
>>
>>    http://www.haskell.org/haskellwiki/Prime_numbers
>>
>> is quick and easy.  I keep it nearby for all those sudden attacks of
>> needing to solve yet another projecteuler problem.
> 
> The second prime sieve did not create an implicit heap as advertised.
> I've fixed that and also cleaned up the page a bit, moving this sieve to
> the section "Implicit Heap".
> 
> 
> Regards,
> apfelmus
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From catanzar at EECS.Berkeley.EDU  Sun Jun  8 19:28:49 2008
From: catanzar at EECS.Berkeley.EDU (Bryan Catanzaro)
Date: Sun Jun  8 19:21:21 2008
Subject: [Haskell-cafe] Printing a random list
Message-ID: <4D711340-1377-433C-8E1C-122003B979EF@EECS.Berkeley.EDU>

I'm just starting out with Haskell, and I could use some help.  I'm  
trying to create a random list and print it out, which seems simple  
enough, but has been giving me problems.  Here's what I have:

module Main
     where
       import IO
       import Random

       randomList :: Random a => a -> a-> [IO a]
       randomList lbound ubound = randomRIO(lbound, ubound) :  
randomList lbound ubound


       main = do
         myRandomList <- sequence(randomList(0::Int 255))
         putStrLn(show(take(10 myRandomList)))



-----

So, I have tried to make a randomList action which defines an infinite  
random list, bounded by lbound and ubound.  It seems that to print  
this, I need to convert between randomList, which is of type [IO a] to  
something like IO [a], which is what sequence should do for me.  Then  
I just want to print out the first 10 elements.

I'm currently getting the error "Only unit numeric type pattern is  
valid", pointing to 0::Int 255 in the code.  I'm not sure what this  
means.

I'm sure I'm looking at this the wrong way, since I'm new to Haskell  
and haven't quite wrapped my head around it yet.  Maybe you can fix  
the problem by showing me a more Haskell approach to creating a random  
list and printing it...  =)

Thanks!

- bryan catanzaro

From dons at galois.com  Sun Jun  8 19:33:11 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  8 19:25:34 2008
Subject: [Haskell-cafe] Printing a random list
In-Reply-To: <4D711340-1377-433C-8E1C-122003B979EF@EECS.Berkeley.EDU>
References: <4D711340-1377-433C-8E1C-122003B979EF@EECS.Berkeley.EDU>
Message-ID: <20080608233311.GB18376@scytale.galois.com>

catanzar:
> I'm just starting out with Haskell, and I could use some help.  I'm  
> trying to create a random list and print it out, which seems simple  
> enough, but has been giving me problems.  Here's what I have:
> 
> module Main
>     where
>       import IO
>       import Random
> 
>       randomList :: Random a => a -> a-> [IO a]
>       randomList lbound ubound = randomRIO(lbound, ubound) :  
> randomList lbound ubound
> 
> 
>       main = do
>         myRandomList <- sequence(randomList(0::Int 255))
>         putStrLn(show(take(10 myRandomList)))
> 
> 
> 
> -----
> 
> So, I have tried to make a randomList action which defines an infinite  
> random list, bounded by lbound and ubound.  It seems that to print  
> this, I need to convert between randomList, which is of type [IO a] to  
> something like IO [a], which is what sequence should do for me.  Then  
> I just want to print out the first 10 elements.
> 
> I'm currently getting the error "Only unit numeric type pattern is  
> valid", pointing to 0::Int 255 in the code.  I'm not sure what this  
> means.

Missing parenthesis around the (0 :: Int) type annotation.

> I'm sure I'm looking at this the wrong way, since I'm new to Haskell  
> and haven't quite wrapped my head around it yet.  Maybe you can fix  
> the problem by showing me a more Haskell approach to creating a random  
> list and printing it...  =)
> 

For lists, best to use the randomRs function,

    import System.Random

    main = do
        g <- newStdGen
        print (take 10 (randomRs (0,255) g :: [Int]))

Running it:

    $ runhaskell A.hs
    [11,90,187,119,240,57,241,52,143,86]

Cheers,
  Don
From xj2106 at columbia.edu  Sun Jun  8 19:40:55 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sun Jun  8 19:37:50 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <484C328F.5080205@um.es> (Alberto Ruiz's message of "Sun, 08 Jun
	2008 21:27:11 +0200")
References: <87y75gx3te.fsf@columbia.edu>
	<200806081454.18467.toman144@student.liu.se>
	<87r6b8vwre.fsf@columbia.edu> <484C328F.5080205@um.es>
Message-ID: <877iczwl4o.fsf@columbia.edu>

Alberto Ruiz <aruiz@um.es> writes:

> My experience is that Haskell allocation time is very fast and usually
> negligible in most non trivial matrix computations.
>
> A good thing about
>
> sum v = constant 1 (dim v) <.> v
>
> is that a constant vector is efficiently created internally (not from
> an intermediate Haskell list), and the inner product will be computed
> by the possibly optimized blas version available in your machine.
>
> You can also write simple definitions like the next one for the
> average of the rows of a matrix as a simple vector-matrix product:
>
> mean m = w <> m
>     where w = constant k r
>           r = rows m
>           k = 1 / fromIntegral r
>
> I prefer high level "index free" matrix operations to C-like
> code. Definitions are clearer, have less bugs, and are also more
> efficient if you use optimized numerical libs.
>
> In any case, many algorithms can be solved by the recursive approach
> described by Tomas.

After reading don's blog, I tried to make a test with both
methods.  The code is very simple, as following

module Main where
import System
import Numeric.LinearAlgebra

vsum1 :: Vector Double -> Double
vsum1 v = constant 1 (dim v) <.> v

vsum2 :: Vector Double -> Double
vsum2 v = go (d - 1) 0
    where
      d = dim v
      go :: Int -> Double -> Double
      go 0 s = s + (v @> 0)
      go !j !s = go (j - 1) (s + (v @> j))


mean :: Vector Double -> Double
mean v = vsum v / fromIntegral (dim v)
    where vsum = vsum1

main :: IO ()
main = do
  fn:nrow:ncol:_ <- getArgs
  print . mean . flatten =<< fromFile fn (read nrow, read ncol)

Compile it with "-O2 -optc-O2", and run with a data set of
length 5000000.  The results are

with "vsum1":
 80,077,984 bytes allocated in the heap
      2,208 bytes copied during GC (scavenged)
         64 bytes copied during GC (not scavenged)
 40,894,464 bytes maximum residency (2 sample(s))
  %GC time       0.0%  (0.0% elapsed)
  Alloc rate    35,235,448 bytes per MUT second
./vsum1 huge 5000000 1  2.25s user 0.09s system 99% cpu 2.348 total

This is reasonable, exactly two copies of vector with size
of 40MB.

with "vsum2":
560,743,120 bytes allocated in the heap
     19,160 bytes copied during GC (scavenged)
     15,920 bytes copied during GC (not scavenged)
 40,919,040 bytes maximum residency (2 sample(s))
  %GC time       0.3%  (0.3% elapsed)
  Alloc rate    222,110,261 bytes per MUT second
./mean2 huge 5000000 1  2.53s user 0.06s system 99% cpu 2.598 total

This is strange.  A lot of extra usage of heap?  Probably
because '@>' is not efficient?  So it looks like the
inner-product approach wins with a fairly margin.
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From catanzar at EECS.Berkeley.EDU  Sun Jun  8 19:46:51 2008
From: catanzar at EECS.Berkeley.EDU (Bryan Catanzaro)
Date: Sun Jun  8 19:39:16 2008
Subject: [Haskell-cafe] Printing a random list
In-Reply-To: <20080608233311.GB18376@scytale.galois.com>
References: <4D711340-1377-433C-8E1C-122003B979EF@EECS.Berkeley.EDU>
	<20080608233311.GB18376@scytale.galois.com>
Message-ID: <9DDAB370-CE8F-4EA8-B287-0995F3CD7055@EECS.Berkeley.EDU>

Thanks for the response, it does compile after I juggled some  
parentheses around.  And also I appreciate the pointer to the better  
way of making a random list.  So that problem is solved.

However, when I ran my random list generator, the interpreter had a  
stack overflow.  Here's my code again:
---
module Main
     where
       import IO
       import Random

       randomList :: Random a => a -> a-> [IO a]
       randomList lbound ubound = randomRIO(lbound, ubound) :  
randomList lbound ubound


       main = do
         myRandomList <- sequence(randomList (0::Int) 255)
         putStrLn(show(take 10 myRandomList))
---

It seems that this code somehow tries to evaluate every element of the  
infinite list defined by randomList.  Can you tell me why it is not  
lazily evaluating this list?  I can get around this by changing main  
to do this instead:

---
       main = do
         myRandomList <- sequence(take 10 (randomList (0::Int) 255))
         putStrLn(show(myRandomList))
---

But I don't understand why sequence(randomList (0::Int) 255) actually  
tries to evaluate the entire infinite list, instead of just lazily  
defining a list with the proper types, that I evaluate later when I  
take elements from it.

Thanks for your help!

- bryan

On Jun 8, 2008, at 4:33 PM, Don Stewart wrote:

> catanzar:
>> I'm just starting out with Haskell, and I could use some help.  I'm
>> trying to create a random list and print it out, which seems simple
>> enough, but has been giving me problems.  Here's what I have:
>>
>> module Main
>>    where
>>      import IO
>>      import Random
>>
>>      randomList :: Random a => a -> a-> [IO a]
>>      randomList lbound ubound = randomRIO(lbound, ubound) :
>> randomList lbound ubound
>>
>>
>>      main = do
>>        myRandomList <- sequence(randomList(0::Int 255))
>>        putStrLn(show(take(10 myRandomList)))
>>
>>
>>
>> -----
>>
>> So, I have tried to make a randomList action which defines an  
>> infinite
>> random list, bounded by lbound and ubound.  It seems that to print
>> this, I need to convert between randomList, which is of type [IO a]  
>> to
>> something like IO [a], which is what sequence should do for me.  Then
>> I just want to print out the first 10 elements.
>>
>> I'm currently getting the error "Only unit numeric type pattern is
>> valid", pointing to 0::Int 255 in the code.  I'm not sure what this
>> means.
>
> Missing parenthesis around the (0 :: Int) type annotation.
>
>> I'm sure I'm looking at this the wrong way, since I'm new to Haskell
>> and haven't quite wrapped my head around it yet.  Maybe you can fix
>> the problem by showing me a more Haskell approach to creating a  
>> random
>> list and printing it...  =)
>>
>
> For lists, best to use the randomRs function,
>
>    import System.Random
>
>    main = do
>        g <- newStdGen
>        print (take 10 (randomRs (0,255) g :: [Int]))
>
> Running it:
>
>    $ runhaskell A.hs
>    [11,90,187,119,240,57,241,52,143,86]
>
> Cheers,
>  Don

From bos at serpentine.com  Sun Jun  8 20:01:48 2008
From: bos at serpentine.com (Bryan O'Sullivan)
Date: Sun Jun  8 19:54:54 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <6d74b0d20806081101n34e1d99l567c551f82b156ec@mail.gmail.com>
References: <48492F38.3070107@um.es>	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>	<87prquxqig.fsf@columbia.edu>	<C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
	<6d74b0d20806081101n34e1d99l567c551f82b156ec@mail.gmail.com>
Message-ID: <484C72EC.2010003@serpentine.com>

Judah Jacobson wrote:

> My preference is to use an autoconf script to solve that problem.
> ("build-type: Configure" in the cabal file.)

That approach would not work well for BLAS.  The various BLAS libraries
have profoundly different performance characteristics, and you wouldn't
want to get the wrong one for your system, if you had both installed.

	<b
From dons at galois.com  Sun Jun  8 20:16:22 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  8 20:08:49 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <877iczwl4o.fsf@columbia.edu>
References: <87y75gx3te.fsf@columbia.edu>
	<200806081454.18467.toman144@student.liu.se>
	<87r6b8vwre.fsf@columbia.edu> <484C328F.5080205@um.es>
	<877iczwl4o.fsf@columbia.edu>
Message-ID: <20080609001622.GC18376@scytale.galois.com>

Below are some notes on this for Simon PJ and Alberto.

In general, GHC is doing very well here, with only one small wibble preventing the 
recursive version running as fast as the C version.

xj2106:
> Alberto Ruiz <aruiz@um.es> writes:
> 
> > My experience is that Haskell allocation time is very fast and usually
> > negligible in most non trivial matrix computations.
> >
> > A good thing about
> >
> > sum v = constant 1 (dim v) <.> v
> >
> > is that a constant vector is efficiently created internally (not from
> > an intermediate Haskell list), and the inner product will be computed
> > by the possibly optimized blas version available in your machine.
> >
> > You can also write simple definitions like the next one for the
> > average of the rows of a matrix as a simple vector-matrix product:
> >
> > mean m = w <> m
> >     where w = constant k r
> >           r = rows m
> >           k = 1 / fromIntegral r
> >
> > I prefer high level "index free" matrix operations to C-like
> > code. Definitions are clearer, have less bugs, and are also more
> > efficient if you use optimized numerical libs.
> >
> > In any case, many algorithms can be solved by the recursive approach
> > described by Tomas.
> 
> After reading don's blog, I tried to make a test with both
> methods.  The code is very simple, as following
> 
> module Main where
> import System
> import Numeric.LinearAlgebra
> 
> vsum1 :: Vector Double -> Double
> vsum1 v = constant 1 (dim v) <.> v
> 
> vsum2 :: Vector Double -> Double
> vsum2 v = go (d - 1) 0
>     where
>       d = dim v
>       go :: Int -> Double -> Double
>       go 0 s = s + (v @> 0)
>       go !j !s = go (j - 1) (s + (v @> j))
> 
> 
> mean :: Vector Double -> Double
> mean v = vsum v / fromIntegral (dim v)
>     where vsum = vsum1
> 
> main :: IO ()
> main = do
>   fn:nrow:ncol:_ <- getArgs
>   print . mean . flatten =<< fromFile fn (read nrow, read ncol)
> 
> Compile it with "-O2 -optc-O2", and run with a data set of
> length 5000000.  The results are
> 
> with "vsum1":
>  80,077,984 bytes allocated in the heap
>       2,208 bytes copied during GC (scavenged)
>          64 bytes copied during GC (not scavenged)
>  40,894,464 bytes maximum residency (2 sample(s))
>   %GC time       0.0%  (0.0% elapsed)
>   Alloc rate    35,235,448 bytes per MUT second
> ./vsum1 huge 5000000 1  2.25s user 0.09s system 99% cpu 2.348 total
> 
> This is reasonable, exactly two copies of vector with size
> of 40MB.
> 
> with "vsum2":
> 560,743,120 bytes allocated in the heap
>      19,160 bytes copied during GC (scavenged)
>      15,920 bytes copied during GC (not scavenged)
>  40,919,040 bytes maximum residency (2 sample(s))
>   %GC time       0.3%  (0.3% elapsed)
>   Alloc rate    222,110,261 bytes per MUT second
> ./mean2 huge 5000000 1  2.53s user 0.06s system 99% cpu 2.598 total
> 
> This is strange.  A lot of extra usage of heap?  Probably
> because '@>' is not efficient?  So it looks like the
> inner-product approach wins with a fairly margin.

Yes, I'd suspect that @> isn't fully unlifted, so you get some heap
allocation on each index, each time around the loop? We'd have to look
at how @> was defined to spot why. 

I began with:
    
    $ cabal install hmatrix

which failed, due to missing linking against gfortran and glscblas
Added those to the cabal file, and hmatrix was installed.

Looking at the core we get from vsum2, we see:

vsum2 compiles quite well

      $wgo_s1Nn :: Int# -> Double# -> Double#

      $wgo_s1Nn =
        \ (ww3_s1Mc :: Int#) (ww4_s1Mg :: Double#) ->
          case ww3_s1Mc of ds_X17R {
            __DEFAULT ->
              case Data.Packed.Internal.Vector.$wat
                     @ Double Foreign.Storable.$f9 ww_s1Ms ww1_s1Mu (I# ds_X17R)
              of { D# y_a1KQ ->
              $wgo_s1Nn (-# ds_X17R 1) (+## ww4_s1Mg y_a1KQ)
              };
            0 -> +## ww4_s1Mg ww2_s1M7
          };
    } in  $wgo_s1Nn (-# ww_s1Ms 1) 0.0

But note the return value from $wat is boxed, only to be immediately
unboxed. That looks to be the source of the heap allocations.

Let's see if we can help that.

Vector is defined as:

    data Vector t = V { dim  :: Int              -- ^ number of elements
                      , fptr :: ForeignPtr t     -- ^ foreign pointer to the memory block
                      }

While a much better definition would be:

   data Vector t = V { dim  :: {-# UNPACK #-} !Int               -- ^ number of elements
                     , fptr :: {-# UNPACK #-} !(ForeignPtr t)    -- ^ foreign pointer to the memory block
                     }
     
And we can add some inlining to at' and at.
That might be enough for GHC to see through to the D# boxing.

Now they're fully unfolded and specialised into our source program,

                    True ->
                      case unsafeDupablePerformIO
                             @ Double
                             ((\ (eta1_a1KA :: State# RealWorld) ->
                                 case noDuplicate# eta1_a1KA of s'_a1KB { __DEFAULT ->
                                 case readDoubleOffAddr# @ RealWorld ww1_s1NB ds_X184 s'_a1KB
                                 of wild2_a1Lc { (# s2_a1Le, x_a1Lf #) ->
                                 case touch# @ ForeignPtrContents ww2_s1NC s2_a1Le
                                 of s_a1KS { __DEFAULT ->
     BAD    ----->               (# s_a1KS, D# x_a1Lf #)
                                 }
                                 }
                                 })
                              `cast` (sym ((:CoIO) Double)
                                      :: State# RealWorld
                                         -> (# State# RealWorld, Double #)
                                           ~
                                         IO Double))
                      of wild11_a1LC { D# y_a1LE ->
                      $wgo_s1Oz (-# ds_X184 1) (+## ww4_s1Nq y_a1LE)

But still the readDoubleOffAddr# result is boxed into D#, and then unboxed in the loop.
A GHC optimiser flaw? Possibly the same as:

    http://hackage.haskell.org/trac/ghc/ticket/2289

Simon PJ, does that seem right?


While vsum1 is pretty much unoptimised calls into C;

    vsum1 :: Data.Packed.Internal.Vector.Vector Double
                  -> Double

    vsum1 =
      \ (v_anC :: Data.Packed.Internal.Vector.Vector Double) ->
        Numeric.LinearAlgebra.Linear.dot
          @ Double
          Data.Packed.Internal.Matrix.$f2
          (Data.Packed.Internal.Matrix.$sconstantAux
             Data.Packed.Internal.Matrix.cconstantR
             lit
             (case v_anC of tpl_B2 { Data.Packed.Internal.Vector.V ipv_B3 ipv1_B4 ->
              ipv_B3
              }))
          v_anC

Alberto, I would modify the other types in hmatrix similary,

    data Matrix t = MC { rows :: {-# UNPACK #-} !Int, ... cols :: !Int, cdat :: !(Vector t) }
                  | MF { rows :: {-# UNPACK #-} !Int, ...cols :: !Int, fdat :: !(Vector t) }

ensuring we can keep these things in registers. But it would be wise to have some
benchmarking too. Alberto, what do you think? Do you have some test data we could
play with to see if unboxing the haskell skin over the underlying C calls helps
with Haskell-side loops and iterative calls?

In general, though, hmatrix looks *very* well written. I'd have good
confidence in this library for performance work.

-- Don
From xj2106 at columbia.edu  Sun Jun  8 20:15:55 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sun Jun  8 20:12:50 2008
Subject: [Haskell-cafe] Re: Patrick Perry's BLAS package
In-Reply-To: <484C72EC.2010003@serpentine.com> (Bryan O'Sullivan's message of
	"Sun, 08 Jun 2008 17:01:48 -0700")
References: <48492F38.3070107@um.es>
	<D9C5AC31-9F18-4A85-B3F8-70BFDDFA42B8@stanford.edu>
	<87prquxqig.fsf@columbia.edu>
	<C8A60588-F028-403A-8422-4CDE5A9D0A6D@stanford.edu>
	<6d74b0d20806081101n34e1d99l567c551f82b156ec@mail.gmail.com>
	<484C72EC.2010003@serpentine.com>
Message-ID: <87y75fv4xw.fsf@columbia.edu>

"Bryan O'Sullivan" <bos@serpentine.com> writes:

> Judah Jacobson wrote:
>
>> My preference is to use an autoconf script to solve that problem.
>> ("build-type: Configure" in the cabal file.)
>
> That approach would not work well for BLAS.  The various BLAS libraries
> have profoundly different performance characteristics, and you wouldn't
> want to get the wrong one for your system, if you had both installed.

Is the blas library linked statically?  It looks to me that
the binary is dynamically linked.

	linux-vdso.so.1 =>  (0x00007fff003fe000)
	libgsl.so.0 => /usr/lib/libgsl.so.0 (0x00002af4aa8cc000)
	libblas.so.0 => /usr/lib/libblas.so.0 (0x00002af4aac91000)
	liblapack.so.0 => /usr/lib/liblapack.so.0 (0x00002af4aaeb0000)
	libutil.so.1 => /lib/libutil.so.1 (0x00002af4ab612000)
	libdl.so.2 => /lib/libdl.so.2 (0x00002af4ab815000)
	libm.so.6 => /lib/libm.so.6 (0x00002af4aba19000)
	libgmp.so.3 => /usr/lib/libgmp.so.3 (0x00002af4abc9b000)
	librt.so.1 => /lib/librt.so.1 (0x00002af4abedb000)
	libc.so.6 => /lib/libc.so.6 (0x00002af4ac0e4000)
	libgslcblas.so.0 => /usr/lib/libgslcblas.so.0 (0x00002af4ac424000)
	libgfortran.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/libgfortran.so.1 (0x00002af4ac654000)
	libatlas.so.0 => /usr/lib/libatlas.so.0 (0x00002af4ac8eb000)
	libpthread.so.0 => /lib/libpthread.so.0 (0x00002af4ad123000)
	libcblas.so.0 => /usr/lib/libcblas.so.0 (0x00002af4ad33e000)
	libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00002af4ad55d000)
	/lib64/ld-linux-x86-64.so.2 (0x00002af4aa6b0000)

And presumably the various BLAS implementations share
identical interface.  You can still change the library at
run-time with LD_LIBRARY_PATH.  Or am I missing something?

Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From oddron at gmail.com  Sun Jun  8 20:25:41 2008
From: oddron at gmail.com (Ronald Guida)
Date: Sun Jun  8 20:18:02 2008
Subject: [Haskell-cafe] Printing a random list
In-Reply-To: <9DDAB370-CE8F-4EA8-B287-0995F3CD7055@EECS.Berkeley.EDU>
References: <4D711340-1377-433C-8E1C-122003B979EF@EECS.Berkeley.EDU>
	<20080608233311.GB18376@scytale.galois.com>
	<9DDAB370-CE8F-4EA8-B287-0995F3CD7055@EECS.Berkeley.EDU>
Message-ID: <62728db30806081725r4b57898w859e74bb3866adb8@mail.gmail.com>

Bryan Catanzaro wrote:
> However, when I ran my random list generator, the interpreter had a stack
> overflow.  Here's my code again:
> ---
> module Main
>    where
>      import IO
>      import Random
>
>      randomList :: Random a => a -> a-> [IO a]
>      randomList lbound ubound = randomRIO(lbound, ubound) : randomList
> lbound ubound
>
>
>      main = do
>        myRandomList <- sequence(randomList (0::Int) 255)
>        putStrLn(show(take 10 myRandomList))
> ---
>
> It seems that this code somehow tries to evaluate every element of the
> infinite list defined by randomList.

You are correct.

> Can you tell me why it is not lazily evaluating this list?

Whenever you use IO, there is a baton being passed along behind the
scenes.  The baton is called "RealWorld#" and it represents the fact
that interactions with global state and the outside world have to be
serialized.

In particular, whenever you use the global random number generator, a
global state variable has to be updated.  This has to be serialized,
thus the baton has to be passed along from one action to the next.

When you "sequence" a list of IO actions, you are effectively sending
the baton along that list, and you don't get it back until the end of
the list is reached.  Your code is sending the baton into an infinite
list of actions, never to be returned.

>  I can get around this by changing main to do this
> instead:
>
> ---
>      main = do
>        myRandomList <- sequence(take 10 (randomList (0::Int) 255))
>        putStrLn(show(myRandomList))
> ---

Now you are sending the baton into a list of only 10 actions.  The
baton comes back, and the program goes on.

If you don't know in advance how many random numbers you need, and if
you are satisfied with the global random number generator, then Don
Stewart's solution is a better approach.

Don Stewart wrote:
>   main = do
>         g <- newStdGen
>         print (take 10 (randomRs (0,255) g :: [Int]))

If you want to be able to reproduce the same sequence of random
numbers, for example for testing and debugging purposes, then you can
use mkStdGen to create your own random number generator, independent
of the global one.  The catch is that you will have to thread the
state of the random number generator through your code.  Once you
learn about monads (if you haven't already), you'll recognize that you
can use the State monad for your random number generator.
From dons at galois.com  Sun Jun  8 21:25:25 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun  8 21:17:49 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <20080609001622.GC18376@scytale.galois.com>
References: <87y75gx3te.fsf@columbia.edu>
	<200806081454.18467.toman144@student.liu.se>
	<87r6b8vwre.fsf@columbia.edu> <484C328F.5080205@um.es>
	<877iczwl4o.fsf@columbia.edu>
	<20080609001622.GC18376@scytale.galois.com>
Message-ID: <20080609012525.GA18748@scytale.galois.com>


Problem solved. The Haskell loop now wins.

> > After reading don's blog, I tried to make a test with both
> > methods.  The code is very simple, as following
> > 
> > module Main where
> > import System
> > import Numeric.LinearAlgebra
> > 
> > vsum1 :: Vector Double -> Double
> > vsum1 v = constant 1 (dim v) <.> v
> > 
> > vsum2 :: Vector Double -> Double
> > vsum2 v = go (d - 1) 0
> >     where
> >       d = dim v
> >       go :: Int -> Double -> Double
> >       go 0 s = s + (v @> 0)
> >       go !j !s = go (j - 1) (s + (v @> j))
> > 
> > 
> > mean :: Vector Double -> Double
> > mean v = vsum v / fromIntegral (dim v)
> >     where vsum = vsum1
> > 
> > main :: IO ()
> > main = do
> >   fn:nrow:ncol:_ <- getArgs
> >   print . mean . flatten =<< fromFile fn (read nrow, read ncol)
> > 
> > Compile it with "-O2 -optc-O2", and run with a data set of
> > length 5000000.  The results are
> > 
> > with "vsum1":
> >  80,077,984 bytes allocated in the heap
> >       2,208 bytes copied during GC (scavenged)
> >          64 bytes copied during GC (not scavenged)
> >  40,894,464 bytes maximum residency (2 sample(s))
> >   %GC time       0.0%  (0.0% elapsed)
> >   Alloc rate    35,235,448 bytes per MUT second
> > ./vsum1 huge 5000000 1  2.25s user 0.09s system 99% cpu 2.348 total
> > 
> > This is reasonable, exactly two copies of vector with size
> > of 40MB.
> > 
> > with "vsum2":
> > 560,743,120 bytes allocated in the heap
> >      19,160 bytes copied during GC (scavenged)
> >      15,920 bytes copied during GC (not scavenged)
> >  40,919,040 bytes maximum residency (2 sample(s))
> >   %GC time       0.3%  (0.3% elapsed)
> >   Alloc rate    222,110,261 bytes per MUT second
> > ./mean2 huge 5000000 1  2.53s user 0.06s system 99% cpu 2.598 total
> > 
> > This is strange.  A lot of extra usage of heap?  Probably
> > because '@>' is not efficient?  So it looks like the
> > inner-product approach wins with a fairly margin.
  
> Looking at the core we get from vsum2, we see:
> 
> vsum2 compiles quite well
> 
>       $wgo_s1Nn :: Int# -> Double# -> Double#
> 
>       $wgo_s1Nn =
>         \ (ww3_s1Mc :: Int#) (ww4_s1Mg :: Double#) ->
>           case ww3_s1Mc of ds_X17R {
>             __DEFAULT ->
>               case Data.Packed.Internal.Vector.$wat
>                      @ Double Foreign.Storable.$f9 ww_s1Ms ww1_s1Mu (I# ds_X17R)
>               of { D# y_a1KQ ->
>               $wgo_s1Nn (-# ds_X17R 1) (+## ww4_s1Mg y_a1KQ)
>               };
>             0 -> +## ww4_s1Mg ww2_s1M7
>           };
>     } in  $wgo_s1Nn (-# ww_s1Ms 1) 0.0
> 
> But note the return value from $wat is boxed, only to be immediately
> unboxed. That looks to be the source of the heap allocations.
> 
> Let's see if we can help that.

Ah, of course. The problem is the unsafePerformIO used to wrap up the
'peek'. This blocks the optimisations somewhat, after we unpack the Vector type.. 

So if we rewrite 'safeRead' to not use unsafePerformIO, but instead:

    safeRead v = inlinePerformIO . withForeignPtr (fptr v)

    inlinePerformIO (IO m) = case m realWorld# of (# _, r #) -> r

Along with this change to Vector:

    data Vector t = V { dim  :: {-# UNPACK #-} !Int
                      , fptr :: {-# UNPACK #-} !(ForeignPtr t)
                      }

and some inlining for the bounds checks.
Following bytestrings, we see the performance go from, with a 180M input
file:
    
Goal:
    vsum1:
        $ ghc-core A.hs -optc-O2 -fvia-C  -fbang-patterns
        $ time ./A data 4000 2500
        0.9999727441161678

        ./A data 4000 2500  5.37s user 0.20s system 99% cpu 5.609 total
        160,081,136 bytes allocated in the heap
        155 Mb total memory in use

Before:
vsum2-old:

         $wgo_s1Ns =
        \ (ww3_s1Me :: Int#) (ww4_s1Mi :: Double#) ->
          case ww3_s1Me of ds_X17Y {
            __DEFAULT ->
              case Data.Packed.Internal.Vector.$wat
                     @ Double Foreign.Storable.$f9 ww_s1Mu ww1_s1Mw (I# ds_X17Y)
              of wild1_a1Hg { D# y_a1Hi ->
              $wgo_s1Ns (-# ds_X17Y 1) (+## ww4_s1Mi y_a1Hi)
              };
            0 -> +## ww4_s1Mi ww2_s1M9
          };
    } in  $wgo_s1Ns (-# ww_s1Mu 1) 0.0
 
    ./A data 4000 2500 +RTS -sstderr 
    0.999972744115876

    ./A data 4000 2500 +RTS -sstderr  6.04s user 0.15s system 99% cpu 6.203 total    
    1,121,416,400 bytes allocated in the heap
    78 Mb total memory in use

After:
    True ->
          case readDoubleOffAddr#
                 @ RealWorld ww1_s1Nr ds_X180 realWorld#
          of wild2_a1HS { (# s2_a1HU, x_a1HV #) ->
          case touch# @ ForeignPtrContents ww2_s1Ns s2_a1HU
          of s_a1HG { __DEFAULT ->
          $wgo_s1Ok (-# ds_X180 1) (+## ww4_s1Ng x_a1HV)
          }

    No needless boxing.

    $ time ./A data 4000 2500 +RTS -sstderr          
    ./A data 4000 2500 +RTS -sstderr 
    0.999972744115876

    ./A data 4000 2500 +RTS -sstderr  5.41s user 0.10s system 99% cpu 5.548 total
     80,071,072 bytes allocated in the heap

    78 Mb total memory in use

And the total runtime and allocation now is better than the fully 'C' version.
Yay.

Patch attached to the darcs version of hmatrix.
Similar changes can likely be done to the other data types in hmatrix,
for pretty much ideal code.

-- Don
    
-------------- next part --------------
Sun Jun  8 18:21:18 PDT 2008  Don Stewart <dons@galois.com>
  * Use unpacking and inlining to ensure Vector can be stored unlifted at runtime

New patches:

[Use unpacking and inlining to ensure Vector can be stored unlifted at runtime
Don Stewart <dons@galois.com>**20080609012118] {
hunk ./lib/Data/Packed/Internal/Vector.hs 24
+import GHC.Base
+import GHC.IOBase
+
hunk ./lib/Data/Packed/Internal/Vector.hs 28
-data Vector t = V { dim  :: Int              -- ^ number of elements
-                  , fptr :: ForeignPtr t     -- ^ foreign pointer to the memory block
+data Vector t = V { dim  :: {-# UNPACK #-} !Int              -- ^ number of elements
+                  , fptr :: {-# UNPACK #-}!(ForeignPtr t)    -- ^ foreign pointer to the memory block
hunk ./lib/Data/Packed/Internal/Vector.hs 59
-safeRead v = unsafePerformIO . withForeignPtr (fptr v)
+safeRead v = inlinePerformIO . withForeignPtr (fptr v)
+{-# INLINE safeRead #-}
+
+inlinePerformIO :: IO a -> a
+inlinePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
+{-# INLINE inlinePerformIO #-}
hunk ./lib/Data/Packed/Internal/Vector.hs 88
+{-# INLINE at #-}
}

Context:

[range checking and other additions to the mutable interface
Alberto Ruiz <aruiz@um.es>**20080606154148] 
[safe wrappers and examples/parallel.hs
Alberto Ruiz <aruiz@um.es>**20080606120801] 
[really add Data.Packed.ST.hs
Alberto Ruiz <aruiz@um.es>**20080605123525] 
[added acknowledgement to Bulat
Alberto Ruiz <aruiz@um.es>**20080605122046] 
[remove updateVector and updateMatrix
Alberto Ruiz <aruiz@um.es>**20080605121008] 
[first version of Data.Packed.ST
Alberto Ruiz <aruiz@um.es>**20080605120440] 
[Data.Packed.Convert
Alberto Ruiz <aruiz@um.es>**20080603090037] 
[added updateMatrix
Alberto Ruiz <aruiz@um.es>**20080601120950] 
[added updateVector
Alberto Ruiz <aruiz@um.es>**20080601113907] 
[TAG 0.3.0.0
Alberto Ruiz <aruiz@um.es>**20080527125906] 
Patch bundle hash:
189a5974a11e189e967d537176cf24e388e332e3
From goalieca at gmail.com  Sun Jun  8 22:15:15 2008
From: goalieca at gmail.com (Ryan Dickie)
Date: Sun Jun  8 22:07:38 2008
Subject: [Haskell-cafe] Vancouver Haskell users meeting
In-Reply-To: <20080606043330.GA3478@cyberberry.com>
References: <48444E7C.7050602@moonloop.net>
	<20080606043330.GA3478@cyberberry.com>
Message-ID: <4c69c1be0806081915i558f6214i6b1b90eb03a3487c@mail.gmail.com>

Same deal but i'm in Ottawa for the summer. I'll be back around september.

--ryan

2008/6/6 Asumu Takikawa <asumu@cyberberry.com>:
> Hi. I'd be interested in a meeting like this, but unfortunately since
> UBC is done for winter term I'm out of Canada for the summer. If anyone
> organizes a meet-up come fall I'd happily attend.
>
> Cheers,
> AT
>
> On 12:48 Mon 02 Jun     , Jon Strait wrote:
>>    Anyone else here from Vancouver (Canada)?  I thought it would be great
>>    to have a little informal get-together at a local cafe and share how
>>    we're currently using Haskell, or really anything (problems,
>>    comparisons, useful software tools, etc.) in relation to Haskell.
>>    I'm scheduling a meeting for this Thursday, June 5th. for 7PM at
>>    [1]Waazubee Cafe.  (At Commercial Dr. and 1st Ave.)
>>    They have wireless internet access.  I'll get a table near the back,
>>    bring my laptop, and will have a copy of Hudak's SOE book (the front
>>    cover is impossible to miss) out on the table.
>>    If anyone wants to meet, but this Thursday is not a good day for you,
>>    let me know what days are better and we'll move the meeting.  If anyone
>>    is sure that they will come this Thursday, you might let me know, so I
>>    can have an idea about the resistance in changing the day, if needed.
>>    Thanks,
>>    Jon
>>
>> References
>>
>>    1. http://www.waazubee.com/content/directions.php
>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.6 (GNU/Linux)
>
> iD8DBQFISL4aPVZMXBlgx7ERAv/OAJwP/1bfduqEa6bTBEaOV3420puRKACfU+Pa
> sZtx9R39ZlrrjUp8/zMlNhk=
> =+LbA
> -----END PGP SIGNATURE-----
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
From vigalchin at gmail.com  Sun Jun  8 22:17:14 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sun Jun  8 22:09:40 2008
Subject: [Haskell-cafe] FunPtr error?
Message-ID: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>

Hello,

     I am getting what is to me a mysterious error in a test case that I am
writing:
vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
Setup.lhs build
Preprocessing executables for Test-1.0...
Building Test-1.0...
[1 of 1] Compiling Main             ( ./timer.hs,
dist/build/timer/timer-tmp/Main.o )

./timer.hs:11:45: Not in scope: data constructor `FunPtr'

It seems like the compiler is complaining about the lack of FunPtr in it's
symbol table but System.Posix is imported:

module Main where

import System.Posix
import Foreign
import Foreign.C
import Foreign.Ptr

main = do

         let event = Sigevent{sigevFunction=(FunPtr
(notifyFunc))}                    <<<<<< error here

         timerId <- timerCreate Clock_Realtime Nothing

         timerDelete timerId

         return ()

notifyFunc :: Sigval -> IO ()
notifyFunc sigval = do
   putStrLn "timer POP!!!!!!!"
   return ()

I am probably looking right at the answer and not seeing it. ??

Thanks, Vasili
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From lrpalmer at gmail.com  Sun Jun  8 23:01:03 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Sun Jun  8 22:53:24 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
Message-ID: <7ca3f0160806082001v2264fd02n69d9bf06da672227@mail.gmail.com>

2008/6/8 Galchin, Vasili <vigalchin@gmail.com>:
> Hello,
>
>      I am getting what is to me a mysterious error in a test case that I am
> writing:
> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> Setup.lhs build
> Preprocessing executables for Test-1.0...
> Building Test-1.0...
> [1 of 1] Compiling Main             ( ./timer.hs,
> dist/build/timer/timer-tmp/Main.o )
>
> ./timer.hs:11:45: Not in scope: data constructor `FunPtr'

There is a *type* called FunPtr in scope, but not a data constructor
as you are using it.  That is, you could say:

  foo :: FunPtr (Int -> IO ())

That is, use the type called FunPtr, but you may not use a *function*
called FunPtr, because it doesn't exist.  You need to use functions
like nullFunPtr, castPtrToFunPtr, etc. to construct FunPtrs.

Luke
From vigalchin at gmail.com  Sun Jun  8 23:07:37 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sun Jun  8 22:59:59 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <7ca3f0160806082001v2264fd02n69d9bf06da672227@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<7ca3f0160806082001v2264fd02n69d9bf06da672227@mail.gmail.com>
Message-ID: <5ae4f2ba0806082007j7c02b68ch368c4a6aad27eeb0@mail.gmail.com>

ah ..,. right ,..... my bad.

Vasili

On Sun, Jun 8, 2008 at 10:01 PM, Luke Palmer <lrpalmer@gmail.com> wrote:

> 2008/6/8 Galchin, Vasili <vigalchin@gmail.com>:
> > Hello,
> >
> >      I am getting what is to me a mysterious error in a test case that I
> am
> > writing:
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> > Setup.lhs build
> > Preprocessing executables for Test-1.0...
> > Building Test-1.0...
> > [1 of 1] Compiling Main             ( ./timer.hs,
> > dist/build/timer/timer-tmp/Main.o )
> >
> > ./timer.hs:11:45: Not in scope: data constructor `FunPtr'
>
> There is a *type* called FunPtr in scope, but not a data constructor
> as you are using it.  That is, you could say:
>
>  foo :: FunPtr (Int -> IO ())
>
> That is, use the type called FunPtr, but you may not use a *function*
> called FunPtr, because it doesn't exist.  You need to use functions
> like nullFunPtr, castPtrToFunPtr, etc. to construct FunPtrs.
>
> Luke
>
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From byorgey at gmail.com  Sun Jun  8 23:43:58 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Sun Jun  8 23:36:19 2008
Subject: [Haskell-cafe] Package updates on haskell.org
In-Reply-To: <20080605224735.GD20317@scytale.galois.com>
References: <20080605224735.GD20317@scytale.galois.com>
Message-ID: <22fcbd520806082043pf032794s8cf99e1b998cf421@mail.gmail.com>

On Thu, Jun 5, 2008 at 6:47 PM, Don Stewart <dons@galois.com> wrote:

> The HWN, which I'm sadly too busy to maintain now,


Does this imply that you're looking for someone to take over the HWN?  I'd
be willing.

-Brent
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From vigalchin at gmail.com  Sun Jun  8 23:46:23 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sun Jun  8 23:38:46 2008
Subject: Fwd: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806082012h2766337bqed0f88cb177f3b11@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<7ca3f0160806082001v2264fd02n69d9bf06da672227@mail.gmail.com>
	<5ae4f2ba0806082012h2766337bqed0f88cb177f3b11@mail.gmail.com>
Message-ID: <5ae4f2ba0806082046i7e116808l414397f040753249@mail.gmail.com>

So Luke .. how do I go from (Sigval -> ()), i..e notifyFunc, to FunPtr using
the suggested data constructors?

On Sun, Jun 8, 2008 at 10:01 PM, Luke Palmer <lrpalmer@gmail.com> wrote:

> 2008/6/8 Galchin, Vasili <vigalchin@gmail.com>:
> > Hello,
> >
> >      I am getting what is to me a mysterious error in a test case that I
> am
> > writing:
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> > Setup.lhs build
> > Preprocessing executables for Test-1.0...
> > Building Test-1.0...
> > [1 of 1] Compiling Main             ( ./timer.hs,
> > dist/build/timer/timer-tmp/Main.o )
> >
> > ./timer.hs:11:45: Not in scope: data constructor `FunPtr'
>
> There is a *type* called FunPtr in scope, but not a data constructor
> as you are using it.  That is, you could say:
>
>  foo :: FunPtr (Int -> IO ())
>
> That is, use the type called FunPtr, but you may not use a *function*
> called FunPtr, because it doesn't exist.  You need to use functions
> like nullFunPtr, castPtrToFunPtr, etc. to construct FunPtrs.
>
> Luke
>
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From bulat.ziganshin at gmail.com  Mon Jun  9 01:54:28 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Mon Jun  9 01:46:57 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
Message-ID: <1097402345.20080609095428@gmail.com>

Hello Vasili,

Monday, June 9, 2008, 6:17:14 AM, you wrote:

1. standard place to import FunPtr from is Foreign.Ptr, not System.Posix
2. FunPtr is exported as abstract type, without constructors. you
can't construct values of this type directly. instead you should use
"wrapper" generators as in the example that Clause has wrote. read it
carefully :)


> Hello,

> ???? I am getting what is to me a mysterious error in a test case that I am writing:
> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell Setup.lhs build
> Preprocessing executables for Test-1.0...
>  Building Test-1.0...
> [1 of 1] Compiling Main???????????? ( ./timer.hs,
> dist/build/timer/timer-tmp/Main.o )

> ./timer.hs:11:45: Not in scope: data constructor `FunPtr'

> It seems like the compiler is complaining about the lack of FunPtr
> in it's symbol table but System.Posix is imported:
>  
> module Main where

> import System.Posix
> import Foreign
> import Foreign.C
> import Foreign.Ptr

> main = do

> ???????? let event = Sigevent{sigevFunction=(FunPtr (notifyFunc))}? <<<<<< error here
>  
> ???????? timerId <- timerCreate Clock_Realtime Nothing

> ???????? timerDelete timerId

> ???????? return ()

> notifyFunc :: Sigval -> IO ()
> notifyFunc sigval = do
> ?? putStrLn "timer POP!!!!!!!"
>  ?? return ()

> I am probably looking right at the answer and not seeing it. ??

> Thanks, Vasili



>   


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From bulat.ziganshin at gmail.com  Mon Jun  9 01:55:15 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Mon Jun  9 01:47:42 2008
Subject: [Haskell-cafe] Package updates on haskell.org
In-Reply-To: <22fcbd520806082043pf032794s8cf99e1b998cf421@mail.gmail.com>
References: <20080605224735.GD20317@scytale.galois.com>
	<22fcbd520806082043pf032794s8cf99e1b998cf421@mail.gmail.com>
Message-ID: <1608367796.20080609095515@gmail.com>

Hello Brent,

Monday, June 9, 2008, 7:43:58 AM, you wrote:

>  The HWN, which I'm sadly too busy to maintain now,

> Does this imply that you're looking for someone to take over the HWN?? I'd be willing.

it will be cool!


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From dons at galois.com  Mon Jun  9 02:01:03 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun  9 01:53:36 2008
Subject: [Haskell-cafe] Package updates on haskell.org
In-Reply-To: <22fcbd520806082043pf032794s8cf99e1b998cf421@mail.gmail.com>
References: <20080605224735.GD20317@scytale.galois.com>
	<22fcbd520806082043pf032794s8cf99e1b998cf421@mail.gmail.com>
Message-ID: <20080609060103.GL18376@scytale.galois.com>

byorgey:
>    On Thu, Jun 5, 2008 at 6:47 PM, Don Stewart <[1]dons@galois.com> wrote:
> 
>      The HWN, which I'm sadly too busy to maintain now,
> 
>    Does this imply that you're looking for someone to take over the HWN?  I'd
>    be willing.

Yep, I've spoken with Brent. He's just starting his PhD, so a perfect
candidate to take over the weekly news. More announcements to follow.

Thanks for the offer ,  Brent!

-- Don
From vigalchin at gmail.com  Mon Jun  9 02:24:59 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun  9 02:17:20 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <1097402345.20080609095428@gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
Message-ID: <5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>

Thanks. Clause?

regards, Vasili

On Mon, Jun 9, 2008 at 12:54 AM, Bulat Ziganshin <bulat.ziganshin@gmail.com>
wrote:

> Hello Vasili,
>
> Monday, June 9, 2008, 6:17:14 AM, you wrote:
>
> 1. standard place to import FunPtr from is Foreign.Ptr, not System.Posix
> 2. FunPtr is exported as abstract type, without constructors. you
> can't construct values of this type directly. instead you should use
> "wrapper" generators as in the example that Clause has wrote. read it
> carefully :)
>
>
> > Hello,
>
> >      I am getting what is to me a mysterious error in a test case that I
> am writing:
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> Setup.lhs build
> > Preprocessing executables for Test-1.0...
> >  Building Test-1.0...
> > [1 of 1] Compiling Main             ( ./timer.hs,
> > dist/build/timer/timer-tmp/Main.o )
>
> > ./timer.hs:11:45: Not in scope: data constructor `FunPtr'
>
> > It seems like the compiler is complaining about the lack of FunPtr
> > in it's symbol table but System.Posix is imported:
> >
> > module Main where
>
> > import System.Posix
> > import Foreign
> > import Foreign.C
> > import Foreign.Ptr
>
> > main = do
>
> >          let event = Sigevent{sigevFunction=(FunPtr (notifyFunc))}
> <<<<<< error here
> >
> >          timerId <- timerCreate Clock_Realtime Nothing
>
> >          timerDelete timerId
>
> >          return ()
>
> > notifyFunc :: Sigval -> IO ()
> > notifyFunc sigval = do
> >    putStrLn "timer POP!!!!!!!"
> >     return ()
>
> > I am probably looking right at the answer and not seeing it. ??
>
> > Thanks, Vasili
>
>
>
> >
>
>
> --
> Best regards,
>  Bulat                            mailto:Bulat.Ziganshin@gmail.com
>
>
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From apfelmus at quantentunnel.de  Mon Jun  9 05:28:48 2008
From: apfelmus at quantentunnel.de (apfelmus)
Date: Mon Jun  9 05:21:19 2008
Subject: [Haskell-cafe] Re: Quick question for a slow program
In-Reply-To: <484C5B79.3060405@cisco.com>
References: <171dfd0a0806070226k7ad4ceaal4cdb4a0892e43519@mail.gmail.com>	<484AFEED.908@cisco.com>	<g2gnoq$ncq$1@ger.gmane.org>
	<484C5B79.3060405@cisco.com>
Message-ID: <g2it4h$521$1@ger.gmane.org>

Lanny Ripple wrote:
> At least when I teased apart why the first one worked it looked
> heap-like.  Each step of the foldr pulled off the smallest nonprime
> and merged the next two lists guaranteeing that the next smallest
> nonprime would be at the head of the next step.

Well, there is heap and heap. It's true that the tree of calls to  merge 
  fulfills the heap property, see the following diagrams:

   merge                        before evaluation
    /  \
    4  merge
    :   /  \
    6   9  merge
    :   :   /  \
    8  12  25  merge
    :  ...  :   /  \
   ...     30  49  ...
            :   :
           ... ...

     4                          first element
     :
    merge
    /   \
   6     9
   :     :
   8    merge
   :    /   \
  ... 12    25
       :     :
      ...   merge
            /   \
          30    49
           :     :
          ...   merge
                /   \
               ...  ...

     4                          first and second element
     :
     6
     :
    merge
    /  \
   8    9
   :    :
  ...  merge
       /  \
     12   25
      :    :
     ...  merge
          /  \
        30   49
         :    :
        ...  merge
             /  \
           ...  ...

and so on. But as you can see, the heap is not balanced,  foldr1 merge 
only generates a linear chain of  merge  nodes. A balanced tree like

         merge
         /   \
     merge   merge
     /   \   /   \
     4   9  25   49
     :   :   :   :
    ... ... ... ...

would be better, except that we need a variant that with an infinite 
number of leaves. The function  foldTree  builds such a tree.

There is also the complication that the heap "bites its own tail" in 
that the multiples of a prime, and hence the heap, are not available 
until the prime itself has been calculated from the heap. The  People a 
  data structure solves this.


Regards,
apfelmus

From ko at daimi.au.dk  Mon Jun  9 09:20:33 2008
From: ko at daimi.au.dk (Klaus Ostermann)
Date: Mon Jun  9 09:12:55 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
Message-ID: <484D2E21.7000005@daimi.au.dk>

At first I'd like to thank Claus, Ryan, Edsko, Luke and Derek for their 
quite helpful replies to my previous thread.

In the course of following their advice I encountered the problem of 
moving a "forall" quantifier over a wrapper type constructor.

If I have

 > newtype Wrapper a = Wrapper a
 
and I instantiate Wrapper with a polymorphic type, then it is possible 
to move the quantifier outside:

 > outside :: Wrapper (forall a. (t a)) -> (forall a. Wrapper (t a))
 > outside(Wrapper x) = Wrapper x

(surprisingly the code does not work with the implementation 'outside x 
= x'; I guess this is a ghc bug)

However, the other way around does not work:

 > inside :: (forall a. Wrapper (t a))-> Wrapper (forall a. (t a))
 > inside x= x

results in the following error:

Couldn't match expected type `forall a. t a'
       against inferred type `t a'
  Expected type: Wrapper (forall a1. t a1)
  Inferred type: Wrapper (t a)
In the expression: x
In the definition of `inside': inside x = x

Any ideas on how to make this work?

Klaus
From devriese at cs.tcd.ie  Mon Jun  9 09:40:49 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Mon Jun  9 09:33:11 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <484D2E21.7000005@daimi.au.dk>
References: <484D2E21.7000005@daimi.au.dk>
Message-ID: <20080609134049.GA19510@netsoc.tcd.ie>

On Mon, Jun 09, 2008 at 03:20:33PM +0200, Klaus Ostermann wrote:
> At first I'd like to thank Claus, Ryan, Edsko, Luke and Derek for their 
> quite helpful replies to my previous thread.
> 
> In the course of following their advice I encountered the problem of 
> moving a "forall" quantifier over a wrapper type constructor.
> 
> If I have
> 
> > newtype Wrapper a = Wrapper a
> 
> and I instantiate Wrapper with a polymorphic type, then it is possible 
> to move the quantifier outside:
> 
> > outside :: Wrapper (forall a. (t a)) -> (forall a. Wrapper (t a))
> > outside(Wrapper x) = Wrapper x
> 
> (surprisingly the code does not work with the implementation 'outside x 
> = x'; I guess this is a ghc bug)

Not a bug; those two types are not the same. In the code you've given,
ghc needs to find evidence that it can create a element of type (Wrapper
(t a)) for any any; fortunately, it can do so because it has 'x', which
can create a 't a' for any 'a'.
> 
> 
> > inside :: (forall a. Wrapper (t a))-> Wrapper (forall a. (t a))
> > inside x= x
> 
> results in the following error:
 
But here we have an argument that can return a Wrapper (t a) for any
'a'; that does *not* mean it can return a wrapper of a polymorphic type.
If you think about 'a' as an actual argument, then you could pass 'Int'
to get a Wrapper (t Int), Bool to get a wrapper (t Bool), or even
(forall a. a -> a) to get a Wrapper (t (forall a. a -> a)), but no
argument at all could make a Wrapper (forall a. t a).

Edsko
From ko at daimi.au.dk  Mon Jun  9 09:55:20 2008
From: ko at daimi.au.dk (Klaus Ostermann)
Date: Mon Jun  9 09:47:40 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <20080609134049.GA19510@netsoc.tcd.ie>
References: <484D2E21.7000005@daimi.au.dk>
	<20080609134049.GA19510@netsoc.tcd.ie>
Message-ID: <17733353.post@talk.nabble.com>



> But here we have an argument that can return a Wrapper (t a) for any
> 'a'; that does *not* mean it can return a wrapper of a polymorphic type.
> If you think about 'a' as an actual argument, then you could pass 'Int'
> to get a Wrapper (t Int), Bool to get a wrapper (t Bool), or even
> (forall a. a -> a) to get a Wrapper (t (forall a. a -> a)), but no
> argument at all could make a Wrapper (forall a. t a).

I just found out that it *is* possible to implement the inside function,
namely as follows:

> inside :: forall t. ((forall a. Wrapper (t a))-> Wrapper (forall a. (t
> a)))
> inside x = Wrapper f
>   where f :: forall a. (t a)
>         f = unwrap x
>         unwrap (Wrapper z) = z

I guess this solves my problem. Sorry for bothering you with this question.
I still find it a bit weird to write all these obfuscated identity functions
to make the type checker happy, though.

Klaus

-- 
View this message in context: http://www.nabble.com/Moving-%22forall%22-over-type-constructors-tp17732668p17733353.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From ketil at malde.org  Mon Jun  9 10:04:48 2008
From: ketil at malde.org (Ketil Malde)
Date: Mon Jun  9 09:56:29 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	(ajb@spamcop.net's message of "Sat\,
	07 Jun 2008 02\:45\:43 -0400")
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
Message-ID: <87ve0ibt6n.fsf@malde.org>

ajb@spamcop.net writes:

>>   null
>>   filter
>>   map
>>   lookup

> On the contrary, these are terrible names _because_ they conflict
> with the Prelude.

I agree.  One solution would be to stuff these into Data.List.

> It's okay if you highly encourage or effectively mandate qualified
> import, like Data.Map does.

I think designing modules for qualified-only use is a mistake.  I also
think import lists get quite ugly, with multiple instances of

      import qualified Data.Set as S
      import Data.Set (Set)

for multiple - sometimes even the majority - of modules.

Add to this that people will assign a variation of abbreviations for
modules, we quickly lose consistency.

And - is there a way to make GHCi use aliased qualification?  I find
my self typing detailed taxonomies all the time there.

For Haskell', I would relly like to have good, generic
classes/interfaces for this, so that a) code becomes readable
(including import lists), and b) code can be written more generically,
and c) it becomes easier to switch between e.g. different string
types. 

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From devriese at cs.tcd.ie  Mon Jun  9 10:04:13 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Mon Jun  9 09:56:38 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <17733353.post@talk.nabble.com>
References: <484D2E21.7000005@daimi.au.dk>
	<20080609134049.GA19510@netsoc.tcd.ie>
	<17733353.post@talk.nabble.com>
Message-ID: <20080609140413.GC19510@netsoc.tcd.ie>

On Mon, Jun 09, 2008 at 06:55:20AM -0700, Klaus Ostermann wrote:
> 
> 
> > But here we have an argument that can return a Wrapper (t a) for any
> > 'a'; that does *not* mean it can return a wrapper of a polymorphic type.
> > If you think about 'a' as an actual argument, then you could pass 'Int'
> > to get a Wrapper (t Int), Bool to get a wrapper (t Bool), or even
> > (forall a. a -> a) to get a Wrapper (t (forall a. a -> a)), but no
> > argument at all could make a Wrapper (forall a. t a).
> 
> I just found out that it *is* possible to implement the inside function,
> namely as follows:
> 
> > inside :: forall t. ((forall a. Wrapper (t a))-> Wrapper (forall a. (t
> > a)))
> > inside x = Wrapper f
> >   where f :: forall a. (t a)
> >         f = unwrap x
> >         unwrap (Wrapper z) = z
> 
> I guess this solves my problem. Sorry for bothering you with this question.
> I still find it a bit weird to write all these obfuscated identity functions
> to make the type checker happy, though.

As I said, the types are not isomorphic -- it you think of type
parameters as arguments you will see why. 

Edsko
From leather at cs.uu.nl  Mon Jun  9 10:59:49 2008
From: leather at cs.uu.nl (Sean Leather)
Date: Mon Jun  9 10:52:09 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <3c6288ab0806090756g1ad94967v9e6f6a8c75f33e10@mail.gmail.com>
References: <484D2E21.7000005@daimi.au.dk>
	<20080609134049.GA19510@netsoc.tcd.ie> <17733353.post@talk.nabble.com>
	<20080609140413.GC19510@netsoc.tcd.ie>
	<3c6288ab0806090756g1ad94967v9e6f6a8c75f33e10@mail.gmail.com>
Message-ID: <3c6288ab0806090759q4fcbdb5bu2da7c620fa4d5f7f@mail.gmail.com>

Hi,

> I just found out that it *is* possible to implement the inside function,
> > namely as follows:
> >
> > > inside :: forall t. ((forall a. Wrapper (t a))-> Wrapper (forall a. (t
> > > a)))
> > > inside x = Wrapper f
> > >   where f :: forall a. (t a)
> > >         f = unwrap x
> > >         unwrap (Wrapper z) = z
> >
> > I guess this solves my problem. Sorry for bothering you with this
> question.
> > I still find it a bit weird to write all these obfuscated identity
> functions
> > to make the type checker happy, though.
>
> As I said, the types are not isomorphic -- it you think of type
> parameters as arguments you will see why.


I found these examples interesting, mostly because I don't understand it
very well. So, I simplified Klaus' code a bit and derived the following:

-----
{-# LANGUAGE Rank2Types #-}

-- Wrapper
newtype W a = W { unW :: a }

inside :: ((forall a. W (t a))-> W (forall a. (t a)))
--inside (W x) = W x -- (a) FAILS
--inside = W . unW -- (b) FAILS
inside x = W (unW x) -- (c) WORKS
-----

Can someone comment on the differences between the following in terms of
type-checking or inference? Considering the errors I got, I'm guess the
issue is the same for the pattern-matching (a) and the point-free (b)
versions. Are there any pointers for developing a better understanding or
intuition of this?

Thanks,
Sean
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From olivier.boudry at gmail.com  Mon Jun  9 11:25:22 2008
From: olivier.boudry at gmail.com (Olivier Boudry)
Date: Mon Jun  9 11:17:42 2008
Subject: [Haskell-cafe] ANNOUNCE: hfann-01
Message-ID: <f5fae3f60806090825v570e344v8a0c4a1e094a5be1@mail.gmail.com>

Hi all,

I'm pleased to announce the first release of the hfann module (
http://code.haskell.org/~oboudry/hfann/). This module is an interface to the
"Fast Artificial Neural Network (FANN)" library (see
http://leenissen.dk/fann/).

This is an early release. At the moment the hfann module does not cover all
the functions found in the FANN library but it should be useable to train
and use simple Neural Networks. At least is can be used to run an equivalent
of the "Getting Started" example found in
http://leenissen.dk/fann/html/files2/gettingstarted-txt.html.

The module was developped on Windows XP with GHC-6.8.2.

The README should provide you with all required information to install this
module. The haddock documentation should give enough information to get
started using it.

== Installation ==

Download version 2.0 of the FANN library from:

    http://leenissen.dk/fann/download.php

and build it according to the instruction found on:

    http://leenissen.dk/fann/html/files2/installation-txt.html

Get the hfann module

    darcs get http://code.haskell.org/~oboudry/hfann/

Build it using Cabal

    runghc Setup.lhs configure
    runghc Setup.lhs build
    runghc Setup.lhs haddock
    runghc Setup.lhs install

== Examples ==

Training an ANN to the xor function:

> import HFANN

> main = do
>   withStandardFann [2,3,1] $ \fann -> do
>     setActivationFunctionHidden fann fannSigmoidSymetric
>     setActivationFunctionOutput fann fannSigmoidSymetric

>     trainOnFile fann "xor.data" -- train data
>                      20000      -- max epochs
>                      100        -- epochs between reports
>                      0.001      -- desired error

>     saveFann fann "xor.ann"

C:\Temp\Haskell\hfann\examples\xor>Train.exe
Max epochs    20000. Desired error: 0.0010000000.
Epochs            1. Current error: 0.2503675520. Bit fail 4.
Epochs          100. Current error: 0.0181358512. Bit fail 0.
Epochs          169. Current error: 0.0009599295. Bit fail 0.


Using the trained ANN on the 4 possible input values to the xor function (-1
= False, 1 = True).

> import HFANN

> main = do
>   withSavedFann "xor.ann" $ \fann -> do
>     mapM_ (\x -> runFann fann x >>= print) [[-1,-1],[-1,1],[1,-1],[1,1]]

C:\Temp\Haskell\hfann\examples\xor>Use.exe
[-0.950566361876292]
[0.9178714756661263]
[0.9457588340834527]
[-0.9482816646878051]

The "xor.data" training data content:
4 2 1
-1 -1
-1
-1 1
1
1 -1
1
1 1
-1

The files for this example can be found in the "examples/xor" directory

==

Bug reports, suggestions and comments are welcome. You can send them
directly to my e-mail address.

Olivier.
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From aruiz at um.es  Mon Jun  9 12:10:09 2008
From: aruiz at um.es (Alberto Ruiz)
Date: Mon Jun  9 12:02:32 2008
Subject: [Haskell-cafe] "sum" in hmatrix and blas?
In-Reply-To: <20080609012525.GA18748@scytale.galois.com>
References: <87y75gx3te.fsf@columbia.edu>
	<200806081454.18467.toman144@student.liu.se>
	<87r6b8vwre.fsf@columbia.edu> <484C328F.5080205@um.es>
	<877iczwl4o.fsf@columbia.edu>
	<20080609001622.GC18376@scytale.galois.com>
	<20080609012525.GA18748@scytale.galois.com>
Message-ID: <484D55E1.6060607@um.es>

Patch applied!

I will also make the recommended changes in the Matrix type and prepare 
some benchmarks for this kind of Haskell loops.

In fact, such excellent performance will also be very useful in image 
processing algorithms which must read and write a large number of C 
array elements. I now think that some C auxiliary functions in the 
easyVision library for operations not available in the IPP can be 
replaced by much nicer Haskell versions.

I'm currently working on the implementation of interest point 
descriptors based on histograms of local gradient directions. This may 
be a very good benchmark. I will prepare a first version and post here 
the results for discussion.

Don, many thanks for your all your help!

Alberto

Don Stewart wrote:
> Problem solved. The Haskell loop now wins.
> 
>>> After reading don's blog, I tried to make a test with both
>>> methods.  The code is very simple, as following
>>>
>>> module Main where
>>> import System
>>> import Numeric.LinearAlgebra
>>>
>>> vsum1 :: Vector Double -> Double
>>> vsum1 v = constant 1 (dim v) <.> v
>>>
>>> vsum2 :: Vector Double -> Double
>>> vsum2 v = go (d - 1) 0
>>>     where
>>>       d = dim v
>>>       go :: Int -> Double -> Double
>>>       go 0 s = s + (v @> 0)
>>>       go !j !s = go (j - 1) (s + (v @> j))
>>>
>>>
>>> mean :: Vector Double -> Double
>>> mean v = vsum v / fromIntegral (dim v)
>>>     where vsum = vsum1
>>>
>>> main :: IO ()
>>> main = do
>>>   fn:nrow:ncol:_ <- getArgs
>>>   print . mean . flatten =<< fromFile fn (read nrow, read ncol)
>>>
>>> Compile it with "-O2 -optc-O2", and run with a data set of
>>> length 5000000.  The results are
>>>
>>> with "vsum1":
>>>  80,077,984 bytes allocated in the heap
>>>       2,208 bytes copied during GC (scavenged)
>>>          64 bytes copied during GC (not scavenged)
>>>  40,894,464 bytes maximum residency (2 sample(s))
>>>   %GC time       0.0%  (0.0% elapsed)
>>>   Alloc rate    35,235,448 bytes per MUT second
>>> ./vsum1 huge 5000000 1  2.25s user 0.09s system 99% cpu 2.348 total
>>>
>>> This is reasonable, exactly two copies of vector with size
>>> of 40MB.
>>>
>>> with "vsum2":
>>> 560,743,120 bytes allocated in the heap
>>>      19,160 bytes copied during GC (scavenged)
>>>      15,920 bytes copied during GC (not scavenged)
>>>  40,919,040 bytes maximum residency (2 sample(s))
>>>   %GC time       0.3%  (0.3% elapsed)
>>>   Alloc rate    222,110,261 bytes per MUT second
>>> ./mean2 huge 5000000 1  2.53s user 0.06s system 99% cpu 2.598 total
>>>
>>> This is strange.  A lot of extra usage of heap?  Probably
>>> because '@>' is not efficient?  So it looks like the
>>> inner-product approach wins with a fairly margin.
>   
>> Looking at the core we get from vsum2, we see:
>>
>> vsum2 compiles quite well
>>
>>       $wgo_s1Nn :: Int# -> Double# -> Double#
>>
>>       $wgo_s1Nn =
>>         \ (ww3_s1Mc :: Int#) (ww4_s1Mg :: Double#) ->
>>           case ww3_s1Mc of ds_X17R {
>>             __DEFAULT ->
>>               case Data.Packed.Internal.Vector.$wat
>>                      @ Double Foreign.Storable.$f9 ww_s1Ms ww1_s1Mu (I# ds_X17R)
>>               of { D# y_a1KQ ->
>>               $wgo_s1Nn (-# ds_X17R 1) (+## ww4_s1Mg y_a1KQ)
>>               };
>>             0 -> +## ww4_s1Mg ww2_s1M7
>>           };
>>     } in  $wgo_s1Nn (-# ww_s1Ms 1) 0.0
>>
>> But note the return value from $wat is boxed, only to be immediately
>> unboxed. That looks to be the source of the heap allocations.
>>
>> Let's see if we can help that.
> 
> Ah, of course. The problem is the unsafePerformIO used to wrap up the
> 'peek'. This blocks the optimisations somewhat, after we unpack the Vector type.. 
> 
> So if we rewrite 'safeRead' to not use unsafePerformIO, but instead:
> 
>     safeRead v = inlinePerformIO . withForeignPtr (fptr v)
> 
>     inlinePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
> 
> Along with this change to Vector:
> 
>     data Vector t = V { dim  :: {-# UNPACK #-} !Int
>                       , fptr :: {-# UNPACK #-} !(ForeignPtr t)
>                       }
> 
> and some inlining for the bounds checks.
> Following bytestrings, we see the performance go from, with a 180M input
> file:
>     
> Goal:
>     vsum1:
>         $ ghc-core A.hs -optc-O2 -fvia-C  -fbang-patterns
>         $ time ./A data 4000 2500
>         0.9999727441161678
> 
>         ./A data 4000 2500  5.37s user 0.20s system 99% cpu 5.609 total
>         160,081,136 bytes allocated in the heap
>         155 Mb total memory in use
> 
> Before:
> vsum2-old:
> 
>          $wgo_s1Ns =
>         \ (ww3_s1Me :: Int#) (ww4_s1Mi :: Double#) ->
>           case ww3_s1Me of ds_X17Y {
>             __DEFAULT ->
>               case Data.Packed.Internal.Vector.$wat
>                      @ Double Foreign.Storable.$f9 ww_s1Mu ww1_s1Mw (I# ds_X17Y)
>               of wild1_a1Hg { D# y_a1Hi ->
>               $wgo_s1Ns (-# ds_X17Y 1) (+## ww4_s1Mi y_a1Hi)
>               };
>             0 -> +## ww4_s1Mi ww2_s1M9
>           };
>     } in  $wgo_s1Ns (-# ww_s1Mu 1) 0.0
>  
>     ./A data 4000 2500 +RTS -sstderr 
>     0.999972744115876
> 
>     ./A data 4000 2500 +RTS -sstderr  6.04s user 0.15s system 99% cpu 6.203 total    
>     1,121,416,400 bytes allocated in the heap
>     78 Mb total memory in use
> 
> After:
>     True ->
>           case readDoubleOffAddr#
>                  @ RealWorld ww1_s1Nr ds_X180 realWorld#
>           of wild2_a1HS { (# s2_a1HU, x_a1HV #) ->
>           case touch# @ ForeignPtrContents ww2_s1Ns s2_a1HU
>           of s_a1HG { __DEFAULT ->
>           $wgo_s1Ok (-# ds_X180 1) (+## ww4_s1Ng x_a1HV)
>           }
> 
>     No needless boxing.
> 
>     $ time ./A data 4000 2500 +RTS -sstderr          
>     ./A data 4000 2500 +RTS -sstderr 
>     0.999972744115876
> 
>     ./A data 4000 2500 +RTS -sstderr  5.41s user 0.10s system 99% cpu 5.548 total
>      80,071,072 bytes allocated in the heap
> 
>     78 Mb total memory in use
> 
> And the total runtime and allocation now is better than the fully 'C' version.
> Yay.
> 
> Patch attached to the darcs version of hmatrix.
> Similar changes can likely be done to the other data types in hmatrix,
> for pretty much ideal code.
> 
> -- Don
>     
> 
From Joseph.Re at MorganStanley.com  Mon Jun  9 13:48:48 2008
From: Joseph.Re at MorganStanley.com (Re, Joseph (IT))
Date: Mon Jun  9 13:41:51 2008
Subject: [Haskell-cafe] Unable to hc-build ghc 6.6.1
Message-ID: <507725E31752A74CB00728FA6C17D99C09E1039D@NYWEXMB29.msad.ms.com>

I'm trying to do a registered hc-build on linux2.4 x86 with ghc 6.6.1.
After fixing mk/bootstrap.mk to include "-lncurses" in HC_BOOT_LIBS to
get past an undefined reference to "tputs" et al, I've gotten stuck with
the following undefined reference error:

------------------------------------------------------------------------
== gmake all -wr;
 in /tmp/ghc-6.6.1/utils/runstdtest
------------------------------------------------------------------------
gmake[1]: Nothing to be done for `all'.
Finished making all in runstdtest: 0
------------------------------------------------------------------------
== gmake all -wr;
 in /tmp/ghc-6.6.1/utils/genapply
------------------------------------------------------------------------
gcc -o genapply  -fno-defer-pop -fomit-frame-pointer -fno-builtin
-DDONT_WANT_WIN32_DLL_SUPPORT -D__GLASGOW_HASKELL__=606  -O
-I/tmp/ghc-6.6.1/includes -I/tmp/ghc-6.6.1/libraries/base/include
-I/tmp/ghc-6.6.1/libraries/unix/include
-I/tmp/ghc-6.6.1/libraries/parsec/include
-I/tmp/ghc-6.6.1/libraries/readline/include    -L/tmp/ghc-6.6.1/rts
-L/tmp/ghc-6.6.1/libraries/base -L/tmp/ghc-6.6.1/libraries/base/cbits
-L/tmp/ghc-6.6.1/libraries/haskell98 -L/tmp/ghc-6.6.1/libraries/parsec
-L/tmp/ghc-6.6.1/libraries/regex-base
-L/tmp/ghc-6.6.1/libraries/regex-compat
-L/tmp/ghc-6.6.1/libraries/regex-posix -L/tmp/ghc-6.6.1/libraries/Cabal
-L/tmp/ghc-6.6.1/libraries/template-haskell
-L/tmp/ghc-6.6.1/libraries/readline -L/tmp/ghc-6.6.1/libraries/unix
-L/tmp/ghc-6.6.1/libraries/unix/cbits -u
"base_GHCziBase_Izh_static_info" -u "base_GHCziBase_Czh_static_info" -u
"base_GHCziFloat_Fzh_static_info" -u "base_GHCziFloat_Dzh_static_info"
-u "base_GHCziPtr_Ptr_static_info" -u "base_GHCziWord_Wzh_static_info"
-u "base_GHCziInt_I8zh_static_info" -u "base_GHCziInt_I16zh_static_info"
-u "base_GHCziInt_I32zh_static_info" -u
"base_GHCziInt_I64zh_static_info" -u "base_GHCziWord_W8zh_static_info"
-u "base_GHCziWord_W16zh_static_info" -u
"base_GHCziWord_W32zh_static_info" -u "base_GHCziWord_W64zh_static_info"
-u "base_GHCziStable_StablePtr_static_info" -u
"base_GHCziBase_Izh_con_info" -u "base_GHCziBase_Czh_con_info" -u
"base_GHCziFloat_Fzh_con_info" -u "base_GHCziFloat_Dzh_con_info" -u
"base_GHCziPtr_Ptr_con_info" -u "base_GHCziStable_StablePtr_con_info" -u
"base_GHCziBase_False_closure" -u "base_GHCziBase_True_closure" -u
"base_GHCziPack_unpackCString_closure" -u
"base_GHCziIOBase_stackOverflow_closure" -u
"base_GHCziIOBase_heapOverflow_closure" -u
"base_GHCziIOBase_NonTermination_closure" -u
"base_GHCziIOBase_BlockedOnDeadMVar_closure" -u
"base_GHCziIOBase_Deadlock_closure" -u
"base_GHCziWeak_runFinalizzerBatch_closure" -u "__stginit_Prelude"
GenApply.o     -lHSreadline -lreadline -lHStemplate-haskell -lHSunix
-lHSunix_cbits -lHSCabal -lHShaskell98 -lHSregex-compat -lHSregex-posix
-lHSregex-base -lHSbase -lHSbase_cbits -lHSparsec -lHSrts -lgmp -lm
-lncurses  -ldl -lrt
GenApply.o(.text+0x13a55): In function `s5cr_info':
: undefined reference to `base_DataziList_zdsintersperse_info'
GenApply.o(.text+0x14c11): In function `s58p_info':
: undefined reference to `base_DataziList_zdsintersperse_info'
GenApply.o(.text+0x17d79): In function `s54x_info':
: undefined reference to `base_DataziList_zdsintersperse_info'
collect2: ld returned 1 exit status
gmake[1]: *** [genapply] Error 1
Failed making all in genapply: 1
gmake: *** [all] Error 1
gmake: Leaving directory `/tmp/ghc-6.6.1/utils'

Does anyone know why this might be occuring? The only reference to
"base_DataziList_zdsintersperse_info" on google didn't seem to have an
answer.  For reference my mk/build.mk is:

SRC_HC_OPTS     = -H32m -O -fvia-C -Rghc-timing -keep-hc-files
GhcLibHcOpts    = -O
GhcLibWays      =
SplitObjs       = NO

just as the example one given on
http://hackage.haskell.org/trac/ghc/wiki/Building/Porting.
Also- in case this is related- I moved AutoApply_thr.thr_hc to
AutoApply_thr.hc (and likewise for debug, thr_debug, and thr_p).

Thanks,
Joseph Re
--------------------------------------------------------

NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.
From olivier.boudry at gmail.com  Mon Jun  9 13:52:26 2008
From: olivier.boudry at gmail.com (Olivier Boudry)
Date: Mon Jun  9 13:44:46 2008
Subject: [Haskell-cafe] ANNOUNCE: hfann-01
In-Reply-To: <20080609152905.GD23950@scytale.galois.com>
References: <f5fae3f60806090825v570e344v8a0c4a1e094a5be1@mail.gmail.com>
	<20080609152905.GD23950@scytale.galois.com>
Message-ID: <f5fae3f60806091052o4a18ee5ame547ca30ce892fee@mail.gmail.com>

On Mon, Jun 9, 2008 at 11:29 AM, Don Stewart <dons@galois.com> wrote:

> Excellent. Would you like to upload it to hackage.haskell.org, so it can
> be easily installed with the 'cabal install' tool?
>
>
Hi all,

As suggested by Don, I just uploaded the hfann package to
hackage.haskell.org.

It's available here:

    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hfann

Best regards,

Olivier.
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From vigalchin at gmail.com  Mon Jun  9 14:18:29 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun  9 14:11:03 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
Message-ID: <5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>

In any case, what I want to do is store FunPtr in  a data type and marshall
into a C struct as a C function pointer.

Vasili

On Mon, Jun 9, 2008 at 1:24 AM, Galchin, Vasili <vigalchin@gmail.com> wrote:

> Thanks. Clause?
>
> regards, Vasili
>
>
> On Mon, Jun 9, 2008 at 12:54 AM, Bulat Ziganshin <
> bulat.ziganshin@gmail.com> wrote:
>
>> Hello Vasili,
>>
>> Monday, June 9, 2008, 6:17:14 AM, you wrote:
>>
>> 1. standard place to import FunPtr from is Foreign.Ptr, not System.Posix
>> 2. FunPtr is exported as abstract type, without constructors. you
>> can't construct values of this type directly. instead you should use
>> "wrapper" generators as in the example that Clause has wrote. read it
>> carefully :)
>>
>>
>> > Hello,
>>
>> >      I am getting what is to me a mysterious error in a test case that I
>> am writing:
>> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
>> Setup.lhs build
>> > Preprocessing executables for Test-1.0...
>> >  Building Test-1.0...
>> > [1 of 1] Compiling Main             ( ./timer.hs,
>> > dist/build/timer/timer-tmp/Main.o )
>>
>> > ./timer.hs:11:45: Not in scope: data constructor `FunPtr'
>>
>> > It seems like the compiler is complaining about the lack of FunPtr
>> > in it's symbol table but System.Posix is imported:
>> >
>> > module Main where
>>
>> > import System.Posix
>> > import Foreign
>> > import Foreign.C
>> > import Foreign.Ptr
>>
>> > main = do
>>
>> >          let event = Sigevent{sigevFunction=(FunPtr (notifyFunc))}
>> <<<<<< error here
>> >
>> >          timerId <- timerCreate Clock_Realtime Nothing
>>
>> >          timerDelete timerId
>>
>> >          return ()
>>
>> > notifyFunc :: Sigval -> IO ()
>> > notifyFunc sigval = do
>> >    putStrLn "timer POP!!!!!!!"
>> >     return ()
>>
>> > I am probably looking right at the answer and not seeing it. ??
>>
>> > Thanks, Vasili
>>
>>
>>
>> >
>>
>>
>> --
>> Best regards,
>>  Bulat                            mailto:Bulat.Ziganshin@gmail.com
>>
>>
>
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From duncan.coutts at worc.ox.ac.uk  Mon Jun  9 14:41:05 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Mon Jun  9 14:29:31 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <87ve0ibt6n.fsf@malde.org>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org>
Message-ID: <1213036865.15010.448.camel@localhost>


On Mon, 2008-06-09 at 16:04 +0200, Ketil Malde wrote:

> I think designing modules for qualified-only use is a mistake.  I also
> think import lists get quite ugly, with multiple instances of
> 
>       import qualified Data.Set as S
>       import Data.Set (Set)
> 
> for multiple - sometimes even the majority - of modules.

As far as I can see that is the only downside, having to import more
than once to get the type name unqualified with the rest of the module
qualified.

> Add to this that people will assign a variation of abbreviations for
> modules, we quickly lose consistency.

The obvious consistent thing to do is to use the last part of the module
name, at least for short names like Set and Map. For ByteString it is
more of a mouthful.

      import qualified Data.Set as Set
      import Data.Set (Set)

      Set.empty, Set.insert etc etc.

> And - is there a way to make GHCi use aliased qualification?  I find
> my self typing detailed taxonomies all the time there.

The ghci syntax currently is:
:m Data.Set
wouldn't it be much nicer as:
import Data.Set
then we could have the obvious:
import Data.Set as Set


Duncan

From ryani.spam at gmail.com  Mon Jun  9 15:16:25 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun  9 15:08:54 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
Message-ID: <2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>

> type Notify = Sigval -> IO ()
> foreign import ccall "wrapper" mkNotify :: Notify -> IO (FunPtr Notify)

then
> main = do
>    notifyFPtr <- mkNotify notifyFunc
>    -- rest of code here
>
>    -- then, when you are done and nothing is referencing the pointer any more
>    freeHaskellFunPtr notifyFPtr

On 6/9/08, Galchin, Vasili <vigalchin@gmail.com> wrote:
> In any case, what I want to do is store FunPtr in  a data type and marshall
> into a C struct as a C function pointer.
>
> Vasili

This will be suitable for that purpose.

  -- ryan
From vogt.adam at gmail.com  Mon Jun  9 15:45:44 2008
From: vogt.adam at gmail.com (Adam Vogt)
Date: Mon Jun  9 15:38:09 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <1213036865.15010.448.camel@localhost>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org> <1213036865.15010.448.camel@localhost>
Message-ID: <20080609194544.GA2753@dell>

* On Monday, June 09 2008, Duncan Coutts wrote:
>> And - is there a way to make GHCi use aliased qualification?  I find
>> my self typing detailed taxonomies all the time there.
>
>The ghci syntax currently is:
>:m Data.Set
>wouldn't it be much nicer as:
>import Data.Set
>then we could have the obvious:
>import Data.Set as Set

ghci does load modules when you type "import Data.Set" already, but it 
doesn't parse "import Data.Set as Set"
From johan.tibell at gmail.com  Mon Jun  9 15:53:50 2008
From: johan.tibell at gmail.com (Johan Tibell)
Date: Mon Jun  9 15:46:11 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <87ve0ibt6n.fsf@malde.org>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org>
Message-ID: <90889fe70806091253v925f596mc2b02c8ce3586167@mail.gmail.com>

On Mon, Jun 9, 2008 at 4:04 PM, Ketil Malde <ketil@malde.org> wrote:
> I think designing modules for qualified-only use is a mistake.  I also
> think import lists get quite ugly, with multiple instances of

I was only suggesting avoiding namespacing prefixes/suffixes in
identifiers. Other than that things would be the same. You don't have
to import things as qualified. However, if you're going to try to
avoid using identifiers in your exported interface because they would
collide with other modules I would advice against it. I agree with you
that the module imports get a bit ugly. I prefer that to the
alternative though.

> Add to this that people will assign a variation of abbreviations for
> modules, we quickly lose consistency.

It's a shame that we have such deep hierarchies otherwise we wouldn't
need to always alias out module imports. I think Python get's it
right:

import os

... os.tmpname ...

Duncan's recommendation of just taking the part after the last dot
seems like a good rule of thumb. Doing

import qualified Data.Map as M

does gain you much in my opinion. Compare M.empty to emptyM. No
difference, you still can't deduce the module by just looking at the
call site.

Cheers,

Johan
From xj2106 at columbia.edu  Mon Jun  9 15:58:28 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Mon Jun  9 15:55:25 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <90889fe70806091253v925f596mc2b02c8ce3586167@mail.gmail.com>
	(Johan Tibell's message of "Mon, 9 Jun 2008 21:53:50 +0200")
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org>
	<90889fe70806091253v925f596mc2b02c8ce3586167@mail.gmail.com>
Message-ID: <87hcc2v0rf.fsf@columbia.edu>

"Johan Tibell" <johan.tibell@gmail.com> writes:

> Duncan's recommendation of just taking the part after the last dot
> seems like a good rule of thumb. Doing
>
> import qualified Data.Map as M
>
> does gain you much in my opinion. Compare M.empty to emptyM. No
> difference, you still can't deduce the module by just looking at the
> call site.

I would prefer `M.empty' to `emptyM'.  At least, by looking
at `M.empty', you know that this `empty' is from `M' and you
can easily check out what `M' is from the import list.  I
personally always found myself unproductively tracing back
something like `emptyM' to its origin.

>
>
> Cheers,
>
> Johan
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From nicolas.pouillard at gmail.com  Mon Jun  9 16:05:53 2008
From: nicolas.pouillard at gmail.com (Nicolas Pouillard)
Date: Mon Jun  9 15:58:34 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <90889fe70806091253v925f596mc2b02c8ce3586167@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org>
	<90889fe70806091253v925f596mc2b02c8ce3586167@mail.gmail.com>
Message-ID: <1213041478-sup-9212@ausone.local>

Excerpts from johan.tibell's message of Mon Jun 09 21:53:50 +0200 2008:
> On Mon, Jun 9, 2008 at 4:04 PM, Ketil Malde <ketil@malde.org> wrote:
> > I think designing modules for qualified-only use is a mistake.  I also
> > think import lists get quite ugly, with multiple instances of
> 
> I was only suggesting avoiding namespacing prefixes/suffixes in
> identifiers. Other than that things would be the same. You don't have
> to import things as qualified. However, if you're going to try to
> avoid using identifiers in your exported interface because they would
> collide with other modules I would advice against it. I agree with you
> that the module imports get a bit ugly. I prefer that to the
> alternative though.
> 
> > Add to this that people will assign a variation of abbreviations for
> > modules, we quickly lose consistency.
> 
> It's a shame that we have such deep hierarchies otherwise we wouldn't
> need to always alias out module imports. I think Python get's it
> right:
> 
> import os
> 
> ... os.tmpname ...
> 
> Duncan's recommendation of just taking the part after the last dot
> seems like a good rule of thumb. Doing
> 
> import qualified Data.Map as M
> 
> does gain you much in my opinion. Compare M.empty to emptyM. No
> difference, you still can't deduce the module by just looking at the
> call site.

Coming  from a world where qualified names at call sites or full import (open)
are  the  default  rules  (OCaml),  I  much  prefer  the import way (where you
specify  names  that  gets  imported) and thus prefer when names don't collide
(except  for  modules  like  Data.Map  or  ByteString  where  I  use  the "as"
notation).

The  key point for me is to be able to trace as fast as possible what precisely
use a module by looking (only) at the top of the file.

Best regards,

-- 
Nicolas Pouillard aka Ertai
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From sebastian.sylvan at gmail.com  Mon Jun  9 16:53:28 2008
From: sebastian.sylvan at gmail.com (Sebastian Sylvan)
Date: Mon Jun  9 16:45:48 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
Message-ID: <3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>

On Thu, Jun 5, 2008 at 4:19 PM, Johan Tibell <johan.tibell@gmail.com> wrote:

>
>
> * Why is this practice common in Haskell
>
> Here are some guesses:
>
> 1. It's common in papers. However, papers and libraries are quite
> different. The former usually build up a small vocabulary and having
> short names is a big win. Papers rarely make use of the module system
> at all. The latter are included as pieces of large programs and their
> names need to be adjusted accordingly.
>
> 2. It's the default. You have to add "qualified" to all your imports
> to make them qualified. In most language imports are qualified by
> default. I think the latter would have been a better choice but we
> have to live with the current design so bite the bullet and add those
> qualified keywords to your imports.
>
> 3. Lack of common interfaces. An example would be two different set
> implementations that essentially have the same interface but since
> there is no explicitly shared interface, defined using a type class,
> you sometimes end up with different names. The lack of type families
> might explain why e.g. collection classes don't share interfaces.
>
> 4. Haskell is a very expressive language. You can often write a whole
> function definition on one line! Adding those module qualifications
> makes your code slightly longer and it might just break your beautiful
> one liner into two lines.
>

Another BIG reason: It's impossible to export a whole hierarchy qualified.
I.e it would be neat if the user could write:

import Graphics.UI.Gtk

And then have Gtk re-export sub-modules qualified, so you could write
"Button.new", "Window.new" etc. etc. As it stands you have two options:
prefix all the "new" functions with the kind of widget they create
(buttonNew, windowNew), or force the user to add a gazillion qualified
imports.

Ideally you would be able to add "qualified" to the module export statement,
and have it automatically bring in that module qualified (it should also
support an "as" so you'd write "qualified module Graphics.UI.Gtk.Button as
Button" in the export list to get the above behaviour.)


-- 
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862
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From mail at joachim-breitner.de  Mon Jun  9 16:57:38 2008
From: mail at joachim-breitner.de (Joachim Breitner)
Date: Mon Jun  9 16:50:07 2008
Subject: [Haskell-cafe] File locking wishlist
In-Reply-To: <1212679364.3483.14.camel@otto.ehbuehl.net>
References: <1212679364.3483.14.camel@otto.ehbuehl.net>
Message-ID: <1213045058.21568.10.camel@otto.ehbuehl.net>

Hi again,

Am Donnerstag, den 05.06.2008, 17:22 +0200 schrieb Joachim Breitner:
> Hi,
> 
> for a program of mine (darcswatch[1]), a rather long running process is
> run at certain events (by cron, and by new emails). I want to achieve
> that:
>  * Only one instance of the program runs at a time.
>  * If new events come in while the program runs, it should re-run itself
>  * There is information attached to the events (only one Bool ATM)
> 
> So I?d like to implement something with this, or a similar, interface:
> 
> =======================================================================
> module MyLocking where
> 
> -- | tries to get the lock. If it fails, notifies the running process
> --   to re-start itself afterwards, with the given information
> --   returns True if the lock was aquired
> lockOrMark :: Show a => FilePath -> a -> IO Bool
> 
> -- | release the lock. If new events have come in, they are returned
> --   in the list, and the lock is still kept. If the list is empty,
> --   the lock was successfully released.
> releaseLock :: Read a => FilePath -> IO [a]
> ?=======================================================================

I wrote a module that provides this API. It can be found here:
http://darcs.nomeata.de/darcswatch/src/LockRestart.hs

I use it for darcswatch, you can see the relevant change here:
http://darcs.nomeata.de/cgi-bin/darcsweb.cgi?r=darcswatch;a=filediff;h=20080609203612-23c07-aec8c4e1f22a9c3bdd44d062ab26f7d18a880a18.gz;f=src/Main.hs

Actually, since only the call to "or" in the third changed line from the
bottom is special to darcswatch, this can be moved into LockRestart, so
the change to the program is reduced to this:

         config <- read `fmap` readFile (confdir ++ "config")
+
+	 lockRestart (cOutput config) patchNew or True (do_work config)
+
+do_work config patchNew = do
         putStrLn "Reading repositories..."

or even

         config <- read `fmap` readFile (confdir ++ "config")
+
+	 lockRestart (cOutput config) patchNew or True $ \patchNew -> do
+       
         putStrLn "Reading repositories..."

if you prefer.


Enjoy,
Joachim Breitner


-- 
Joachim Breitner
  e-Mail: mail@joachim-breitner.de
  Homepage: http://www.joachim-breitner.de
  ICQ#: 74513189
  Jabber-ID: nomeata@joachim-breitner.de
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From dbueno at gmail.com  Mon Jun  9 23:00:10 2008
From: dbueno at gmail.com (Denis Bueno)
Date: Mon Jun  9 22:52:32 2008
Subject: [Haskell-cafe] ANN: funsat 0.5, a SAT solver written in Haskell
Message-ID: <6dbd4d000806092000g131716a8v44cc45a81fae027@mail.gmail.com>

Hi all,

It is my pleasure to announce the first reasonable release of funsat,
a modern, DPLL-style SAT solver written in Haskell.  Funsat solves
formulas in conjunctive normal form and produces a total variable
assignment for satisfiable problems.  It is available from Hackage:

    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat
    http://churn.ath.cx/funsat.html

As well as in a Git repo, which contains many benchmark files funsat can solve.

    git clone http://churn.ath.cx/funsat

Funsat is intended to be reasonably efficient for practical problems
and convenient to use as a constraint-solving backend in other
software.

The former is achieved by using several well-known techniques from the
literature including two-watched literals, conflict-directed learning,
non-chronological backtracking, a VSIDS-like dynamic variable
ordering, and restarts.  The latter is supported currently by
efficient unsatisfiable core generation, which generates a minimal
unsatisfiable problem for a given unsatisfiable problem.  In the
future, I plan to add support for converting boolean circuits into
CNF, as well as support for other types of constraints.

Please try it out and report bugs!  (This email is the one listed on
the website.)

-- 
 Denis
From vigalchin at gmail.com  Mon Jun  9 23:54:20 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun  9 23:46:39 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
Message-ID: <5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>

Ryan,

     I tried but the compiler didn't seem to like the keyword "import":

vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
Setup.lhs build
Preprocessing executables for Test-1.0...
Building Test-1.0...
[1 of 1] Compiling Main             ( ./timer.hs,
dist/build/timer/timer-tmp/Main.o )

./timer.hs:29:8: parse error on input `import'


.... source ...:

module Main where

import System.Posix
import Foreign
import Foreign.C
import Foreign.Ptr

type Notify = Sigval -> IO ()

main = do

         notifyFPtr <- mkNotify notifyFunc

         let event = Sigevent{sigevFunction=notifyFPtr}

         timerId <- timerCreate Clock_Realtime Nothing

         timerDelete timerId

         return ()

notifyFunc :: Sigval -> IO ()
notifyFunc sigval = do
   putStrLn "timer POP!!!!!!!"
   return ()


foreign import ccall "wrapper"
   mkNotify :: Notify -> IO (FunPtr Notify)
~

Everything looks ok to me. ??

Regards, Vasili

On Mon, Jun 9, 2008 at 2:16 PM, Ryan Ingram <ryani.spam@gmail.com> wrote:

> > type Notify = Sigval -> IO ()
> > foreign import ccall "wrapper" mkNotify :: Notify -> IO (FunPtr Notify)
>
> then
> > main = do
> >    notifyFPtr <- mkNotify notifyFunc
> >    -- rest of code here
> >
> >    -- then, when you are done and nothing is referencing the pointer any
> more
> >    freeHaskellFunPtr notifyFPtr
>
> On 6/9/08, Galchin, Vasili <vigalchin@gmail.com> wrote:
> > In any case, what I want to do is store FunPtr in  a data type and
> marshall
> > into a C struct as a C function pointer.
> >
> > Vasili
>
> This will be suitable for that purpose.
>
>  -- ryan
>
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From judah.jacobson at gmail.com  Tue Jun 10 00:25:39 2008
From: judah.jacobson at gmail.com (Judah Jacobson)
Date: Tue Jun 10 00:17:57 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
Message-ID: <6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>

2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
> Ryan,
>
>      I tried but the compiler didn't seem to like the keyword "import":
>
> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> Setup.lhs build
> Preprocessing executables for Test-1.0...
> Building Test-1.0...
> [1 of 1] Compiling Main             ( ./timer.hs,
> dist/build/timer/timer-tmp/Main.o )
>
> ./timer.hs:29:8: parse error on input `import'
>

Hi Vasili,

To fix that error, you probably just need to add the line "Extensions:
ForeignFunctionInterface" to the .cabal file.   (That is the
equivalent of calling ghc by itself with the command-line arguments
-fffi or -XForeignFunctionInterface.)

Hope that helps,
-Judah
From vigalchin at gmail.com  Tue Jun 10 00:32:15 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun 10 00:24:34 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
Message-ID: <5ae4f2ba0806092132k5cb08c90tc0809dc2e0542044@mail.gmail.com>

Thanks Judah ... getting closer now.

Vasili

On Mon, Jun 9, 2008 at 11:25 PM, Judah Jacobson <judah.jacobson@gmail.com>
wrote:

> 2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
> > Ryan,
> >
> >      I tried but the compiler didn't seem to like the keyword "import":
> >
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> > Setup.lhs build
> > Preprocessing executables for Test-1.0...
> > Building Test-1.0...
> > [1 of 1] Compiling Main             ( ./timer.hs,
> > dist/build/timer/timer-tmp/Main.o )
> >
> > ./timer.hs:29:8: parse error on input `import'
> >
>
> Hi Vasili,
>
> To fix that error, you probably just need to add the line "Extensions:
> ForeignFunctionInterface" to the .cabal file.   (That is the
> equivalent of calling ghc by itself with the command-line arguments
> -fffi or -XForeignFunctionInterface.)
>
> Hope that helps,
> -Judah
>
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From vigalchin at gmail.com  Tue Jun 10 02:01:54 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun 10 01:54:12 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
Message-ID: <5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>

I have tried various things to no avail ....

vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
Setup.lhs build
Preprocessing executables for Test-1.0...
Building Test-1.0...
[1 of 1] Compiling Main             ( ./timer.hs,
dist/build/timer/timer-tmp/Main.o )

./timer.hs:22:0:
    Unacceptable argument type in foreign declaration: Sigval
    When checking declaration:
        foreign import ccall safe "wrapper" mkNotify
          :: Notify -> IO (FunPtr Notify)

=> here is my Sigval def

data Sigval = SivalInt Int | SivalPtr (Ptr Char)

I did a find/grep for "Unacceptable argument" in the ghc compiler source and
assuming no typo I didn't find. ??

Thanks.

Kind regards, Vasili




On Mon, Jun 9, 2008 at 11:25 PM, Judah Jacobson <judah.jacobson@gmail.com>
wrote:

> 2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
> > Ryan,
> >
> >      I tried but the compiler didn't seem to like the keyword "import":
> >
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> > Setup.lhs build
> > Preprocessing executables for Test-1.0...
> > Building Test-1.0...
> > [1 of 1] Compiling Main             ( ./timer.hs,
> > dist/build/timer/timer-tmp/Main.o )
> >
> > ./timer.hs:29:8: parse error on input `import'
> >
>
> Hi Vasili,
>
> To fix that error, you probably just need to add the line "Extensions:
> ForeignFunctionInterface" to the .cabal file.   (That is the
> equivalent of calling ghc by itself with the command-line arguments
> -fffi or -XForeignFunctionInterface.)
>
> Hope that helps,
> -Judah
>
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From jules at jellybean.co.uk  Tue Jun 10 07:01:29 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Tue Jun 10 06:53:50 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <87ve0ibt6n.fsf@malde.org>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>	<200806061412.23585.g9ks157k@acme.softbase.org>	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org>
Message-ID: <484E5F09.2030009@jellybean.co.uk>

Ketil Malde wrote:
> And - is there a way to make GHCi use aliased qualification?  I find
> my self typing detailed taxonomies all the time there.
> 
> For Haskell', I would relly like to have good, generic
> classes/interfaces for this, so that a) code becomes readable
> (including import lists), and b) code can be written more generically,
> and c) it becomes easier to switch between e.g. different string
> types. 

Class abstraction is not zero cost. Abstract far enough that GHC can't 
see how to resolve dictionaries at compile time (insufficient inlining) 
and you will not only slow things down just because of the dictionary 
cost, you'll also break all those nice RULES and lose your fusion.

As for import syntax / readability, whilst I'm familiar with the 
problems (most are mentioned in this thread) I'm not aware of any 
concrete proposal to improve the situation.

Jules
From icfp.publicity at googlemail.com  Tue Jun 10 08:47:31 2008
From: icfp.publicity at googlemail.com (Matthew Fluet (ICFP Publicity Chair))
Date: Tue Jun 10 08:39:48 2008
Subject: [Haskell-cafe] DEFUN08: Final Call for Talks & Tutorials (deadline:
	June 27)
Message-ID: <53ff55480806100547h4befc974mfede15c2e21eabed@mail.gmail.com>

                   Final Call for Talks and Tutorials
     ACM SIGPLAN 2008 Developer Tracks on Functional Programming
                http://www.deinprogramm.de/defun-2008/
             Victoria, BC, Canada, 25, 27 September, 2008
       The workshop will be held in conjunction with ICFP 2008.
               http://www.icfpconference.org/icfp2008/

Important dates

Proposal Deadline: June 27, 2008, 0:00 UTC
Notification:      July 14, 2008

DEFUN 2008 invites functional programmers who know how to solve
problems with functional progamming to give talks and lead tutorials
at the The ICFP Developer Tracks.

We want to know about your favorite programming techniques, powerful
libraries, and engineering approaches you've used that the world
should know about and apply to other projects. We want to know how to
be productive using functional programming, write better code, and
avoid common pitfalls.

We invite proposals for presentations in the following categories:

How-to talks:
  45-minute "how-to" talks that provide specific information on how to
  solve specific problems using functional programming. These talks
  focus on concrete examples, but provide useful information for
  developers working on different projects or in different contexts.

  Examples:
  - "How I made Haskell an extension language for SAP R/3."
  - "How I replaced /sbin/init by a Scheme program."
  - "How I hooked up my home appliances to an Erlang control system."
  - "How I got an SML program to drive my BMW."

General language tutorials:
  Half-day general language tutorials for specific functional
  languages, given by recognized experts for the respective languages.

Technology tutorials:
  Half-day tutorials on techniques, technologies, or solving specific
  problems in functional programming.

  Examples:
  - how to make the best use of specific FP programming techniques
  - how to inject FP into a development team used to more conventional
    technologies
  - how to connect FP to existing libraries / frameworks / platforms
  - how to deliver high-performance systems with FP
  - how to deliver high-reliability systems with FP

Remember that your audience will include computing professionals who
are not academics and who may not already be experts on functional
programming.

Presenters of tutorials will receive free registration to ICFP 2008.

Submission guidelines

Submit a proposal of 150 words or less for either a 45-minute talk
with a short Q&A session at the end, or a 300-word-or-less proposal
for a 3-hour tutorial, where you present your material, but also give
participants a chance to practice it on their own laptops.

Some advice:
- Give it a simple and straightforward title or name; avoid fancy
  titles or puns that would make it harder for attendees to figure out
  what you'll be talking about.
- Clearly identify the level of the talk: What knowledge should people
  have when they come to the presentation or tutorial?
- Explain why people will want to attend:
  is the language or library useful for a wide range of attendees? Is
  the pitfall you're identifying common enough that a wide range of
  attendees is likely to encounter it?
- Explain what benefits attendees are expected to take home to their
  own projects.
- For a tutorial, explain how you want to structure the time, and what
  you expect to have attendees to do on their laptops. List what
  software you'll expect attendees to have installed prior to coming.

Submit your proposal in plain text electronically to
defun-2008-submission-AT-deinprogramm.de by the beginning of Friday,
June 27, Universal Coordinated Time.

Organizers
Kathleen Fisher         AT&T Labs
Simon Peyton Jones      Microsoft Research
Mike Sperber (co-chair) DeinProgramm
Don Stewart (co-chair)  Galois
From igloo at earth.li  Tue Jun 10 11:54:32 2008
From: igloo at earth.li (Ian Lynagh)
Date: Tue Jun 10 11:46:49 2008
Subject: [Haskell-cafe] Unable to hc-build ghc 6.6.1
In-Reply-To: <507725E31752A74CB00728FA6C17D99C09E1039D@NYWEXMB29.msad.ms.com>
References: <507725E31752A74CB00728FA6C17D99C09E1039D@NYWEXMB29.msad.ms.com>
Message-ID: <20080610155432.GA30373@matrix.chaos.earth.li>

On Mon, Jun 09, 2008 at 01:48:48PM -0400, Re, Joseph (IT) wrote:
> I'm trying to do a registered hc-build on linux2.4 x86 with ghc 6.6.1.

You're likely to find it easier to bootstrap by installing a bindist
onto the machine, unless that is impossible for some reason.

> GenApply.o(.text+0x13a55): In function `s5cr_info':
> : undefined reference to `base_DataziList_zdsintersperse_info'

Nothing comes to mind. Were the libraries rebuilt after building
GenApply on the machine on which the hc files were generated?


Thanks
Ian

From Joseph.Re at MorganStanley.com  Tue Jun 10 12:08:14 2008
From: Joseph.Re at MorganStanley.com (Re, Joseph (IT))
Date: Tue Jun 10 12:01:28 2008
Subject: [Haskell-cafe] Unable to hc-build ghc 6.6.1
In-Reply-To: <20080610155432.GA30373@matrix.chaos.earth.li>
References: <507725E31752A74CB00728FA6C17D99C09E1039D@NYWEXMB29.msad.ms.com>
	<20080610155432.GA30373@matrix.chaos.earth.li>
Message-ID: <507725E31752A74CB00728FA6C17D99C09E1080D@NYWEXMB29.msad.ms.com>

> From: Ian Lynagh [mailto:igloo@earth.li] 
> You're likely to find it easier to bootstrap by installing a 
> bindist onto the machine, unless that is impossible for some reason.

Unfortunately it is due to policy.

> > GenApply.o(.text+0x13a55): In function `s5cr_info':
> > : undefined reference to `base_DataziList_zdsintersperse_info'
> 
> Nothing comes to mind. Were the libraries rebuilt after 
> building GenApply on the machine on which the hc files were generated?

Nope. After building the hc tarball with a new copy of ghc 6.6.1 on the
host machine, I pulled it along with a new copy of the source tarball
from http://www.haskell.org/ghc onto the target machine. Untarred the hc
files, changed mk/build.mk and fixed mk/bootstrap.mk, and ran
distrib/hc-build.
--------------------------------------------------------

NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.
From zunino at di.unipi.it  Tue Jun 10 12:12:57 2008
From: zunino at di.unipi.it (Roberto Zunino)
Date: Tue Jun 10 12:05:25 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <3c6288ab0806090759q4fcbdb5bu2da7c620fa4d5f7f@mail.gmail.com>
References: <484D2E21.7000005@daimi.au.dk>	<20080609134049.GA19510@netsoc.tcd.ie>
	<17733353.post@talk.nabble.com>	<20080609140413.GC19510@netsoc.tcd.ie>	<3c6288ab0806090756g1ad94967v9e6f6a8c75f33e10@mail.gmail.com>
	<3c6288ab0806090759q4fcbdb5bu2da7c620fa4d5f7f@mail.gmail.com>
Message-ID: <484EA809.8050101@di.unipi.it>

Sean Leather wrote:
> inside :: ((forall a. W (t a))-> W (forall a. (t a)))
> --inside (W x) = W x -- (a) FAILS
> --inside = W . unW -- (b) FAILS
> inside x = W (unW x) -- (c) WORKS
>
> Are there any pointers for developing a better understanding or
> intuition of this?

Usually, making type arguments explicit helps: that is, assume that each
polymorphic value is actually a function expecting a type (the a in
forall a. ...) and returning the value related to that type. The last
'inside' definition becomes:

  inside x = W (\type -> unW (x type))

Note that we do not know at this time what will be the actual "type"
above. But that's OK, since we can return a type-lambda.

Instead, pattern matching desugars to:

  inside x = case x of ...

But wait! x is a function (because it's polymorphic) and we can not
pattern match on that! And, at this time, we do not know the
type-argument for x. So we are stuck.

Also, type-lambdas and type-arguments are hard to insert in W . unW .

For more tricks with type-lambdas, look up "System F".

Hope this helps,
Zun.
From derek.a.elkins at gmail.com  Tue Jun 10 12:35:44 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Tue Jun 10 12:28:05 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <484EA809.8050101@di.unipi.it>
References: <484D2E21.7000005@daimi.au.dk>
	<20080609134049.GA19510@netsoc.tcd.ie> <17733353.post@talk.nabble.com>
	<20080609140413.GC19510@netsoc.tcd.ie>
	<3c6288ab0806090756g1ad94967v9e6f6a8c75f33e10@mail.gmail.com>
	<3c6288ab0806090759q4fcbdb5bu2da7c620fa4d5f7f@mail.gmail.com>
	<484EA809.8050101@di.unipi.it>
Message-ID: <1213115744.7306.48.camel@derek-laptop>

On Tue, 2008-06-10 at 18:12 +0200, Roberto Zunino wrote:
> Sean Leather wrote:
> > inside :: ((forall a. W (t a))-> W (forall a. (t a)))
> > --inside (W x) = W x -- (a) FAILS
> > --inside = W . unW -- (b) FAILS
> > inside x = W (unW x) -- (c) WORKS
> >
> > Are there any pointers for developing a better understanding or
> > intuition of this?
> 
> Usually, making type arguments explicit helps: that is, assume that each
> polymorphic value is actually a function expecting a type (the a in
> forall a. ...) and returning the value related to that type. The last
> 'inside' definition becomes:
> 
>   inside x = W (\type -> unW (x type))
> 
> Note that we do not know at this time what will be the actual "type"
> above. But that's OK, since we can return a type-lambda.
> 
> Instead, pattern matching desugars to:
> 
>   inside x = case x of ...
> 
> But wait! x is a function (because it's polymorphic) and we can not
> pattern match on that! And, at this time, we do not know the
> type-argument for x. So we are stuck.
> 
> Also, type-lambdas and type-arguments are hard to insert in W . unW .

This is the lack of impredicativity.

W :: a -> W a
To get the result type W (forall a. t a), W must instantiate the a in
W's type to (forall a. t a).  Further we then pass it to (.) which has
type (b -> c) -> (a -> b) -> a -> c and thus require instantiating both
a and b to higher-rank types.  A predicative type system does not allow
instantiating type variables to quantified types.


From ryani.spam at gmail.com  Tue Jun 10 14:18:13 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Tue Jun 10 14:10:44 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
	<5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
Message-ID: <2f9b2d30806101118v1c261690h1f3088a1e8d553c@mail.gmail.com>

I'm not super experienced with the FFI (foreign function interface); I
only used C types that you can get from #include <HsFFI.h>, like
Word32.

You might need to make Sigval an instance of Storable, or do some
magic with ForeignPtrs.  Good luck! :)

  -- ryan


On 6/9/08, Galchin, Vasili <vigalchin@gmail.com> wrote:
> I have tried various things to no avail ....
>
> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$
> runhaskell Setup.lhs build
> Preprocessing executables for Test-1.0...
> Building Test-1.0...
> [1 of 1] Compiling Main             ( ./timer.hs,
> dist/build/timer/timer-tmp/Main.o )
>
> ./timer.hs:22:0:
>     Unacceptable argument type in foreign declaration: Sigval
>     When checking declaration:
>         foreign import ccall safe "wrapper" mkNotify
>           :: Notify -> IO (FunPtr Notify)
>
> => here is my Sigval def
>
> data Sigval = SivalInt Int | SivalPtr (Ptr Char)
>
> I did a find/grep for "Unacceptable argument" in the ghc compiler source and
> assuming no typo I didn't find. ??
>
> Thanks.
>
> Kind regards, Vasili
>
>
>
>
> On Mon, Jun 9, 2008 at 11:25 PM, Judah Jacobson <judah.jacobson@gmail.com>
> wrote:
>
> > 2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
> >
> > > Ryan,
> > >
> > >      I tried but the compiler didn't seem to like the keyword "import":
> > >
> > >
> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$
> runhaskell
> > > Setup.lhs build
> > > Preprocessing executables for Test-1.0...
> > > Building Test-1.0...
> > > [1 of 1] Compiling Main             ( ./timer.hs,
> > > dist/build/timer/timer-tmp/Main.o )
> > >
> > > ./timer.hs:29:8: parse error on input `import'
> > >
> >
> > Hi Vasili,
> >
> > To fix that error, you probably just need to add the line "Extensions:
> > ForeignFunctionInterface" to the .cabal file.   (That is the
> > equivalent of calling ghc by itself with the command-line arguments
> > -fffi or -XForeignFunctionInterface.)
> >
> > Hope that helps,
> > -Judah
> >
>
>
From ryani.spam at gmail.com  Tue Jun 10 14:23:36 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Tue Jun 10 14:15:53 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <2f9b2d30806101118v1c261690h1f3088a1e8d553c@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
	<5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
	<2f9b2d30806101118v1c261690h1f3088a1e8d553c@mail.gmail.com>
Message-ID: <2f9b2d30806101123s169efbf1te0abcfcb79f6bc46@mail.gmail.com>

Also, if you always plan to partially apply your notification function
and you just want a simple callback:

void (*pCallbackFn)(void);

You should be able to do something like this:

> type Callback = IO ()
> foreign import ccall "wrapper" mkCallback :: Callback -> IO (FunPtr Callback)

You can then do something like

> main = do
>    let event = Sigval { ... fill in here ... }
>    callback <- mkCallback (notify event)
>    ...
>    freeHaskellFunPtr callback


On 6/10/08, Ryan Ingram <ryani.spam@gmail.com> wrote:
> I'm not super experienced with the FFI (foreign function interface); I
> only used C types that you can get from #include <HsFFI.h>, like
> Word32.
>
> You might need to make Sigval an instance of Storable, or do some
> magic with ForeignPtrs.  Good luck! :)
>
>  -- ryan
>
>
> On 6/9/08, Galchin, Vasili <vigalchin@gmail.com> wrote:
> > I have tried various things to no avail ....
> >
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$
> > runhaskell Setup.lhs build
> > Preprocessing executables for Test-1.0...
> > Building Test-1.0...
> > [1 of 1] Compiling Main             ( ./timer.hs,
> > dist/build/timer/timer-tmp/Main.o )
> >
> > ./timer.hs:22:0:
> >     Unacceptable argument type in foreign declaration: Sigval
> >     When checking declaration:
> >         foreign import ccall safe "wrapper" mkNotify
> >           :: Notify -> IO (FunPtr Notify)
> >
> > => here is my Sigval def
> >
> > data Sigval = SivalInt Int | SivalPtr (Ptr Char)
> >
> > I did a find/grep for "Unacceptable argument" in the ghc compiler source and
> > assuming no typo I didn't find. ??
> >
> > Thanks.
> >
> > Kind regards, Vasili
> >
> >
> >
> >
> > On Mon, Jun 9, 2008 at 11:25 PM, Judah Jacobson <judah.jacobson@gmail.com>
> > wrote:
> >
> > > 2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
> > >
> > > > Ryan,
> > > >
> > > >      I tried but the compiler didn't seem to like the keyword "import":
> > > >
> > > >
> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$
> > runhaskell
> > > > Setup.lhs build
> > > > Preprocessing executables for Test-1.0...
> > > > Building Test-1.0...
> > > > [1 of 1] Compiling Main             ( ./timer.hs,
> > > > dist/build/timer/timer-tmp/Main.o )
> > > >
> > > > ./timer.hs:29:8: parse error on input `import'
> > > >
> > >
> > > Hi Vasili,
> > >
> > > To fix that error, you probably just need to add the line "Extensions:
> > > ForeignFunctionInterface" to the .cabal file.   (That is the
> > > equivalent of calling ghc by itself with the command-line arguments
> > > -fffi or -XForeignFunctionInterface.)
> > >
> > > Hope that helps,
> > > -Judah
> > >
> >
> >
>
From ryani.spam at gmail.com  Tue Jun 10 14:28:34 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Tue Jun 10 14:20:50 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <1213115744.7306.48.camel@derek-laptop>
References: <484D2E21.7000005@daimi.au.dk>
	<20080609134049.GA19510@netsoc.tcd.ie> <17733353.post@talk.nabble.com>
	<20080609140413.GC19510@netsoc.tcd.ie>
	<3c6288ab0806090756g1ad94967v9e6f6a8c75f33e10@mail.gmail.com>
	<3c6288ab0806090759q4fcbdb5bu2da7c620fa4d5f7f@mail.gmail.com>
	<484EA809.8050101@di.unipi.it> <1213115744.7306.48.camel@derek-laptop>
Message-ID: <2f9b2d30806101128i14c0380bj70626a5f8e5a34c4@mail.gmail.com>

On 6/10/08, Derek Elkins <derek.a.elkins@gmail.com> wrote:
> This is the lack of impredicativity.
>
> W :: a -> W a
> To get the result type W (forall a. t a), W must instantiate the a in
> W's type to (forall a. t a).  Further we then pass it to (.) which has
> type (b -> c) -> (a -> b) -> a -> c and thus require instantiating both
> a and b to higher-rank types.  A predicative type system does not allow
> instantiating type variables to quantified types.

Although if I am reading the literature correctly, that definition
will likely typecheck in the next GHC...

http://research.microsoft.com/~simonpj/papers/boxy/

  -- ryan
From Joseph.Re at MorganStanley.com  Tue Jun 10 15:19:37 2008
From: Joseph.Re at MorganStanley.com (Re, Joseph (IT))
Date: Tue Jun 10 15:12:28 2008
Subject: [Haskell-cafe] Unable to hc-build ghc 6.6.1
References: <507725E31752A74CB00728FA6C17D99C09E1039D@NYWEXMB29.msad.ms.com>
	<20080610155432.GA30373@matrix.chaos.earth.li> 
Message-ID: <507725E31752A74CB00728FA6C17D99C09E10993@NYWEXMB29.msad.ms.com>

> -----Original Message-----
> > From: Ian Lynagh [mailto:igloo@earth.li]
> > Nothing comes to mind. Were the libraries rebuilt after building 
> > GenApply on the machine on which the hc files were generated?
> 
> Nope. After building the hc tarball with a new copy of ghc 
> 6.6.1 on the host machine, I pulled it along with a new copy 
> of the source tarball from http://www.haskell.org/ghc onto 
> the target machine. Untarred the hc files, changed 
> mk/build.mk and fixed mk/bootstrap.mk, and ran distrib/hc-build.

Just wanted to note that I get the same error with ghc 6.4.2 (after
patching ghc/Makefile's ordering of the SUBDIRS line as noted in
http://hackage.haskell.org/trac/ghc/ticket/841, adding "-lncurses" to
mk/bootstrap.mk, and removing ghc 6.6.1 to prevent conflicts).
--------------------------------------------------------

NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.
From stansife at caltech.edu  Tue Jun 10 20:23:58 2008
From: stansife at caltech.edu (Eric Stansifer)
Date: Tue Jun 10 20:16:13 2008
Subject: [Haskell-cafe] lhs syntax highlighting in vim
Message-ID: <2e58fd390806101723p3e74c6cfkce28786e9325afbd@mail.gmail.com>

Hello,

The syntax highlighting file for literate haskell in vim says that its
maintainer is haskell-cafe@haskell.org, so hopefully one of you will
find this relevant.

In literate haskell files, vim optionally highlights the non-code text
according to TeX markup.  The syntax highlighting file looks for key
phrases (e.g., "\documentclass") to decide whether to use TeX markup
highlighting;  but it (erroneously, in my opinion, and at variance
with the documentation) will use TeX markup highlighting on any lhs
file that contains the '%' character anywhere in it.  The bug is in
line 74 of version 1.01 of the lhaskell.vim syntax highlighting file.

Thanks,
Eric
From derek.a.elkins at gmail.com  Tue Jun 10 23:28:25 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Tue Jun 10 23:20:49 2008
Subject: [Haskell-cafe] Moving "forall" over type constructors
In-Reply-To: <2f9b2d30806101128i14c0380bj70626a5f8e5a34c4@mail.gmail.com>
References: <484D2E21.7000005@daimi.au.dk>
	<20080609134049.GA19510@netsoc.tcd.ie> <17733353.post@talk.nabble.com>
	<20080609140413.GC19510@netsoc.tcd.ie>
	<3c6288ab0806090756g1ad94967v9e6f6a8c75f33e10@mail.gmail.com>
	<3c6288ab0806090759q4fcbdb5bu2da7c620fa4d5f7f@mail.gmail.com>
	<484EA809.8050101@di.unipi.it> <1213115744.7306.48.camel@derek-laptop>
	<2f9b2d30806101128i14c0380bj70626a5f8e5a34c4@mail.gmail.com>
Message-ID: <1213154905.7306.59.camel@derek-laptop>

On Tue, 2008-06-10 at 11:28 -0700, Ryan Ingram wrote:
> On 6/10/08, Derek Elkins <derek.a.elkins@gmail.com> wrote:
> > This is the lack of impredicativity.
> >
> > W :: a -> W a
> > To get the result type W (forall a. t a), W must instantiate the a in
> > W's type to (forall a. t a).  Further we then pass it to (.) which has
> > type (b -> c) -> (a -> b) -> a -> c and thus require instantiating both
> > a and b to higher-rank types.  A predicative type system does not allow
> > instantiating type variables to quantified types.
> 
> Although if I am reading the literature correctly, that definition
> will likely typecheck in the next GHC...
> 
> http://research.microsoft.com/~simonpj/papers/boxy/

Actually some support was hacked into the current version of GHC.
http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#impredicative-polymorphism

From aeyakovenko at gmail.com  Wed Jun 11 00:13:17 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Wed Jun 11 00:05:33 2008
Subject: [Haskell-cafe] blas: ghc-6.8.2: unable to load package `blas-0.4'
Message-ID: <e26d18e40806102113q16864322xa93c86f4e3a5cbf0@mail.gmail.com>

Patric,

I am trying to use your blas package, but I am getting a missing symbol error.

> import Data.Matrix.Dense.IO
> mm::(IOMatrix (Int,Int) Double) <- newListMatrix (1,1) [1.0]
Loading package storable-complex-0.1 ... linking ... done.
Loading package ieee-0.1 ... linking ... done.
Loading package old-locale-1.0.0.0 ... linking ... done.
Loading package old-time-1.0.0.0 ... linking ... done.
Loading package random-1.0.0.0 ... linking ... done.
Loading package QuickCheck-1.1.0.0 ... linking ... done.
Loading package blas-0.4 ... linking ... <interactive>:
/usr/lib/blas-0.4/ghc-6.8.2/HSblas-0.4.o: unknown symbol `cblas_ddot'
ghc-6.8.2: unable to load package `blas-0.4'

any ideas what i am missing?

Thanks,
Anatoly
From dons at galois.com  Wed Jun 11 00:15:07 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 11 00:07:23 2008
Subject: [Haskell-cafe] blas: ghc-6.8.2: unable to load package `blas-0.4'
In-Reply-To: <e26d18e40806102113q16864322xa93c86f4e3a5cbf0@mail.gmail.com>
References: <e26d18e40806102113q16864322xa93c86f4e3a5cbf0@mail.gmail.com>
Message-ID: <20080611041507.GA32117@scytale.galois.com>

aeyakovenko:
> Patric,
> 
> I am trying to use your blas package, but I am getting a missing symbol error.
> 
> > import Data.Matrix.Dense.IO
> > mm::(IOMatrix (Int,Int) Double) <- newListMatrix (1,1) [1.0]
> Loading package storable-complex-0.1 ... linking ... done.
> Loading package ieee-0.1 ... linking ... done.
> Loading package old-locale-1.0.0.0 ... linking ... done.
> Loading package old-time-1.0.0.0 ... linking ... done.
> Loading package random-1.0.0.0 ... linking ... done.
> Loading package QuickCheck-1.1.0.0 ... linking ... done.
> Loading package blas-0.4 ... linking ... <interactive>:
> /usr/lib/blas-0.4/ghc-6.8.2/HSblas-0.4.o: unknown symbol `cblas_ddot'
> ghc-6.8.2: unable to load package `blas-0.4'
> 
> any ideas what i am missing?

Missing -lcblas perhaps? The C library isn't being found.

-- Don
From aeyakovenko at gmail.com  Wed Jun 11 00:28:27 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Wed Jun 11 00:20:42 2008
Subject: [Haskell-cafe] blas: ghc-6.8.2: unable to load package `blas-0.4'
In-Reply-To: <20080611041507.GA32117@scytale.galois.com>
References: <e26d18e40806102113q16864322xa93c86f4e3a5cbf0@mail.gmail.com>
	<20080611041507.GA32117@scytale.galois.com>
Message-ID: <e26d18e40806102128l49f615a1v751438633fd0fecf@mail.gmail.com>

>> /usr/lib/blas-0.4/ghc-6.8.2/HSblas-0.4.o: unknown symbol `cblas_ddot'
>> ghc-6.8.2: unable to load package `blas-0.4'
>>
>> any ideas what i am missing?
>
> Missing -lcblas perhaps? The C library isn't being found.

$ ll /usr/lib/libcblas.*
lrwxrwxrwx 1 root root 25 Jun 10 20:57 /usr/lib/libcblas.a ->
blas/reference/libcblas.a
lrwxrwxrwx 1 root root 26 Jun 10 20:57 /usr/lib/libcblas.so ->
blas/reference/libcblas.so
lrwxrwxrwx 1 root root 28 Jun 10 20:57 /usr/lib/libcblas.so.0 ->
blas/reference/libcblas.so.0

I think its installed correctly,

$ nm /usr/lib/libcblas.*  | grep cblas_ddot
cblas_ddot.o:
00000000 T cblas_ddot
nm: /usr/lib/libcblas.so: no symbols
nm: /usr/lib/libcblas.so.0: no symbols
From aeyakovenko at gmail.com  Wed Jun 11 00:38:36 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Wed Jun 11 00:30:52 2008
Subject: [Haskell-cafe] blas: ghc-6.8.2: unable to load package `blas-0.4'
In-Reply-To: <e26d18e40806102128l49f615a1v751438633fd0fecf@mail.gmail.com>
References: <e26d18e40806102113q16864322xa93c86f4e3a5cbf0@mail.gmail.com>
	<20080611041507.GA32117@scytale.galois.com>
	<e26d18e40806102128l49f615a1v751438633fd0fecf@mail.gmail.com>
Message-ID: <e26d18e40806102138s58e2f49el1a492b357c7038e7@mail.gmail.com>

nevermind, i am a little slow today.  ghci -lcblas
From clawsie at fastmail.fm  Wed Jun 11 01:51:53 2008
From: clawsie at fastmail.fm (brad clawsie)
Date: Wed Jun 11 01:44:18 2008
Subject: [Haskell-cafe] wanted: Network.Curl examples
Message-ID: <864p808qo6.fsf@laptop.gateway.2wire.net>

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

in search of some trivial examples using Network.Curl, preferrably
posted here:

http://haskell.org/haskellwiki/Network.Curl

some of this stuff i can figure out, but setting the curl
WriteFunction, as discussed here:

http://code.haskell.org/~dons/docs/curl/Network-Curl-Opts.html#t%3AWriteFunction

is nonobvious.

any info would be useful, curl is a great library and it would be nice
if using it were more straightforward

thanks
brad
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Version: GnuPG v2.0.9 (FreeBSD)

iEYEARECAAYFAkhPaAAACgkQxRg3RkRK91OQrQCfTt+xzvqIAxDkqq8/P85ZZjON
HWgAoK3L/1JUQjdaWHcHfutKvI3nPJUc
=BfuR
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From duncan.coutts at worc.ox.ac.uk  Wed Jun 11 06:05:09 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun 11 05:53:28 2008
Subject: [Haskell-cafe] blas: ghc-6.8.2: unable to load package `blas-0.4'
In-Reply-To: <e26d18e40806102138s58e2f49el1a492b357c7038e7@mail.gmail.com>
References: <e26d18e40806102113q16864322xa93c86f4e3a5cbf0@mail.gmail.com>
	<20080611041507.GA32117@scytale.galois.com>
	<e26d18e40806102128l49f615a1v751438633fd0fecf@mail.gmail.com>
	<e26d18e40806102138s58e2f49el1a492b357c7038e7@mail.gmail.com>
Message-ID: <1213178709.15010.476.camel@localhost>


On Tue, 2008-06-10 at 21:38 -0700, Anatoly Yakovenko wrote:
> nevermind, i am a little slow today.  ghci -lcblas

You should not need to do this manually. The blas package should say
that it needs this library, in which case ghc and ghci will pick it up
automatically. Using "ghci -package foo" is supposed to "Just Work"tm.
If it doesn't then that's generally the fault of the package.

Duncan

From igloo at earth.li  Wed Jun 11 06:29:35 2008
From: igloo at earth.li (Ian Lynagh)
Date: Wed Jun 11 06:21:49 2008
Subject: [Haskell-cafe] lhs syntax highlighting in vim
In-Reply-To: <2e58fd390806101723p3e74c6cfkce28786e9325afbd@mail.gmail.com>
References: <2e58fd390806101723p3e74c6cfkce28786e9325afbd@mail.gmail.com>
Message-ID: <20080611102935.GA14493@matrix.chaos.earth.li>

On Wed, Jun 11, 2008 at 01:23:58AM +0100, Eric Stansifer wrote:
> 
> The syntax highlighting file for literate haskell in vim says that its
> maintainer is haskell-cafe@haskell.org, so hopefully one of you will
> find this relevant.
> 
> In literate haskell files, vim optionally highlights the non-code text
> according to TeX markup.  The syntax highlighting file looks for key
> phrases (e.g., "\documentclass") to decide whether to use TeX markup
> highlighting;  but it (erroneously, in my opinion, and at variance
> with the documentation) will use TeX markup highlighting on any lhs
> file that contains the '%' character anywhere in it.  The bug is in
> line 74 of version 1.01 of the lhaskell.vim syntax highlighting file.

I agree that this is wrong. It used to only look at the first 20 lines,
so we were covering the case where a TeX file began with some TeX
comments. We'd also look for ^\s*%, rather than a % anywhere. If we are
going to look at the whole file then checking for comments isn't
necessary.


Thanks
Ian

From silva.samuel at gmail.com  Wed Jun 11 06:44:57 2008
From: silva.samuel at gmail.com (Samuel Silva)
Date: Wed Jun 11 06:37:15 2008
Subject: [Haskell-cafe] running haddock and lhs2TeX
Message-ID: <382ead9b0806110344h7a68b9cco154e8275ea9ffaa6@mail.gmail.com>

Hello

I'm using haddock to my Literate Haskell code, and it runs very well.
I prefer Literate Haskell instead Haskell because old code remain untouched.
It also is possible run latex over my code.
But running lhs2TeX is even better.
However lhs2TeX doesn't proccess with some haddock information.
I won't change or format haddock documentation but using two tools is
a valuable help at development.
I would know that somebody solve thi issue and how?

To solve this issue I build processor, using perl, that escapes
characters like | and @.
This preprocessor just escapes characters within \begin{code} ... \end{code}.

#####################################################################
# This scripts process Literate Haskell Script itself to be process
#   by lhs2TeX with haddock comments.
#

use strict;
use warnings;
my @tag=();
while (<>) {
    if ($_ =~ /\\begin{(.*)}/) {push @tag => $1;}
    elsif ($_ =~ /\\end{(.*)}/ and $1 eq $tag[@tag-1]) {pop @tag;}
    if ( elem("code",@tag) and /(.*)--(.*)/) {
        print $1 => process($2) => "\n";
    }
    else {        print;    }
}
sub process{
    my ($input) = @_;
    $input =~ s/\|/\|\|/g;          # escapes |
    $input =~ s/\@/\@\@/g;    # escapes @
    $input =~ s/\^//g;               # drop ^
    $input =~ s/\"/\'/g;             # change " into '
    return "--$input";
}
sub elem {
    my ($x,@xs) = @_;
    my $res = 0;
    for (@xs) {$res=1 if $x eq $_}
    return $res;
}
#####################################################################


-- 
Don't hug that, Hugs ME!
Samuel Silva
From chris at eidhof.nl  Wed Jun 11 08:11:02 2008
From: chris at eidhof.nl (Chris Eidhof)
Date: Wed Jun 11 08:03:17 2008
Subject: [Haskell-cafe] wanted: Network.Curl examples
In-Reply-To: <864p808qo6.fsf@laptop.gateway.2wire.net>
References: <864p808qo6.fsf@laptop.gateway.2wire.net>
Message-ID: <A850D98D-4A37-48A9-98CD-B4E444E55FA3@eidhof.nl>

Hey Brad,

I wrote a blog-post with some curl-examples in there, it's a small  
mashup of last.fm and upcoming, check it at

http://tinyurl.com/5d8jx7

Enjoy,
-chris

On 11 jun 2008, at 07:51, brad clawsie wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> in search of some trivial examples using Network.Curl, preferrably
> posted here:
>
> http://haskell.org/haskellwiki/Network.Curl
>
> some of this stuff i can figure out, but setting the curl
> WriteFunction, as discussed here:
>
> http://code.haskell.org/~dons/docs/curl/Network-Curl-Opts.html#t%3AWriteFunction
>
> is nonobvious.
>
> any info would be useful, curl is a great library and it would be nice
> if using it were more straightforward
>
> thanks
> brad
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v2.0.9 (FreeBSD)
>
> iEYEARECAAYFAkhPaAAACgkQxRg3RkRK91OQrQCfTt+xzvqIAxDkqq8/P85ZZjON
> HWgAoK3L/1JUQjdaWHcHfutKvI3nPJUc
> =BfuR
> -----END PGP SIGNATURE-----
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From andrewcoppin at btinternet.com  Wed Jun 11 14:17:03 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun 11 14:16:19 2008
Subject: [Haskell-cafe] Simple list processing
Message-ID: <4850169F.4050003@btinternet.com>

OK, so this is a fairly basic question about list processing.

Several times now, I have found myself wanting to process a list to 
produce a new list. However, the way later elements are processed 
depends on what the earlier elements are - in other words, this isn't a 
simple "map".

What is the best way to handle this?

According to the theory, anything that consumes a list and produces a 
value is some kind of fold. [Assuming it traverses the list in a 
sensible order!] So it looks like you could implement this as a fold. 
But should that be a LEFT-fold or a RIGHT-fold? (I always get confused 
between the two!)

Actually, anything that takes a value and processes it repeatedly to 
produce a list is technically an unfold. [Again assuming a sensible 
processing order.] So it looks like this function could also be an 
UNfold. As in, you take a list as input, and keep unfolding until that 
list becomes empty.

So it looks like this can be implemented as a fold or an unfold. But 
neither way looks especially easy. Both of these patterns seem to be 
more general than necessary; I only want to take 1 element of input and 
produce 1 element of output, but keeping track of a running state. I 
guess I could use some sort of state monad and make the whole thing 
monadic - but that again is overkill for what I'm trying to do.

Any hints here?

From dons at galois.com  Wed Jun 11 14:25:17 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 11 14:17:47 2008
Subject: [Haskell-cafe] Simple list processing
In-Reply-To: <4850169F.4050003@btinternet.com>
References: <4850169F.4050003@btinternet.com>
Message-ID: <20080611182517.GF25521@scytale.galois.com>

andrewcoppin:
> OK, so this is a fairly basic question about list processing.
> 
> Several times now, I have found myself wanting to process a list to 
> produce a new list. However, the way later elements are processed 
> depends on what the earlier elements are - in other words, this isn't a 
> simple "map".
> 
> What is the best way to handle this?
> 
> According to the theory, anything that consumes a list and produces a 
> value is some kind of fold. [Assuming it traverses the list in a 
> sensible order!] So it looks like you could implement this as a fold. 
> But should that be a LEFT-fold or a RIGHT-fold? (I always get confused 
> between the two!)
> 

Sounds like a mapAccum, a combination of map and fold,

    http://haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v%3AmapAccumL

If you gave a concrete example it would be easier to diagnose.

-- Don
From daniel.is.fischer at web.de  Wed Jun 11 15:03:11 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Wed Jun 11 14:53:40 2008
Subject: [Haskell-cafe] Simple list processing
In-Reply-To: <4850169F.4050003@btinternet.com>
References: <4850169F.4050003@btinternet.com>
Message-ID: <200806112103.11835.daniel.is.fischer@web.de>

Am Mittwoch, 11. Juni 2008 20:17 schrieb Andrew Coppin:
>
> So it looks like this can be implemented as a fold or an unfold. But
> neither way looks especially easy. Both of these patterns seem to be
> more general than necessary; I only want to take 1 element of input and
> produce 1 element of output, but keeping track of a running state.

scanl might be a sufficiently lightweight way to do that (or it might not, 
depending on what you actually want to do).

From chris at eidhof.nl  Wed Jun 11 16:35:56 2008
From: chris at eidhof.nl (Chris Eidhof)
Date: Wed Jun 11 16:28:13 2008
Subject: [Haskell-cafe] Simple list processing
In-Reply-To: <4850169F.4050003@btinternet.com>
References: <4850169F.4050003@btinternet.com>
Message-ID: <7097A73D-758B-4C7C-A982-6086DDF0C847@eidhof.nl>

Hey Andrew,

On 11 jun 2008, at 20:17, Andrew Coppin wrote:
> According to the theory, anything that consumes a list and produces  
> a value is some kind of fold. [Assuming it traverses the list in a  
> sensible order!] So it looks like you could implement this as a  
> fold. But should that be a LEFT-fold or a RIGHT-fold? (I always get  
> confused between the two!)
Check out http://foldl.com/ and http://foldr.com ;)

-chris
From thomas.dubuisson at gmail.com  Wed Jun 11 16:46:23 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Wed Jun 11 16:40:00 2008
Subject: [Haskell-cafe] Simple list processing
In-Reply-To: <20080611182517.GF25521@scytale.galois.com>
References: <4850169F.4050003@btinternet.com>
	<20080611182517.GF25521@scytale.galois.com>
Message-ID: <1213217183.3033.1.camel@localhost.localdomain>

Why is there no mapAccumL' (strict)?  Just a library deficiency that we
can remedy or am I missing something?

Don Stewart wrote:
> andrewcoppin:
> > OK, so this is a fairly basic question about list processing.
> > 
> > Several times now, I have found myself wanting to process a list to 
> > produce a new list. However, the way later elements are processed 
> > depends on what the earlier elements are - in other words, this isn't a 
> > simple "map".
> > 
> > What is the best way to handle this?
> > 
> > According to the theory, anything that consumes a list and produces a 
> > value is some kind of fold. [Assuming it traverses the list in a 
> > sensible order!] So it looks like you could implement this as a fold. 
> > But should that be a LEFT-fold or a RIGHT-fold? (I always get confused 
> > between the two!)
> > 
> 
> Sounds like a mapAccum, a combination of map and fold,
> 
>     http://haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v%3AmapAccumL
> 
> If you gave a concrete example it would be easier to diagnose.
> 
> -- Don
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From byorgey at gmail.com  Wed Jun 11 17:11:29 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Wed Jun 11 17:03:45 2008
Subject: [Haskell-cafe] Haskell Weekly News: Issue 72 - June 11, 2008
Message-ID: <22fcbd520806111411s54723e70x1af8ba04c98b2622@mail.gmail.com>

---------------------------------------------------------------------------
Haskell Weekly News
http://sequence.complete.org/hwn/20080611
Issue 72 - June 11, 2008
---------------------------------------------------------------------------

   Welcome to issue 72 of HWN, a newsletter covering developments in the
   [1]Haskell community.

   Greetings, Haskellites! As many of you have already heard, Don Stewart
   has passed on the editorship of the HWN to me (Brent Yorgey). I'd like
   to thank Don and John Goerzen for their great work putting it together
   in the past, and I'm excited to make the HWN once again into a
   reliable, useful compendium of happenings in the Haskell community. You
   can expect to see a few changes---for example, hackage uploads will no
   longer be listed in the HWN (unless they are announced on the haskell
   or haskell-cafe mailing lists), since you can now see a dynamically
   updated list on the front page of the Haskell wiki. This edition
   includes all the announcements going back to Issue 71, but only some of
   the blog posts, since I couldn't find a way to get old feed data from
   Planet Haskell. Hopefully next week things will settle down to
   something more normal(ish) and I can begin tinkering with the format.
   Feel free to send suggestions and/or stories for inclusion to me,
   byorgey at gmail dot com. Enjoy---'Putting the W back in HWN!'

Announcements

   hfann. Olivier Boudry [2]announced the first release of the [3]hfann
   module, an interface to the [4]'Fast Artificial Neural Network (FANN)'
   library.

   funsat. Denis Bueno [5]announced a release of [6]funsat, a modern,
   DPLL-style SAT solver written in Haskell. Funsat solves formulas in
   conjunctive normal form and produces a total variable assignment for
   satisfiable problems.

   DEFUN08: Call for talks and tutorials. Matthew Fluet [7]announced the
   final call for talks and tutorials at [8]DEFUN 2008, to be held in
   conjunction with [9]ICFP.

   Cabal-1.4 Release Candidate. Duncan Coutts [10]announced the second
   release candidate for [11]Cabal-1.4.

   Programmer's Minesweeper. Bertram Felgenhauer [12]announced a Haskell
   implementation of [13]Programmer's Minesweeper, which allows
   programmers to implement minesweeper strategies and run them.

   hackage RSS feed. Don Stewart [14]announced a new [15]RSS feed for the
   most recently uploaded packages on [16]Hackage.

   BLAS bindings. Patrick Perry [17]announced a set of bindings for the
   [18]BLAS linear algebra library.

   Xen Control bindings. Thomas DuBuisson [19]announced the [20]hsXenCtrl
   package, with FFI bindings to [21]Xen.

   bloomfilter. Bryan O'Sullivan [22]announced the availability of a fast
   Bloom filter library for Haskell. A Bloom filter is a probabilistic
   data structure that provides a fast set membership querying capability.
   It does not give false negatives, but has a tunable false positive
   rate.

   HCAR. Janis Voigtlaender [23]announced the 14th edition of the
   [24]Haskell Community and Activities Report (HCAR).

   HSmugMug. Daniel Patterson [25]announced [26]HSmugMug, a Haskell
   wrapper to the photo hosting site [27]SmugMug's API.

   LIPL. Sam Lee [28]announced the release of [29]LIPL, a tiny functional
   language implemented as a term project to learn Haskell.

   Glome 0.51. Jim Snow [30]announced version 0.51 of [31]glome, a
   raytracer written in Haskell.

   ChessLibrary. Andrew Wagner [32]announced the [33]ChessLibrary project,
   and mentioned that he is looking for an experienced haskeller to serve
   as a mentor for this project.

   xmonad-utils. Gwern Branwen [34]announced the upload to hackage of
   [35]xmonad-utils, a couple of small Xlib programs which might be useful
   for xmonad users.

   Roguestar. Christopher Lane Hinson [36]announced the release of
   [37]Roguestar 0.2, a science fiction themed roguelike (turn-based,
   chessboard-tiled, role playing) game written in Haskell.

   Streaming Component Combinators. Mario Blazevic [38]announced the 0.1
   release of [39]Streaming Component Combinators in Haskell, based on
   earlier work done in [40]OmniMark.

   Twitter client. Chris Eidhof [41]announced a simple [42]terminal-based
   Twitter client.

   Monad.Reader call for copy. Wouter Swierstra [43]issued a call for copy
   for [44]The Monad.Reader. The submission deadline for Issue 11 is
   August 1.

   category-extras. Edward Kmett [45]announced a new release of the
   [46]category-extras package, involving all sorts of new categorical
   goodness.

   Session Types for Haskell. Matthew Sackman [47]announced the
   availability of [48]Session Types for Haskell. Session types are a
   means of describing communication between multiple threads, and
   statically verifying that the communication being performed is safe and
   conforms to the specification.

   Haddock 2.1.0. David Waern [49]announced the release of [50]Haddock
   2.1.0.

   ReviewBoard. Adam Smyczek [51]announced the release of [52]Haskell
   bindings to [53]ReviewBoard, a development tool designed to monitor
   code changes and analyze dependencies.

   diagrams. Brent Yorgey [54]announced the initial release of
   [55]Graphics.Rendering.Diagrams, an embedded domain-specific language
   for creating simple pictures and diagrams, built on top of the Cairo
   vector graphics library.

   HXT. Uwe Schmidt [56]announced a new release of the [57]Haskell XML
   Toolbox.

   GSoC. Malcolm Wallace [58]announced the seven student projects chosen
   to be funded by the [59]Google Summer of Code.

   bytestring. Don Stewart [60]announced a new major release of
   [61]bytestring, the efficient string library for Haskell, suitable for
   high-performance scenarios.

   HXQ. Leonidas Fegaras [62]announced the release of [63]HXQ, an
   [64]XQuery compiler/interpreter for Haskell.

   Win32-notify. Niklas Broberg [65]announced the first release of
   [66]Win32-notify, an inotify-alike for Windows.

   cpuid. Martin Grabmueller [67]announced the new [68]cpuid package,
   which provides functionality for accessing information about the
   currently running IA-32 processor.

   Emping. Hans van Thiel [69]announced version 0.5 of the [70]Emping
   package, a utility which derives the shortest rules from a table of
   rules.

   datapacker. John Goerzen [71]announced the first release of
   [72]datapacker, a tool to pack files into a minimum number of CDs,
   DVDs, or any other arbitrary bin.

   darcswatch. Joachim Breitner [73]announced the release of
   [74]darcswatch, a tool for tracking darcs patches and repositories.

   Generic Haskell. Thomas van Noort [75]announced the fifth release of
   [76]Generic Haskell, an extension of Haskell that facilitates generic
   programming.

   drawingcombinators. Luke Palmer [77]announced the release of
   [78]graphics-drawingcombinators, a wrapper around OpenGL with a
   functional interface.

   The Monad.Reader. Wouter Swierstra [79]announced the publication of
   Issue 10 of [80]The Monad.Reader, a quarterly magazine about functional
   programming.

   Well-Typed LLP. Ian Lynagh [81]announced that he, Bj?rn Bringert and
   Duncan Coutts have set up a Haskell consultancy company, [82]Well-Typed
   LLP. Their services include application development, library and tool
   maintenance, project advice, and training.

   hgdbmi. Evan Martin [83]announced the [84]hgdbmi package, which wraps
   the operations of attaching GDB to a process and parsing the GDB/MI
   output.

   xmonad. Don Stewart [85]announced the release of [86]xmonad version
   0.7. Updates include improved integration with GNOME, more flexible
   "rules", various stability fixes, and of course, many new and
   interesting features in the extension library.

   Haskell Server Pages. Niklas Broberg [87]announced a new release of
   [88]Haskell Server Pages, a programming model for writing dynamic web
   pages in Haskell, both server-side and client-side.

   Network.MiniHTTP. Adam Langley [89]announced a release of
   [90]network-minihttp, a small bytestring HTTP library.

   Disciplined Disciple Compiler. Ben Lippmeier [91]announced the initial
   alpha release of the [92]Disciplined Disciple Compiler, an explicitly
   lazy dialect of Haskell.

   haskell-src-exts. Niklas Broberg [93]announced a new release for
   [94]haskell-src-exts, a package for handling and manipulating Haskell
   source code.

   omnicodec. Magnus Therning [95]announced the package [96]omnicodec,
   containing two command line utilities for encoding and decoding data.

Blog noise

   [97]Haskell news from the [98]blogosphere.
     * [99]Christophe Poucet (vincenz): ICFP Contest 2008
     * [100]Real-World Haskell: CUFP 2007 videos now easier to view
     * [101]Wrap-up: mergesort in haskell
     * [102]jbofihe and Haskell
     * [103]Writing a Regular Expression parser in Haskell: Part 3
     * [104]Real World Haskell
     * [105]London Haskell Users Group: Next meeting: Paradise, a DSEL for
       derivatives pricing
     * [106]Christophe Poucet (vincenz): Lazy memoization
     * [107]Neil Mitchell: GSoC Hoogle: Week 2
     * [108]Magnus Therning: Google Treasure Hunt primes question
     * [109]Roman Cheplyaka: Status report: week 2
     * [110]Andy Gill: The unknown cost of dictionaries
     * [111]Edward Kmett: Zapping Adjunctions
     * [112]Edward Kmett: Representing Adjunctions
     * [113]Andy Gill: Performance problems with functional representation
       of derivatives
     * [114]Conal Elliott: Functional linear maps

Quotes of the Week

     * roconnor: if you click your heels and say ``there is no binding
       like gtk2hs'' then dcoutts will appear and answer your question.
     * mauke: the first rule of fix club is "the first rule of fix club is
       "the first rule of fix club is...
     * oerjan: so does this mean that a comonad is like a wildlife
       preserve on an island in a sea of nuclear waste?
     * quicksilver: head-explosion is the solution, not the problem.
     * Botje: [on googling for polyvariadic typeclasses] OH GOD THE FIRST
       HIT IS OLEGS SITE! / *ahum* / I meant, "yay, reading material"
     * Baughn: From my point of view, anyone who understands everything
       ghc can do is /scary/. I'm sure that will change once I reach that
       level myself, but then again, there's also the possibility that
       I'll be in a permanent state of autophobia.
     * newsham: I think the problem with people asking homework questions
       in this channel is that the people in this channel don't have
       enough homework questions of their own to do.
     * quicksilver: *** quicksilver beats Deewiant with the
       i-will-not-use-fail-stick [Deewiant] quicksilver: I'm willing to
       accept a good alternative. [quicksilver] no. all you are permitted
       to accept is a beating.
     * mar77a: MONAD ARGHH GHGRHGH HGHRGHR RUN
     * Cale: Types are a bit like the nubs on lego bricks which provide
       structural integrity while suggesting how the bricks should fit
       together.
     * quicksilver: zip`ap`tail the aztec god of consecutive numbers

About the Haskell Weekly News

   New editions are posted to [115]the Haskell mailing list as well as to
   [116]the Haskell Sequence and [117]Planet Haskell. [118]RSS is also
   available, and headlines appear on [119]haskell.org. Headlines are
   available as [120]PDF.

   To help create new editions of this newsletter, please see the
   [121]contributing information. Send stories to byorgey at gmail dot
   com. The darcs repository is available at darcs get
   [122]http://code.haskell.org/~byorgey/code/hwn/

References

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  35.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad-utils
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  39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/scc-0.1
  40.
http://www.idealliance.org/papers/extreme/proceedings/html/2006/Blazevic01/EML2006Blazevic01.html
  41. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39648
  42. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/twitter
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  46.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/category-extras
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  48. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sessions
  49. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39352
  50.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.1.0
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  53. http://code.google.com/p/reviewboard/
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  55.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/diagrams-0.1
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  57. http://www.fh-wedel.de/~si/HXmlToolbox/index.html
  58. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39040
  59. http://code.google.com/soc/2008/haskell/about.html
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  61. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring
  62. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38991
  63. http://lambda.uta.edu/HXQ/
  64. http://www.w3.org/TR/xquery/
  65. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38965
  66.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Win32-notify-0.1
  67. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38922
  68. http://uebb.cs.tu-berlin.de/~magr/projects/cpuid/doc/
  69. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38870
  70. http://home.telfort.nl/sp969709/emp/empug.html
  71. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38773
  72. http://software.complete.org/datapacker
  73. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38736
  74. http://darcswatch.nomeata.de/
  75. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38676
  76. http://www.generic-haskell.org/
  77. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38542
  78.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphics-drawingcombinators-0.1
  79. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38505
  80. http://www.haskell.org/haskellwiki/The_Monad.Reader
  81. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38419
  82. http://www.well-typed.com/
  83. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38173
  84. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgdbmi
  85. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38167
  86. http://xmonad.org/
  87. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37996
  88. http://code.google.com/p/hsp
  89. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37853
  90.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-minihttp-0.2
  91. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37831
  92. http://www.haskell.org/haskellwiki/DDC
  93. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37703
  94.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts-0.3.2
  95. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37688
  96. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/omnicodec
  97. http://planet.haskell.org/
  98. http://haskell.org/haskellwiki/Blog_articles
  99. http://cpoucet.wordpress.com/2008/06/11/icfp-contest-2008/
 100.
http://www.realworldhaskell.org/blog/2008/06/10/cufp-2007-videos-now-easier-to-view/
 101. http://muharem.wordpress.com/2008/06/10/wrap-up-mergesort-in-haskell/
 102. http://chrisdone.com/blog/2008/06/10/jbofihe-and-haskell/
 103.
http://blogs.msdn.com/matt/archive/2008/06/09/writing-a-regular-expression-parser-in-haskell-part-3.aspx
 104. http://tapestryjava.blogspot.com/2008/06/real-world-haskell.html
 105.
http://www.londonhug.net/2008/06/09/next-meeting-paradise-a-dsel-for-derivatives-pricing/
 106. http://cpoucet.wordpress.com/2008/04/25/lazy-memoization/
 107. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-2.html
 108. http://therning.org/magnus/archives/353
 109. http://physics-dph.blogspot.com/2008/06/status-report-week-2.html
 110. http://blog.unsafeperformio.com/?p=24
 111. http://comonad.com/reader/2008/zapping-strong-adjunctions/
 112. http://comonad.com/reader/2008/representing-adjunctions/
 113. http://blog.unsafeperformio.com/?p=23
 114. http://feeds.feedburner.com/~r/conal/~3/304291460/
 115. http://www.haskell.org/mailman/listinfo/haskell
 116. http://sequence.complete.org/
 117. http://planet.haskell.org/
 118. http://sequence.complete.org/node/feed
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 120. http://code.haskell.org/~byorgey/code/hwn/archives/20080611.pdf
 121. http://haskell.org/haskellwiki/HWN
 122. http://code.haskell.org/~byorgey/code/hwn/
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From patperry at stanford.edu  Wed Jun 11 20:13:45 2008
From: patperry at stanford.edu (Patrick Perry)
Date: Wed Jun 11 20:06:04 2008
Subject: [Haskell-cafe] ANN: blas-0.4.1
Message-ID: <5E451F8D-AE36-4FBE-A1B4-DBA25F0022CD@stanford.edu>

There were a few hiccups in the release of 0.4, so this version is to  
make installation go a little smoother for people.  There are now  
installation instructions (the INSTALL file) and configuration  
settings for some common CBLAS (ATLAS, MKL, vecLib, GSL).  The default  
is now to assume that ATLAS is installed, so hopefully most people  
won't have to fuss too much with this.

Alberto Ruiz reported two small issues with precision in the unit  
tests, and those have now been fixed.


Patrick

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From qdunkan at gmail.com  Wed Jun 11 20:18:02 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Wed Jun 11 20:10:27 2008
Subject: [Haskell-cafe] appending an element to a list
In-Reply-To: <48405717.20206@daimi.au.dk>
References: <483EE208.2010601@inf.fu-berlin.de> <483EF36B.5040100@daimi.au.dk>
	<48404039.6030605@cisco.com> <48405717.20206@daimi.au.dk>
Message-ID: <2518b95d0806111718u59c26afasf27638125db14215@mail.gmail.com>

> Lets look at the actual reductions going on. To make the example easier,
> I would like to use last instead of your complicated until. It shouldn't
> make a difference.

[ winds up doing twice as much work ]

This was also my intuition.  I had a function that built up a large
output list by generating chunks and ++ them onto the output (e.g.
basically concatMap).  My intuition was that this would get gradually
slower because each (++) implied a copy of the previous part of the
list.  So if I have another function consuming the eventual output it
will get slower and slower because demanding an element will reduce
the (++)s for each chunk, and copy the element 1000 times if I have
appended 1000 chunks by now.

So I switched to using DList, which has O(1) append.  Then I ran
timing on a list that wound up adding up a million or so chunks... and
both versions were exactly the same speed (and -O2 gave both an
equally big speed boost).

In fact, when I try with a toy example, the DList using one is much
slower than the concatMap using one, which I don't quite understand.
Shouldn't concatMap be quite inefficient?

The program below gives me this output:

15000000
45.7416
15000000
110.2112

-O2 brings both implementations to 45.

Interestingly, if I call 't1' from ghci, it sucks up 1gb of memory and
slows the system to a crawl until I kill it.. this is *after* it's
computed a result and given me my prompt back... even if its somehow
keeping the whole list around in some ghci variable (where?), isn't
1gb+ a lot even for 15m boxed Integers?  And why does it continue to
grow after the function has completed?  The compiled version doesn't
have this problem.


import System.CPUTime
import qualified Data.DList as DList

dconcat_map f xs = DList.toList (DList.concat (map (DList.fromList . f) xs))

mkchunk n = [n, n*2, n*3]

main = do
    t1
    t2

t1 = do
    let a = concatMap mkchunk [0..5000000]
    t <- getCPUTime
    print (last a)
    t2 <- getCPUTime
    print (fromIntegral (t2 - t) / fromIntegral cpuTimePrecision)

t2 = do
    let a = dconcat_map mkchunk [0..5000000]
    t <- getCPUTime
    print (last a)
    t2 <- getCPUTime
    print (fromIntegral (t2 - t) / fromIntegral cpuTimePrecision)
From patperry at stanford.edu  Wed Jun 11 20:52:29 2008
From: patperry at stanford.edu (Patrick Perry)
Date: Wed Jun 11 20:44:43 2008
Subject: [Haskell-cafe] ANN: ieee-0.2
Message-ID: <0EF1EF82-7B8A-4AC5-B8CB-BA15EB127108@stanford.edu>

ieee is a library that provides approximate comparison of floating  
point numbers based, NaN-aware minimum and maximum, and a type class  
for approximate comparisons.

This version fixes a bug in the comparison implementation for Maybe.

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ieee
From isaacdupree at charter.net  Wed Jun 11 20:56:17 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Wed Jun 11 20:48:21 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48505344.4010809@web.de>
References: <48505344.4010809@web.de>
Message-ID: <48507431.2080908@charter.net>

Stephan Friedrichs wrote:
> Hello,
> 
> I've implemented Chris Okasaki's random-access list[1] which provides 
> typical list operations (cons, head, tail) in O(1) and yet offers 
> indexed random-access in O(log n). It's uploaded on hackage[2].
> 
> It's still an early version which I'll extend, but especially at this 
> eary stage I'd appreciate your feedback concerning what's still missing 
> / to be fixed / to be improved.

Great to see it, it deserved implementing, IIRC!  I don't remember 
enough about it.. (and don't have Okasaki anywhere handy). Can it be 
lazy or infinitely long? (Data.Sequence can't, but it's fast on both 
ends and has fast concatenation.)  Anyway, document that.  If it can't 
be lazy/infinite, does it have any advantage over using 
Data.Sequence?(constant factor of speed?, possible operations?, 
something I'm forgetting?)

Is "RandomAccessList" the best name for something that's not O(1), just 
O(log n)?  Or just that "RandomAccessList" is just much longer than "[]"?

don't use those unorthodox infix function names.. `cons` is hardly worse 
than .:. , `append` or `mappend` than .+. , and .!. than, hmm.. . 
Export a ++ and ! (!! ?) if you're really dedicated. But I'd prefer an 
`at` that's the same partial indexing operation, rather than the name 
.!. (I think this "at" was a new name being put somewhere else? partly 
because "!" is trying to be gradually used only to refer to strictness?)

"extractHead" is an ugly name for a nevertheless standardish-meaning 
function... what is it usually called? uncons? headTail? (Data.Sequence, 
which is meant to be left-right symmetric, calls it "viewr"... except 
your version doesn't have the Maybe, it's partial instead, fails on 
empty lists)

For "index", don't use Monad, use Maybe (I think that's what the recent 
libraries@haskell.org discussion concluded, in the context of switching 
Data.Map back to Maybe).  Also, Data.List has genericLength etc, to 
support.  Isn't "index" (like Data.List.genericIndex) supposed to be a 
name for a partial operation, not one that returns a Maybe?  Shouldn't 
"size" be named "length" (or exported as both names, since e.g. 
Data.Map.size, .List.length) (why is it O(1) not O(log n)? Is it 
possible for these RandomAccessLists to be longer than maxBound::Int?)?

for e.g. toList, is the O(n) cost spread over traversing/demanding the 
items of the generated list, or all up-front, or somewhere in between?

Why is zip slow with unbalanced lists?  Obviously, it could be 
implemented O(min(m,n)*(log m + log n)) just indexing each one, which 
would be faster for really unbalanced-size lists...  Obviously, I don't 
understand the implementation.  BTW, looking at the file,
data RandomAccessList a
         = RandomAccessList {-# UNPACK #-} !Int ![(Int, CBTree a)]
Marking a list strict like that doesn't have much effect because it only 
makes the first (:) or [] strict. Did you mean for an element-strict or 
spine-strict(which would necessarily be non-infinite) list?

-Isaac


> 
> Regards,
> Stephan
> 
> [1] Chris Okasaki: "Purely Functional Data Structures"
> [2] 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/random-access-list 
> 
> 
> 

From derek.a.elkins at gmail.com  Wed Jun 11 21:09:52 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Wed Jun 11 21:02:07 2008
Subject: [Haskell-cafe] appending an element to a list
In-Reply-To: <2518b95d0806111718u59c26afasf27638125db14215@mail.gmail.com>
References: <483EE208.2010601@inf.fu-berlin.de>
	<483EF36B.5040100@daimi.au.dk> <48404039.6030605@cisco.com>
	<48405717.20206@daimi.au.dk>
	<2518b95d0806111718u59c26afasf27638125db14215@mail.gmail.com>
Message-ID: <1213232992.7306.62.camel@derek-laptop>

On Wed, 2008-06-11 at 17:18 -0700, Evan Laforge wrote:
> > Lets look at the actual reductions going on. To make the example easier,
> > I would like to use last instead of your complicated until. It shouldn't
> > make a difference.
> 
> [ winds up doing twice as much work ]
> 
> This was also my intuition.  I had a function that built up a large
> output list by generating chunks and ++ them onto the output (e.g.
> basically concatMap).  My intuition was that this would get gradually
> slower because each (++) implied a copy of the previous part of the
> list.  So if I have another function consuming the eventual output it
> will get slower and slower because demanding an element will reduce
> the (++)s for each chunk, and copy the element 1000 times if I have
> appended 1000 chunks by now.
> 
> So I switched to using DList, which has O(1) append.  Then I ran
> timing on a list that wound up adding up a million or so chunks... and
> both versions were exactly the same speed (and -O2 gave both an
> equally big speed boost).
> 
> In fact, when I try with a toy example, the DList using one is much
> slower than the concatMap using one, which I don't quite understand.
> Shouldn't concatMap be quite inefficient?

concatMap is very efficient.  (++) isn't slow.  Left associative uses of
(++) are slow.  concatMap = foldr ((++) . f) []

> 
> The program below gives me this output:
> 
> 15000000
> 45.7416
> 15000000
> 110.2112
> 
> -O2 brings both implementations to 45.
> 
> Interestingly, if I call 't1' from ghci, it sucks up 1gb of memory and
> slows the system to a crawl until I kill it.. this is *after* it's
> computed a result and given me my prompt back... even if its somehow
> keeping the whole list around in some ghci variable (where?), isn't
> 1gb+ a lot even for 15m boxed Integers?  And why does it continue to
> grow after the function has completed?  The compiled version doesn't
> have this problem.
> 
> 
> import System.CPUTime
> import qualified Data.DList as DList
> 
> dconcat_map f xs = DList.toList (DList.concat (map (DList.fromList . f) xs))
> 
> mkchunk n = [n, n*2, n*3]
> 
> main = do
>     t1
>     t2
> 
> t1 = do
>     let a = concatMap mkchunk [0..5000000]
>     t <- getCPUTime
>     print (last a)
>     t2 <- getCPUTime
>     print (fromIntegral (t2 - t) / fromIntegral cpuTimePrecision)
> 
> t2 = do
>     let a = dconcat_map mkchunk [0..5000000]
>     t <- getCPUTime
>     print (last a)
>     t2 <- getCPUTime
>     print (fromIntegral (t2 - t) / fromIntegral cpuTimePrecision)
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From page at ou.edu  Wed Jun 11 23:17:40 2008
From: page at ou.edu (Rex Page)
Date: Wed Jun 11 23:10:00 2008
Subject: [Haskell-cafe] monomorphism restriction
Message-ID: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>

Definition of f:
    f = foldr (+) 0
Types:
    0 :: (Num t) => t
    foldr (+) 0 :: Num a => [a] -> a
    f :: [Integer] -> Integer

Please remind me, again, of the advantages of f being something different from 
the formula defining it.

  - Rex Page
From dons at galois.com  Wed Jun 11 23:24:02 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 11 23:16:20 2008
Subject: [Haskell-cafe] monomorphism restriction
In-Reply-To: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
References: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
Message-ID: <20080612032402.GA25431@scytale.galois.com>

page:
> Definition of f:
>    f = foldr (+) 0
> Types:
>    0 :: (Num t) => t
>    foldr (+) 0 :: Num a => [a] -> a
>    f :: [Integer] -> Integer
> 
> Please remind me, again, of the advantages of f being something different 
> from the formula defining it.

Overloaded 'constants' take a dictionary as an argument, so while you
think the value might be computed only once, it make actually be
recomputed each time. This can be a killer performance penalty for
overloaded numeric constants.

Of course, disabling this is pretty simple.

-- Don
From aeyakovenko at gmail.com  Thu Jun 12 02:50:09 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Thu Jun 12 02:42:23 2008
Subject: [Haskell-cafe] -fvia-C error
Message-ID: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>

any idea what could be causing this error when i add the -fvia-C option

/tmp/ghc32300_0/ghc32300_0.hc:6:23:
     error: SFMT_wrap.h: No such file or directory
make: *** [release] Error 1

I am also passing these options:

-O2 -fexcess-precision -funbox-strict-fields -fglasgow-exts
-fbang-patterns -lcblas

Thanks,
Anatoly
From dons at galois.com  Thu Jun 12 03:07:33 2008
From: dons at galois.com (Don Stewart)
Date: Thu Jun 12 02:59:49 2008
Subject: [Haskell-cafe] -fvia-C error
In-Reply-To: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
References: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
Message-ID: <20080612070733.GB26022@scytale.galois.com>

aeyakovenko:
> any idea what could be causing this error when i add the -fvia-C option
> 
> /tmp/ghc32300_0/ghc32300_0.hc:6:23:
>      error: SFMT_wrap.h: No such file or directory
> make: *** [release] Error 1
> 
> I am also passing these options:
> 
> -O2 -fexcess-precision -funbox-strict-fields -fglasgow-exts
> -fbang-patterns -lcblas

When compiling something linked against the mersenne random package?

-- Don
From aeyakovenko at gmail.com  Thu Jun 12 03:30:51 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Thu Jun 12 03:23:02 2008
Subject: [Haskell-cafe] -fvia-C error
In-Reply-To: <20080612070733.GB26022@scytale.galois.com>
References: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
	<20080612070733.GB26022@scytale.galois.com>
Message-ID: <e26d18e40806120030w56c24f09r80bd86de0cc7bcbc@mail.gmail.com>

> When compiling something linked against the mersenne random package?

yes, does it not work with fvia-C?
From duncan.coutts at worc.ox.ac.uk  Thu Jun 12 03:43:38 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Thu Jun 12 03:31:42 2008
Subject: [Haskell-cafe] -fvia-C error
In-Reply-To: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
References: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
Message-ID: <1213256618.15010.499.camel@localhost>


On Wed, 2008-06-11 at 23:50 -0700, Anatoly Yakovenko wrote:
> any idea what could be causing this error when i add the -fvia-C option
> 
> /tmp/ghc32300_0/ghc32300_0.hc:6:23:
>      error: SFMT_wrap.h: No such file or directory
> make: *** [release] Error 1

Some package you're using is a FFI binding that uses that C header file
(SFMT_wrap.h). When you compile via C and crank up the optimisation it's
quite possible for C calls to be inlined from the package in which
they're defined into your code and hence you code ends up needing the
headers too.

You can get the above problem if a package uses a private header file
and does not install it.

Do you recognise SFMT_wrap.h? What package do you think it is that uses
it?

Duncan

From duncan.coutts at worc.ox.ac.uk  Thu Jun 12 03:52:49 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Thu Jun 12 03:40:53 2008
Subject: [Haskell-cafe] -fvia-C error
In-Reply-To: <20080612070733.GB26022@scytale.galois.com>
References: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
	<20080612070733.GB26022@scytale.galois.com>
Message-ID: <1213257169.15010.506.camel@localhost>


On Thu, 2008-06-12 at 00:07 -0700, Don Stewart wrote:
> aeyakovenko:
> > any idea what could be causing this error when i add the -fvia-C option
> > 
> > /tmp/ghc32300_0/ghc32300_0.hc:6:23:
> >      error: SFMT_wrap.h: No such file or directory
> > make: *** [release] Error 1
> > 
> > I am also passing these options:
> > 
> > -O2 -fexcess-precision -funbox-strict-fields -fglasgow-exts
> > -fbang-patterns -lcblas
> 
> When compiling something linked against the mersenne random package?

Don, this does not work:

includes:         SFMT.h SFMT_wrap.h
install-includes: SFMT.h

You cannot limit the scope of the SFMT_wrap.h to be just this package.
You can limit .h scope to one file or global -- nothing in between.

You can limit it to just that file by specifying the .h file in the
foreign import declaration:

> foreign import ccall "private.h foo" foo :: IO ()

Alternatively you can also install SFMT_wrap.h.

Duncan

From lemming at henning-thielemann.de  Thu Jun 12 05:09:03 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 12 05:01:15 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48507431.2080908@charter.net>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
Message-ID: <Pine.LNX.4.64.0806121104390.12961@anubis.informatik.uni-halle.de>


On Wed, 11 Jun 2008, Isaac Dupree wrote:

> "extractHead" is an ugly name for a nevertheless standardish-meaning 
> function... what is it usually called? uncons? headTail? (Data.Sequence, 
> which is meant to be left-right symmetric, calls it "viewr"... except your 
> version doesn't have the Maybe, it's partial instead, fails on empty lists)

I like the 'viewL' and 'viewR' kind of functions, they are safer than 
'head' and 'tail', 'init' and 'last'. But since in most cases I used 
'viewL' in connection with 'maybe', the continuation style functions

switchL :: b -> (a -> Seq a -> b) -> Seq a -> b
switchR :: b -> (Seq a -> a -> b) -> Seq a -> b

are even more convenient. They replace 'case' on those structures where 
you do not have access to the constructors.

From lemming at henning-thielemann.de  Thu Jun 12 05:20:06 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 12 05:12:45 2008
Subject: [Haskell-cafe] Simple list processing
In-Reply-To: <1213217183.3033.1.camel@localhost.localdomain>
References: <4850169F.4050003@btinternet.com>
	<20080611182517.GF25521@scytale.galois.com>
	<1213217183.3033.1.camel@localhost.localdomain>
Message-ID: <Pine.LNX.4.64.0806121113300.12961@anubis.informatik.uni-halle.de>


On Wed, 11 Jun 2008, Thomas M. DuBuisson wrote:

> Why is there no mapAccumL' (strict)?  Just a library deficiency that we
> can remedy or am I missing something?

The strictness in foldl' is needed to avoid that unevaluated computations 
accumulate until the end of the list. In mapAccumL and scanl this danger 
is smaller. If you process the elements of the output list in order then 
the intermediate states are also computed step by step. However, if you 
evaluate only the last element of the output list you have the same 
problem like with foldl.

From silva.samuel at gmail.com  Thu Jun 12 06:08:18 2008
From: silva.samuel at gmail.com (Samuel Silva)
Date: Thu Jun 12 06:00:32 2008
Subject: [Haskell-cafe] Problems with Validate from HaXML
Message-ID: <382ead9b0806120308l15d0f2ffg976c98f70d2c9fe7@mail.gmail.com>

Hello

I'm working with large DTDs from http://www.recordare.com/dtds/,
particulary partwise.dtd and timewise.dtd.
I check these DTDs with some tools, like Altova XML Spy and Microsoft
Visual Studio, and DTDs are valid.
However Validate tool from HaXML doesn't validate same DTDs.
Result from Validate is:
$ Validate partwise.dtd
Validate: In a sequence:
  in content spec of ELEMENT decl: note
  When looking for a non-empty sequence with separators:
        Expected % but found |
    in file note.mod  at line 51 col 45
      used by  file partwise.dtd  at line 120 col 1
  when looking for a content particle
  when looking for a content particle

Problematic definition is in "note.mod" file, presented below:
<!ELEMENT note
	(((grace, %full-note;, (tie, tie?)?) |
	  (cue, %full-note;, duration) |
	  (%full-note;, duration, (tie, tie?)?)),
	 instrument?, %editorial-voice;, type?, dot*,
	 accidental?, time-modification?, stem?, notehead?,
	 staff?, beam*, notations*, lyric*)>

I'm trying using DtdToHaskell tool from HaXML to build parser from
MusicXML to Haskell types.
There are other ways to build XML parser using HaXML?
I'm already using HaXML, with HaXML combinators, to write MusicXML.

Thanks.

-- 
Don't hug that, Hugs ME!
Samuel Silva
From ross at soi.city.ac.uk  Thu Jun 12 06:59:35 2008
From: ross at soi.city.ac.uk (Ross Paterson)
Date: Thu Jun 12 06:51:48 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48507431.2080908@charter.net>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
Message-ID: <20080612105935.GA2933@soi.city.ac.uk>

On Wed, Jun 11, 2008 at 08:56:17PM -0400, Isaac Dupree wrote:
> Stephan Friedrichs wrote:
>> I've implemented Chris Okasaki's random-access list[1] which provides  
>> typical list operations (cons, head, tail) in O(1) and yet offers  
>> indexed random-access in O(log n). It's uploaded on hackage[2].
>>
>> It's still an early version which I'll extend, but especially at this  
>> eary stage I'd appreciate your feedback concerning what's still missing 
>> / to be fixed / to be improved.
>
> Great to see it, it deserved implementing, IIRC!  I don't remember  
> enough about it.. (and don't have Okasaki anywhere handy). Can it be  
> lazy or infinitely long? (Data.Sequence can't, but it's fast on both  
> ends and has fast concatenation.)  Anyway, document that.  If it can't  
> be lazy/infinite, does it have any advantage over using  
> Data.Sequence?(constant factor of speed?, possible operations?,  
> something I'm forgetting?)

The O(1) size function settles the finiteness question.

In tests we did for the finger tree paper, we found that skew binary
random access lists are 1.6-1.7 times faster than Data.Sequence for
stack operations and indexing, but not much faster for updates.

foldr is defined using foldr' on lists, introducing strictness without
the user asking for it.  In any case, it would be better to define
the Foldable instance directly over the internal structure.  Then you
wouldn't need toList.  A similar Traversable instance would also be a
good idea.

> Why is zip slow with unbalanced lists?  Obviously, it could be  
> implemented O(min(m,n)*(log m + log n)) just indexing each one, which  
> would be faster for really unbalanced-size lists...

It could be made O(min(m,n)) by toListing the longer one and traversing
the shorter one adding corresponding elements from the list.

I agree about using Maybe instead of Monad, and would generally prefer
view functions to null/head/tail combinations.
From peteg42 at gmail.com  Thu Jun 12 08:29:14 2008
From: peteg42 at gmail.com (Peter Gammie)
Date: Thu Jun 12 08:21:32 2008
Subject: [Haskell-cafe] Problems with Validate from HaXML
In-Reply-To: <382ead9b0806120308l15d0f2ffg976c98f70d2c9fe7@mail.gmail.com>
References: <382ead9b0806120308l15d0f2ffg976c98f70d2c9fe7@mail.gmail.com>
Message-ID: <717927700806120529j65049b7ejfc93840671b58ea0@mail.gmail.com>

Hello,

I have the same problems. I believe I sent Malcolm some patches. If
not, look here:

http://peteg.org/haskell/HaXml/

I am away from my laptop right now so I cannot readily tell you
whether a "darcs get" will do the job. In any case, there is a bug in
the DTD parser that is easily fixed. (Try downloading the Parser.hs
file if the darcs get fails.)

Hope that helps.

cheers
peter

On 6/12/08, Samuel Silva <silva.samuel@gmail.com> wrote:
> Hello
>
> I'm working with large DTDs from http://www.recordare.com/dtds/,
> particulary partwise.dtd and timewise.dtd.
> I check these DTDs with some tools, like Altova XML Spy and Microsoft
> Visual Studio, and DTDs are valid.
> However Validate tool from HaXML doesn't validate same DTDs.
> Result from Validate is:
> $ Validate partwise.dtd
> Validate: In a sequence:
>  in content spec of ELEMENT decl: note
>  When looking for a non-empty sequence with separators:
>        Expected % but found |
>    in file note.mod  at line 51 col 45
>      used by  file partwise.dtd  at line 120 col 1
>  when looking for a content particle
>  when looking for a content particle
>
> Problematic definition is in "note.mod" file, presented below:
> <!ELEMENT note
>        (((grace, %full-note;, (tie, tie?)?) |
>          (cue, %full-note;, duration) |
>          (%full-note;, duration, (tie, tie?)?)),
>         instrument?, %editorial-voice;, type?, dot*,
>         accidental?, time-modification?, stem?, notehead?,
>         staff?, beam*, notations*, lyric*)>
>
> I'm trying using DtdToHaskell tool from HaXML to build parser from
> MusicXML to Haskell types.
> There are other ways to build XML parser using HaXML?
> I'm already using HaXML, with HaXML combinators, to write MusicXML.
>
> Thanks.
>
> --
> Don't hug that, Hugs ME!
> Samuel Silva
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From bertram.felgenhauer at googlemail.com  Thu Jun 12 08:56:23 2008
From: bertram.felgenhauer at googlemail.com (Bertram Felgenhauer)
Date: Thu Jun 12 08:48:39 2008
Subject: [Haskell-cafe] -fvia-C error
In-Reply-To: <1213257169.15010.506.camel@localhost>
References: <e26d18e40806112350x321d750j509507ee0cca04d7@mail.gmail.com>
	<20080612070733.GB26022@scytale.galois.com>
	<1213257169.15010.506.camel@localhost>
Message-ID: <20080612125623.GA4186@zombie.inf.tu-dresden.de>

Duncan Coutts wrote:
> Don, this does not work:
> 
> includes:         SFMT.h SFMT_wrap.h
> install-includes: SFMT.h

Sorry, that was my fault.

(It does work with ghc 6.9, but that's not much of an excuse)

Bertram
From isaacdupree at charter.net  Thu Jun 12 09:47:50 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Thu Jun 12 09:40:00 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <Pine.LNX.4.64.0806121104390.12961@anubis.informatik.uni-halle.de>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<Pine.LNX.4.64.0806121104390.12961@anubis.informatik.uni-halle.de>
Message-ID: <48512906.8020103@charter.net>

Henning Thielemann wrote:
> 
> On Wed, 11 Jun 2008, Isaac Dupree wrote:
> 
>> "extractHead" is an ugly name for a nevertheless standardish-meaning 
>> function... what is it usually called? uncons? headTail? 
>> (Data.Sequence, which is meant to be left-right symmetric, calls it 
>> "viewr"... except your version doesn't have the Maybe, it's partial 
>> instead, fails on empty lists)
> 
> I like the 'viewL' and 'viewR' kind of functions, they are safer than 
> 'head' and 'tail', 'init' and 'last'. But since in most cases I used 
> 'viewL' in connection with 'maybe', the continuation style functions
> 
> switchL :: b -> (a -> Seq a -> b) -> Seq a -> b
> switchR :: b -> (Seq a -> a -> b) -> Seq a -> b

I think you got L and R backwards? it's a little confusing to me, but 
following Data.Sequence I think they're meant to match whether repeated 
L or R makes a foldl or a foldr.

> are even more convenient. They replace 'case' on those structures where 
> you do not have access to the constructors.

on the other hand, they look harder to use with the upcoming (in GHC 
6.9/6.10) "view patterns", a simple example being

foo (viewr -> Nothing) = ...
foo (viewr -> Just (a, as)) = ...

equivalent to

foo s = case viewr s of
   Nothing -> ...
   Just (a, as) -> ...

(for view patterns, it's also proposed but not implemented to have 
special syntax for Maybe and/or tuples to make it even more convenient 
for these purposes... I'm not sure if it'd be a good idea either)

I also mentioned the continuation style functions for Data.Map's 
maybe-returning in the discussion... they're most convenient if you want 
to destruct them right away, but harder to apply combinators to (e.g. 
Maybe monad. which doesn't work for Data.Sequence because they use their 
own custom view datatype -- was that a bad choice for them?  "Maybe" of 
a tuple has an extra laziness-spot that shouldn't really be there, 
though)  Anyway, people didn't seem to respond to that idea of 
continuation-style returning, not sure why.  On the other hand, also, 
the only thing defending the function from using the arguments in a way 
it shouldn't, is parametricity... less obvious than with algrebraic data 
returns

-Isaac
From lemming at henning-thielemann.de  Thu Jun 12 10:07:27 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 12 09:59:39 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48512906.8020103@charter.net>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<Pine.LNX.4.64.0806121104390.12961@anubis.informatik.uni-halle.de>
	<48512906.8020103@charter.net>
Message-ID: <Pine.LNX.4.64.0806121604510.14892@anubis.informatik.uni-halle.de>


On Thu, 12 Jun 2008, Isaac Dupree wrote:

> Henning Thielemann wrote:
>> 
>> On Wed, 11 Jun 2008, Isaac Dupree wrote:
>> 
>>> "extractHead" is an ugly name for a nevertheless standardish-meaning 
>>> function... what is it usually called? uncons? headTail? (Data.Sequence, 
>>> which is meant to be left-right symmetric, calls it "viewr"... except your 
>>> version doesn't have the Maybe, it's partial instead, fails on empty 
>>> lists)
>> 
>> I like the 'viewL' and 'viewR' kind of functions, they are safer than 
>> 'head' and 'tail', 'init' and 'last'. But since in most cases I used 
>> 'viewL' in connection with 'maybe', the continuation style functions
>> 
>> switchL :: b -> (a -> Seq a -> b) -> Seq a -> b
>> switchR :: b -> (Seq a -> a -> b) -> Seq a -> b
>
> I think you got L and R backwards?

Why do you think so?

http://cvs.haskell.org/Hugs/pages/libraries/base/Data-Sequence.html#v%3Aviewl

> it's a little confusing to me, but following Data.Sequence I think 
> they're meant to match whether repeated L or R makes a foldl or a foldr.

viewl is like a 'case' for distinction of [] and (:) and thus can be used 
to implement both foldl and foldr.
From isaacdupree at charter.net  Thu Jun 12 10:10:56 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Thu Jun 12 10:03:05 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <Pine.LNX.4.64.0806121604510.14892@anubis.informatik.uni-halle.de>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<Pine.LNX.4.64.0806121104390.12961@anubis.informatik.uni-halle.de>
	<48512906.8020103@charter.net>
	<Pine.LNX.4.64.0806121604510.14892@anubis.informatik.uni-halle.de>
Message-ID: <48512E70.1030807@charter.net>

Henning Thielemann wrote:
> 
> On Thu, 12 Jun 2008, Isaac Dupree wrote:
> 
>> Henning Thielemann wrote:
>>>
>>> On Wed, 11 Jun 2008, Isaac Dupree wrote:
>>>
>>>> "extractHead" is an ugly name for a nevertheless standardish-meaning 
>>>> function... what is it usually called? uncons? headTail? 
>>>> (Data.Sequence, which is meant to be left-right symmetric, calls it 
>>>> "viewr"... except your version doesn't have the Maybe, it's partial 
>>>> instead, fails on empty lists)
>>>
>>> I like the 'viewL' and 'viewR' kind of functions, they are safer than 
>>> 'head' and 'tail', 'init' and 'last'. But since in most cases I used 
>>> 'viewL' in connection with 'maybe', the continuation style functions
>>>
>>> switchL :: b -> (a -> Seq a -> b) -> Seq a -> b
>>> switchR :: b -> (Seq a -> a -> b) -> Seq a -> b
>>
>> I think you got L and R backwards?
> 
> Why do you think so?
> 
> http://cvs.haskell.org/Hugs/pages/libraries/base/Data-Sequence.html#v%3Aviewl 

Because I was confused.  Looking again, you seem to be right...

>> it's a little confusing to me, but following Data.Sequence I think 
>> they're meant to match whether repeated L or R makes a foldl or a foldr.
> 
> viewl is like a 'case' for distinction of [] and (:) and thus can be 
> used to implement both foldl and foldr.

yes, but in the sense that foldr is more "natural" for lists than foldl, 
requiring just replacing the constructors "directly"

From deduktionstheorem at web.de  Thu Jun 12 14:47:12 2008
From: deduktionstheorem at web.de (Stephan Friedrichs)
Date: Thu Jun 12 14:39:27 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48507431.2080908@charter.net>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
Message-ID: <48516F30.4050604@web.de>

Isaac Dupree wrote:
 > [...]
 >
 > Great to see it, it deserved implementing, IIRC!  I don't remember 
enough about it.. (and don't have Okasaki anywhere handy). Can it be 
lazy or infinitely long?

No, it has to be finite as it's actually a list of complete binary trees 
whose size depend on the skew binary representation of the list's size. 
I'll document this.

 > [...]
 >
 > Is "RandomAccessList" the best name for something that's not O(1), 
just O(log n)?  Or just that "RandomAccessList" is just much longer than 
"[]"?

Well Chris Okasaki called them "Skew Binary Random-Access Lists", which 
is even longer :)

 >
 > don't use those unorthodox infix function names.. `cons` is hardly 
worse than .:. , `append` or `mappend` than .+. , and .!. than, hmm.. . 
Export a ++ and ! (!! ?) if you're really dedicated. But I'd prefer an 
`at` that's the same partial indexing operation, rather than the name 
.!. (I think this "at" was a new name being put somewhere else? partly 
because "!" is trying to be gradually used only to refer to strictness?)

Good point!

 >
 > "extractHead" is an ugly name for a nevertheless standardish-meaning 
function... what is it usually called? uncons? headTail? (Data.Sequence, 
which is meant to be left-right symmetric, calls it "viewr"... except 
your version doesn't have the Maybe, it's partial instead, fails on 
empty lists)

Yes, I wasn't happy with that one either. The view-concept of 
Data.Sequence is a good idea.

 >
 > For "index", don't use Monad, use Maybe (I think that's what the 
recent libraries@haskell.org discussion concluded, in the context of 
switching Data.Map back to Maybe).

I was just copying the idea from Data.Map and it's usually a good thing 
to have functions as general as possible, or why is it not?

 > Also, Data.List has genericLength etc, to

At the moment, I'm using the Int type for size and indexing only for one 
reason: I haven't found a proper way to generalize it. I'd really like 
to use the Ix class, but it doesn't provide enough functionality, it 
only works on fixed-size intervals (i. e. for arrays, which don't change 
their size, but a list does). Maybe someone has an idea of how to 
realize lists with a variable starting index and size?

 > support.  Isn't "index" (like Data.List.genericIndex) supposed to be 
a name for a partial operation, not one that returns a Maybe?  Shouldn't 
"size" be named "length" (or exported as both names, since e.g. 
Data.Map.size, .List.length) (why is it O(1) not O(log n)? Is it 
possible for these RandomAccessLists to be longer than maxBound::Int?)?

The size function is in O(1) because I cache it, otherwise it would be

size (RandomAccessList xs) = sum (map fst xs)

which is O(log n). I consider the caching useful, as most applications 
will check 0 <= i < size quite often.

 >
 > for e.g. toList, is the O(n) cost spread over traversing/demanding 
the items of the generated list, or all up-front, or somewhere in between?
 >
 > Why is zip slow with unbalanced lists?  Obviously, it could be 
implemented O(min(m,n)*(log m + log n)) just indexing each one, which 
would be faster for really unbalanced-size lists...  Obviously, I don't

If two lists have exactly the same size, all the complete binary trees 
holding the data have the same size as well. This can be zipped directly 
and is a bit (~5% in my tests) faster.

 > understand the implementation.  BTW, looking at the file,
 > data RandomAccessList a
 >         = RandomAccessList {-# UNPACK #-} !Int ![(Int, CBTree a)]
 > Marking a list strict like that doesn't have much effect because it 
only makes the first (:) or [] strict. Did you mean for an 
element-strict or spine-strict(which would necessarily be non-infinite) 
list?

Oh, you're right, I just meant to mark the Int strict. It obviously was 
too late yesterday!

Thanks for this feedback!
//Stephan

-- 

Fr?her hie? es ja: Ich denke, also bin ich.
Heute wei? man: Es geht auch so.

  - Dieter Nuhr
From chaddai.fouche at gmail.com  Thu Jun 12 15:43:32 2008
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Thu Jun 12 15:35:50 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48516F30.4050604@web.de>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<48516F30.4050604@web.de>
Message-ID: <e9350eaf0806121243u48f72e9cv84fa1105fda23981@mail.gmail.com>

2008/6/12 Stephan Friedrichs <deduktionstheorem@web.de>:
>> For "index", don't use Monad, use Maybe (I think that's what the recent
>> libraries@haskell.org discussion concluded, in the context of switching
>> Data.Map back to Maybe).
>
> I was just copying the idea from Data.Map and it's usually a good thing to
> have functions as general as possible, or why is it not?
>

Mainly because it's too easy to use them in a Monad that does not have
a meaningful fail(), like IO, many beginners do this error and are
surprised when their program is less robust that it should be. On the
other hand it's pretty easy to get an error out of a Maybe (for
example you can use fromMaybe with error() to get a meaningful error
output).

>> Also, Data.List has genericLength etc, to
>
> At the moment, I'm using the Int type for size and indexing only for one
> reason: I haven't found a proper way to generalize it. I'd really like to
> use the Ix class, but it doesn't provide enough functionality, it only works
> on fixed-size intervals (i. e. for arrays, which don't change their size,
> but a list does). Maybe someone has an idea of how to realize lists with a
> variable starting index and size?

Given that this structure isn't lazy enough, I really don't see a
problem with using Int (any random access list with a size that needs
an Integer would blow the memory anyway...).

-- 
Jeda?
From aditya_siram at hotmail.com  Thu Jun 12 17:07:12 2008
From: aditya_siram at hotmail.com (Aditya Siram)
Date: Thu Jun 12 16:59:23 2008
Subject: [Haskell-cafe] Cabal-Install Fails To Compile
Message-ID: <BLU108-W36DD0E576AC2C91FEC9563F4AD0@phx.gbl>


Hi all,
I downloaded cabal-install and the cabal-1.4 branch from darcs. The following error occurs when building:
> runhaskell Setup.hs build

Building cabal-install-0.4.9...
[19 of 27] Compiling Hackage.SrcDist  ( Hackage/SrcDist.hs, dist/build/cabal/cabal-tmp/Hackage/SrcDist.o )

Hackage/SrcDist.hs:58:59:
    Couldn't match expected type `Char'
           against inferred type `Distribution.Simple.PreProcess.PPSuffixHandler'
      Expected type: FilePath
      Inferred type: [Distribution.Simple.PreProcess.PPSuffixHandler]
    In the fifth argument of `prepareSnapshotTree', namely
        `knownSuffixHandlers'
    In the second argument of `(>>=)', namely
        `prepareSnapshotTree
           verbosity pkg mb_lbi tmpDir knownSuffixHandlers'


According to ghc-pkg compiling and installing the cabal-1.4 branch added cabal-1.3.12. Is this the problem? 

-Deech 
_________________________________________________________________
It?s easy to add contacts from Facebook and other social sites through Windows Live? Messenger. Learn how.
https://www.invite2messenger.net/im/?source=TXT_EML_WLH_LearnHow
From dons at galois.com  Thu Jun 12 17:12:48 2008
From: dons at galois.com (Don Stewart)
Date: Thu Jun 12 17:05:01 2008
Subject: [Haskell-cafe] Cabal-Install Fails To Compile
In-Reply-To: <BLU108-W36DD0E576AC2C91FEC9563F4AD0@phx.gbl>
References: <BLU108-W36DD0E576AC2C91FEC9563F4AD0@phx.gbl>
Message-ID: <20080612211248.GA28501@scytale.galois.com>

Could you try the cabal-1.4 package just put up on hackage.haskell.org?

aditya_siram:
> 
> Hi all,
> I downloaded cabal-install and the cabal-1.4 branch from darcs. The following error occurs when building:
> > runhaskell Setup.hs build
> 
> Building cabal-install-0.4.9...
> [19 of 27] Compiling Hackage.SrcDist  ( Hackage/SrcDist.hs, dist/build/cabal/cabal-tmp/Hackage/SrcDist.o )
> 
> Hackage/SrcDist.hs:58:59:
>     Couldn't match expected type `Char'
>            against inferred type `Distribution.Simple.PreProcess.PPSuffixHandler'
>       Expected type: FilePath
>       Inferred type: [Distribution.Simple.PreProcess.PPSuffixHandler]
>     In the fifth argument of `prepareSnapshotTree', namely
>         `knownSuffixHandlers'
>     In the second argument of `(>>=)', namely
>         `prepareSnapshotTree
>            verbosity pkg mb_lbi tmpDir knownSuffixHandlers'
> 
> 
> According to ghc-pkg compiling and installing the cabal-1.4 branch added cabal-1.3.12. Is this the problem? 
> 
> -Deech 
> _________________________________________________________________
> It?s easy to add contacts from Facebook and other social sites through Windows Live? Messenger. Learn how.
> https://www.invite2messenger.net/im/?source=TXT_EML_WLH_LearnHow_______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
From cdsmith at gmail.com  Thu Jun 12 15:50:05 2008
From: cdsmith at gmail.com (Chris Smith)
Date: Thu Jun 12 17:37:11 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<48516F30.4050604@web.de>
	<e9350eaf0806121243u48f72e9cv84fa1105fda23981@mail.gmail.com>
Message-ID: <g2ruld$nk$1@ger.gmane.org>

Chadda? Fouch? wrote:
> Given that this structure isn't lazy enough, I really don't see a
> problem with using Int (any random access list with a size that needs an
> Integer would blow the memory anyway...).

Bad way to think about things.  The implications of using Int as the 
result type of a function extend far beyond just storing the result 
type.  They also include doing other computations that depend on the 
result type, and with enough type inference, the broken Int type 
propogates throughout the program.

-- 
Chris


From deduktionstheorem at web.de  Thu Jun 12 18:25:57 2008
From: deduktionstheorem at web.de (Stephan Friedrichs)
Date: Thu Jun 12 18:18:08 2008
Subject: [Haskell-cafe] ANN: random-access-list-0.1
In-Reply-To: <g2ruld$nk$1@ger.gmane.org>
References: <48505344.4010809@web.de>
	<48507431.2080908@charter.net>	<48516F30.4050604@web.de>	<e9350eaf0806121243u48f72e9cv84fa1105fda23981@mail.gmail.com>
	<g2ruld$nk$1@ger.gmane.org>
Message-ID: <4851A275.6050804@web.de>

Chris Smith wrote:
> Chadda? Fouch? wrote:
>> Given that this structure isn't lazy enough, I really don't see a
>> problem with using Int (any random access list with a size that needs an
>> Integer would blow the memory anyway...).
> 
> Bad way to think about things.  The implications of using Int as the 
> result type of a function extend far beyond just storing the result 
> type.  They also include doing other computations that depend on the 
> result type, and with enough type inference, the broken Int type 
> propogates throughout the program.
> 

I'd like not to be restricted to Int, but what's the proper way to do 
so? Just adding "genericFun = fromInteger . toInteger . fun" functions 
is just as bad as using Ints directly. What I need is something like a 
more general Ix class that is not limited to a fixed interval:

class Ix2 i where
	-- convert starting index and given index to an Int for internal
	-- representation
	toIndex   :: i -> i -> Int

	-- given an internal Int index and a starting index, return the
	-- representing index
	fromIndex :: Int -> i -> i

	-- translate a starting index and a number of elements into a
	-- size
	size      :: i -> Int -> i

This is meant to work with a starting-index and a given index, so that a 
list does not have to start at index 0. Is there something like this? Or 
is it somehow possible to use the existing Ix class to do that?

//Stephan

-- 

Fr?her hie? es ja: Ich denke, also bin ich.
Heute wei? man: Es geht auch so.

  - Dieter Nuhr
From duncan.coutts at worc.ox.ac.uk  Thu Jun 12 22:58:59 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Thu Jun 12 22:46:57 2008
Subject: [Haskell-cafe] Cabal-Install Fails To Compile
In-Reply-To: <BLU108-W36DD0E576AC2C91FEC9563F4AD0@phx.gbl>
References: <BLU108-W36DD0E576AC2C91FEC9563F4AD0@phx.gbl>
Message-ID: <1213325939.15010.508.camel@localhost>


On Thu, 2008-06-12 at 16:07 -0500, Aditya Siram wrote:
> Hi all,
> I downloaded cabal-install and the cabal-1.4 branch from darcs. The following error occurs when building:
> > runhaskell Setup.hs build
> 
> Building cabal-install-0.4.9...
> [19 of 27] Compiling Hackage.SrcDist  ( Hackage/SrcDist.hs, dist/build/cabal/cabal-tmp/Hackage/SrcDist.o )
> 
> Hackage/SrcDist.hs:58:59:
>     Couldn't match expected type `Char'
>            against inferred type `Distribution.Simple.PreProcess.PPSuffixHandler'
>       Expected type: FilePath
>       Inferred type: [Distribution.Simple.PreProcess.PPSuffixHandler]
>     In the fifth argument of `prepareSnapshotTree', namely
>         `knownSuffixHandlers'
>     In the second argument of `(>>=)', namely
>         `prepareSnapshotTree
>            verbosity pkg mb_lbi tmpDir knownSuffixHandlers'

Yeah, sorry that was my fault. You caught it in the few hours when the
two darcs versions were not compatible. They work now, or as Don says,
get the actual releases from hackage.

Duncan

From thomas.dubuisson at gmail.com  Fri Jun 13 00:47:44 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Fri Jun 13 00:41:24 2008
Subject: [Haskell-cafe] [WARN] Bug fix release of pureMD5 (Was: pureMD5)
In-Reply-To: <2bfa72fa0806121914w6a8a4ff6k34b7ea39f9ef9ce2@mail.gmail.com>
References: <2bfa72fa0806121914w6a8a4ff6k34b7ea39f9ef9ce2@mail.gmail.com>
Message-ID: <1213332464.3124.14.camel@localhost.localdomain>

Cafe,
Daniel Larsson noticed a correctness issue with the pureMD5 package.
This issue would affect you if you built the value incrementally via the
'updateMD5' function (vs just using 'md5') and didn't provide 512 bit
long bytestrings (an MD5 block of operation).

As you can probably tell, I didn't invest enough into the
non-performance aspects of pureMD5.  Faced with actual users ;-), I have
released version 0.2.0 which has the bug fix, a new API (type prevention
from re-finalizing a digest), and a reasonable set of quickchecks
(covering Show / Binary instances, known answer and incremented
hashing).  Oh, also the module name has changed to place it inline with
'Crypto' package naming while not colliding.

Sorry if this causes anyone headaches.

Daniel,
Good catch, I hope this didn't consume much of your time.  Thanks a
bunch!

TomMD

On Fri, 2008-06-13 at 04:14 +0200, Daniel Larsson wrote:
> Hi Thomas,
> 
> 
> I was fiddling around with your pureMD5 package, and encountered some
> problems with using the md5Update/md5Finalize sequence. I tried to
> calculate the md5 of some scattered data, but it kept returning the
> wrong values. It seems that each md5Update must supply an exact
> blockSize number of bits, since the mdLeftOver part isn't taken into
> account in subsequent calls to md5Update.
> 
> 
> I wrote a small patch, and a simple QuickCheck property, to support
> calculating md5 of scattered data, attached to this mail. Hopefully I
> didn't mess up something...
> 
> 
> --
> Daniel
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From dcespin at fastmail.fm  Fri Jun 13 05:15:25 2008
From: dcespin at fastmail.fm (Dominic Espinosa)
Date: Fri Jun 13 05:10:18 2008
Subject: [Haskell-cafe] Difficulty installing hscurses
Message-ID: <20080613091525.GC3105@argivia.columbus.rr.com>

Hello,

I'm trying to install hscurses on debian-testing. I have ghc6 installed,
which I've written some toy programs with, but I haven't tried to
install any Hackage packages until now.

hscurses depends on old-time and old-locale (those names make me raise
my eyebrows a bit). In turn, old-time seems to depend on old-locale. So,
I tried installing old-locale first. In installed fine. Now I'm trying
to install old-time:

$ runhaskell Setup.hs configure
Warning: defaultUserHooks in Setup script is deprecated.
Configuring old-time-1.0.0.0...
Warning: The 'build-type' is 'Configure' but there is no 'configure' script.

(given these warnings, I don't really expect the next command to
succeed, but what the hell:)

$ runhaskell Setup.hs build

Preprocessing library old-time-1.0.0.0...
Building old-time-1.0.0.0...

System/Time.hsc:118:7:
    Could not find module `System.Locale':
      it was found in multiple packages: old-locale-1.0.0.0 base

No idea what to do here. Is old-time conflicting with whatever "time"
package superseded it, or what?

I'm new to Haskell, and understanding the guts of its packaging system
is a bit beyond me right now. Sorry if this is a FAQ or something, but I
tried some Google searches and found nothing useful.

Any help or tips appreciated.
From isaacdupree at charter.net  Fri Jun 13 07:15:18 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Fri Jun 13 07:07:25 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48516EEA.6020203@web.de>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<48516EEA.6020203@web.de>
Message-ID: <485256C6.2010204@charter.net>

Stephan Friedrichs wrote:
> Isaac Dupree wrote:
>> [...]
>>
>> Great to see it, it deserved implementing, IIRC!  I don't remember 
>> enough about it.. (and don't have Okasaki anywhere handy). Can it be 
>> lazy or infinitely long?
> 
> No, it has to be finite as it's actually a list of complete binary trees 
> whose size depend on the skew binary representation of the list's size. 
> I'll document this.

okay then

>> [...]
>>
>> Is "RandomAccessList" the best name for something that's not O(1), 
>> just O(log n)?  Or just that "RandomAccessList" is just much longer 
>> than "[]"?
> 
> Well Chris Okasaki called them "Skew Binary Random-Access Lists", which 
> is even longer :)

:)

hmm.. IndexableList? (just a thought, not sure whether I like it any better)

>>
>> don't use those unorthodox infix function names.. `cons` is hardly 
>> worse than .:. , `append` or `mappend` than .+. , and .!. than, hmm.. 
>> . Export a ++ and ! (!! ?) if you're really dedicated. But I'd prefer 
>> an `at` that's the same partial indexing operation, rather than the 
>> name .!. (I think this "at" was a new name being put somewhere else? 
>> partly because "!" is trying to be gradually used only to refer to 
>> strictness?)
> 
> Good point!
> 
>>
>> "extractHead" is an ugly name for a nevertheless standardish-meaning 
>> function... what is it usually called? uncons? headTail? 
>> (Data.Sequence, which is meant to be left-right symmetric, calls it 
>> "viewr"... except your version doesn't have the Maybe, it's partial 
>> instead, fails on empty lists)
> 
> Yes, I wasn't happy with that one either. The view-concept of 
> Data.Sequence is a good idea.

yeah, it's a good idea, although I'm not sure how much I like the 
particular syntax of how it's done in Data.Sequence (the view-types' 
constructor names, mostly)

>>
>> For "index", don't use Monad, use Maybe (I think that's what the 
>> recent libraries@haskell.org discussion concluded, in the context of 
>> switching Data.Map back to Maybe).
> 
> I was just copying the idea from Data.Map and it's usually a good thing 
> to have functions as general as possible, or why is it not?

To summarize: Monad isn't the proper abstraction for failable/Maybe. 
Maybe is an algebraic data type that *exactly* represents the spirit of 
what you're trying to do: e.g. Conor McBride said: "Maybe is the most 
general abstraction. Requiring (>>=), or even (<*>) seems excessive. 
What we need is "any f with zero and return", so why not pick the 
canonical, initial, inductively defined such thing?"  In this case the 
typeclass adds no generality to the function's behaviour (Maybe can be 
trivially converted to any other type, with a combinator even).  And the 
confusion that results, when the function is almost always used at type 
Maybe anyway.  If you want to read the whole discussion... if you 
haven't been subscribed to libraries@haskell.org , it's archived:
http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9082

>> Also, Data.List has genericLength etc, to 
> 
> At the moment, I'm using the Int type for size and indexing only for one 
> reason: I haven't found a proper way to generalize it. I'd really like 
> to use the Ix class, but it doesn't provide enough functionality, it 
> only works on fixed-size intervals (i. e. for arrays, which don't change 
> their size, but a list does). Maybe someone has an idea of how to 
> realize lists with a variable starting index and size?

fair enough.  If your implementation only supports sizes up to that of 
Int (which is reasonable for a strict finite type... whereas something 
like ([1..2^34] `genericIndex` (2^33)) can probably complete in a small 
amount of memory and only a moderate amount of time on a modern machine, 
even a 32-bit one, due to laziness and garbage collection)

>> support.  Isn't "index" (like Data.List.genericIndex) supposed to be a 
>> name for a partial operation, not one that returns a Maybe?  Shouldn't 
>> "size" be named "length" (or exported as both names, since e.g. 
>> Data.Map.size, .List.length) (why is it O(1) not O(log n)? Is it 
>> possible for these RandomAccessLists to be longer than maxBound::Int?)?
> 
> The size function is in O(1) because I cache it, otherwise it would be
> 
> size (RandomAccessList xs) = sum (map fst xs)
> 
> which is O(log n). I consider the caching useful, as most applications 
> will check 0 <= i < size quite often.

sounds good

> 
>>
>> for e.g. toList, is the O(n) cost spread over traversing/demanding the 
>> items of the generated list, or all up-front, or somewhere in between?
>>
>> Why is zip slow with unbalanced lists?  Obviously, it could be 
>> implemented O(min(m,n)*(log m + log n)) just indexing each one, which 
>> would be faster for really unbalanced-size lists...  Obviously, I don't 
> 
> If two lists have exactly the same size, all the complete binary trees 
> holding the data have the same size as well. This can be zipped directly 
> and is a bit (~5% in my tests) faster.

okay, that sounds like a fair optimization, since zipping same-size 
lists is a nice thing to do anyway.  But the asymptotic speed ideally 
should still be O(min(m,n)), if possible?

>> understand the implementation.  BTW, looking at the file,
>> data RandomAccessList a
>>         = RandomAccessList {-# UNPACK #-} !Int ![(Int, CBTree a)]
>> Marking a list strict like that doesn't have much effect because it 
>> only makes the first (:) or [] strict. Did you mean for an 
>> element-strict or spine-strict(which would necessarily be 
>> non-infinite) list?
> 
> Oh, you're right, I just meant to mark the Int strict. It obviously was 
> too late yesterday!
> 
> Thanks for this feedback!
> //Stephan
> 

From claus.reinke at talk21.com  Fri Jun 13 08:28:55 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Fri Jun 13 08:21:12 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
References: <48505344.4010809@web.de>
	<48507431.2080908@charter.net><48516EEA.6020203@web.de>
	<485256C6.2010204@charter.net>
Message-ID: <005201c8cd51$0d775ab0$213c7ad5@cr3lt>

> To summarize: Monad isn't the proper abstraction for failable/Maybe. 
> Maybe is an algebraic data type that *exactly* represents the spirit of 
> what you're trying to do: e.g. Conor McBride said: "Maybe is the most 
> general abstraction. Requiring (>>=), or even (<*>) seems excessive. 
> What we need is "any f with zero and return", so why not pick the 
> canonical, initial, inductively defined such thing?"  In this case the 
> typeclass adds no generality to the function's behaviour (Maybe can be 
> trivially converted to any other type, with a combinator even).  And the 
> confusion that results, when the function is almost always used at type 
> Maybe anyway.  If you want to read the whole discussion... if you 
> haven't been subscribed to libraries@haskell.org , it's archived:
> http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9082

Thanks for the summary. I had been wondering about this
change of mood, and I disagree with the suggestion that
Maybe Nothing is the right replacement for Monad fail. 

Whether fail should be in Monad, or whether we really want 
MonadZero, MonadPlus, MonadError, or something else 
entirely has been open for discussion, but it is easily shown
that Maybe is not the most general abstraction - it loses 
information wrt to (Either String), for instance:

Prelude> let {f [] = fail "empty"; f [_] = fail "singleton"; f l = return l }
Prelude> f [] :: Maybe [Bool]
Nothing
Prelude> f [True] :: Maybe [Bool]
Nothing
Prelude> f [True,False] :: Maybe [Bool]
Just [True,False]
Prelude>
Prelude> :m +Control.Monad.Error
Prelude Control.Monad.Error> f [] :: Either String [Bool]
Left "empty"
Prelude Control.Monad.Error> f [True] :: Either String [Bool]
Left "singleton"
Prelude Control.Monad.Error> f [True,False] :: Either String [Bool]
Right [True,False]

You can specialise Monad to Maybe, but you can't get
back to the general handling of failure without losing the
failure messages!

Choosing Maybe over (Either String) means: "I don't care
about the failure messages" (not that String is necessarily the
best way to represent failure conditions, but that is another
story again). As anyone who has ever tried to use a Parser
based on that choice can attest, that choice should not be
taken lightly ("Compilation failed. There were errors.").

Claus


From isaacdupree at charter.net  Fri Jun 13 08:59:34 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Fri Jun 13 08:51:41 2008
Subject: Maybe-summary was: Re: [Haskell-cafe] Re: [Haskell] ANN:
	random-access-list-0.1
In-Reply-To: <005201c8cd51$0d775ab0$213c7ad5@cr3lt>
References: <48505344.4010809@web.de>
	<48507431.2080908@charter.net><48516EEA.6020203@web.de>
	<485256C6.2010204@charter.net>
	<005201c8cd51$0d775ab0$213c7ad5@cr3lt>
Message-ID: <48526F36.3020202@charter.net>

Claus Reinke wrote:
>> To summarize: Monad isn't the proper abstraction for failable/Maybe. 
>> Maybe is an algebraic data type that *exactly* represents the spirit 
>> of what you're trying to do: e.g. Conor McBride said: "Maybe is the 
>> most general abstraction. Requiring (>>=), or even (<*>) seems 
>> excessive. What we need is "any f with zero and return", so why not 
>> pick the canonical, initial, inductively defined such thing?"  In this 
>> case the typeclass adds no generality to the function's behaviour 
>> (Maybe can be trivially converted to any other type, with a combinator 
>> even).  And the confusion that results, when the function is almost 
>> always used at type Maybe anyway.  If you want to read the whole 
>> discussion... if you haven't been subscribed to libraries@haskell.org 
>> , it's archived:
>> http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9082
> 
> Thanks for the summary. I had been wondering about this
> change of mood, and I disagree with the suggestion that
> Maybe Nothing is the right replacement for Monad fail.
> Whether fail should be in Monad, or whether we really want MonadZero, 
> MonadPlus, MonadError, or something else entirely has been open for 
> discussion, but it is easily shown
> that Maybe is not the most general abstraction - it loses information 
> wrt to (Either String), for instance:
> 
> Prelude> let {f [] = fail "empty"; f [_] = fail "singleton"; f l = 
> return l }

okay, I see, it's just that most partial functions in Data.* / container 
libraries don't really have multiple failure modes that need 
distinguishing.  You could say, in a type/information-theoretic mindset, 
that even your "f [_]" above loses information because it doesn't vary 
based on the _ (and so it isn't reversible) (and this is very common and 
normal especially for error messages, but there's a large design space 
for places where they're needed, depending on whether a machine needs to 
understand the message, etc.)  I think we didn't conclude much about 
e.g. parser-library return types, because we (thankfully) weren't trying to.

-Isaac
From duncan.coutts at worc.ox.ac.uk  Fri Jun 13 09:17:47 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Fri Jun 13 09:06:50 2008
Subject: [Haskell-cafe] Difficulty installing hscurses
In-Reply-To: <20080613091525.GC3105@argivia.columbus.rr.com>
References: <20080613091525.GC3105@argivia.columbus.rr.com>
Message-ID: <1213363067.15010.513.camel@localhost>


On Fri, 2008-06-13 at 05:15 -0400, Dominic Espinosa wrote:
> Hello,
> 
> I'm trying to install hscurses on debian-testing. I have ghc6 installed,
> which I've written some toy programs with, but I haven't tried to
> install any Hackage packages until now.
> 
> hscurses depends on old-time and old-locale (those names make me raise
> my eyebrows a bit). In turn, old-time seems to depend on old-locale. So,
> I tried installing old-locale first. In installed fine. Now I'm trying
> to install old-time:

I think you must be using ghc-6.6.x in which case you do not need
old-time and indeed you cannot install it. The modules in old-time were
included in the base package in ghc-6.6.x and split out into the
old-time package in ghc-6.8.x.

So the problem is that hscurses is not buildable out-of-the-box with
ghc-6.6.x. You can probably hack it by editing the hscurses.cabal file
and removing old-locale and old-time from the build-depends field.

On the hackage page for hscurses
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hscurses

it says:
Built on ghc-6.8

what this doesn't say clearly is that this means it did not build on
ghc-6.6.

Duncan

From jules at jellybean.co.uk  Fri Jun 13 09:33:00 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Fri Jun 13 09:25:10 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <005201c8cd51$0d775ab0$213c7ad5@cr3lt>
References: <48505344.4010809@web.de>	<48507431.2080908@charter.net><48516EEA.6020203@web.de>	<485256C6.2010204@charter.net>
	<005201c8cd51$0d775ab0$213c7ad5@cr3lt>
Message-ID: <4852770C.2020907@jellybean.co.uk>

> Whether fail should be in Monad, or whether we really want MonadZero, 
> MonadPlus, MonadError, or something else entirely has been open for 
> discussion, but it is easily shown
> that Maybe is not the most general abstraction - it loses information 
> wrt to (Either String), for instance:
> 
> Prelude> let {f [] = fail "empty"; f [_] = fail "singleton"; f l = 

Yes. But that's not what we're talking about.

We're talking about lookup and index which both have one and exactly one 
failure mode : not found.

For these functions, Maybe a is both the most general and the most 
precise type.

It is trivial to upgrade Maybe a by decorating it with an error should 
you choose to do so:

maybe (throwError "better error message here") return

which I sometimes define as 'withError' or similar.

d <- M.lookup "foo" `withError` "Variable foo not in symbol table"

Jules
From cetin.sert at gmail.com  Fri Jun 13 09:41:29 2008
From: cetin.sert at gmail.com (Cetin Sert)
Date: Fri Jun 13 09:33:38 2008
Subject: [Haskell-cafe] cgi liftM liftIO
Message-ID: <1ff5dedc0806130641u461a22c7n7d5b23e4956a39d2@mail.gmail.com>

Hi,

Could someone please care to explain what I am doing wrong below in cgiMain2
and how can I fix it?


./Main.hs:25:15:
    No instance for (MonadCGI IO)
      arising from a use of `output' at ./Main.hs:25:15-20
    Possible fix: add an instance declaration for (MonadCGI IO)
    In the first argument of `($)', namely `output'
    In the expression: output $ renderHtml $ page "import" fileForm
    In the definition of `upload':
        upload = output $ renderHtml $ page "import" fileForm

./Main.hs:57:29:
    Couldn't match expected type `CGI CGIResult'
           against inferred type `IO CGIResult'
    In the first argument of `handleErrors', namely `cgiMain2'
    In the second argument of `($)', namely `handleErrors cgiMain2'
    In the expression: runCGI $ handleErrors cgiMain2


import IO
import Network.CGI
import Text.XHtml

import qualified Data.ByteString.Lazy as BS

import Control.Monad (liftM)
import Data.Maybe (fromJust)

import Interact

fileForm = form ! [method "post", enctype "multipart/form-data"] <<
             [afile "file", submit "" "Upload"]

page t b = header << thetitle << t +++ body << b

cgiMain1 = do
  getInputFPS "file" ? ?ms ? maybe upload contents ms ? return
  where
    upload   = output $ renderHtml $ page "import" fileForm
    contents = outputFPS

cgiMain2 = do
  getInputFPS "file" ? ?ms ? maybe upload contents ms ? return
  where
    upload   = output $ renderHtml $ page "import" fileForm
    contents = ?s ? do
                      (i,o,h,_) ? runUnzip
                      BS.hPutStr i s
                      c ? BS.hGetContents o
                      outputFPS c


{-
                      (i,o,h,_) ? runUnzip
                      BS.hPutStr i s
                      BS.hGetContents o ? outputFPS
-}



{-
liftM :: (Monad m) => (a1 -> r) -> m a1 -> m r
liftIO :: (MonadIO m) => IO a -> m a

saveFile n =
    do cont <- liftM fromJust $ getInputFPS "file"
       let f = uploadDir ++ "/" ++ basename n
       liftIO $ BS.writeFile f cont
       return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++
".")
-}

runUnzip = runInteractiveCommand "unzip -l /dev/stdin"

main = runCGI $ handleErrors cgiMain2

Best Regards,
Cetin Sert

P/s: what are lifts o_O?
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From jeff.polakow at db.com  Fri Jun 13 10:15:35 2008
From: jeff.polakow at db.com (Jeff Polakow)
Date: Fri Jun 13 10:07:49 2008
Subject: [Haskell-cafe] Announce: Fortress talk in New York City
Message-ID: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>

Hello,

There will be a talk on Fortress ( a new OO/Functional language from Sun) 
on Wednesday June 25 at 6:30pm in Manhattan. 

Abstract:

The Java Programming Language revolutionized programming with two simple 
concepts:   "Write once run anywhere", and Garbage Collection.  This led 
to a big step up in programmer productivity.  Project Fortress does it 
again.    This time we give you multiprocessor performance without 
having to code threads, locks, or load balancing.  Can you say "Implicit 
Parallelism" and "Transactional Memory"?  We also give you a growable 
language (small fixed core), strong static typing (more errors caught at 
compile time), and mathematical notation.   This talk will focus on the 
strengths of Fortress as a programming language, as well as a deep dive 
into implementation issues.

More information is available at http://lisp.meetup.com/59

-Jeff


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From darrinth at gmail.com  Fri Jun 13 10:19:52 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Fri Jun 13 10:11:59 2008
Subject: [Haskell-cafe] Announce: Fortress talk in New York City
In-Reply-To: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>
References: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>
Message-ID: <a2e649c70806130719l2460e296hf130eab5f90c3ad2@mail.gmail.com>

2008/6/13 Jeff Polakow <jeff.polakow@db.com>:
> There will be a talk on Fortress ( a new OO/Functional language from Sun) on
> Wednesday June 25 at 6:30pm in Manhattan.
>

Sounds interesting. Any plans to post video?

--
Darrin
From lemming at henning-thielemann.de  Fri Jun 13 10:28:10 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Fri Jun 13 10:20:28 2008
Subject: [Haskell-cafe] Announce: Fortress talk in New York City
In-Reply-To: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>
References: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>
Message-ID: <Pine.LNX.4.64.0806131626250.28251@anubis.informatik.uni-halle.de>


On Fri, 13 Jun 2008, Jeff Polakow wrote:

> Hello,
>
> There will be a talk on Fortress ( a new OO/Functional language from Sun)
> on Wednesday June 25 at 6:30pm in Manhattan.
>
> Abstract:
>
> The Java Programming Language revolutionized programming with two simple
> concepts:   "Write once run anywhere", and Garbage Collection.  This led
> to a big step up in programmer productivity.  Project Fortress does it
> again.    This time we give you multiprocessor performance without
> having to code threads, locks, or load balancing.  Can you say "Implicit
> Parallelism" and "Transactional Memory"?  We also give you a growable
> language (small fixed core), strong static typing (more errors caught at
> compile time), and mathematical notation.   This talk will focus on the
> strengths of Fortress as a programming language, as well as a deep dive
> into implementation issues.
>
> More information is available at http://lisp.meetup.com/59
>
> -Jeff
>
>
> ---
>
> This e-mail may contain confidential and/or privileged information.

You send potentially confidential information to a public mailing list?
  Is this new language secret? :-)

From si at fh-wedel.de  Fri Jun 13 10:31:19 2008
From: si at fh-wedel.de (Uwe Schmidt)
Date: Fri Jun 13 10:23:29 2008
Subject: [Haskell-cafe] [WARN] Bug fix release of pureMD5 (Was: pureMD5)
In-Reply-To: <1213332464.3124.14.camel@localhost.localdomain>
References: <2bfa72fa0806121914w6a8a4ff6k34b7ea39f9ef9ce2@mail.gmail.com>
	<1213332464.3124.14.camel@localhost.localdomain>
Message-ID: <200806131631.19734.si@fh-wedel.de>

Thomas M. DuBuisson wrote:

> As you can probably tell, I didn't invest enough into the
> non-performance aspects of pureMD5.  Faced with actual users ;-), I have
> released version 0.2.0 which has the bug fix, a new API (type prevention
> from re-finalizing a digest), and a reasonable set of quickchecks
> (covering Show / Binary instances, known answer and incremented
> hashing).  Oh, also the module name has changed to place it inline with
> 'Crypto' package naming while not colliding.

there is a small bug in pureMD5.cabal

the line
  hs-source-dirs: Data,Test

should be
  hs-source-dirs:	.

otherwise the sources are not found (at least on my linux box)

Cheers,

Uwe
From claus.reinke at talk21.com  Fri Jun 13 10:43:19 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Fri Jun 13 10:35:36 2008
Subject: Maybe-summary was: Re: [Haskell-cafe] Re: [Haskell]
	ANN:random-access-list-0.1
References: <48505344.4010809@web.de><48507431.2080908@charter.net><48516EEA.6020203@web.de><485256C6.2010204@charter.net><005201c8cd51$0d775ab0$213c7ad5@cr3lt>
	<48526F36.3020202@charter.net>
Message-ID: <006e01c8cd63$d48d8540$213c7ad5@cr3lt>

>>> http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9082
.. 
>> that Maybe is not the most general abstraction - it loses information 
>> wrt to (Either String), for instance:
>> 
>> Prelude> let {f [] = fail "empty"; f [_] = fail "singleton"; f l = 
>> return l }
> 
> okay, I see, it's just that most partial functions in Data.* / container 
> libraries don't really have multiple failure modes that need 
> distinguishing.  

Yes, I noticed that Ross was careful to note that in the message
that started that thread. I was more concerned with that specific
case being generalized to an argument against not-just-Maybe
(I think that was the title on the old wiki?).

And single failure mode in the components doesn't imply
single failure mode in combinations, either. Consider

    import Control.Monad
    import Control.Monad.Error

    f 1 = return 1
    f _ = fail "f"

    g 2 = return 2
    g _ = fail "g"

If I call 'f', and it fails, I know that it was 'f' that failed, and it
could only fail in a single way, so there's really no point in not
replacing 'fail "f"' with 'Nothing', right (and the same goes for
'g')? Wrong (or Left;-)! 

Combining functions with single failure modes gives combinations 
with multiple failure modes (think of different branches in a parser/
type system/.., or of different phases in a compiler). Compare the 
two outputs of 'test' below:

    forg n = f n `mplus` g n
    gorf n = g n `mplus` f n

    fandg n = f n >>= g
    gandf n = g n >>= f

    test = do
      print ([forg 3, gorf 3, fandg 1, fandg 2]::[Maybe Int])
      print ([forg 3, gorf 3, fandg 1, fandg 2]::[Either String Int])

I don't know whether that is an immediate concern for the
particular functions under discussion from the 'containers' 
package, apart from all the extra lifting (and re-adding of
sensible failure messages) when wanting to use those functions 
in a non-Maybe Monad? 

But it is a concern in general monadic programming (and it 
often requires extra work to ensure that failure paths combine 
as well as success paths).

Claus

PS: There was also the argument that there are cases where
local failure handling is just not sensible (what the Erlangers
call "don't program defensively", or "let it crash"), and 
where trying to return and handle those 'Nothing's would
only make the code less readable as the problem gets
passed from Pontius to Pilatus. The "let someone else
clean up" approach is also supported by the not-just-Maybe
pattern, although not as well in Haskell as in Erlang 
(with its supervisor trees and heart-beat monitoring).


From Alistair.Bayley at invesco.com  Fri Jun 13 10:43:13 2008
From: Alistair.Bayley at invesco.com (Bayley, Alistair)
Date: Fri Jun 13 10:44:20 2008
Subject: [Haskell-cafe] Announce: Fortress talk in New York City
In-Reply-To: <Pine.LNX.4.64.0806131626250.28251@anubis.informatik.uni-halle.de>
References: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>
	<Pine.LNX.4.64.0806131626250.28251@anubis.informatik.uni-halle.de>
Message-ID: <125EACD0CAE4D24ABDB4D148C4593DA9049E940D@GBLONXMB02.corp.amvescap.net>

> From: haskell-cafe-bounces@haskell.org 
> [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of 
> Henning Thielemann
> 
> > There will be a talk on Fortress...
> >
> > ---
> >
> > This e-mail may contain confidential and/or privileged information.
> 
> You send potentially confidential information to a public 
> mailing list?

I realise this is tongue-in-cheek...


>   Is this new language secret? :-)

.. but I'm not so sure about this. If this is a serious question, here
are some links:

  http://research.sun.com/projects/plrg/
  http://research.sun.com/projects/plrg/Publications/index.html
  http://projectfortress.sun.com/Projects/Community

BTW, check out the crappy auto-appended disclaimer (over which I have no
control) on this message. Makes Jeff's look positively appealing.

Alistair
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From jmaessen at alum.mit.edu  Fri Jun 13 11:14:22 2008
From: jmaessen at alum.mit.edu (Jan-Willem Maessen)
Date: Fri Jun 13 11:06:35 2008
Subject: [Haskell-cafe] Announce: Fortress talk in New York City
In-Reply-To: <125EACD0CAE4D24ABDB4D148C4593DA9049E940D@GBLONXMB02.corp.amvescap.net>
References: <OF6E6B4212.73E18BD3-ON85257467.004CF664-85257467.004E554F@db.com>
	<Pine.LNX.4.64.0806131626250.28251@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E940D@GBLONXMB02.corp.amvescap.net>
Message-ID: <0D52D25D-CA3E-4C45-B4D2-753EDCB0D856@alum.mit.edu>


On Jun 13, 2008, at 10:43 AM, Bayley, Alistair wrote:

>> From: haskell-cafe-bounces@haskell.org
>> [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of
>> Henning Thielemann
>>
>>> There will be a talk on Fortress...
>>>
>>> ---
>>>
>>> This e-mail may contain confidential and/or privileged information.
>>
>> You send potentially confidential information to a public
>> mailing list?
>
> I realise this is tongue-in-cheek...
>
>
>>  Is this new language secret? :-)
>
> .. but I'm not so sure about this. If this is a serious question, here
> are some links:
>
>  http://research.sun.com/projects/plrg/
>  http://research.sun.com/projects/plrg/Publications/index.html
>  http://projectfortress.sun.com/Projects/Community

Let me assure the readers there's nothing confidential or privileged  
about Christine's talk! :-)  It is, after all, an open source project.

-Jan-Willem Maessen
  Project Fortress, Sun Microsystems Laboratories
  [who will be off teaching Fortress in Prague at the time]

From darrinth at gmail.com  Fri Jun 13 11:19:33 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Fri Jun 13 11:11:40 2008
Subject: [Haskell-cafe] cabal-install failure
Message-ID: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>

Cabal-install is looking good. It now, for the record, has only two
deps outside of Cabal-1.4.

I installed cabal-install-0.5 on ubuntu with the haskell.org linux
binary for ghc 6.8.2.

I then tried cabal-install yi

Got this output:
... many successful installs ...
Registering vty-3.0.1...
Reading package info from "dist/installed-pkg-config" ... done.
Saving old package config file... done.
Writing new package config file... done.
Downloading yi-0.3...
[1 of 1] Compiling Main             ( Setup.hs, dist/setup/Main.o )

Setup.hs:9:0:
    Warning: Deprecated use of `showPackageId'
             (imported from Distribution.Simple, but defined in
Distribution.Package):
             use the Text class instead
Linking dist/setup/setup ...
Warning: defaultUserHooks in Setup script is deprecated.
Configuring yi-0.3...
Warning: Instead of 'ghc-options: -DDYNAMIC -DFRONTEND_VTY' use 'cpp-options:
-DDYNAMIC -DFRONTEND_VTY'
setup: alex version >=2.0.1 && <3 is required but it could not be found.
cabal: Error: some packages failed to install:
yi-0.3 failed during the configure step. The exception was:
exit: ExitFailure 1

Is this a cabal problem of package problem? I would have expected it
to fail immediately instead of discover this problem so far into
process.

Thanks.

--
Darrin
From deduktionstheorem at web.de  Fri Jun 13 11:38:48 2008
From: deduktionstheorem at web.de (Stephan Friedrichs)
Date: Fri Jun 13 11:31:00 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <485256C6.2010204@charter.net>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
	<48516EEA.6020203@web.de> <485256C6.2010204@charter.net>
Message-ID: <48529488.6090107@web.de>

Isaac Dupree wrote:
> [...]
>>
>> Well Chris Okasaki called them "Skew Binary Random-Access Lists", 
>> which is even longer :)
> 
> :)
> 
> hmm.. IndexableList? (just a thought, not sure whether I like it any 
> better)

RAList?
IList? <- (will I be sued by a large computer company for that?)

> [...]
>> Yes, I wasn't happy with that one either. The view-concept of 
>> Data.Sequence is a good idea.
 >
 > yeah, it's a good idea, although I'm not sure how much I like the
 > particular syntax of how it's done in Data.Sequence (the view-types'
 > constructor names, mostly)

I now have

data View a
	= Empty
	| Cons a (RandomAccessList a)

and

view :: RandomAccessList a -> a

additionally, I renamed "extractHead" to "uncons" (which is OK, because 
I also have "cons") but still left "head" and "tail" with the typical 
list-like behaviour (causing an error on empty lists).

> [Monad vs. Maybe]

That's quite convincing, most of all that "fail" has rather strange 
definitions for many Monads (because it originally does not belong to 
monads, does it?).

> [...]
>>
>> The size function is in O(1) because I cache it, otherwise it would be
>>
>> size (RandomAccessList xs) = sum (map fst xs)
>>
>> which is O(log n). I consider the caching useful, as most applications 
>> will check 0 <= i < size quite often.
> 
> sounds good
> 
> [...]
>
>> If two lists have exactly the same size, all the complete binary trees 
>> holding the data have the same size as well. This can be zipped 
>> directly and is a bit (~5% in my tests) faster.
> 
> okay, that sounds like a fair optimization, since zipping same-size 
> lists is a nice thing to do anyway.  But the asymptotic speed ideally 
> should still be O(min(m,n)), if possible?

Well... I guess that's possible converting the shorter one into a list 
and using fold for zipping. I'll have a close look at this!


-- 

Fr?her hie? es ja: Ich denke, also bin ich.
Heute wei? man: Es geht auch so.

  - Dieter Nuhr
From stephen at enterity.com  Fri Jun 13 12:38:25 2008
From: stephen at enterity.com (Stephen Howard)
Date: Fri Jun 13 12:29:56 2008
Subject: [Haskell-cafe] working with Random.randoms
Message-ID: <4852A281.8000508@enterity.com>

Hi List,

I am a newcomer doing my obligatory struggling with Haskell's type 
system, and I've got a nut I've not been able to crack.  Given:

import Random

random_test :: Int -> String
random_test n = do
    g <- getStdGen
    take n (randoms g)::String

I'm expecting that I ought to be able to pass this action an integer and 
get back a random string that long (given, not all characters may be 
printable).

But GHCI tells me:

RandomTest.hs:7:4:
    Couldn't match `[]' against `IO'
      Expected type: []
      Inferred type: IO
    In a 'do' expression: g <- getStdGen
    In the definition of `random_test':
        random_test n = do
                          g <- getStdGen
                            take n (randoms g) :: String

And yet, when I run these lines in GHCI by hand, things seem to work 
(though the string is the same set of random characters each time, 
another bit that I need to solve):

Prelude> :module Random
Prelude Random> g <- getStdGen
Prelude Random> take 5 (randoms g)::String
"\1025049\315531\882767\1032009\334825"


I'm guessing that randoms is returning an IO type but I'm not sure how 
to go about extracting the String to return to the calling action.  
Changing the type signature to Int -> IO  String only gives me a 
different error.

Where am I going wrong?

thanks,
Stephen
From daniel.is.fischer at web.de  Fri Jun 13 13:05:21 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Fri Jun 13 12:55:32 2008
Subject: [Haskell-cafe] working with Random.randoms
In-Reply-To: <4852A281.8000508@enterity.com>
References: <4852A281.8000508@enterity.com>
Message-ID: <200806131905.21945.daniel.is.fischer@web.de>

Am Freitag, 13. Juni 2008 18:38 schrieb Stephen Howard:
> Hi List,
>
> I am a newcomer doing my obligatory struggling with Haskell's type
> system, and I've got a nut I've not been able to crack.  Given:
>
> import Random
>
> random_test :: Int -> String
> random_test n = do
>     g <- getStdGen
>     take n (randoms g)::String
>
> I'm expecting that I ought to be able to pass this action an integer and
> get back a random string that long (given, not all characters may be
> printable).
>
> But GHCI tells me:
>
> RandomTest.hs:7:4:
>     Couldn't match `[]' against `IO'
>       Expected type: []
>       Inferred type: IO
>     In a 'do' expression: g <- getStdGen
>     In the definition of `random_test':
>         random_test n = do
>                           g <- getStdGen
>                             take n (randoms g) :: String
>
> And yet, when I run these lines in GHCI by hand, things seem to work
> (though the string is the same set of random characters each time,
> another bit that I need to solve):
>
> Prelude> :module Random
> Prelude Random> g <- getStdGen
> Prelude Random> take 5 (randoms g)::String
> "\1025049\315531\882767\1032009\334825"
>
>
> I'm guessing that randoms is returning an IO type but I'm not sure how

No, getStdGen is what's in IO, it has type IO StdGen. Since you can't get rid 
of IO safely, the type of random_test must be Int -> IO String.
Best practice is to separate into a pure part:

pure_random_test :: Int -> StdGen -> String
pure_random_test n g = take n (randoms g)

and the IO bound part:

random_test :: Int -> IO String
random_test n = do
	g <- getStdGen
	return $ pure_random_test n g

or, if we like it better:

random_test n = fmap (pure_random_test n) getStdGen

> to go about extracting the String to return to the calling action.
> Changing the type signature to Int -> IO  String only gives me a
> different error.
>
> Where am I going wrong?

You must put the String (take n (randoms g)) into the IO monad.

The way it works in ghci is due to the fact, that in ghci, you are basically 
in an IO loop/do-block.
When you type 
g <- getStdGen
the action is performed, and the result is bound to the identifier g.
When you then type
take 5 (randoms g),
it's transformed into
do .....
    let it = take 5 (randoms g)
    print it
    return it

Within one session, all calls to getStdGen return the same StdGen, that's why 
you always get the same sequence of random Chars.
>
> thanks,
> Stephen

HTH,
Daniel

From aditya_siram at hotmail.com  Fri Jun 13 15:01:10 2008
From: aditya_siram at hotmail.com (Aditya Siram)
Date: Fri Jun 13 14:53:18 2008
Subject: [Haskell-cafe] Cabal-Install Fails To Compile
In-Reply-To: <1213325939.15010.508.camel@localhost>
References: <BLU108-W36DD0E576AC2C91FEC9563F4AD0@phx.gbl>
	<1213325939.15010.508.camel@localhost>
Message-ID: <BLU108-W9AC16C9E007E52E6FF77BF4AC0@phx.gbl>


Thanks so much for your help. Actually Don got it fixed within twenty minutes but I mistakenly didn't cc the group. But it works perfectly now.

-Deech
----------------------------------------
> Subject: Re: [Haskell-cafe] Cabal-Install Fails To Compile
> From: duncan.coutts@worc.ox.ac.uk
> To: aditya_siram@hotmail.com
> CC: haskell-cafe@haskell.org
> Date: Fri, 13 Jun 2008 03:58:59 +0100
> 
> 
> On Thu, 2008-06-12 at 16:07 -0500, Aditya Siram wrote:
>> Hi all,
>> I downloaded cabal-install and the cabal-1.4 branch from darcs. The following error occurs when building:
>>> runhaskell Setup.hs build
>> 
>> Building cabal-install-0.4.9...
>> [19 of 27] Compiling Hackage.SrcDist  ( Hackage/SrcDist.hs, dist/build/cabal/cabal-tmp/Hackage/SrcDist.o )
>> 
>> Hackage/SrcDist.hs:58:59:
>>     Couldn't match expected type `Char'
>>            against inferred type `Distribution.Simple.PreProcess.PPSuffixHandler'
>>       Expected type: FilePath
>>       Inferred type: [Distribution.Simple.PreProcess.PPSuffixHandler]
>>     In the fifth argument of `prepareSnapshotTree', namely
>>         `knownSuffixHandlers'
>>     In the second argument of `(>>=)', namely
>>         `prepareSnapshotTree
>>            verbosity pkg mb_lbi tmpDir knownSuffixHandlers'
> 
> Yeah, sorry that was my fault. You caught it in the few hours when the
> two darcs versions were not compatible. They work now, or as Don says,
> get the actual releases from hackage.
> 
> Duncan
> 

_________________________________________________________________
Search that pays you back! Introducing Live Search cashback.
http://search.live.com/cashback/?&pkw=form=MIJAAF/publ=HMTGL/crea=srchpaysyouback
From wren at freegeek.org  Fri Jun 13 16:29:07 2008
From: wren at freegeek.org (wren ng thornton)
Date: Fri Jun 13 16:21:41 2008
Subject: [Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
In-Reply-To: <48507431.2080908@charter.net>
References: <48505344.4010809@web.de> <48507431.2080908@charter.net>
Message-ID: <4852D893.7050107@freegeek.org>

Isaac Dupree wrote:
> "extractHead" is an ugly name for a nevertheless standardish-meaning 
> function... what is it usually called? uncons? headTail? (Data.Sequence, 
> which is meant to be left-right symmetric, calls it "viewr"... except 
> your version doesn't have the Maybe, it's partial instead, fails on 
> empty lists)


Views are nice, but these other functions are needed too. As for 
"extractHead", what about "split"? (cf. Control.Monad.Logic.msplit[1])

[1] http://tinyurl.com/37f4ga
http://hackage.haskell.org/packages/archive/logict/0.2.3/doc/html/Control-Monad-Logic-Class.html

-- 
Live well,
~wren
From duncan.coutts at worc.ox.ac.uk  Fri Jun 13 17:22:06 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Fri Jun 13 17:10:33 2008
Subject: [Haskell-cafe] cabal-install failure
In-Reply-To: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
Message-ID: <1213392126.15010.547.camel@localhost>


On Fri, 2008-06-13 at 11:19 -0400, Darrin Thompson wrote:
> Cabal-install is looking good. It now, for the record, has only two
> deps outside of Cabal-1.4.
> 
> I installed cabal-install-0.5 on ubuntu with the haskell.org linux
> binary for ghc 6.8.2.
> 
> I then tried cabal-install yi
> 
> Got this output:
> ... many successful installs ...
> Registering vty-3.0.1...
> Reading package info from "dist/installed-pkg-config" ... done.
> Saving old package config file... done.
> Writing new package config file... done.
> Downloading yi-0.3...
> [1 of 1] Compiling Main             ( Setup.hs, dist/setup/Main.o )
> 
> Setup.hs:9:0:
>     Warning: Deprecated use of `showPackageId'
>              (imported from Distribution.Simple, but defined in
> Distribution.Package):
>              use the Text class instead
> Linking dist/setup/setup ...
> Warning: defaultUserHooks in Setup script is deprecated.
> Configuring yi-0.3...
> Warning: Instead of 'ghc-options: -DDYNAMIC -DFRONTEND_VTY' use 'cpp-options:
> -DDYNAMIC -DFRONTEND_VTY'
> setup: alex version >=2.0.1 && <3 is required but it could not be found.
> cabal: Error: some packages failed to install:
> yi-0.3 failed during the configure step. The exception was:
> exit: ExitFailure 1
> 
> Is this a cabal problem of package problem? I would have expected it
> to fail immediately instead of discover this problem so far into
> process.

So it's failing when configuring yi because alex is not installed.

So the question is when should this get checked? I think it's not
unreasonable to have the check where it is now though perhaps we could
do better by bringing it forward.

The point is, cabal-install only checks that haskell packages are
available before beginning to install stuff. It leaves all the other
checks (build tools, C libs, custom checks in Setup.hs script etc) to be
done at the configure phase of each package.

In theory it's not impossible to imagine doing the configure phase of
every package before doing the build phase of any package but it's not
clear that it gains us that much and it's a bit more complex to do it
that way.

Duncan

From david.waern at gmail.com  Fri Jun 13 18:07:13 2008
From: david.waern at gmail.com (David Waern)
Date: Fri Jun 13 17:59:21 2008
Subject: [Haskell-cafe] ANN: Haddock Trac
Message-ID: <bb52000e0806131507x6ad904e0n4aa27b9d978ba5b2@mail.gmail.com>

Hi everyone,

there's now a Haddock bug-tracker and wiki at
http://trac.haskell.org/haddock. Please use it to submit bug reports
and feature requests!

David
From jason.dusek at gmail.com  Fri Jun 13 19:39:35 2008
From: jason.dusek at gmail.com (Jason Dusek)
Date: Fri Jun 13 19:31:41 2008
Subject: [Haskell-cafe] LDAP 0.6.3 build failure
Message-ID: <42784f260806131639w7e1b9169y9d1ed738c035f8ec@mail.gmail.com>

  I'm trying to build the LDAP libs, version 0.6.3, on a recent
  MacBook Air with OpenLDAP 2.3.27 (the version of OpenLDAP
  shipped by Apple).

  The "atom sorting error" I get from `ld` is outside my range
  of knowledge -- if some could advise me on how to get around
  it, I'd be much obliged. I'm using the Apple toolchain to do
  do the build.

-- 
_jsn


 :; Setup configure && Setup build
Configuring LDAP-0.6.3...
Preprocessing library LDAP-0.6.3...
Building LDAP-0.6.3...
ar: creating archive dist/build/libHSLDAP-0.6.3.a
ld: atom sorting error for
_LDAPzm0zi6zi3_LDAPziTypesLL_Berval_closure_tbl and
_LDAPzm0zi6zi3_LDAPziTypesLL_CLDAP_closure_tbl in
dist/build/LDAP/TypesLL.o
ld: atom sorting error for
_LDAPzm0zi6zi3_LDAPziTypesLL_Berval_closure_tbl and
_LDAPzm0zi6zi3_LDAPziTypesLL_CLDAP_closure_tbl
From judah.jacobson at gmail.com  Fri Jun 13 20:21:31 2008
From: judah.jacobson at gmail.com (Judah Jacobson)
Date: Fri Jun 13 20:13:37 2008
Subject: [Haskell-cafe] LDAP 0.6.3 build failure
In-Reply-To: <42784f260806131639w7e1b9169y9d1ed738c035f8ec@mail.gmail.com>
References: <42784f260806131639w7e1b9169y9d1ed738c035f8ec@mail.gmail.com>
Message-ID: <6d74b0d20806131721s52f3857etace97e204011f27@mail.gmail.com>

On Fri, Jun 13, 2008 at 4:39 PM, Jason Dusek <jason.dusek@gmail.com> wrote:
>  I'm trying to build the LDAP libs, version 0.6.3, on a recent
>  MacBook Air with OpenLDAP 2.3.27 (the version of OpenLDAP
>  shipped by Apple).
>
>  The "atom sorting error" I get from `ld` is outside my range
>  of knowledge -- if some could advise me on how to get around
>  it, I'd be much obliged. I'm using the Apple toolchain to do
>  do the build.
>

That "error" is actually a harmless warning; in my experience it can
be safely ignored.  More information at:

http://www.nabble.com/Re%3A--Fwd%3A-Re%3A-Problem-building-hdbc-sqlite3-with-ghc-6.8.2--p14602140.html

-Judah
From ryani.spam at gmail.com  Fri Jun 13 20:27:01 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Fri Jun 13 20:19:07 2008
Subject: [Haskell-cafe] monomorphism restriction
In-Reply-To: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
References: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
Message-ID: <2f9b2d30806131727s624ee38dja867b926bbde0cc1@mail.gmail.com>

On 6/11/08, Rex Page <page@ou.edu> wrote:
> Please remind me, again, of the advantages of f being something different
> from the formula defining it.

fibs !a !b = a : fibs b (a+b)
-- fibs :: Num a => a -> a -> [a]

n = head $ drop 1000000 $ fibs 1 1
-- n :: Integer (due to monomorphism restriction.)

sumns 0 = 0
sumns x = sumns (x-1) + n

Without the monomorphism restriction, computing n is a function call;
it is evaluated each time it is asked for.

With the monomorphism restriction, n is a CAF and it is updated in
place after it's been evaluated for the first time.

Evaluating "sumns 1000" could take 1000 times as long without the
monomorphism restriction, which definitely seems surprising as a user
until you understand whatis going on behind the scenes with dictionary
passing.

If you do not want the MR, you have these options:
1) turn off explicitly (in GHC you can use -fno-monomorphism restriction)
2) add a type signature yourself (f :: Num a => [a] -> a)
3) eta-expand (f xs = foldr (+) 0 xs)

  -- ryan
From jonathanccast at fastmail.fm  Wed Jun 11 23:48:56 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Fri Jun 13 21:05:46 2008
Subject: [Haskell-cafe] monomorphism restriction
In-Reply-To: <20080612032402.GA25431@scytale.galois.com>
References: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
	<20080612032402.GA25431@scytale.galois.com>
Message-ID: <1213242536.6353.6.camel@jonathans-macbook>

On Wed, 2008-06-11 at 20:24 -0700, Don Stewart wrote:
> page:
> > Definition of f:
> >    f = foldr (+) 0
> > Types:
> >    0 :: (Num t) => t
> >    foldr (+) 0 :: Num a => [a] -> a
> >    f :: [Integer] -> Integer
> > 
> > Please remind me, again, of the advantages of f being something different 
> > from the formula defining it.
> 
> Overloaded 'constants' take a dictionary as an argument, so while you
> think the value might be computed only once, it make actually be
> recomputed each time. This can be a killer performance penalty for
> overloaded numeric constants.
> 
> Of course, disabling this is pretty simple.

This doesn't apply to f, though --- it has a function type, so the user
presumably already knows it won't be subject to updating, no?
Distinguishing functions from variables by the form of declaration,
rather than the type, seems somewhat questionable to me.

jcc


From gwern0 at gmail.com  Fri Jun 13 22:10:52 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Fri Jun 13 22:04:09 2008
Subject: [Haskell-cafe] cabal-install failure
In-Reply-To: <1213392126.15010.547.camel@localhost>
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
	<1213392126.15010.547.camel@localhost>
Message-ID: <20080614021052.GA8862@craft>

On 2008.06.13 22:22:06 +0100, Duncan Coutts <duncan.coutts@worc.ox.ac.uk> scribbled 2.1K characters:
>
> On Fri, 2008-06-13 at 11:19 -0400, Darrin Thompson wrote:
> > Cabal-install is looking good. It now, for the record, has only two
> > deps outside of Cabal-1.4.
> >
> > I installed cabal-install-0.5 on ubuntu with the haskell.org linux
> > binary for ghc 6.8.2.
> >
> > I then tried cabal-install yi
> >
> > Got this output:
> > ... many successful installs ...
> > Registering vty-3.0.1...
> > Reading package info from "dist/installed-pkg-config" ... done.
> > Saving old package config file... done.
> > Writing new package config file... done.
> > Downloading yi-0.3...
> > [1 of 1] Compiling Main             ( Setup.hs, dist/setup/Main.o )
> >
> > Setup.hs:9:0:
> >     Warning: Deprecated use of `showPackageId'
> >              (imported from Distribution.Simple, but defined in
> > Distribution.Package):
> >              use the Text class instead
> > Linking dist/setup/setup ...
> > Warning: defaultUserHooks in Setup script is deprecated.
> > Configuring yi-0.3...
> > Warning: Instead of 'ghc-options: -DDYNAMIC -DFRONTEND_VTY' use 'cpp-options:
> > -DDYNAMIC -DFRONTEND_VTY'
> > setup: alex version >=2.0.1 && <3 is required but it could not be found.
> > cabal: Error: some packages failed to install:
> > yi-0.3 failed during the configure step. The exception was:
> > exit: ExitFailure 1
> >
> > Is this a cabal problem of package problem? I would have expected it
> > to fail immediately instead of discover this problem so far into
> > process.
>
> So it's failing when configuring yi because alex is not installed.
>
> So the question is when should this get checked? I think it's not
> unreasonable to have the check where it is now though perhaps we could
> do better by bringing it forward.
>
> The point is, cabal-install only checks that haskell packages are
> available before beginning to install stuff. It leaves all the other
> checks (build tools, C libs, custom checks in Setup.hs script etc) to be
> done at the configure phase of each package.
>
> In theory it's not impossible to imagine doing the configure phase of
> every package before doing the build phase of any package but it's not
> clear that it gains us that much and it's a bit more complex to do it
> that way.
>
> Duncan

I think this may be Cabal's fault anyway. The yi.cabal includes the line:
         build-tools:   alex >= 2.0.1 && < 3

in the 'executable yi' section, right after the build-depends, so Yi is being straightforward and upfront about its needs. Now, Cabal is obviously checking that the build-depends is satisfied first, but why isn't it checking that alex is available when it has the information it needs to check, presumably anything in build-tools is *required*, and the field name suggests that it would be checked?

--
gwern
watchers 5.0i Fax UXO NORAD Consulting meta Gatt of data
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From vigalchin at gmail.com  Sat Jun 14 01:59:31 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sat Jun 14 01:51:38 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
	<5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
Message-ID: <5ae4f2ba0806132259o26632f1bsa159839029529fc@mail.gmail.com>

If I change

     data Sigval = SivalInt Int | SivalPtr (Ptr Char)
to ...

    newtype Sigval = Sivalint Int | SivalPtr (Ptr Char)

then my test case builds and links. ??


Regards, Vasili




On Mon, Jun 9, 2008 at 11:01 PM, Galchin, Vasili <vigalchin@gmail.com>
wrote:

> I have tried various things to no avail ....
>
> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
> Setup.lhs build
> Preprocessing executables for Test-1.0...
> Building Test-1.0...
> [1 of 1] Compiling Main             ( ./timer.hs,
> dist/build/timer/timer-tmp/Main.o )
>
> ./timer.hs:22:0:
>     Unacceptable argument type in foreign declaration: Sigval
>     When checking declaration:
>         foreign import ccall safe "wrapper" mkNotify
>           :: Notify -> IO (FunPtr Notify)
>
> => here is my Sigval def
>
> data Sigval = SivalInt Int | SivalPtr (Ptr Char)
>
> I did a find/grep for "Unacceptable argument" in the ghc compiler source
> and assuming no typo I didn't find. ??
>
> Thanks.
>
> Kind regards, Vasili
>
>
>
>
>  On Mon, Jun 9, 2008 at 11:25 PM, Judah Jacobson <judah.jacobson@gmail.com>
> wrote:
>
>> 2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
>> > Ryan,
>> >
>> >      I tried but the compiler didn't seem to like the keyword "import":
>> >
>> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
>> > Setup.lhs build
>> > Preprocessing executables for Test-1.0...
>> > Building Test-1.0...
>> > [1 of 1] Compiling Main             ( ./timer.hs,
>> > dist/build/timer/timer-tmp/Main.o )
>> >
>> > ./timer.hs:29:8: parse error on input `import'
>> >
>>
>> Hi Vasili,
>>
>> To fix that error, you probably just need to add the line "Extensions:
>> ForeignFunctionInterface" to the .cabal file.   (That is the
>> equivalent of calling ghc by itself with the command-line arguments
>> -fffi or -XForeignFunctionInterface.)
>>
>> Hope that helps,
>> -Judah
>>
>
>
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From aneumann at inf.fu-berlin.de  Sat Jun 14 02:05:48 2008
From: aneumann at inf.fu-berlin.de (Adrian Neumann)
Date: Sat Jun 14 01:58:09 2008
Subject: [Haskell-cafe] cgi liftM liftIO
In-Reply-To: <1ff5dedc0806130641u461a22c7n7d5b23e4956a39d2@mail.gmail.com>
References: <1ff5dedc0806130641u461a22c7n7d5b23e4956a39d2@mail.gmail.com>
Message-ID: <EFDC92D1-38FE-424D-B600-A36CAE32B3BD@inf.fu-berlin.de>

I think you need to put liftIO in front of the IO actions you want to  
do inside the CGI Monad. Like in this example

 > http://www.haskell.org/haskellwiki/ 
Practical_web_programming_in_Haskell#File_uploads

(Why did I need to use google to find that? The wiki search in awful.  
Searching for CGI returns nothing, whereas with google the above is  
the first hit.)

Am 13.06.2008 um 15:41 schrieb Cetin Sert:

> Hi,
>
> Could someone please care to explain what I am doing wrong below in  
> cgiMain2 and how can I fix it?
>
>
> ./Main.hs:25:15:
>     No instance for (MonadCGI IO)
>       arising from a use of `output' at ./Main.hs:25:15-20
>     Possible fix: add an instance declaration for (MonadCGI IO)
>     In the first argument of `($)', namely `output'
>     In the expression: output $ renderHtml $ page "import" fileForm
>     In the definition of `upload':
>         upload = output $ renderHtml $ page "import" fileForm
>
> ./Main.hs:57:29:
>     Couldn't match expected type `CGI CGIResult'
>            against inferred type `IO CGIResult'
>     In the first argument of `handleErrors', namely `cgiMain2'
>     In the second argument of `($)', namely `handleErrors cgiMain2'
>     In the expression: runCGI $ handleErrors cgiMain2
>
>
> import IO
> import Network.CGI
> import Text.XHtml
>
> import qualified Data.ByteString.Lazy as BS
>
> import Control.Monad (liftM)
> import Data.Maybe (fromJust)
>
> import Interact
>
> fileForm = form ! [method "post", enctype "multipart/form-data"] <<
>              [afile "file", submit "" "Upload"]
>
> page t b = header << thetitle << t +++ body << b
>
> cgiMain1 = do
>   getInputFPS "file" ? ?ms ? maybe upload contents ms ? return
>   where
>     upload   = output $ renderHtml $ page "import" fileForm
>     contents = outputFPS
>
> cgiMain2 = do
>   getInputFPS "file" ? ?ms ? maybe upload contents ms ? return
>   where
>     upload   = output $ renderHtml $ page "import" fileForm
>     contents = ?s ? do
>                       (i,o,h,_) ? runUnzip
>                       BS.hPutStr i s
>                       c ? BS.hGetContents o
>                       outputFPS c
>
>
> {-
>                       (i,o,h,_) ? runUnzip
>                       BS.hPutStr i s
>                       BS.hGetContents o ? outputFPS
> -}
>
>
>
> {-
> liftM :: (Monad m) => (a1 -> r) -> m a1 -> m r
> liftIO :: (MonadIO m) => IO a -> m a
>
> saveFile n =
>     do cont <- liftM fromJust $ getInputFPS "file"
>        let f = uploadDir ++ "/" ++ basename n
>        liftIO $ BS.writeFile f cont
>        return $ paragraph << ("Saved as " +++ anchor ! [href f] <<  
> f +++ ".")
> -}
>
> runUnzip = runInteractiveCommand "unzip -l /dev/stdin"
>
> main = runCGI $ handleErrors cgiMain2
>
> Best Regards,
> Cetin Sert
>
> P/s: what are lifts o_O?
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

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From gwern0 at gmail.com  Sat Jun 14 02:12:04 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Sat Jun 14 02:04:55 2008
Subject: [Haskell-cafe] cgi liftM liftIO
In-Reply-To: <EFDC92D1-38FE-424D-B600-A36CAE32B3BD@inf.fu-berlin.de>
References: <1ff5dedc0806130641u461a22c7n7d5b23e4956a39d2@mail.gmail.com>
	<EFDC92D1-38FE-424D-B600-A36CAE32B3BD@inf.fu-berlin.de>
Message-ID: <20080614061204.GA7160@craft>

On 2008.06.14 08:05:48 +0200, Adrian Neumann <aneumann@inf.fu-berlin.de> scribbled 4.0K characters:
> I think you need to put liftIO in front of the IO actions you want to do
> inside the CGI Monad. Like in this example
>
> > http://www.haskell.org/haskellwiki/
> Practical_web_programming_in_Haskell#File_uploads
>
> (Why did I need to use google to find that? The wiki search in awful.
> Searching for CGI returns nothing, whereas with google the above is the
> first hit.)

IIRC, MediaWiki search will not search for anything shorter than 4 characters (as an optimization, I think). This is admittedly annoying when you are searching not for 'the' but 'IRC' or 'CGI'...

--
gwern
William Gap subversives Lexis-Nexis SADMS Blowpipe GRU Posse ISCS mailbomb
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From vigalchin at gmail.com  Sat Jun 14 02:40:42 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sat Jun 14 02:32:47 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806132259o26632f1bsa159839029529fc@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
	<5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
	<5ae4f2ba0806132259o26632f1bsa159839029529fc@mail.gmail.com>
Message-ID: <5ae4f2ba0806132340w39031820q3e1e86723760469@mail.gmail.com>

oops .. my bad ...

If I change data Sigval = SivalInt Int

to newtype Sigval = SivalInt Int

OR

       data Sigval = SivalPtr (Ptr Char)

    to newtype Sigval = SivalPtr (Ptr Char).


Why should "newtype" instead of a data type allow my test case to build?

Vasili



On Fri, Jun 13, 2008 at 10:59 PM, Galchin, Vasili <vigalchin@gmail.com>
wrote:

> If I change
>
>      data Sigval = SivalInt Int | SivalPtr (Ptr Char)
> to ...
>
>     newtype Sigval = Sivalint Int | SivalPtr (Ptr Char)
>
> then my test case builds and links. ??
>
>
> Regards, Vasili
>
>
>
>
> On Mon, Jun 9, 2008 at 11:01 PM, Galchin, Vasili <vigalchin@gmail.com>
> wrote:
>
>> I have tried various things to no avail ....
>>
>> vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
>> Setup.lhs build
>> Preprocessing executables for Test-1.0...
>> Building Test-1.0...
>> [1 of 1] Compiling Main             ( ./timer.hs,
>> dist/build/timer/timer-tmp/Main.o )
>>
>> ./timer.hs:22:0:
>>     Unacceptable argument type in foreign declaration: Sigval
>>     When checking declaration:
>>         foreign import ccall safe "wrapper" mkNotify
>>           :: Notify -> IO (FunPtr Notify)
>>
>> => here is my Sigval def
>>
>> data Sigval = SivalInt Int | SivalPtr (Ptr Char)
>>
>> I did a find/grep for "Unacceptable argument" in the ghc compiler source
>> and assuming no typo I didn't find. ??
>>
>> Thanks.
>>
>> Kind regards, Vasili
>>
>>
>>
>>
>>  On Mon, Jun 9, 2008 at 11:25 PM, Judah Jacobson <
>> judah.jacobson@gmail.com> wrote:
>>
>>> 2008/6/9 Galchin, Vasili <vigalchin@gmail.com>:
>>> > Ryan,
>>> >
>>> >      I tried but the compiler didn't seem to like the keyword "import":
>>> >
>>> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell
>>> > Setup.lhs build
>>> > Preprocessing executables for Test-1.0...
>>> > Building Test-1.0...
>>> > [1 of 1] Compiling Main             ( ./timer.hs,
>>> > dist/build/timer/timer-tmp/Main.o )
>>> >
>>> > ./timer.hs:29:8: parse error on input `import'
>>> >
>>>
>>> Hi Vasili,
>>>
>>> To fix that error, you probably just need to add the line "Extensions:
>>> ForeignFunctionInterface" to the .cabal file.   (That is the
>>> equivalent of calling ghc by itself with the command-line arguments
>>> -fffi or -XForeignFunctionInterface.)
>>>
>>> Hope that helps,
>>> -Judah
>>>
>>
>>
>
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From xs at xaph.net  Sat Jun 14 03:19:19 2008
From: xs at xaph.net (Rafal Kolanski)
Date: Sat Jun 14 03:11:29 2008
Subject: [Haskell-cafe] monomorphism restriction
In-Reply-To: <2f9b2d30806131727s624ee38dja867b926bbde0cc1@mail.gmail.com>
References: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
	<2f9b2d30806131727s624ee38dja867b926bbde0cc1@mail.gmail.com>
Message-ID: <485370F7.20308@xaph.net>


Ryan Ingram wrote:
> sumns 0 = 0
> sumns x = sumns (x-1) + n
> 
> Without the monomorphism restriction, computing n is a function call;
> it is evaluated each time it is asked for.

I'm relatively new to Haskell, and since this topic already came up, I
was wondering if anyone could explain to me how this ties into implicit
parameters which "escape" from their respective functions?

For instance, if I just state:
maxLength = maxLengthParameter ?config
without providing a type signature and then use it, I get warned that
?config "escapes" from maxLength and that I should provide a type
signature or turn off the monomorphism restriction.

I find implicit parameters are a really nice way to pass a configuration
to a whole tree of functions (in this case an LZSS compressor) without
having to explicitly add it as a parameter to every single one of the
functions.

What are the performance implications of turning off the restriction and
allowing implicit parameters to "escape"? Are there general performance
implications of implicit parameters I am not aware of?

Yours Sincerely,

Rafal Kolanski.


From duncan.coutts at worc.ox.ac.uk  Sat Jun 14 03:56:34 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sat Jun 14 03:44:23 2008
Subject: [Haskell-cafe] cabal-install failure
In-Reply-To: <20080614021052.GA8862@craft>
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
	<1213392126.15010.547.camel@localhost>  <20080614021052.GA8862@craft>
Message-ID: <1213430194.15010.556.camel@localhost>


On Fri, 2008-06-13 at 22:10 -0400, Gwern Branwen wrote:

> I think this may be Cabal's fault anyway. The yi.cabal includes the line:
>          build-tools:   alex >= 2.0.1 && < 3
> 
> in the 'executable yi' section, right after the build-depends, so Yi
> is being straightforward and upfront about its needs. Now, Cabal is
> obviously checking that the build-depends is satisfied first, but why
> isn't it checking that alex is available when it has the information
> it needs to check, presumably anything in build-tools is *required*,
> and the field name suggests that it would be checked?

Yes, you're right. This is the ticket you filed last time:

http://hackage.haskell.org/trac/hackage/ticket/227

and my comment:

        One problem is that not all build-tools correspond to haskell
        packages. Some do some don't. We have a hard coded list of them
        at the moment (which can be extended in Setup.hs files) so we
        could extend that with what haskell package if any the tools
        correspond to. Any better suggestions to make it a tad more
        generic?

If anyone has a godd suggestion I'm happy to hear it. Otherwise we can
just add a Maybe Dependency to the Program type to indicate that some
build tools have a corresponding haskell package.

Duncan

From claus.reinke at talk21.com  Sat Jun 14 06:03:38 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Sat Jun 14 05:55:56 2008
Subject: [Haskell-cafe] cabal-install failure
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com><1213392126.15010.547.camel@localhost>
	<20080614021052.GA8862@craft>
	<1213430194.15010.556.camel@localhost>
Message-ID: <008501c8ce05$ec0ef260$f82b8351@cr3lt>

> http://hackage.haskell.org/trac/hackage/ticket/227
> 
>        One problem is that not all build-tools correspond to haskell
>        packages. Some do some don't. We have a hard coded list of them
>        at the moment (which can be extended in Setup.hs files) so we
>        could extend that with what haskell package if any the tools
>        correspond to. Any better suggestions to make it a tad more
>        generic?

That list seems to be in Distribution/Simple/Program.hs, in case 
anyone else is looking for it. Encoded information includes: 
dependency name, program name (if different from dependency),
option to get version info and code to extract it (with one apparently
very special case being hsc2hs).

Btw, most of the version extraction code looks like a regular 
expression match - wouldn't that make the specification easier
(and turn the comments into part of the spec)?

> If anyone has a godd suggestion I'm happy to hear it. Otherwise we can
> just add a Maybe Dependency to the Program type to indicate that some
> build tools have a corresponding haskell package.

I'm not sure what you're suggesting there (currently even those
tools that can be built with Cabal do not register with Cabal), but 
here are my suggestions:

1. Haskell tools should register with Cabal, whether built with it
    (such as Alex, Happy, ..) or not (such as GHC, ..). That 
    registration should include any build-relevant information
    (versions/variants, ..).

2. When checking a build-tools dependency, Cabal checks
    (a) whether the tool is registered with Cabal
    (b) whether the tool is registered with the system installation manager
    (c) whether the tool can be found by other means (configure,
            built-in rules, ..)

In other words, make tools look like packages (lifetime dependency
management, not just build support), and make system packages look 
like Cabal packages (Cabal as the interface to native managers), using 
special treatment only if absolutely necessary. I thought those suggestions
were clear from my earlier messages?-)

Claus

http://www.haskell.org/pipermail/haskell-cafe/2008-May/043368.html
http://www.haskell.org/pipermail/haskell-cafe/2008-June/043977.html
http://www.haskell.org/pipermail/haskell-cafe/2008-June/043910.html


From jon.fairbairn at cl.cam.ac.uk  Sat Jun 14 06:30:38 2008
From: jon.fairbairn at cl.cam.ac.uk (Jon Fairbairn)
Date: Sat Jun 14 06:22:55 2008
Subject: [Haskell-cafe] Re: working with Random.randoms
References: <4852A281.8000508@enterity.com>
Message-ID: <wfskvgcnqp.fsf@calligramme.charmers>

Stephen Howard <stephen@enterity.com> writes:

> I am a newcomer doing my obligatory struggling with
> Haskell's type system, 

That's your mistake. Don't struggle with the type system,
the type system is your friend; when it tells you you are
doing something wrong, it's usually right.

> and I've got a nut I've not been able to crack.  Given:
>
> import Random
>
> random_test :: Int -> String
> random_test n = do
>    g <- getStdGen
>    take n (randoms g)::String

My immediate reaction on seeing this is that "do" is for
manipulating monads, but the only monad you've indicated in
the type is [] (from String = [Char]), and that's probably
an accident.

In GHCi:

Prelude> :t Random.getStdGen
Random.getStdGen :: IO System.Random.StdGen

What this says is that getStdGen isn't a function, which is
to say it doesn't always return the same value (ie it isn't
pure -- it wouldn't be much use if it were!). In effect it
uses the real world to get a new value, and such things are
kept safely in the IO monad. In C, everything is in the IO
monad; there's no way of telling from the type whether
something is pure or not?. In Haskell (apart from some
ugliness that's supposed to stay hidden) you have to
distinguish between pure and impure, and the type checker
keeps track of all this for you.

> And yet, when I run these lines in GHCI by hand,

The top level of GHCi is IO (which shouldn't come as a
surprise!)

> things seem to work (though the string is the same set of
> random characters each time, another bit that I need to
> solve

That's a somewhat obscure aspect of GHCi, I think, to do
with "not reverting top-level expressions".  If you do this:

Prelude> :set +r
Prelude> g <- Random.getStdGen -- what's the type?
1954047482 7573
Prelude> g <- Random.getStdGen -- what's the type?
1626678354 7697
Prelude> 

you see that you get a different StdGen each time.

> I'm guessing that randoms is returning an IO type but I'm
> not sure how to go about extracting the String to return to
> the calling action.  Changing the type signature to Int ->
> IO  String only gives me a different error.

If you do any IO, you've done some IO! So you need to lift
out the StdGen and pass that to the functions that you want
to use it.

main :: IO()
   do gen <- getStdGen
      the_list <- real_programme gen
      print the_list

You should be able to deduce from the fact that the first
argument of real_programme here is of type StdGen (not IO
anything) and its result type is [something] that
real_programme is pure, and gen has only one value
throughout. So if you want more than one random list out of
it, you either need to use Random.split or pass more than
one gen in.


[1] Were you truly perverse, you could define your own
libraries in Haskell so that YourInt = IO Int; YourDouble =
IO Double etc, and make appropriate classes in place of Num
&c (hiding the proper ones), so that

+ :: YourInt -> YourInt -> YourInt

and so on (you'd have to define your own Bool and if, too,
but Haskell can do that). Then the type checker would
overlook all sorts of mistakes that it could otherwise have
caught.


-- 
J?n Fairbairn                                 Jon.Fairbairn@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html  (updated 2008-04-26)

From c-bauer-olsbruecken at t-online.de  Sat Jun 14 06:45:58 2008
From: c-bauer-olsbruecken at t-online.de (Christoph Bauer)
Date: Sat Jun 14 06:38:16 2008
Subject: [Haskell-cafe] ANN: Topkata
Message-ID: <87zlpoguqh.fsf@elefant.olsbruecken.local>

Hi All,

Topkata is a simple OpenGL Game written in Haskell. It's not very
advanced. Goal so far is to guide a ball trough an labyrinth to the
opposite corner.  The web page shows an screenshot. It's only tested
under Linux.

http://home.arcor.de/chr_bauer/topkata.html

Feedback&Patches are welcome. BTW, I had a lot of support in #haskell!

Christoph Bauer
From ndmitchell at gmail.com  Sat Jun 14 06:50:07 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Sat Jun 14 06:42:11 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <87zlpoguqh.fsf@elefant.olsbruecken.local>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
Message-ID: <404396ef0806140350w2eb18cf4n68b7d2f08ece7025@mail.gmail.com>

Hi Christoph,

>  opposite corner.  The web page shows an screenshot. It's only tested
>  under Linux.

Looks cool! Could you upload it to hackage?

http://hackage.haskell.org/

Once its on hackage, using cabal install, it should be possible to get
your game going with as little as:

cabal install topkata && topkata

That would be awsome for trying it out!

Thanks

Neil
From gwern0 at gmail.com  Sat Jun 14 08:30:12 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Sat Jun 14 08:22:57 2008
Subject: [Haskell-cafe] ANN: Mueval 0.21
Message-ID: <20080614123012.GA29554@craft>

Hiya everyone. I'd like to announce the release of a little CLI program I whipped up. It's called mueval <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval>.

WHAT:
Mueval grew out of my discontent with Lambdabot: it's really neat to be able to run expressions like this:

07:53 < ivanm> > filter (\ x -> isLetter x || x == '\t') "asdf$#$     dfs"
07:55 < lambdabot>  "asdfdfs"

But lambdabot is crufty and very difficult to install or run. IMO, we need a replacement or rewrite, but one of the things that make this difficult is that lambdabot uses hs-plugins to get that sort of evaluation functionality, and hs-plugins is half the problem. We want some sort of standalone executable which provides that functionality. Now, 'ghc -e' is obviously unsuited because there is no sandboxing, so what I've done is basically marry the GHC API (as rendered less sharp-edged by Hint) with a bunch of resource limits and sandboxing (as largely stolen from lambdabot).

EXAMPLES:
The end result is an adorable little program, which you can use like this:

 bash-3.2$ mueval --expression '1*100+1'
 Expression type: (Num t) => t
 result: "101"

 bash-3.2$ mueval --expression "filter (\`notElem\` ['A'..'Z']) \"abcXsdzWEE\""
 Expression type: [Char]
 result: "\"abcsdz\""

Note that mueval will avoid all the attacks I've been able to test on it:

 bash-3.2$ mueval --expression 'let x = x in x'
 Expression type: t
 result: "mueval: Time limit exceeded

 bash-3.2$ mueval --expression "let foo = readFile \"/etc/passwd\" >>= print in foo"
 Expression type: IO ()
 result: "<IO ()>"

 bash-3.2$ mueval --module System.IO.Unsafe --expression "let foo = unsafePerformIO readFile \"/etc/passwd\" in foo"
 mueval: Unknown or untrusted module supplied! Aborting.


SUMMARY:
Anyway, it's my hope that this will be useful as an example or useful in itself for people endeavouring to fix the lambdabot situation or just in safely running code period.

GETTING:
You can download mueval at the usual place: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval>. (There will probably be a darcs repository at some point.)

-----
TODO:
Mueval isn't feature-complete yet. The last thing I want to add is an ability to change the current user to 'mubot', which presumably the user will have set up to have access to next to nothing much like is already often done with daemons, but I haven't been able to figure out how to do this - the only suitable function I've found is 'setUID', and that requires one to be root...

--
gwern
SHA Fetish Ceridian Eurosat munitions MCI spies 26 M.P.R.I. ISN
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From mycatownz at foxbox.lurkingfox.co.uk  Sat Jun 14 09:10:05 2008
From: mycatownz at foxbox.lurkingfox.co.uk (Richard)
Date: Sat Jun 14 09:02:09 2008
Subject: [Haskell-cafe] Hoogle totally broken?
Message-ID: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>

It'd seem that (at least the online version of) Hoogle is totally broken
and useless. See, for example, the output when looking for:
	Monad m => m a -> (a -> m b) -> m b (i.e. (>>=)'s type)
over at:
http://haskell.org/hoogle/?q=Monad+m+%3D>+m+a+->+(a+->+m+b)+->+m+b

Data.Generics.Sche...	everywhere	:: (a -> a) -> a -> a
Data.Generics.Sche...	everywhere'	:: (a -> a) -> a -> a
Prelude.	($)	:: (a -> b) -> a -> b
Prelude.	($!)	:: (a -> b) -> a -> b
Data.Function.	($)	:: (a -> b) -> a -> b
Prelude.	maybe	:: b -> (a -> b) -> Maybe a -> b
Data.Maybe.	maybe	:: b -> (a -> b) -> Maybe a -> b

... and so on. (>>=) isn't there at all!?
From byorgey at gmail.com  Sat Jun 14 09:14:55 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Sat Jun 14 09:06:59 2008
Subject: [Haskell-cafe] Hoogle totally broken?
In-Reply-To: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>
References: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>
Message-ID: <22fcbd520806140614p53dc3054ib329b53fa58ad1b@mail.gmail.com>

On Sat, Jun 14, 2008 at 9:10 AM, Richard <mycatownz@foxbox.lurkingfox.co.uk>
wrote:

> It'd seem that (at least the online version of) Hoogle is totally broken
> and useless. See, for example, the output when looking for:
>        Monad m => m a -> (a -> m b) -> m b (i.e. (>>=)'s type)
> over at:
> http://haskell.org/hoogle/?q=Monad+m+%3D>+m+a+->+(a+->+m+b)+->+m+b
>
> Data.Generics.Sche...   everywhere      :: (a -> a) -> a -> a
> Data.Generics.Sche...   everywhere'     :: (a -> a) -> a -> a
> Prelude.        ($)     :: (a -> b) -> a -> b
> Prelude.        ($!)    :: (a -> b) -> a -> b
> Data.Function.  ($)     :: (a -> b) -> a -> b
> Prelude.        maybe   :: b -> (a -> b) -> Maybe a -> b
> Data.Maybe.     maybe   :: b -> (a -> b) -> Maybe a -> b
>
> ... and so on. (>>=) isn't there at all!?
>

It's well-known that the current version of Hoogle doesn't deal well with
type constructors, like the 'm' in your type above.  However, you're (we're
all) in luck, since Neil Mitchell is working on a new version of Hoogle for
GSoC as we speak! =)

-Brent
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From lemming at henning-thielemann.de  Sat Jun 14 09:23:28 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 09:15:36 2008
Subject: [Haskell-cafe] working with Random.randoms
In-Reply-To: <4852A281.8000508@enterity.com>
References: <4852A281.8000508@enterity.com>
Message-ID: <Pine.LNX.4.64.0806141521220.15299@anubis.informatik.uni-halle.de>


On Fri, 13 Jun 2008, Stephen Howard wrote:

> Hi List,
>
> I am a newcomer doing my obligatory struggling with Haskell's type system, 
> and I've got a nut I've not been able to crack.  Given:
>
> import Random
>
> random_test :: Int -> String
> random_test n = do
>   g <- getStdGen
>   take n (randoms g)::String
>
> I'm expecting that I ought to be able to pass this action an integer and get 
> back a random string that long (given, not all characters may be printable).

If you only need an arbitrary sequence and it is ok for you to get always 
the same one, you can construct a random generator using mkStdGen.
From tom.davie at gmail.com  Sat Jun 14 09:23:03 2008
From: tom.davie at gmail.com (Thomas Davie)
Date: Sat Jun 14 09:15:46 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <87zlpoguqh.fsf@elefant.olsbruecken.local>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
Message-ID: <4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>

On 14 Jun 2008, at 12:45, Christoph Bauer wrote:

> Hi All,
>
> Topkata is a simple OpenGL Game written in Haskell. It's not very
> advanced. Goal so far is to guide a ball trough an labyrinth to the
> opposite corner.  The web page shows an screenshot. It's only tested
> under Linux.
>
> http://home.arcor.de/chr_bauer/topkata.html
>
> Feedback&Patches are welcome. BTW, I had a lot of support in #haskell!

Looks awesome, and I completely agree with Niel -- hackage it up!

In the mean time -- who knows enough to make ghc target ARM, and get  
this to link against the iPhone libraries?  This would be quite a coup  
if it could be made to run there!

Bob
From daniel.is.fischer at web.de  Sat Jun 14 09:27:09 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Sat Jun 14 09:17:17 2008
Subject: [Haskell-cafe] Hoogle totally broken?
In-Reply-To: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>
References: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>
Message-ID: <200806141527.09196.daniel.is.fischer@web.de>

Am Samstag, 14. Juni 2008 15:10 schrieb Richard:
> It'd seem that (at least the online version of) Hoogle is totally broken
> and useless. See, for example, the output when looking for:
> 	Monad m => m a -> (a -> m b) -> m b (i.e. (>>=)'s type)
> over at:
> http://haskell.org/hoogle/?q=Monad+m+%3D>+m+a+->+(a+->+m+b)+->+m+b
>
> Data.Generics.Sche...	everywhere	:: (a -> a) -> a -> a
> Data.Generics.Sche...	everywhere'	:: (a -> a) -> a -> a
> Prelude.	($)	:: (a -> b) -> a -> b
> Prelude.	($!)	:: (a -> b) -> a -> b
> Data.Function.	($)	:: (a -> b) -> a -> b
> Prelude.	maybe	:: b -> (a -> b) -> Maybe a -> b
> Data.Maybe.	maybe	:: b -> (a -> b) -> Maybe a -> b
>
> ... and so on. (>>=) isn't there at all!?

It's near the bottom of page 4 of the results.
hoogle doesn't do an exact search, it reports all "close enough matches", 
which sometimes is less useful than other times. One great thing about 
hoogle's notion of 'close enough' is that it includes permutations of 
parameters, one less good thing is that it's not particularly faithful to 
type constructors. 
I think Neil's in the process of writing hoogle 4, which supposedly will be 
better with such things. However, in spite of hoogle's quirks and 
shortcomings, if you get used to them, it's a very useful tool already.

Cheers,
Daniel

From ndmitchell at gmail.com  Sat Jun 14 09:44:02 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Sat Jun 14 09:36:06 2008
Subject: [Haskell-cafe] Hoogle totally broken?
In-Reply-To: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>
References: <20080614131005.GA22204@foxbox.lurkingfox.co.uk>
Message-ID: <404396ef0806140644i373ced85pd86ce9b16796d650@mail.gmail.com>

Hi Richard,

> It'd seem that (at least the online version of) Hoogle is totally broken
>  and useless.

To finish your sentance: "when searching for types with higher-kinded
type classes". In practice, this usually means Monad and occasionally
Functor.

>  ... and so on. (>>=) isn't there at all!?

It is, but its on page 4. That's clearly a bug, and a well known one.

I am currently writing Hoogle 4, details can be found here:
http://neilmitchell.blogspot.com/2008/04/summer-of-code-2008.html

To quote from that page:

<quote>
# Removal of all bugs

Hoogle 3 has a number of embarrassing bugs, some of which are not
easily fixed. The nastiest of these is to do with monads, which are
horribly mistreated. Since I now know the underlying issues which have
caused a problem with Hoogle 3, things like higher-kinded type classes
can be solved in a more principled manner.
</quote>

So try again in 3 months, and the issue will be gone :-)

Thanks

Neil
From lemming at henning-thielemann.de  Sat Jun 14 09:48:26 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 09:40:30 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>


On Mon, 9 Jun 2008, Sebastian Sylvan wrote:

> Another BIG reason: It's impossible to export a whole hierarchy qualified.
> I.e it would be neat if the user could write:
>
> import Graphics.UI.Gtk
>
> And then have Gtk re-export sub-modules qualified, so you could write
> "Button.new", "Window.new" etc. etc. As it stands you have two options:
> prefix all the "new" functions with the kind of widget they create
> (buttonNew, windowNew), or force the user to add a gazillion qualified
> imports.

The problem would be again that no one knows, where "Window" comes from. 
Better would be

import Graphics.UI.Gtk (Window, Button, )

Don't know if this extension would be worth the trouble.

From lemming at henning-thielemann.de  Sat Jun 14 09:48:36 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 09:40:42 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <1213036865.15010.448.camel@localhost>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<200806061412.23585.g9ks157k@acme.softbase.org>
	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>
	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>
	<87ve0ibt6n.fsf@malde.org> <1213036865.15010.448.camel@localhost>
Message-ID: <Pine.LNX.4.64.0806141542200.15299@anubis.informatik.uni-halle.de>


On Mon, 9 Jun 2008, Duncan Coutts wrote:

> On Mon, 2008-06-09 at 16:04 +0200, Ketil Malde wrote:
>
>> And - is there a way to make GHCi use aliased qualification?  I find
>> my self typing detailed taxonomies all the time there.
>
> The ghci syntax currently is:
> :m Data.Set
> wouldn't it be much nicer as:
> import Data.Set
> then we could have the obvious:
> import Data.Set as Set

This would be nice! Feature request?

From golubovsky at gmail.com  Sat Jun 14 10:26:47 2008
From: golubovsky at gmail.com (Dimitry Golubovsky)
Date: Sat Jun 14 10:18:50 2008
Subject: [Haskell-cafe] External query interface to HackageDB?
Message-ID: <bcba51a0806140726i358d4746vd69034bb9d026102@mail.gmail.com>

Hi,

Is there any way to query the latest version of a particular package
stored on Hackage, that was successfully built?

I mean, not _how_ to do that (I have some ideas that I have to
download directory listings, looking for failure logs, etc.), but is
there any tool or interface already available that does similar
things?

Unfortunately, tarfiles provided on Hackage (like 00-index.tar.gz) do
not help, e. g. BerkeleyDB failed to build in all three versions, yet
its all cabal files are included in the tarball:

tar tvf 00-index.tar.gz
...
-rw-r--r-- www-data/www-data  1055 2007-04-06 13:03
./BerkeleyDB/0.1/BerkeleyDB.cabal
-rw-r--r-- www-data/www-data  1061 2007-04-06 16:59
./BerkeleyDB/0.2/BerkeleyDB.cabal
-rw-rw-r-- www-data/www-data  1236 2008-01-11 14:42
./BerkeleyDB/0.3/BerkeleyDB.cabal

I remember, in the past, HackageDB was expected to become a database
of some sort: is there any database-like backend that would accept
queries, other than just parsing Apache dir listings?

My final goal, given some master-list of package names, to be able to
retrieve latest succesfully built (not just uploaded) releases from
Hackage

Thanks.

-- 
Dimitry Golubovsky

Anywhere on the Web
From sebastian.sylvan at gmail.com  Sat Jun 14 10:28:21 2008
From: sebastian.sylvan at gmail.com (Sebastian Sylvan)
Date: Sat Jun 14 10:20:26 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
Message-ID: <3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>

On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>
>
> On Mon, 9 Jun 2008, Sebastian Sylvan wrote:
>
>  Another BIG reason: It's impossible to export a whole hierarchy qualified.
>> I.e it would be neat if the user could write:
>>
>> import Graphics.UI.Gtk
>>
>> And then have Gtk re-export sub-modules qualified, so you could write
>> "Button.new", "Window.new" etc. etc. As it stands you have two options:
>> prefix all the "new" functions with the kind of widget they create
>> (buttonNew, windowNew), or force the user to add a gazillion qualified
>> imports.
>>
>
> The problem would be again that no one knows, where "Window" comes from.
> Better would be
>
I really don't see how this is a big problem. Lots of languages do
hierarchical import (e.g. .Net languages) and I don't think I've ever heard
anyone complain about this particular aspect of it. The worst case scenario
is that you need a little bit of tool support to help you sort it out. Plus,
it's not like you can't just qualify the import to make it easier to see
where it comes from if you really think it's a problem:

import qualified Graphics.UI.GTK as GTK

and then use GTK.Button.new etc.


-- 
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862
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From lemming at henning-thielemann.de  Sat Jun 14 10:38:33 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 10:30:39 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>


On Sat, 14 Jun 2008, Sebastian Sylvan wrote:

> On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>
>> The problem would be again that no one knows, where "Window" comes from.
>> Better would be
>>
> I really don't see how this is a big problem. Lots of languages do
> hierarchical import (e.g. .Net languages) and I don't think I've ever heard
> anyone complain about this particular aspect of it.

It's not a problem for you and thus you do not pay attention to these 
complaints, I suspect. Maybe the people who would complain about the 
importing style, simply don't use the mentioned languages.

> The worst case scenario is that you need a little bit of tool support to 
> help you sort it out. Plus, it's not like you can't just qualify the 
> import to make it easier to see where it comes from if you really think 
> it's a problem:

Cf.
   http://www.haskell.org/haskellwiki/Import_modules_properly

  Haskell can re-export modules, which makes tracing identifiers more 
difficult. I want to be able to read modules without using a tool.
From c-bauer-olsbruecken at t-online.de  Sat Jun 14 10:53:50 2008
From: c-bauer-olsbruecken at t-online.de (Christoph Bauer)
Date: Sat Jun 14 10:45:57 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <404396ef0806140350w2eb18cf4n68b7d2f08ece7025@mail.gmail.com>
	(Neil Mitchell's message of "Sat, 14 Jun 2008 11:50:07 +0100")
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<404396ef0806140350w2eb18cf4n68b7d2f08ece7025@mail.gmail.com>
Message-ID: <87ve0cvzi9.fsf@elefant.olsbruecken.local>

Hello Neil,

> Looks cool! Could you upload it to hackage?

Thank you. Ok, I uploaded the current version. At the moment you have
to run topkata in the topkata-0.0 directory with
./dist/build/topkata/topkata, because it has to find its texture/sound
files. Furthermore I encounter problems (i.e. segmentation faults) on Gentoo
with the openal package. But openal-soft-1.4.272 works fine.

Christoph Bauer
From byorgey at gmail.com  Sat Jun 14 11:06:38 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Sat Jun 14 10:58:42 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <22fcbd520806140806w33fb2060y9f00b3e6ff0d3daa@mail.gmail.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<404396ef0806140350w2eb18cf4n68b7d2f08ece7025@mail.gmail.com>
	<87ve0cvzi9.fsf@elefant.olsbruecken.local>
	<22fcbd520806140806w33fb2060y9f00b3e6ff0d3daa@mail.gmail.com>
Message-ID: <22fcbd520806140806y311f4f9ax8aaa42763bb7dc8f@mail.gmail.com>

On Sat, Jun 14, 2008 at 10:53 AM, Christoph Bauer <
c-bauer-olsbruecken@t-online.de> wrote:

> Hello Neil,
>
> > Looks cool! Could you upload it to hackage?
>
> Thank you. Ok, I uploaded the current version. At the moment you have
> to run topkata in the topkata-0.0 directory with
> ./dist/build/topkata/topkata, because it has to find its texture/sound
> files.


There's a way to put something in the .cabal file about extra data files,
and have it install them in a certain location that you can then find
programmatically.  I forget the details, but I think it's pretty easy to set
up.  Maybe take a look through the Cabal documentation.  Or maybe Duncan
will jump in and explain. =)

-Brent
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From ndmitchell at gmail.com  Sat Jun 14 11:09:13 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Sat Jun 14 11:01:17 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <22fcbd520806140806y311f4f9ax8aaa42763bb7dc8f@mail.gmail.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<404396ef0806140350w2eb18cf4n68b7d2f08ece7025@mail.gmail.com>
	<87ve0cvzi9.fsf@elefant.olsbruecken.local>
	<22fcbd520806140806w33fb2060y9f00b3e6ff0d3daa@mail.gmail.com>
	<22fcbd520806140806y311f4f9ax8aaa42763bb7dc8f@mail.gmail.com>
Message-ID: <404396ef0806140809x52f28124t4eea5dc78a02ac@mail.gmail.com>

Hi

> > > Looks cool! Could you upload it to hackage?
> >
> > Thank you. Ok, I uploaded the current version. At the moment you have
> > to run topkata in the topkata-0.0 directory with
> > ./dist/build/topkata/topkata, because it has to find its texture/sound
> > files.
>
> There's a way to put something in the .cabal file about extra data files,
> and have it install them in a certain location that you can then find
> programmatically.  I forget the details, but I think it's pretty easy to set

http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html

Thanks

Neil
From odtaa48 at verizon.net  Sat Jun 14 12:14:55 2008
From: odtaa48 at verizon.net (odtaa48)
Date: Sat Jun 14 12:07:24 2008
Subject: [Haskell-cafe] const is question
Message-ID: <000a01c8ce39$c8e1ad30$0201a8c0@Linus>

hello
could someone explain the following differing results 
const id 0   5 -> 5 -- ie. 'takes' the 'last' one
const (id 0) 5 -> 0 -- ie. 'takes' the 'first' one

Thanks


From sfvisser at cs.uu.nl  Sat Jun 14 12:18:48 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Sat Jun 14 12:10:55 2008
Subject: [Haskell-cafe] Lazy IO.
Message-ID: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>

Hi,

I've got a question about lazy IO in Haskell. The most well known
function to do lazy IO is the `hGetContents', which lazily reads all the
contents from a handle and returns this as a regular [Char].

The thing with hGetContents is that is puts the Handle in a semi-closed
state, no one can use the handle anymore. This behaviour is
understandable from the point of safety; it is not yet determined when
the result of hGetContents will actually be computed, using the handle
in the meantime is undesirable.

The point is, I think I really have a situation in which I want to use
the handle again `after' a call to hGetContents. I think I can best
explain this using a code example.

   readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
   readHttpMessage = do
     myStream <- <accept http connection from client>
     request <- hGetContents myStream
     header <- parseHttpHeader request
     bs <- Data.ByteString.Lazy.hGetContents myStream
     return (header, body)

The Data.ByteString.Lazy.hGetContents in the example above obviously
fails because the handle is semi-closed.

So, what I am trying to do here is apply a parser (on that consumes
Char's) to the input stream until it has succeeded. After this I want to
collect the remainings of the stream in a lazy ByteString, or maybe even
something else.

I tried to open the handler again using some internal handle hackery,
but this failed (luckily). In the module GHC.IO there is a function
`lazyRead' that more or less seems to do what I want. But I'll guess
there is a good reason for not exporting it.

Does anyone know a pattern in which I can do this easily?

Thanks,

--
Sebastiaan

From jake.mcarthur at gmail.com  Sat Jun 14 12:22:28 2008
From: jake.mcarthur at gmail.com (Jake Mcarthur)
Date: Sat Jun 14 12:14:35 2008
Subject: [Haskell-cafe] const is question
In-Reply-To: <000a01c8ce39$c8e1ad30$0201a8c0@Linus>
References: <000a01c8ce39$c8e1ad30$0201a8c0@Linus>
Message-ID: <9156AEFC-D4ED-4BF8-BB52-C8531B3FA8CB@gmail.com>

On Jun 14, 2008, at 11:14 AM, odtaa48 wrote:

> const id 0   5 -> 5 -- ie. 'takes' the 'last' one

The type of const is a -> b -> a. The first argument to const here is  
id and the second is 0, so the evaluation of const id 0 is going to  
result in id. Then we apply id to 5, yielding 5. Perhaps it would be  
more clear to write the expression is (const id 0) 5.

> const (id 0) 5 -> 0 -- ie. 'takes' the 'first' one

Here the two arguments to const are (id 0) and 5. Since the effect of  
const is to toss out the second argument, this evaluates to id 0,  
which evaluates to simply 0.

Does that help?

- Jake McArthur
From sfvisser at cs.uu.nl  Sat Jun 14 12:23:52 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Sat Jun 14 12:15:59 2008
Subject: [Haskell-cafe] const is question
In-Reply-To: <000a01c8ce39$c8e1ad30$0201a8c0@Linus>
References: <000a01c8ce39$c8e1ad30$0201a8c0@Linus>
Message-ID: <A722EE92-CC67-4552-857F-D165993F5AEA@cs.uu.nl>

On Jun 14, 2008, at 6:14 PM, odtaa48 wrote:
> hello
> could someone explain the following differing results const id 0    
> 5 -> 5 -- ie. 'takes' the 'last' one
> const (id 0) 5 -> 0 -- ie. 'takes' the 'first' one
>
> Thanks

You can easily see what is happening by rewriting the equations step  
by step. Remember that the const function is (\x y -> x) and the id  
function is (\x -> x).

Example 1:

    const id 0 5
== (const id 0) 5
== id 5
== 5

Example 2:

    const (id 0) 5
== const 0 5
== 0

So, in both cases const takes the first.

--
Sebastiaan.
From felipe.lessa at gmail.com  Sat Jun 14 12:45:23 2008
From: felipe.lessa at gmail.com (Felipe Lessa)
Date: Sat Jun 14 12:37:32 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
Message-ID: <c2701f5c0806140945i38cf0ff6n952a5bff24cca898@mail.gmail.com>

(Sorry, Sebastiaan, I hit send accidentally)

On Sat, Jun 14, 2008 at 1:18 PM, Sebastiaan Visser <sfvisser@cs.uu.nl> wrote:
>  readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
>  readHttpMessage = do
>    myStream <- <accept http connection from client>
>    request <- hGetContents myStream
>    header <- parseHttpHeader request
>    bs <- Data.ByteString.Lazy.hGetContents myStream
>    return (header, body)

Why not

readHttpMessage = do
  myStream <- <accept http connection from client>
  data <- Data.ByteString.Lazy.hGetContents myStream
  (header, rest) <- parseHttpHeader data
  return (header, rest)

i.e. make parseHttpHeader return the rest of the string it didn't parse?

In fact, may I ask why parseHttpHeader is not a pure function?

HTH,

-- Felipe.
From isaacdupree at charter.net  Sat Jun 14 12:49:38 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Sat Jun 14 12:41:40 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
Message-ID: <4853F6A2.50103@charter.net>

Sebastiaan Visser wrote:
> Hi,
> 
> I've got a question about lazy IO in Haskell. The most well known
> function to do lazy IO is the `hGetContents', which lazily reads all the
> contents from a handle and returns this as a regular [Char].
> 
> The thing with hGetContents is that is puts the Handle in a semi-closed
> state, no one can use the handle anymore. This behaviour is
> understandable from the point of safety; it is not yet determined when
> the result of hGetContents will actually be computed, using the handle
> in the meantime is undesirable.
> 
> The point is, I think I really have a situation in which I want to use
> the handle again `after' a call to hGetContents. I think I can best
> explain this using a code example.
> 
>   readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
>   readHttpMessage = do
>     myStream <- <accept http connection from client>
>     request <- hGetContents myStream
>     header <- parseHttpHeader request
>     bs <- Data.ByteString.Lazy.hGetContents myStream
>     return (header, body)

that's impure because parseHttpHeader doesn't return anything telling 
you how much of the stream it's looked at.  Maybe it looked ahead more 
than it needed to, thus deleting part of the body.  I was going to 
suggest, if you can't change parseHttpHeader to use ByteStrings,

 >     bs <- Data.ByteString.Lazy.hGetContents myStream
 >     header <- parseHttpHeader (Data.ByteString.Lazy.unpack bs)

but you still have to get parseHttpHeader (or perhaps if it has similar 
friends) to tell you how much of the string it consumed!  I don't know 
what parsing functions you have available to work with, so I can't tell 
you whether it's possible.

-Isaac
From sfvisser at cs.uu.nl  Sat Jun 14 12:50:50 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Sat Jun 14 12:42:58 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <c2701f5c0806140945i38cf0ff6n952a5bff24cca898@mail.gmail.com>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<c2701f5c0806140945i38cf0ff6n952a5bff24cca898@mail.gmail.com>
Message-ID: <679EFD47-4040-4A36-AA7A-78C3CEE41E3D@cs.uu.nl>

On Jun 14, 2008, at 6:45 PM, Felipe Lessa wrote:
> (Sorry, Sebastiaan, I hit send accidentally)
>
> On Sat, Jun 14, 2008 at 1:18 PM, Sebastiaan Visser  
> <sfvisser@cs.uu.nl> wrote:
>>  readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
>>  readHttpMessage = do
>>    myStream <- <accept http connection from client>
>>    request <- hGetContents myStream
>>    header <- parseHttpHeader request
>>    bs <- Data.ByteString.Lazy.hGetContents myStream
>>    return (header, body)
>
> Why not
>
> readHttpMessage = do
>   myStream <- <accept http connection from client>
>   data <- Data.ByteString.Lazy.hGetContents myStream
>   (header, rest) <- parseHttpHeader data
>   return (header, rest)
>
> i.e. make parseHttpHeader return the rest of the string it didn't  
> parse?

Doesn't this imply that the parseHttpHeader must work on ByteStrings  
instead of regular Strings? Maybe this works for HTTP headers, but  
sometimes ByteStrings are not appropriate. Especially when you are  
not using the regular `System.IO.hGetContents' but the  
`System.IO.UTF8.hGetContents'.

> In fact, may I ask why parseHttpHeader is not a pure function?

This is not a real-life example. It might as well be a pure function.

> HTH,
>
> -- Felipe.

--
Sebastiaan
From sfvisser at cs.uu.nl  Sat Jun 14 12:59:38 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Sat Jun 14 12:51:46 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <4853F6A2.50103@charter.net>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<4853F6A2.50103@charter.net>
Message-ID: <EB754B5E-D5EA-4FD4-B3D3-B0AC51DC9C95@cs.uu.nl>

On Jun 14, 2008, at 6:49 PM, Isaac Dupree wrote:

> Sebastiaan Visser wrote:
>> Hi,
>> I've got a question about lazy IO in Haskell. The most well known
>> function to do lazy IO is the `hGetContents', which lazily reads  
>> all the
>> contents from a handle and returns this as a regular [Char].
>> The thing with hGetContents is that is puts the Handle in a semi- 
>> closed
>> state, no one can use the handle anymore. This behaviour is
>> understandable from the point of safety; it is not yet determined  
>> when
>> the result of hGetContents will actually be computed, using the  
>> handle
>> in the meantime is undesirable.
>> The point is, I think I really have a situation in which I want to  
>> use
>> the handle again `after' a call to hGetContents. I think I can best
>> explain this using a code example.
>>   readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
>>   readHttpMessage = do
>>     myStream <- <accept http connection from client>
>>     request <- hGetContents myStream
>>     header <- parseHttpHeader request
>>     bs <- Data.ByteString.Lazy.hGetContents myStream
>>     return (header, body)
>
> that's impure because parseHttpHeader doesn't return anything  
> telling you how much of the stream it's looked at.  Maybe it looked  
> ahead more than it needed to, thus deleting part of the body.  I  
> was going to suggest, if you can't change parseHttpHeader to use  
> ByteStrings,
>
> >     bs <- Data.ByteString.Lazy.hGetContents myStream
> >     header <- parseHttpHeader (Data.ByteString.Lazy.unpack bs)
>
> but you still have to get parseHttpHeader (or perhaps if it has  
> similar friends) to tell you how much of the string it consumed!  I  
> don't know what parsing functions you have available to work with,  
> so I can't tell you whether it's possible.

It is a regular Parsec parser and I am pretty sure it does not  
consume anything other than the header itself. Maybe I could rewrite  
my parser to work on Word8's instead of Char's, I don't think HTTP  
even allows Unicode characters within HTTP headers.

Thanks. I think I'll try this.

But I'm still curious about how to lazily parse messages with  
arbitrary size Unicode headers and plain (possibly) binary bodies.

> -Isaac

--
Sebastiaan.
From felipe.lessa at gmail.com  Sat Jun 14 13:16:56 2008
From: felipe.lessa at gmail.com (Felipe Lessa)
Date: Sat Jun 14 13:09:00 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <679EFD47-4040-4A36-AA7A-78C3CEE41E3D@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<c2701f5c0806140945i38cf0ff6n952a5bff24cca898@mail.gmail.com>
	<679EFD47-4040-4A36-AA7A-78C3CEE41E3D@cs.uu.nl>
Message-ID: <c2701f5c0806141016p610b12e8y8b8411926d26b868@mail.gmail.com>

On Sat, Jun 14, 2008 at 1:50 PM, Sebastiaan Visser <sfvisser@cs.uu.nl> wrote:
> Doesn't this imply that the parseHttpHeader must work on ByteStrings instead
> of regular Strings?

I made the change because it's easier and faster to go from ByteString
to String than the converse.

> Maybe this works for HTTP headers, but sometimes
> ByteStrings are not appropriate. Especially when you are not using the
> regular `System.IO.hGetContents' but the `System.IO.UTF8.hGetContents'.

You may use the package encoding instead, take a look at [1]. It will
decode a lazy ByteString into a String. In your HTTP parsing example,
you could break the ByteString on "\r\n\r\n" and then decodeLazy only
the first part, while returning the second without modifying it.

[1] http://hackage.haskell.org/packages/archive/encoding/0.4.1/doc/html/Data-Encoding.html#v%3AdecodeLazy

-- Felipe.
From allbery at ece.cmu.edu  Sat Jun 14 13:19:39 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Sat Jun 14 13:11:44 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <EB754B5E-D5EA-4FD4-B3D3-B0AC51DC9C95@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<4853F6A2.50103@charter.net>
	<EB754B5E-D5EA-4FD4-B3D3-B0AC51DC9C95@cs.uu.nl>
Message-ID: <02813790-FD5F-4422-8EF7-CBB5C3121136@ece.cmu.edu>


On 2008 Jun 14, at 12:59, Sebastiaan Visser wrote:

> But I'm still curious about how to lazily parse messages with  
> arbitrary size Unicode headers and plain (possibly) binary bodies.


Sounds like Data.Binary (see hackage) to me.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From sfvisser at cs.uu.nl  Sat Jun 14 13:27:58 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Sat Jun 14 13:20:07 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <c2701f5c0806141016p610b12e8y8b8411926d26b868@mail.gmail.com>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<c2701f5c0806140945i38cf0ff6n952a5bff24cca898@mail.gmail.com>
	<679EFD47-4040-4A36-AA7A-78C3CEE41E3D@cs.uu.nl>
	<c2701f5c0806141016p610b12e8y8b8411926d26b868@mail.gmail.com>
Message-ID: <9C183730-3244-49BA-BAE0-49D49716C976@cs.uu.nl>

On Jun 14, 2008, at 7:16 PM, Felipe Lessa wrote:

> On Sat, Jun 14, 2008 at 1:50 PM, Sebastiaan Visser  
> <sfvisser@cs.uu.nl> wrote:
>> Doesn't this imply that the parseHttpHeader must work on  
>> ByteStrings instead
>> of regular Strings?
>
> I made the change because it's easier and faster to go from ByteString
> to String than the converse.
>
>> Maybe this works for HTTP headers, but sometimes
>> ByteStrings are not appropriate. Especially when you are not using  
>> the
>> regular `System.IO.hGetContents' but the  
>> `System.IO.UTF8.hGetContents'.
>
> You may use the package encoding instead, take a look at [1]. It will
> decode a lazy ByteString into a String. In your HTTP parsing example,
> you could break the ByteString on "\r\n\r\n" and then decodeLazy only
> the first part, while returning the second without modifying it.

Sounds interesting. This could indeed solve (a part of) my problem.

The thing is, when decoding the header - in my web server  
architecture - it is not yet clear what should be done be the body.  
Some `handlers' may want to have it as a String, UTF8 String,  
ByteString or may not even need it at all.

> [1] http://hackage.haskell.org/packages/archive/encoding/0.4.1/doc/ 
> html/Data-Encoding.html#v%3AdecodeLazy


Because HTTP headers are line based and the parser does not need any  
look ahead - the first "\r\n\r\n" is the header delimiter - it might  
be possible to use the hGetLine for the headers. After this I am  
still `free' to decide what to do for the body:  
System.IO.hGetContents, System.IO.UTF8.hGetContents,  
Data.ByteString.Lazy.hGetContents, hClose, etc...

> -- Felipe.

Thanks,
Sebastiaan.
From sebastian.sylvan at gmail.com  Sat Jun 14 13:38:27 2008
From: sebastian.sylvan at gmail.com (Sebastian Sylvan)
Date: Sat Jun 14 13:30:33 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>
	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>
Message-ID: <3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>

On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>
>
> On Sat, 14 Jun 2008, Sebastian Sylvan wrote:
>
>  On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>
>>>
>>> The problem would be again that no one knows, where "Window" comes from.
>>> Better would be
>>>
>>>  I really don't see how this is a big problem. Lots of languages do
>> hierarchical import (e.g. .Net languages) and I don't think I've ever
>> heard
>> anyone complain about this particular aspect of it.
>>
>
> It's not a problem for you and thus you do not pay attention to these
> complaints, I suspect. Maybe the people who would complain about the
> importing style, simply don't use the mentioned languages.
>
>> The worst case scenario is that you need a little bit of tool support to
>> help you sort it out. Plus, it's not like you can't just qualify the import
>> to make it easier to see where it comes from if you really think it's a
>> problem:
>>
>
> Cf.
>  http://www.haskell.org/haskellwiki/Import_modules_properly
>
>  Haskell can re-export modules, which makes tracing identifiers more
> difficult. I want to be able to read modules without using a tool.
>

I'm not sure I understand you point. You're so opposed to the *option* of
allowing hierarchical exports (even though you can still import it qualified
if you personally like having to specify at each callsite exactly where some
identifier is coming from), that you'd rather any library making use of a
module hierarchy is forced to either make the user add dozens of boilerplate
import statements (with "qualified" and "as") or the more common strategy of
prefixing each function call with the module name (buttonNew)? To me a
module system that requires the latter in practice is horribly broken, and
I'm suggesting a low-impact way of fixing it. It may not be the best system
available, but it's a tiny extension of the current.

I really don't see why adding this option hurts you, when it clearly helps
enable doing what this thread advocates (use qualified modules to
distinguish between functions of the same name, rather than adding a bunch
of prefixes/suffixes to the functions).

-- 
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862
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From lemming at henning-thielemann.de  Sat Jun 14 13:53:48 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 13:45:53 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>
	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>


On Sat, 14 Jun 2008, Sebastian Sylvan wrote:

> On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>
>>
>> On Sat, 14 Jun 2008, Sebastian Sylvan wrote:
>>
>>  On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>>
>>>>
>>>> The problem would be again that no one knows, where "Window" comes from.
>>>> Better would be
>>>>
>>>>  I really don't see how this is a big problem. Lots of languages do
>>> hierarchical import (e.g. .Net languages) and I don't think I've ever
>>> heard
>>> anyone complain about this particular aspect of it.
>>>
>>
>> It's not a problem for you and thus you do not pay attention to these
>> complaints, I suspect. Maybe the people who would complain about the
>> importing style, simply don't use the mentioned languages.
>>
>>> The worst case scenario is that you need a little bit of tool support to
>>> help you sort it out. Plus, it's not like you can't just qualify the import
>>> to make it easier to see where it comes from if you really think it's a
>>> problem:
>>>
>>
>> Cf.
>>  http://www.haskell.org/haskellwiki/Import_modules_properly
>>
>>  Haskell can re-export modules, which makes tracing identifiers more
>> difficult. I want to be able to read modules without using a tool.
>>
>
> I'm not sure I understand you point. You're so opposed to the *option* of
> allowing hierarchical exports (even though you can still import it qualified
> if you personally like having to specify at each callsite exactly where some
> identifier is coming from),

I was concerned with the _import_ part of your proposal. (I haven't 
thought about the export part so far.)

> that you'd rather any library making use of a module hierarchy is forced 
> to either make the user add dozens of boilerplate import statements 
> (with "qualified" and "as") or the more common strategy of prefixing 
> each function call with the module name (buttonNew)? To me a module 
> system that requires the latter in practice is horribly broken, and I'm 
> suggesting a low-impact way of fixing it. It may not be the best system 
> available, but it's a tiny extension of the current.
>
> I really don't see why adding this option hurts you, when it clearly helps
> enable doing what this thread advocates (use qualified modules to
> distinguish between functions of the same name, rather than adding a bunch
> of prefixes/suffixes to the functions).

Button.new is my favorite, because with current import variants I can 
easily lookup, what Button and Button.new refer to. I understand your 
proposal in that way that

import Graphics.UI.Gtk

brings module qualifications Window and Button into scope although they 
are not explicitly mentioned. Thus I could no longer find out easily what 
Butten.new means.
From marco-oweber at gmx.de  Sat Jun 14 14:08:28 2008
From: marco-oweber at gmx.de (Marc Weber)
Date: Sat Jun 14 14:00:33 2008
Subject: [Haskell-cafe] ANN: Printf-TH
Message-ID: <20080614180828.GA27701@gmx.de>

Igloo (Ian Lynagh) allowed me kindly taking over maintainance on his
printf library using template haskell written in 2003. I've updated it
so that it compiles with ghc-6.8.2.
You can get it from hackage:
 http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Printf-TH

usage looks like this:

{-# OPTIONS_GHC -XTemplateHaskell #-}
...
import Language.Haskell.TH.Syntax
import Text.Printf.TH (printf)

...
            putStrLn $ $(printf "Foo %H bar") (Just 5)
            putStrLn $ $(printf "%6d") 1
            putStrLn $ $(printf "%6d") (-1)

Short Explanation:
$(printf "%d") will be replaced by a auto generated function taking an int etc

Benefit:
Wrong arg types or wrong printf arg count will result in compile time
errors.

Enjoy
Marc Weber
From sebastian.sylvan at gmail.com  Sat Jun 14 14:21:40 2008
From: sebastian.sylvan at gmail.com (Sebastian Sylvan)
Date: Sat Jun 14 14:13:44 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>
	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>
	<Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>
Message-ID: <3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>

On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>
>
> On Sat, 14 Jun 2008, Sebastian Sylvan wrote:
>
>  On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>
>>>
>>>
>>> On Sat, 14 Jun 2008, Sebastian Sylvan wrote:
>>>
>>>  On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>>
>>>>
>>>>
>>>>> The problem would be again that no one knows, where "Window" comes
>>>>> from.
>>>>> Better would be
>>>>>
>>>>>  I really don't see how this is a big problem. Lots of languages do
>>>>>
>>>> hierarchical import (e.g. .Net languages) and I don't think I've ever
>>>> heard
>>>> anyone complain about this particular aspect of it.
>>>>
>>>>
>>> It's not a problem for you and thus you do not pay attention to these
>>> complaints, I suspect. Maybe the people who would complain about the
>>> importing style, simply don't use the mentioned languages.
>>>
>>>  The worst case scenario is that you need a little bit of tool support to
>>>> help you sort it out. Plus, it's not like you can't just qualify the
>>>> import
>>>> to make it easier to see where it comes from if you really think it's a
>>>> problem:
>>>>
>>>>
>>> Cf.
>>>  http://www.haskell.org/haskellwiki/Import_modules_properly
>>>
>>>  Haskell can re-export modules, which makes tracing identifiers more
>>> difficult. I want to be able to read modules without using a tool.
>>>
>>>
>> I'm not sure I understand you point. You're so opposed to the *option* of
>> allowing hierarchical exports (even though you can still import it
>> qualified
>> if you personally like having to specify at each callsite exactly where
>> some
>> identifier is coming from),
>>
>
> I was concerned with the _import_ part of your proposal. (I haven't thought
> about the export part so far.)
>
>  that you'd rather any library making use of a module hierarchy is forced
>> to either make the user add dozens of boilerplate import statements (with
>> "qualified" and "as") or the more common strategy of prefixing each function
>> call with the module name (buttonNew)? To me a module system that requires
>> the latter in practice is horribly broken, and I'm suggesting a low-impact
>> way of fixing it. It may not be the best system available, but it's a tiny
>> extension of the current.
>>
>> I really don't see why adding this option hurts you, when it clearly helps
>> enable doing what this thread advocates (use qualified modules to
>> distinguish between functions of the same name, rather than adding a bunch
>> of prefixes/suffixes to the functions).
>>
>
> Button.new is my favorite, because with current import variants I can
> easily lookup, what Button and Button.new refer to. I understand your
> proposal in that way that
>
> import Graphics.UI.Gtk
>
> brings module qualifications Window and Button into scope although they are
> not explicitly mentioned. Thus I could no longer find out easily what
> Butten.new means.
>
I don't see why this is so bad when it's exactly what we have for other
identifiers? E.g. if you import Control.Monad you get mapM, but you can't
really say for sure where this identifier comes from, which is no better
than not knowing where "Button.new" comes from. In both cases you have the
option to qualify the module import so you have to say "Monad.mapM" or
"GTK.Button.new" which makes it more apparent.

I suppose you would make the "hiding" clause and the "import list" thing
work with modules too for consistency, so if you really wanted to you could
list the modules/identifiers that you bring in.

Are you saying that you prefer the situation where to use GTK the user would
have to explicitly import every single sub-module in the hierarchy ("import
qualified Graphics.UI.GTK.X as X" where X = {Button,Window, ... etc})? I
don't think that's very nice at all, and I certainly don't like having to
add the module name to the functions... I think lots of libraries are like
that, and we need some mechanism of importing lots of related modules
together so that they come in qualified, without forcing the user to write a
gazillion lines of boilerplate import statements..

I think that if GTK did use this system (rather than append the module name
to the function and export them "flatly") a lot of people would resort to
ugly hacks like putting the import statements in a file somewhere and using
the C preprocessor to include it, yuck! (OTOH this may be just what's
required to convince everyone that we need to improve the module system)...

-- 
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862
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From andrewcoppin at btinternet.com  Sat Jun 14 14:58:07 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Sat Jun 14 15:25:25 2008
Subject: [Haskell-cafe] Documenting the impossible
Message-ID: <485414BF.30307@btinternet.com>

I have a small idea. I'm curios if anybody else thinks it's a good idea...

How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a 
particular point in the program *should* be unreachable?

For example, you look up a key in a Map. You know the key is there, 
because you just put it there yourself two seconds ago. But, 
theoretically, lookup returns a Maybe x so - theoretically - it's 
possible it might return Nothing. No matter what you do, GHC will insert 
code to check whether we have Just x or Nothing, and in the Nothing case 
throw an exception.

Obviously there is no way in hell this code path can ever be executed. 
At least, assuming your code isn't broken... This is where the pragma 
comes in. The idea is that you write something like

  case lookup k m of
    Just v -> process v
    Nothing -> {-# IMPOSSIBLE "lookup in step 3" #-}

When compiled without optimisations, the pragma just causes an exception 
to be thrown, rather like "error" does. When compiled with 
optimisations, the whole case alternative is removed, and no code is 
generated for it. (And if the impossible somehow happens... behaviour is 
undefined.) So you test your program with your code compiled 
unoptimised, and when you're "sure" the impossible can't happen, you 
tell the compiler to remove the check for it. (Actually, it would 
possibly be a good idea to have a switch to turn this on and off 
seperately if needed...)

Does anybody think this is a useful idea? If so I'll add a feature 
request ticket to the GHC Trac. But I want to see if folks like the idea 
first...

(I was thinking the message in the pragma would be what gets displayed 
on screen, along with some auto-generated location info. Just a module 
name and line number ought to be sufficient...)

From derek.a.elkins at gmail.com  Sat Jun 14 15:47:00 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Sat Jun 14 15:39:10 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <1213472820.5557.1.camel@derek-laptop>

On Sat, 2008-06-14 at 19:58 +0100, Andrew Coppin wrote:
> I have a small idea. I'm curios if anybody else thinks it's a good idea...
> 
> How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a 
> particular point in the program *should* be unreachable?
> 
> For example, you look up a key in a Map. You know the key is there, 
> because you just put it there yourself two seconds ago. But, 
> theoretically, lookup returns a Maybe x so - theoretically - it's 
> possible it might return Nothing. No matter what you do, GHC will insert 
> code to check whether we have Just x or Nothing, and in the Nothing case 
> throw an exception.
> 
> Obviously there is no way in hell this code path can ever be executed. 
> At least, assuming your code isn't broken... This is where the pragma 
> comes in. The idea is that you write something like
> 
>   case lookup k m of
>     Just v -> process v
>     Nothing -> {-# IMPOSSIBLE "lookup in step 3" #-}
> 
> When compiled without optimisations, the pragma just causes an exception 
> to be thrown, rather like "error" does. When compiled with 
> optimisations, the whole case alternative is removed, and no code is 
> generated for it. (And if the impossible somehow happens... behaviour is 
> undefined.) So you test your program with your code compiled 
> unoptimised, and when you're "sure" the impossible can't happen, you 
> tell the compiler to remove the check for it. (Actually, it would 
> possibly be a good idea to have a switch to turn this on and off 
> seperately if needed...)
> 
> Does anybody think this is a useful idea? If so I'll add a feature 
> request ticket to the GHC Trac. But I want to see if folks like the idea 
> first...
> 
I think it's a horrible idea.

From lemming at henning-thielemann.de  Sat Jun 14 15:52:25 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 15:44:29 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <Pine.LNX.4.64.0806142144400.17143@anubis.informatik.uni-halle.de>


On Sat, 14 Jun 2008, Andrew Coppin wrote:

> How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a 
> particular point in the program *should* be unreachable?
> ...
> When compiled without optimisations, the pragma just causes an exception to 
> be thrown, rather like "error" does. When compiled with optimisations, the 
> whole case alternative is removed, and no code is generated for it. (And if 
> the impossible somehow happens... behaviour is undefined.) So you test your 
> program with your code compiled unoptimised, and when you're "sure" the 
> impossible can't happen, you tell the compiler to remove the check for it. 
> (Actually, it would possibly be a good idea to have a switch to turn this on 
> and off seperately if needed...)

I think it is another instance of mixing up errors and exceptions (you 
know the haskellwiki pages ...)

Since an 'error' marks a programming error (which should never occur) it 
would not hurt the program if all 'error's are replaced by 'undefined', an 
illegal memory access or any other misbehaviour. So 'error' is exactly 
what you propose as IMPOSSIBLE pragma. A compiler option for replacing all 
'error's by nops would do want you want.
From thomas.dubuisson at gmail.com  Sat Jun 14 15:53:13 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Sat Jun 14 15:46:40 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <1213473193.3124.20.camel@localhost.localdomain>

I think when Andy made HPC he added a way to mark code unreachable so it
wouldn't "harm" your test coverage report.


On Sat, 2008-06-14 at 19:58 +0100, Andrew Coppin wrote:
> I have a small idea. I'm curios if anybody else thinks it's a good idea...
> 
> How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a 
> particular point in the program *should* be unreachable?
> 
> For example, you look up a key in a Map. You know the key is there, 
> because you just put it there yourself two seconds ago. But, 
> theoretically, lookup returns a Maybe x so - theoretically - it's 
> possible it might return Nothing. No matter what you do, GHC will insert 
> code to check whether we have Just x or Nothing, and in the Nothing case 
> throw an exception.
> 
> Obviously there is no way in hell this code path can ever be executed. 
> At least, assuming your code isn't broken... This is where the pragma 
> comes in. The idea is that you write something like
> 
>   case lookup k m of
>     Just v -> process v
>     Nothing -> {-# IMPOSSIBLE "lookup in step 3" #-}
> 
> When compiled without optimisations, the pragma just causes an exception 
> to be thrown, rather like "error" does. When compiled with 
> optimisations, the whole case alternative is removed, and no code is 
> generated for it. (And if the impossible somehow happens... behaviour is 
> undefined.) So you test your program with your code compiled 
> unoptimised, and when you're "sure" the impossible can't happen, you 
> tell the compiler to remove the check for it. (Actually, it would 
> possibly be a good idea to have a switch to turn this on and off 
> seperately if needed...)
> 
> Does anybody think this is a useful idea? If so I'll add a feature 
> request ticket to the GHC Trac. But I want to see if folks like the idea 
> first...
> 
> (I was thinking the message in the pragma would be what gets displayed 
> on screen, along with some auto-generated location info. Just a module 
> name and line number ought to be sufficient...)
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
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From dons at galois.com  Sat Jun 14 15:56:11 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun 14 15:48:23 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <20080614195611.GA30515@scytale.galois.com>

andrewcoppin:
> I have a small idea. I'm curios if anybody else thinks it's a good idea...
> 
> How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a 
> particular point in the program *should* be unreachable?
> 
> For example, you look up a key in a Map. You know the key is there, 
> because you just put it there yourself two seconds ago. But, 
> theoretically, lookup returns a Maybe x so - theoretically - it's 
> possible it might return Nothing. No matter what you do, GHC will insert 
> code to check whether we have Just x or Nothing, and in the Nothing case 
> throw an exception.
> 
> Obviously there is no way in hell this code path can ever be executed. 
> At least, assuming your code isn't broken... This is where the pragma 
> comes in. The idea is that you write something like
> 
>  case lookup k m of
>    Just v -> process v
>    Nothing -> {-# IMPOSSIBLE "lookup in step 3" #-}

You could try using an 'assert' , which has the property of being
compiled out at higher optimisation levels. And you can use 'error' or
'undefined' for undefined behaviour.

    http://www.haskell.org/ghc/docs/latest/html/users_guide/assertions.html

Not very Haskelly though.

-- Don
From dons at galois.com  Sat Jun 14 16:06:05 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun 14 15:58:12 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
Message-ID: <20080614200605.GB30515@scytale.galois.com>

tom.davie:
> On 14 Jun 2008, at 12:45, Christoph Bauer wrote:
> 
> >Hi All,
> >
> >Topkata is a simple OpenGL Game written in Haskell. It's not very
> >advanced. Goal so far is to guide a ball trough an labyrinth to the
> >opposite corner.  The web page shows an screenshot. It's only tested
> >under Linux.
> >
> >http://home.arcor.de/chr_bauer/topkata.html
> >
> >Feedback&Patches are welcome. BTW, I had a lot of support in #haskell!
> 
> Looks awesome, and I completely agree with Niel -- hackage it up!
> 
> In the mean time -- who knows enough to make ghc target ARM, and get  
> this to link against the iPhone libraries?  This would be quite a coup  
> if it could be made to run there!

I'd be interested. We should start a wiki page for Haskell on the
iphone..

-- Don
From ndmitchell at gmail.com  Sat Jun 14 16:29:09 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Sat Jun 14 16:21:12 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <404396ef0806141329w36c54982r1e3c38820894f47d@mail.gmail.com>

Hi

>  How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a
> particular point in the program *should* be unreachable?

Why not make it a function taking a string and returning a value of
any type. Then we can keep our language and not break various
parsing/type checking properties and rules on pragmas. We can even
define it:

impossible = error

Now you can use tools like Catch and Reach to ensure it is impossible.

I think it would be nice to distinguish between:

* error - inserted by the compiler
* impossible - the programmer knows this can't occur
* abort - deliberate aborting because the user made some mistake.

The safe library provides abort already.

Thanks

Neil
From marco-oweber at gmx.de  Sat Jun 14 16:58:32 2008
From: marco-oweber at gmx.de (Marc Weber)
Date: Sat Jun 14 16:50:40 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <20080614205832.GB25415@gmx.de>

>  Does anybody think this is a useful idea? If so I'll add a feature request 
>  ticket to the GHC Trac. But I want to see if folks like the idea first...

Mmmh.. dont' know. Even Java folks don't allow this kind of creeping
bug and I guess they know why. You never want undefined behaviour at
least when using haskell. Because if that error occurs it's hard to
debug, no I don't like that at all.

May I look at your proposal from another view?
Am I right that you ask for not having to run the "fromJust" code to
save some cpu cycles?

Very simple example : 
        let list = [ (a,a*a) | a <- [1..10] ]
        in ..

Now getting the square of 4 (standard)
        fromJust $ lookup 4 list

Removing the fromJust code thingy leads to:

lookupGoodFaith key ((x,v):xs) | key == x = v
                               | otherwise = lookupGoodFaith xs
lookupGoodFaith _ (_,v) = v

Where is the difference? I don't even compare the key of the last list
item, because it must match. So you safe some additional cpu cycles..
The same can be implemented for Data.Map etc..

Marc Weber
From lemming at henning-thielemann.de  Sat Jun 14 17:01:28 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 16:54:17 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <404396ef0806141329w36c54982r1e3c38820894f47d@mail.gmail.com>
References: <485414BF.30307@btinternet.com>
	<404396ef0806141329w36c54982r1e3c38820894f47d@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806142254190.17143@anubis.informatik.uni-halle.de>


On Sat, 14 Jun 2008, Neil Mitchell wrote:

> Hi
>
>>  How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a
>> particular point in the program *should* be unreachable?
>
> Why not make it a function taking a string and returning a value of
> any type. Then we can keep our language and not break various
> parsing/type checking properties and rules on pragmas. We can even
> define it:
>
> impossible = error
>
> Now you can use tools like Catch and Reach to ensure it is impossible.
>
> I think it would be nice to distinguish between:
>
> * error - inserted by the compiler

Example?

> * impossible - the programmer knows this can't occur

This is an error. However the programmer adds a message because he might 
be wrong.

> * abort - deliberate aborting because the user made some mistake.

This is an exception. The signature of a function must reflect this by a 
Maybe, Either type etc.


http://www.haskell.org/haskellwiki/Exception
http://www.haskell.org/haskellwiki/Error
From marco-oweber at gmx.de  Sat Jun 14 17:06:26 2008
From: marco-oweber at gmx.de (Marc Weber)
Date: Sat Jun 14 16:58:31 2008
Subject: [Haskell-cafe] Template Haskell sugar / spliceing in automatically ?
Message-ID: <20080614210626.GC25415@gmx.de>

Hi, I've been thinking about template haskell sugar lately.

Some cool libraries are there such as metaHDBC or the template haskell
printf library.

However they all have one thing in common:

$(printf "...") a b c

$(runStmt "INSERT INTO ( ) VALUES ( ?, ?, ? )" ) 2 3 4


Would it make sense to automatically splice those functions?

{-# auto-splice: runStmt, printf #-}

So that you can just use
        printf "..." a b c
and
        runStmt "INSERT INTO ( ) VALUES ( ?, ?, ? )" 2 3 4
without $() ?

Would this be convinient?

Marc Weber
From ndmitchell at gmail.com  Sat Jun 14 17:16:49 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Sat Jun 14 17:08:53 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <Pine.LNX.4.64.0806142254190.17143@anubis.informatik.uni-halle.de>
References: <485414BF.30307@btinternet.com>
	<404396ef0806141329w36c54982r1e3c38820894f47d@mail.gmail.com>
	<Pine.LNX.4.64.0806142254190.17143@anubis.informatik.uni-halle.de>
Message-ID: <404396ef0806141416t2d4ce383n4ee3b72a31256400@mail.gmail.com>

Hi

> > * error - inserted by the compiler
>
>  Example?

Pattern-match errors.

> > * abort - deliberate aborting because the user made some mistake.
>
>  This is an exception. The signature of a function must reflect this by a
> Maybe, Either type etc.

Disagree. I mean more like:

when (Delete `elem` flags && Keep `elem` flags) $
   abort "User cannot pick both keep and delete on the command line"

Think "die" in Perl world.

Thanks

Neil
From lemming at henning-thielemann.de  Sat Jun 14 17:40:25 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat Jun 14 17:32:28 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <404396ef0806141416t2d4ce383n4ee3b72a31256400@mail.gmail.com>
References: <485414BF.30307@btinternet.com>
	<404396ef0806141329w36c54982r1e3c38820894f47d@mail.gmail.com>
	<Pine.LNX.4.64.0806142254190.17143@anubis.informatik.uni-halle.de>
	<404396ef0806141416t2d4ce383n4ee3b72a31256400@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806142331060.17143@anubis.informatik.uni-halle.de>


On Sat, 14 Jun 2008, Neil Mitchell wrote:

> Hi
>
>>> * error - inserted by the compiler
>>
>>  Example?
>
> Pattern-match errors.

Calling a function with patterns it cannot process is a programming error.

>>> * abort - deliberate aborting because the user made some mistake.
>>
>>  This is an exception. The signature of a function must reflect this by a
>> Maybe, Either type etc.
>
> Disagree. I mean more like:
>
> when (Delete `elem` flags && Keep `elem` flags) $
>   abort "User cannot pick both keep and delete on the command line"
>
> Think "die" in Perl world.

I wouldn't use such a function, because it does not scale. E.g. I cannot 
code a loop which lets the user enter flags until they match the 
conditions. Thus instead of 'abort' I would throw an exception - which is 
equivalent to the use of an exceptional value like Nothing or Left in 
Haskell (maybe wrapped in ErrorT).
From phercek at gmail.com  Sat Jun 14 18:12:26 2008
From: phercek at gmail.com (Peter Hercek)
Date: Sat Jun 14 18:04:40 2008
Subject: [Haskell-cafe] Re: Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <g31fo6$2tm$1@ger.gmane.org>

Andrew Coppin wrote:
<-- cut -->
> When compiled without optimisations, the pragma just causes an exception 
> to be thrown, rather like "error" does. When compiled with 
> optimisations, the whole case alternative is removed, and no code is 
> generated for it. (And if the impossible somehow happens... behaviour is 
> undefined.)

So if the compiler optimizes otherwise well you save how much? Something like:
  * one load from cache (since the next is the pointer which will be needed
    anyway later and moreover it was created just few insturctions before);
    almost always should be in L1; so lets say 2 or 3 ticks; moreover this
    applies only when you do not tag pointers (which can be done for Maybe)
  * run test instruction on it; 1 tick
  * conditional jump; should be doable so that it is predicted correctly by
    default - so you get 1 tick here probably too

So you want to save somewhere about 2 to 5 ticks (which with a bit of luck
  can be shared with other instructions) but you get unsafe execution.
  Does not sound right to me. There should be other optimizations which can
  be done and which save more.
If it is ever done I hope it will be possible to switch it off. Or the
  compiler must prove that what I think is impossible is really impossible
  and then it can do it :-D

Peter.

From derek.a.elkins at gmail.com  Sat Jun 14 19:24:26 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Sat Jun 14 19:16:44 2008
Subject: [Haskell-cafe] Template Haskell sugar / spliceing in
	automatically ?
In-Reply-To: <20080614210626.GC25415@gmx.de>
References: <20080614210626.GC25415@gmx.de>
Message-ID: <1213485866.5557.8.camel@derek-laptop>

On Sat, 2008-06-14 at 23:06 +0200, Marc Weber wrote:
> Hi, I've been thinking about template haskell sugar lately.
> 
> Some cool libraries are there such as metaHDBC or the template haskell
> printf library.
> 
> However they all have one thing in common:
> 
> $(printf "...") a b c
> 
> $(runStmt "INSERT INTO ( ) VALUES ( ?, ?, ? )" ) 2 3 4
> 
> 
> Would it make sense to automatically splice those functions?
> 
> {-# auto-splice: runStmt, printf #-}
> 
> So that you can just use
>         printf "..." a b c
> and
>         runStmt "INSERT INTO ( ) VALUES ( ?, ?, ? )" 2 3 4
> without $() ?
> 
> Would this be convinient?

I've been iffy about this since TH was first created.  It would
certainly be more convenient, but it starts running into some unpleasant
issues.  Admittedly, most of these issues are issues of expectations,
but still.

One example from the CL/Scheme world, is that these macros wouldn't be
proper functions, so e.g. 'map printf' wouldn't work or wouldn't mean
the same thing, 'let formatString = "%s" in printf formatString'
wouldn't work or wouldn't mean the same thing (thus being a violation of
referential transparency, at least at a superficial level).

Let's say we have a function 'mydo' that turns an applicative expression
into one using monadic style.  Then something like
foo = runState (mydo (inc + inc)) 0
brings back some of the issues of programming in an impure language.

Currently, I'm still leaning toward the more explicit syntax.

From isaacdupree at charter.net  Sat Jun 14 19:29:43 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Sat Jun 14 19:21:59 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>	<Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>
	<3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
Message-ID: <48545467.7080209@charter.net>

Sebastian Sylvan wrote:
> On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>
>> On Sat, 14 Jun 2008, Sebastian Sylvan wrote:
>>
>>  On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>>>
>>>> On Sat, 14 Jun 2008, Sebastian Sylvan wrote:
>>>>
>>>>  On 6/14/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>>>
>>>>>
>>>>>> The problem would be again that no one knows, where "Window" comes
>>>>>> from.
>>>>>> Better would be
>>>>>>
>>>>>>  I really don't see how this is a big problem. Lots of languages do
>>>>>>
>>>>> hierarchical import (e.g. .Net languages) and I don't think I've ever
>>>>> heard
>>>>> anyone complain about this particular aspect of it.
>>>>>
>>>>>
>>>> It's not a problem for you and thus you do not pay attention to these
>>>> complaints, I suspect. Maybe the people who would complain about the
>>>> importing style, simply don't use the mentioned languages.
>>>>
>>>>  The worst case scenario is that you need a little bit of tool support to
>>>>> help you sort it out. Plus, it's not like you can't just qualify the
>>>>> import
>>>>> to make it easier to see where it comes from if you really think it's a
>>>>> problem:
>>>>>
>>>>>
>>>> Cf.
>>>>  http://www.haskell.org/haskellwiki/Import_modules_properly
>>>>
>>>>  Haskell can re-export modules, which makes tracing identifiers more
>>>> difficult. I want to be able to read modules without using a tool.
>>>>
>>>>
>>> I'm not sure I understand you point. You're so opposed to the *option* of
>>> allowing hierarchical exports (even though you can still import it
>>> qualified
>>> if you personally like having to specify at each callsite exactly where
>>> some
>>> identifier is coming from),
>>>
>> I was concerned with the _import_ part of your proposal. (I haven't thought
>> about the export part so far.)
>>
>>  that you'd rather any library making use of a module hierarchy is forced
>>> to either make the user add dozens of boilerplate import statements (with
>>> "qualified" and "as") or the more common strategy of prefixing each function
>>> call with the module name (buttonNew)? To me a module system that requires
>>> the latter in practice is horribly broken, and I'm suggesting a low-impact
>>> way of fixing it. It may not be the best system available, but it's a tiny
>>> extension of the current.
>>>
>>> I really don't see why adding this option hurts you, when it clearly helps
>>> enable doing what this thread advocates (use qualified modules to
>>> distinguish between functions of the same name, rather than adding a bunch
>>> of prefixes/suffixes to the functions).
>>>
>> Button.new is my favorite, because with current import variants I can
>> easily lookup, what Button and Button.new refer to. I understand your
>> proposal in that way that
>>
>> import Graphics.UI.Gtk
>>
>> brings module qualifications Window and Button into scope although they are
>> not explicitly mentioned. Thus I could no longer find out easily what
>> Butten.new means.
>>
> I don't see why this is so bad when it's exactly what we have for other
> identifiers? E.g. if you import Control.Monad you get mapM, but you can't
> really say for sure where this identifier comes from, which is no better
> than not knowing where "Button.new" comes from. In both cases you have the
> option to qualify the module import so you have to say "Monad.mapM" or
> "GTK.Button.new" which makes it more apparent.
> 
> I suppose you would make the "hiding" clause and the "import list" thing
> work with modules too for consistency, so if you really wanted to you could
> list the modules/identifiers that you bring in.

yeah, we could come up with a syntax. one that gives privileged meaning 
to hierarchy.  If used according to "design your modules for qualified 
import", it would still allow fairly easy use and looking up function uses.

import Graphics.UI.GTK (import qualified Button, import qualified Window)

then you get Button.f (because Graphics.UI.GTK wasn't imported 
qualified), Graphics.UI.GTK.Button.f, (not f or Graphics.UI.GTK.f 
because of qualified Button)  ... they're normal import statements 
inside.  What it saves is the duplication of Graphics.UI.GTK and 
"....Button as Button".  Not sure I like how long "import qualified" is, 
repeated there, but it seemed much less confusing than anything shorter.

import Data (import qualified Map, Map.Map)
or
import Data (import qualified Map, import Map(Map))
or a shortcut for that common pattern of importing a few things unqualified
import Data (import qualified Map and (Map))
aka. import qualified Data.Map as Map and (Map)
aka. import qualified Data.Map as Map (empty,singleton,...) and (Map)
or perhaps "unqualifying" rather than "and"

personally I would like it if we could also import (f as g) if we wanted 
to rename an "f" we were importing, to "g" in the module and re-exports, 
without having to be concerned about (for lowercase) monomorphism 
restriction, (for types) whether a synonym will work properly everywhere 
(not without extensions!), (for constructor, record fields, and classes) 
simple *impossibility*.  That wish is only related in that it's a 
related generalization, though.

hmm.

-Isaac

> Are you saying that you prefer the situation where to use GTK the user would
> have to explicitly import every single sub-module in the hierarchy ("import
> qualified Graphics.UI.GTK.X as X" where X = {Button,Window, ... etc})? I
> don't think that's very nice at all, and I certainly don't like having to
> add the module name to the functions... I think lots of libraries are like
> that, and we need some mechanism of importing lots of related modules
> together so that they come in qualified, without forcing the user to write a
> gazillion lines of boilerplate import statements..
> 
> I think that if GTK did use this system (rather than append the module name
> to the function and export them "flatly") a lot of people would resort to
> ugly hacks like putting the import statements in a file somewhere and using
> the C preprocessor to include it, yuck! (OTOH this may be just what's
> required to convince everyone that we need to improve the module system)...
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From isaacdupree at charter.net  Sat Jun 14 19:41:59 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Sat Jun 14 19:34:27 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <404396ef0806141416t2d4ce383n4ee3b72a31256400@mail.gmail.com>
References: <485414BF.30307@btinternet.com>	<404396ef0806141329w36c54982r1e3c38820894f47d@mail.gmail.com>	<Pine.LNX.4.64.0806142254190.17143@anubis.informatik.uni-halle.de>
	<404396ef0806141416t2d4ce383n4ee3b72a31256400@mail.gmail.com>
Message-ID: <48545747.3010607@charter.net>

Neil Mitchell wrote:
>>> * abort - deliberate aborting because the user made some mistake.
>>  This is an exception. The signature of a function must reflect this by a
>> Maybe, Either type etc.
> 
> Disagree. I mean more like:
> 
> when (Delete `elem` flags && Keep `elem` flags) $
>    abort "User cannot pick both keep and delete on the command line"
> 
> Think "die" in Perl world.

in that case should use abort :: String -> IO a, not abort :: String -> 
a.  "abort" as "pure function" is just for messy scripting convenience 
a-la Perl.  (Which is not to say that's never useful, of course -- I 
would just try my hardest to avoid it in my code, probably.)

On the other hand, Control.Exception.throw, if it's ever useful, 
obviously isn't meant to indicate a programmer error, but to throw an 
exception (that will probably be caught somewhere in the program's IO). 
  So there's a reason for _|_ besides programmer error (well, there's 
also user-driven nontermination such as when an interpreter is told to 
execute an infinite loop :-)

-Isaac
From jonathanccast at fastmail.fm  Sat Jun 14 22:25:14 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Sat Jun 14 22:17:06 2008
Subject: [Haskell-cafe] monomorphism restriction
In-Reply-To: <485370F7.20308@xaph.net>
References: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
	<2f9b2d30806131727s624ee38dja867b926bbde0cc1@mail.gmail.com>
	<485370F7.20308@xaph.net>
Message-ID: <1213496714.6353.16.camel@jonathans-macbook>

On Sat, 2008-06-14 at 17:19 +1000, Rafal Kolanski wrote:
> Ryan Ingram wrote:
> > sumns 0 = 0
> > sumns x = sumns (x-1) + n
> > 
> > Without the monomorphism restriction, computing n is a function call;
> > it is evaluated each time it is asked for.
> 
> I'm relatively new to Haskell, and since this topic already came up, I
> was wondering if anyone could explain to me how this ties into implicit
> parameters which "escape" from their respective functions?
> 
> For instance, if I just state:
> maxLength = maxLengthParameter ?config
> without providing a type signature and then use it, I get warned that
> ?config "escapes" from maxLength and that I should provide a type
> signature or turn off the monomorphism restriction.

Which means you have to declare ?config at top level and then maxLength
has that value baked into it.

> I find implicit parameters are a really nice way to pass a configuration
> to a whole tree of functions (in this case an LZSS compressor) without
> having to explicitly add it as a parameter to every single one of the
> functions.
> 
> What are the performance implications of turning off the restriction and
> allowing implicit parameters to "escape"? Are there general performance
> implications of implicit parameters I am not aware of?

Implicit parameters get turned into real parameters under the hood.
Turning off the monomorphism restriction (e.g., giving a type signature)
just leaves the implicit parameter in place, so maxLength is a function,
not a value.  You probably /want/ maxLength to be computed from
whatever ?config happens to be in scope, so you won't mind in this case.
But Haskell wants to be sure you know that it is a function, and
laziness's automatic memoization doesn't work for it, before it will
proceed.  That's all that's going on here.

jcc


From dgoldsmith at mac.com  Sun Jun 15 01:41:20 2008
From: dgoldsmith at mac.com (Deborah Goldsmith)
Date: Sun Jun 15 01:33:24 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <20080614200605.GB30515@scytale.galois.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<20080614200605.GB30515@scytale.galois.com>
Message-ID: <9F19B056-4F87-469D-8A3B-7688BC1E2131@mac.com>

On Jun 14, 2008, at 1:06 PM, Don Stewart wrote:
> tom.davie:
>> In the mean time -- who knows enough to make ghc target ARM, and get
>> this to link against the iPhone libraries?  This would be quite a  
>> coup
>> if it could be made to run there!
>
> I'd be interested. We should start a wiki page for Haskell on the
> iphone..

It's an interesting idea, but I think it would need to be a cross- 
compiler. Does ghc support cross-compilation?

Deborah

From magnus at therning.org  Sun Jun 15 02:52:49 2008
From: magnus at therning.org (Magnus Therning)
Date: Sun Jun 15 02:45:01 2008
Subject: [Haskell-cafe] OT: Paper on increasing entropy in software systems
Message-ID: <4854BC41.6080602@therning.org>

This is wildly off topic, but since the Haskell community is a rather
academic one I thought there might be a good chance to find someone who
can point me in the right direction.

I was just listening to Brooks' talk at OOPSLA 2007 and in the Q&A part
at the end he mentions a paper on increasing entropy in software
systems.  He mentions the authors' names but I can't quite make it out
and Google hasn't been very helpful either.  He says the paper ?must be
30 years old? and it sounds like he says it's by Les Bellati and Manny
Leimann (Lehmann?).  As I said, I can't quite make out the names, and
the names ring no bells for me.  Does anyone on the list know what paper
he's referring to?

/M

-- 
Magnus Therning                             (OpenPGP: 0xAB4DFBA4)
magnus?therning?org             Jabber: magnus?therning?gmail?com
http://therning.org/magnus

What if I don't want to obey the laws? Do they throw me in jail with
the other bad monads?
     -- Daveman


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From c-bauer-olsbruecken at t-online.de  Sun Jun 15 03:57:17 2008
From: c-bauer-olsbruecken at t-online.de (Christoph Bauer)
Date: Sun Jun 15 03:49:34 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <404396ef0806140809x52f28124t4eea5dc78a02ac@mail.gmail.com> (Neil
	Mitchell's message of "Sat, 14 Jun 2008 16:09:13 +0100")
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<404396ef0806140350w2eb18cf4n68b7d2f08ece7025@mail.gmail.com>
	<87ve0cvzi9.fsf@elefant.olsbruecken.local>
	<22fcbd520806140806w33fb2060y9f00b3e6ff0d3daa@mail.gmail.com>
	<22fcbd520806140806y311f4f9ax8aaa42763bb7dc8f@mail.gmail.com>
	<404396ef0806140809x52f28124t4eea5dc78a02ac@mail.gmail.com>
Message-ID: <87od635dwi.fsf@elefant.olsbruecken.local>

Hi,

>> There's a way to put something in the .cabal file about extra data files,
>> and have it install them in a certain location that you can then find
>> programmatically.  I forget the details, but I think it's pretty easy to set
>
> http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html

With this summary it was easy. I pushed an patch to
http://home.arcor.de/chr_bauer/topkata.

Christoph
From rvollmert-lists at gmx.net  Sun Jun 15 04:03:03 2008
From: rvollmert-lists at gmx.net (Robert Vollmert)
Date: Sun Jun 15 03:55:11 2008
Subject: [Haskell-cafe] Re: working with Random.randoms
In-Reply-To: <wfskvgcnqp.fsf@calligramme.charmers>
References: <4852A281.8000508@enterity.com>
	<wfskvgcnqp.fsf@calligramme.charmers>
Message-ID: <C5D892A8-4A82-41BB-AB1D-D22E361A40F0@gmx.net>

Great reply!

One minor point: If real_programme is to be pure, you should use let:

On Jun 14, 2008, at 12:30, Jon Fairbairn wrote:
> main :: IO()
>   do gen <- getStdGen
>      the_list <- real_programme gen
       let the_list = real_programme gen
>      print the_list
>
> You should be able to deduce from the fact that the first
> argument of real_programme here is of type StdGen (not IO
> anything) and its result type is [something] that
> real_programme is pure, and gen has only one value
> throughout.

Cheers
Robert

From jon.fairbairn at cl.cam.ac.uk  Sun Jun 15 04:43:19 2008
From: jon.fairbairn at cl.cam.ac.uk (Jon Fairbairn)
Date: Sun Jun 15 04:35:40 2008
Subject: [Haskell-cafe] Re: working with Random.randoms
References: <4852A281.8000508@enterity.com>
	<wfskvgcnqp.fsf@calligramme.charmers>
	<C5D892A8-4A82-41BB-AB1D-D22E361A40F0@gmx.net>
Message-ID: <wfk5grccm0.fsf@calligramme.charmers>

Robert Vollmert <rvollmert-lists@gmx.net> writes:

> Great reply!

Thanks.

> One minor point: If real_programme is to be pure, you should use let:

Whoops! I was thinking "let" but wrote the wrong thing. If
my email had been through a type-checker, it would have
spotted the mistake.

-- 
J?n Fairbairn                                 Jon.Fairbairn@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html  (updated 2008-04-26)

From tom.davie at gmail.com  Sun Jun 15 04:46:52 2008
From: tom.davie at gmail.com (Thomas Davie)
Date: Sun Jun 15 04:38:58 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <9F19B056-4F87-469D-8A3B-7688BC1E2131@mac.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<20080614200605.GB30515@scytale.galois.com>
	<9F19B056-4F87-469D-8A3B-7688BC1E2131@mac.com>
Message-ID: <F1BC46F0-FE0F-4EAD-9164-ECAC0A201F92@gmail.com>


On 15 Jun 2008, at 07:41, Deborah Goldsmith wrote:

> On Jun 14, 2008, at 1:06 PM, Don Stewart wrote:
>> tom.davie:
>>> In the mean time -- who knows enough to make ghc target ARM, and get
>>> this to link against the iPhone libraries?  This would be quite a  
>>> coup
>>> if it could be made to run there!
>>
>> I'd be interested. We should start a wiki page for Haskell on the
>> iphone..
>
> It's an interesting idea, but I think it would need to be a cross- 
> compiler. Does ghc support cross-compilation?

The most obvious place to start I guess would be using -fvia-C and the  
C cross compiler that apple supply.  I'll certainly be looking into  
this as soon as I get an iPhone (which unfortunately I need to wait  
for  3G one in Belgium).

Bob
From ketil at malde.org  Sun Jun 15 05:13:20 2008
From: ketil at malde.org (Ketil Malde)
Date: Sun Jun 15 05:04:59 2008
Subject: [Haskell-cafe] OT: Paper on increasing entropy in software systems
In-Reply-To: <4854BC41.6080602@therning.org> (Magnus Therning's message of
	"Sun\, 15 Jun 2008 07\:52\:49 +0100")
References: <4854BC41.6080602@therning.org>
Message-ID: <871w2z2h8v.fsf@malde.org>

Magnus Therning <magnus@therning.org> writes:

> I was just listening to Brooks' talk at OOPSLA 2007 and in the Q&A part
> at the end he mentions a paper on increasing entropy in software
> systems.  He mentions the authors' names but I can't quite make it out
> and Google hasn't been very helpful either.  He says the paper ?must be
> 30 years old? and it sounds like he says it's by Les Bellati and Manny
> Leimann (Lehmann?).

Wikipedia's entry for "Software entropy" lists this:

  Lehman M.M. and Belady L. (1985). Program Evolution. Process of
  Software Change.

No link, though.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From haskell at brecknell.org  Sun Jun 15 06:30:09 2008
From: haskell at brecknell.org (Matthew Brecknell)
Date: Sun Jun 15 06:22:10 2008
Subject: [Haskell-cafe] OT: Paper on increasing entropy in software systems
In-Reply-To: <871w2z2h8v.fsf@malde.org>
References: <4854BC41.6080602@therning.org> <871w2z2h8v.fsf@malde.org>
Message-ID: <1213525809.5777.1258527019@webmail.messagingengine.com>

> > I was just listening to Brooks' talk at OOPSLA 2007 and in the Q&A part
> > at the end he mentions a paper on increasing entropy in software
> > systems.  He mentions the authors' names but I can't quite make it out
> > and Google hasn't been very helpful either.  He says the paper &#8220;must be
> > 30 years old&#8221; and it sounds like he says it's by Les Bellati and Manny
> > Leimann (Lehmann?).
> 
> Wikipedia's entry for "Software entropy" lists this:
> 
>   Lehman M.M. and Belady L. (1985). Program Evolution. Process of
>   Software Change.
> 
> No link, though.

http://www.amazon.com/exec/obidos/ASIN/0124424406

Using the author names provided by Ketil, scholar.google.com also finds
this:

http://www.research.ibm.com/journal/sj/153/ibmsj1503E.pdf

From r.kelsall at millstream.com  Sun Jun 15 09:25:00 2008
From: r.kelsall at millstream.com (Richard Kelsall)
Date: Sun Jun 15 09:17:04 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <485414BF.30307@btinternet.com>
References: <485414BF.30307@btinternet.com>
Message-ID: <4855182C.2030203@millstream.com>

Andrew Coppin wrote:
> Obviously there is no way in hell this code path can ever be executed. 

Ah, the number of times I've thought that and been wrong :)

 From a simplistic perspective what I think you're asking for is
to have obscure occasions when your program goes wrong with random
consequences and doesn't give you an error message. This a programmer's
worst nightmare. I can think of several dimensions of bug difficulty

When the bug exhibits:
   Hard   : Infrequent at run-time.
   Medium : Frequent at run-time.
   Easy   : Compile-time.

Reproducible:
   Hard   : No obvious pattern or way to induce the error.
   Medium : A reasonably strong correlation with some precursor.
   Easy   : Happens every time you do a particular thing.

Error message:
   Hard   : No error message.
   Medium : Non-specific error message.
   Easy   : Error message that relates to an identifiable
            point in your program with relevant state information.

Error message location:
   Medium : Appears on the screen.
   Easy   : Shown on screen and recorded in a log file.

Where it happens:
   Hard   : Only on your user's machine or with their configuration.
   Easy   : On all machines.


By classifying error messages, for bugs which you have stated are
infrequent and difficult to reproduce, as not needing to be displayed
or logged you have pushed all these bugs into the seriously hard
category. By adding 'undefined' subsequent behaviour you have made
these bugs even more difficult. What we should be doing is pushing
every bug in the opposite direction - towards the easy end of all
the above dimensions.


Richard.
From aneumann at inf.fu-berlin.de  Sun Jun 15 10:27:55 2008
From: aneumann at inf.fu-berlin.de (Adrian Neumann)
Date: Sun Jun 15 10:20:06 2008
Subject: [Haskell-cafe] (no subject)
Message-ID: <F48CA04D-7B5C-4CDF-B213-ECABD98A38D8@inf.fu-berlin.de>

{- I downloaded the source and put my file in the same directory
    You may need to adjust the imports -}
module Main where
import Picture
import Draw -- change xWin to 1000 and yWin to 700 for this to work
import EnableGUI -- I use a Mac
import SOE hiding (Region)
import qualified SOE as G (Region)
import Data.List
import Random

-- lines are not Shapes unfortunately
linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01), 
(0.1,-0.01)]), (-0.1,0), (0.1,0))

main = enableGUI >> do
     w <- openWindow "Lindenmayer System" (xWin, yWin)
     newStdGen
     g <- getStdGen
     drawPic w (aufgabe2 g)
     k <- getKey w
     if (k=='q') then do
         closeWindow w
         return () else do
             clearWindow w
             main

-- one big ugly line of code, not that interesting though
aufgabe2 g= dasBild where
     r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem  
linie (lSystem 20 g)
     dasBild = Region White r `Over` Region Black ( Translate  
(0,-1.8) $ Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2+pi/ 
3) $ Translate (0,2.6) $ r) `Over` Region Green (Shape $ Polygon  
[(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region Yellow  
(Translate (4,1.5) (Shape $ circle (0.5))) `Over`
             Region Blue (Shape $ Rectangle 14 7)

-- start of the interesting part:
-- A - Axiom, the base shape we use for rendering later
--F - Forward
--Branch - what it says

data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done  
deriving Show

-- a Axiom is a region with two connector points
type Axiom = (Region, Vertex, Vertex)

-- this seems not to be used anymore?

scaleAxiom :: Float -> Axiom -> Axiom
scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v)

-- just for testing purposes
testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A  
(Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F  
Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)]  
Done)

-- a 2D rotation matrix
drehM :: Float -> (Float, Float, Float, Float)
drehM w = (cos w, -sin w, sin w, cos w)

-- matrix vector multiplication
(.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex
(.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py)

-- other vector stuff
(.-.) (a,b) (c,d) = (a-c,b-d)
(.+.) (a,b) (c,d) = (a+c,b+d)
(.*.) l (c,d) = (c*l,d*l)
abs' (a,b) = (abs a, abs b)
betr (a,b) = sqrt (a*a+b*b)

-- SOE doesn't come with a way to rotate Regions, so I wrote my own
rotateRegion :: Float -> Region -> Region
rotateRegion f (Shape s) = Shape (rotateS f s)
rotateRegion f (Translate v r) = Translate ((drehM f).**.v)  
(rotateRegion f r)

-- the scaling part is not right I think. Everything seems to break  
if I try to incorporate scaling
-- into the rendering

rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv)  
(rotateRegion f r) where
     x = ((drehM f).**. (fst v,0))
     y = ((drehM f) .**. (0,snd v))
     nv = (abs' x) .+. (abs' y)
rotateRegion f (Complement r) =Complement (rotateRegion f r)
rotateRegion f (Union r1 r2) = Union (rotateRegion f r1)  
(rotateRegion f r2)
rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1)  
(rotateRegion f r2)
rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion f r2)
rotateRegion _ s=s

rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts)
rotateS f x = x

-- nondeterministically generate a word in our LSys language
-- lots of copy&paste here, any way to do this better?

lSystem :: Int -> StdGen -> LSys
lSystem n g = f n g (A undefined) where
     f :: Int -> StdGen -> LSys -> LSys
     f 0 _ _ = Done
     f (n+1) g (A _)
         | choose >= 1 = A (f n ng (F undefined))
         | choose == 0 = A (f n ng (Branch ng [f n ng' (A undefined),  
f n ng'' (A undefined)] undefined)) where
             (choose, ng) = randomR (0::Int,3::Int) g
             (ng', ng'') = split ng
     f (n+1) g (F _)
         | choose >= 1 = F (f n ng (F undefined))
         | choose == 0 = F (f n ng (Branch ng [f n ng' (A undefined),  
f n ng'' (A undefined)] undefined)) where
             (choose, ng) = randomR (0::Int,3::Int) g
             (ng', ng'') = split ng
     f (n+1) g (Branch h lSys _)
         | choose >= 1 = Branch h lSys  (f n ng (F undefined))
         | choose == 0 = Branch h lSys (f n ng (Branch ng [f n ng' (A  
undefined), f n ng'' (A undefined)] undefined)) where
             (choose, ng) = randomR (0::Int,5::Int) g
             (ng', ng'') = split ng

-- recursivly render a LSys
renderLSystem :: Axiom -> LSys -> Region
renderLSystem _ Done = Empty
renderLSystem (r,u,v) (A lSys) = r `Union` renderLSystem (r,u,v) lSys
renderLSystem (r,u,v) (F lSys) = r'' `Union` renderLSystem (r'', u . 
+. o , v .+.o) lSys where
     r'' =  Translate o   $  r
     o = (v .-. u)
renderLSystem (r,u,v) (Branch g lSys rest) =
     theBranches `Union` renderLSystem (r,u,v) rest where
         theBranches = Translate o $ foldr Union Empty $
	-- we need to rotate around the u-Connector, not around (0,0)
	-- thus translation
             map (Translate u) $ zipWith ($) rotations (map  
((Translate ((0,0).-.u)).(renderLSystem (r,u,v))) lSys)
         rotations = map rotateRegion (randomRs (-pi/4,pi/3) g) -- 
branches are rotated randomly
         o = (v .-. u)
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From aneumann at inf.fu-berlin.de  Sun Jun 15 10:50:28 2008
From: aneumann at inf.fu-berlin.de (Adrian Neumann)
Date: Sun Jun 15 10:42:43 2008
Subject: [Haskell-cafe] Lindenmayer Systems, WAS: (no subject)
In-Reply-To: <F48CA04D-7B5C-4CDF-B213-ECABD98A38D8@inf.fu-berlin.de>
References: <F48CA04D-7B5C-4CDF-B213-ECABD98A38D8@inf.fu-berlin.de>
Message-ID: <AD64D226-9416-48C8-8DDF-A4D4CE24BCD7@inf.fu-berlin.de>

I screwed up the email, sorry about that. What I wanted to say was:

Hello,

as homework I was assigned to "design and draw an image" using the  
SOE Graphics library [1]. In order to impress my classmates I decided  
to draw a bush-like thingy using a Lindenmayer-System. It turns out  
quite nice [2], and so I thought I might share my code with you. Of  
course criticism is very welcome.

Ok, here we go:


> {- I downloaded the source and put my file in the same directory
>    You may need to adjust the imports -}
> module Main where
> import Picture
> import Draw -- change xWin to 1000 and yWin to 700 for this to work
> import EnableGUI -- I use a Mac
> import SOE hiding (Region)
> import qualified SOE as G (Region)
> import Data.List
> import Random
>
> -- lines are not Shapes unfortunately
> linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01), 
> (0.1,-0.01)]), (-0.1,0), (0.1,0))
>
> main = enableGUI >> do
>     w <- openWindow "Lindenmayer System" (xWin, yWin)
>     newStdGen
>     g <- getStdGen
>     drawPic w (aufgabe2 g)
>     k <- getKey w
>     if (k=='q') then do
>         closeWindow w
>         return () else do
>             clearWindow w
>             main
>
> -- one big ugly line of code, not that interesting though
> aufgabe2 g= dasBild where
>     r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem  
> linie (lSystem 20 g)
>     dasBild = Region White r `Over` Region Black ( Translate  
> (0,-1.8) $ Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2 
> +pi/3) $ Translate (0,2.6) $ r) `Over` Region Green (Shape $  
> Polygon [(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region  
> Yellow (Translate (4,1.5) (Shape $ circle (0.5))) `Over`
>             Region Blue (Shape $ Rectangle 14 7)
>
> -- start of the interesting part:
> -- A - Axiom, the base shape we use for rendering later
> --F - Forward
> --Branch - what it says
>
> data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done  
> deriving Show
>
> -- a Axiom is a region with two connector points
> type Axiom = (Region, Vertex, Vertex)
>
> -- this seems not to be used anymore?
>
> scaleAxiom :: Float -> Axiom -> Axiom
> scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v)
>
> -- just for testing purposes
> testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A  
> (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F  
> Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)]  
> Done)
>
> -- a 2D rotation matrix
> drehM :: Float -> (Float, Float, Float, Float)
> drehM w = (cos w, -sin w, sin w, cos w)
>
> -- matrix vector multiplication
> (.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex
> (.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py)
>
> -- other vector stuff
> (.-.) (a,b) (c,d) = (a-c,b-d)
> (.+.) (a,b) (c,d) = (a+c,b+d)
> (.*.) l (c,d) = (c*l,d*l)
> abs' (a,b) = (abs a, abs b)
> betr (a,b) = sqrt (a*a+b*b)
>
> -- SOE doesn't come with a way to rotate Regions, so I wrote my own
> rotateRegion :: Float -> Region -> Region
> rotateRegion f (Shape s) = Shape (rotateS f s)
> rotateRegion f (Translate v r) = Translate ((drehM f).**.v)  
> (rotateRegion f r)
>
> -- the scaling part is not right I think. Everything seems to break  
> if I try to incorporate scaling
> -- into the rendering
>
> rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv)  
> (rotateRegion f r) where
>     x = ((drehM f).**. (fst v,0))
>     y = ((drehM f) .**. (0,snd v))
>     nv = (abs' x) .+. (abs' y)
> rotateRegion f (Complement r) =Complement (rotateRegion f r)
> rotateRegion f (Union r1 r2) = Union (rotateRegion f r1)  
> (rotateRegion f r2)
> rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1)  
> (rotateRegion f r2)
> rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion  
> f r2)
> rotateRegion _ s=s
>
> rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts)
> rotateS f x = x
>
> -- nondeterministically generate a word in our LSys language
> -- lots of copy&paste here, any way to do this better?
>
> lSystem :: Int -> StdGen -> LSys
> lSystem n g = f n g (A undefined) where
>     f :: Int -> StdGen -> LSys -> LSys
>     f 0 _ _ = Done
>     f (n+1) g (A _)
>         | choose >= 1 = A (f n ng (F undefined))
>         | choose == 0 = A (f n ng (Branch ng [f n ng' (A  
> undefined), f n ng'' (A undefined)] undefined)) where
>             (choose, ng) = randomR (0::Int,3::Int) g
>             (ng', ng'') = split ng
>     f (n+1) g (F _)
>         | choose >= 1 = F (f n ng (F undefined))
>         | choose == 0 = F (f n ng (Branch ng [f n ng' (A  
> undefined), f n ng'' (A undefined)] undefined)) where
>             (choose, ng) = randomR (0::Int,3::Int) g
>             (ng', ng'') = split ng
>     f (n+1) g (Branch h lSys _)
>         | choose >= 1 = Branch h lSys  (f n ng (F undefined))
>         | choose == 0 = Branch h lSys (f n ng (Branch ng [f n  
> ng' (A undefined), f n ng'' (A undefined)] undefined)) where
>             (choose, ng) = randomR (0::Int,5::Int) g
>             (ng', ng'') = split ng
>
> -- recursivly render a LSys
> renderLSystem :: Axiom -> LSys -> Region
> renderLSystem _ Done = Empty
> renderLSystem (r,u,v) (A lSys) = r `Union` renderLSystem (r,u,v) lSys
> renderLSystem (r,u,v) (F lSys) = r'' `Union` renderLSystem (r'', u . 
> +. o , v .+.o) lSys where
>     r'' =  Translate o   $  r
>     o = (v .-. u)
> renderLSystem (r,u,v) (Branch g lSys rest) =
>     theBranches `Union` renderLSystem (r,u,v) rest where
>         theBranches = Translate o $ foldr Union Empty $
> 	-- we need to rotate around the u-Connector, not around (0,0)
> 	-- thus translation
>             map (Translate u) $ zipWith ($) rotations (map  
> ((Translate ((0,0).-.u)).(renderLSystem (r,u,v))) lSys)
>         rotations = map rotateRegion (randomRs (-pi/4,pi/3) g) -- 
> branches are rotated randomly
>         o = (v .-. u)

What do you think?

Adrian

[1] http://www.haskell.org/soe/graphics.htm
[2] http://img149.imageshack.us/my.php?image=bild1tf4.png


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From gwern0 at gmail.com  Sun Jun 15 12:01:48 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Sun Jun 15 11:54:25 2008
Subject: [Haskell-cafe] Lindenmayer Systems, WAS: (no subject)
In-Reply-To: <AD64D226-9416-48C8-8DDF-A4D4CE24BCD7@inf.fu-berlin.de>
References: <F48CA04D-7B5C-4CDF-B213-ECABD98A38D8@inf.fu-berlin.de>
	<AD64D226-9416-48C8-8DDF-A4D4CE24BCD7@inf.fu-berlin.de>
Message-ID: <20080615160147.GA8943@craft>

On 2008.06.15 16:50:28 +0200, Adrian Neumann <aneumann@inf.fu-berlin.de> scribbled 6.9K characters:
> I screwed up the email, sorry about that. What I wanted to say was:
>
> Hello,
>
> as homework I was assigned to "design and draw an image" using the SOE
> Graphics library [1]. In order to impress my classmates I decided to draw
> a bush-like thingy using a Lindenmayer-System. It turns out quite nice
> [2], and so I thought I might share my code with you. Of course criticism
> is very welcome.
>
> Ok, here we go:
>
>> {- I downloaded the source and put my file in the same directory
>>    You may need to adjust the imports -}
>> module Main where
>> import Picture
>> import Draw -- change xWin to 1000 and yWin to 700 for this to work
>> import EnableGUI -- I use a Mac
>> import SOE hiding (Region)
>> import qualified SOE as G (Region)
>> import Data.List
>> import Random
>>
>> -- lines are not Shapes unfortunately
>> linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01),
>> (0.1,-0.01)]), (-0.1,0), (0.1,0))
>>
>> main = enableGUI >> do
>>     w <- openWindow "Lindenmayer System" (xWin, yWin)
>>     newStdGen
>>     g <- getStdGen
>>     drawPic w (aufgabe2 g)
>>     k <- getKey w
>>     if (k=='q') then do
>>         closeWindow w
>>         return () else do
>>             clearWindow w
>>             main
>>
>> -- one big ugly line of code, not that interesting though
>> aufgabe2 g= dasBild where
>>     r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem linie
>> (lSystem 20 g)
>>     dasBild = Region White r `Over` Region Black ( Translate (0,-1.8) $
>> Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2+pi/3) $
>> Translate (0,2.6) $ r) `Over` Region Green (Shape $ Polygon
>> [(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region Yellow
>> (Translate (4,1.5) (Shape $ circle (0.5))) `Over`
>>             Region Blue (Shape $ Rectangle 14 7)
>>
>> -- start of the interesting part:
>> -- A - Axiom, the base shape we use for rendering later
>> --F - Forward
>> --Branch - what it says
>>
>> data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done
>> deriving Show
>>
>> -- a Axiom is a region with two connector points
>> type Axiom = (Region, Vertex, Vertex)
>>
>> -- this seems not to be used anymore?
>>
>> scaleAxiom :: Float -> Axiom -> Axiom
>> scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v)
>>
>> -- just for testing purposes
>> testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A
>> (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F
>> Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)]
>> Done)
>>
>> -- a 2D rotation matrix
>> drehM :: Float -> (Float, Float, Float, Float)
>> drehM w = (cos w, -sin w, sin w, cos w)
>>
>> -- matrix vector multiplication
>> (.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex
>> (.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py)
>>
>> -- other vector stuff
>> (.-.) (a,b) (c,d) = (a-c,b-d)
>> (.+.) (a,b) (c,d) = (a+c,b+d)
>> (.*.) l (c,d) = (c*l,d*l)
>> abs' (a,b) = (abs a, abs b)
>> betr (a,b) = sqrt (a*a+b*b)
>>
>> -- SOE doesn't come with a way to rotate Regions, so I wrote my own
>> rotateRegion :: Float -> Region -> Region
>> rotateRegion f (Shape s) = Shape (rotateS f s)
>> rotateRegion f (Translate v r) = Translate ((drehM f).**.v)
>> (rotateRegion f r)
>>
>> -- the scaling part is not right I think. Everything seems to break if
>> I try to incorporate scaling
>> -- into the rendering
>>
>> rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv)
>> (rotateRegion f r) where
>>     x = ((drehM f).**. (fst v,0))
>>     y = ((drehM f) .**. (0,snd v))
>>     nv = (abs' x) .+. (abs' y)
>> rotateRegion f (Complement r) =Complement (rotateRegion f r)
>> rotateRegion f (Union r1 r2) = Union (rotateRegion f r1) (rotateRegion
>> f r2)
>> rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1)
>> (rotateRegion f r2)
>> rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion f
>> r2)
>> rotateRegion _ s=s
>>
>> rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts)
>> rotateS f x = x
>>
>> -- nondeterministically generate a word in our LSys language
>> -- lots of copy&paste here, any way to do this better?
>>
>> lSystem :: Int -> StdGen -> LSys
>> lSystem n g = f n g (A undefined) where
>>     f :: Int -> StdGen -> LSys -> LSys
>>     f 0 _ _ = Done
>>     f (n+1) g (A _)
>>         | choose >= 1 = A (f n ng (F undefined))
>>         | choose == 0 = A (f n ng (Branch ng [f n ng' (A undefined), f
>> n ng'' (A undefined)] undefined)) where
>>             (choose, ng) = randomR (0::Int,3::Int) g
>>             (ng', ng'') = split ng
>>     f (n+1) g (F _)
>>         | choose >= 1 = F (f n ng (F undefined))
>>         | choose == 0 = F (f n ng (Branch ng [f n ng' (A undefined), f
>> n ng'' (A undefined)] undefined)) where
>>             (choose, ng) = randomR (0::Int,3::Int) g
>>             (ng', ng'') = split ng
>>     f (n+1) g (Branch h lSys _)
>>         | choose >= 1 = Branch h lSys  (f n ng (F undefined))
>>         | choose == 0 = Branch h lSys (f n ng (Branch ng [f n ng' (A
>> undefined), f n ng'' (A undefined)] undefined)) where
>>             (choose, ng) = randomR (0::Int,5::Int) g
>>             (ng', ng'') = split ng
>>
>> -- recursivly render a LSys
>> renderLSystem :: Axiom -> LSys -> Region
>> renderLSystem _ Done = Empty
>> renderLSystem (r,u,v) (A lSys) = r `Union` renderLSystem (r,u,v) lSys
>> renderLSystem (r,u,v) (F lSys) = r'' `Union` renderLSystem (r'', u .+.
>> o , v .+.o) lSys where
>>     r'' =  Translate o   $  r
>>     o = (v .-. u)
>> renderLSystem (r,u,v) (Branch g lSys rest) =
>>     theBranches `Union` renderLSystem (r,u,v) rest where
>>         theBranches = Translate o $ foldr Union Empty $
>> 	-- we need to rotate around the u-Connector, not around (0,0)
>> 	-- thus translation
>>             map (Translate u) $ zipWith ($) rotations (map ((Translate
>> ((0,0).-.u)).(renderLSystem (r,u,v))) lSys)
>>         rotations = map rotateRegion (randomRs (-pi/4,pi/3) g) --
>> branches are rotated randomly
>>         o = (v .-. u)
>
> What do you think?
>
> Adrian
>
> [1] http://www.haskell.org/soe/graphics.htm
> [2] http://img149.imageshack.us/my.php?image=bild1tf4.png

That's interesting, nice and short. The output actually reminds me a lot of Nymphaea <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/nymphaea>; have you seen't?

--
gwern
Maple 82 Visa/BCC noise noise FCA Blacknet TELINT WISDIM S/Key
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From andrewcoppin at btinternet.com  Sun Jun 15 04:15:49 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Sun Jun 15 15:05:16 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <Pine.LNX.4.64.0806142144400.17143@anubis.informatik.uni-halle.de>
References: <485414BF.30307@btinternet.com>
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Henning Thielemann wrote:
> I think it is another instance of mixing up errors and exceptions (you 
> know the haskellwiki pages ...)
>
> Since an 'error' marks a programming error (which should never occur) 
> it would not hurt the program if all 'error's are replaced by 
> 'undefined', an illegal memory access or any other misbehaviour. So 
> 'error' is exactly what you propose as IMPOSSIBLE pragma. A compiler 
> option for replacing all 'error's by nops would do want you want.

OK, so suppose I write a module that contains a function that accepts a 
number parameter, and that parameter must be greater than 2. I have no 
control over what value users of the library pass to my function. 
Suppose some client calls my function with 1 as an argument - is that an 
error, or an exception?

On the other hand, suppose I write the same function, but now it's not 
exported. So the only code that can possibly call this function is my 
own code. So I can [theoretically] guarantee it will never be called 
with the "wrong" argument [assuming the code I write isn't defective].

As far as I can tell, there's no way of making this distinction in 
Haskell code. You'd use "error" in both cases - or if you're feeling 
brave, remove it in the second case and hope you're right. I'm just 
saying it would be nice to be able to keep it in the code for 
maintainability's sake, but not have the runtime penalty for it once 
you're "sure" your code is safe.

It looks like Don's "assert" thing might be able to do this. [I had no 
idea this existed by the way...]

Hmm, this gives me a new idea for a feature request - how about a 
function that evaluates to the source code line number it was called 
from? ;-)

From lemming at henning-thielemann.de  Sun Jun 15 15:37:21 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun Jun 15 15:29:24 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <4854CFB5.6010009@btinternet.com>
References: <485414BF.30307@btinternet.com>
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Message-ID: <Pine.LNX.4.64.0806152117410.29109@anubis.informatik.uni-halle.de>


On Sun, 15 Jun 2008, Andrew Coppin wrote:

> Henning Thielemann wrote:
>> I think it is another instance of mixing up errors and exceptions (you know 
>> the haskellwiki pages ...)
>> 
>> Since an 'error' marks a programming error (which should never occur) it 
>> would not hurt the program if all 'error's are replaced by 'undefined', an 
>> illegal memory access or any other misbehaviour. So 'error' is exactly what 
>> you propose as IMPOSSIBLE pragma. A compiler option for replacing all 
>> 'error's by nops would do want you want.
>
> OK, so suppose I write a module that contains a function that accepts a 
> number parameter, and that parameter must be greater than 2. I have no 
> control over what value users of the library pass to my function. Suppose 
> some client calls my function with 1 as an argument - is that an error, or an 
> exception?

It's an error, like 'head []' is an error. You must document the condition 
(argument > 2), unfortunately Haskell's type system does not allow to 
state such conditiions conveniently, and then it's the caller's 
responsibility to ensure that the argument is greater than 2.
  I like to distinguish between two kinds of users. (Are there common names 
for them?) The (consumer) user communicates with your program via an 
interface you provide: A GUI, the command line, a network. The user may 
even not know, that the program is written in Haskell. Everything this 
user makes wrong is an exception. You cannot forbid the user to make 
something wrong. The other kind of users are programmers, who call 
functions of your library. This interface is especially fast but in order 
to get the efficiency you can expect some cooperation by the programmer. 
E.g. the programmer of your library must ensure that the argument is 
always greater than 2. Otherwise _he_ has done an _error_.
  However if he writes a program which lets the user enter the number in a 
GUI dialog which is then passed to your library, then he must check the 
number before forwarding it, because the user can do wrong things. If the 
user enters '1' this is an _exception_. If the programmer does not reject 
this input it is an error.

> On the other hand, suppose I write the same function, but now it's not 
> exported. So the only code that can possibly call this function is my own 
> code. So I can [theoretically] guarantee it will never be called with the 
> "wrong" argument [assuming the code I write isn't defective].
>
> As far as I can tell, there's no way of making this distinction in Haskell 
> code. You'd use "error" in both cases - or if you're feeling brave, remove it 
> in the second case and hope you're right. I'm just saying it would be nice to 
> be able to keep it in the code for maintainability's sake, but not have the 
> runtime penalty for it once you're "sure" your code is safe.

In theory you could remove 'error' in both cases, because in theory 
neither you nor the library user makes mistakes. In practice you better 
leave the error, because both of you actually make mistakes.

> It looks like Don's "assert" thing might be able to do this. [I had no idea 
> this existed by the way...]

As far as I understand, 'assert' is a wrapper to 'error' which also 
determines the source code location without using the C preprocessor. Is 
this correct?

> Hmm, this gives me a new idea for a feature request - how about a function 
> that evaluates to the source code line number it was called from? ;-)

Would be also nice for a "single stepper", which shows at which places in 
the source code things are currently evaluated.
From lemming at henning-thielemann.de  Sun Jun 15 15:41:40 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun Jun 15 15:33:40 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <48545467.7080209@charter.net>
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On Sat, 14 Jun 2008, Isaac Dupree wrote:

> yeah, we could come up with a syntax. one that gives privileged meaning to 
> hierarchy.  If used according to "design your modules for qualified import", 
> it would still allow fairly easy use and looking up function uses.
>
> import Graphics.UI.GTK (import qualified Button, import qualified Window)
>
> then you get Button.f (because Graphics.UI.GTK wasn't imported qualified), 
> Graphics.UI.GTK.Button.f, (not f or Graphics.UI.GTK.f because of qualified 
> Button)  ... they're normal import statements inside.  What it saves is the 
> duplication of Graphics.UI.GTK and "....Button as Button".  Not sure I like 
> how long "import qualified" is, repeated there, but it seemed much less 
> confusing than anything shorter.
>
> import Data (import qualified Map, Map.Map)
> or
> import Data (import qualified Map, import Map(Map))
> or a shortcut for that common pattern of importing a few things unqualified
> import Data (import qualified Map and (Map))
> aka. import qualified Data.Map as Map and (Map)
> aka. import qualified Data.Map as Map (empty,singleton,...) and (Map)
> or perhaps "unqualifying" rather than "and"
>
> personally I would like it if we could also import (f as g) if we wanted to 
> rename an "f" we were importing, to "g" in the module and re-exports, without 
> having to be concerned about (for lowercase) monomorphism restriction, (for 
> types) whether a synonym will work properly everywhere (not without 
> extensions!), (for constructor, record fields, and classes) simple 
> *impossibility*.  That wish is only related in that it's a related 
> generalization, though.

nice
From duncan.coutts at worc.ox.ac.uk  Sun Jun 15 15:49:14 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sun Jun 15 15:37:42 2008
Subject: [Haskell-cafe] cabal-install failure
In-Reply-To: <008501c8ce05$ec0ef260$f82b8351@cr3lt>
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
	<1213392126.15010.547.camel@localhost>  <20080614021052.GA8862@craft>
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	<008501c8ce05$ec0ef260$f82b8351@cr3lt>
Message-ID: <1213559354.15010.580.camel@localhost>


On Sat, 2008-06-14 at 11:03 +0100, Claus Reinke wrote:
> > http://hackage.haskell.org/trac/hackage/ticket/227
> > 
> >        One problem is that not all build-tools correspond to haskell
> >        packages. Some do some don't. We have a hard coded list of them
> >        at the moment (which can be extended in Setup.hs files) so we
> >        could extend that with what haskell package if any the tools
> >        correspond to. Any better suggestions to make it a tad more
> >        generic?
> 
> That list seems to be in Distribution/Simple/Program.hs, in case 
> anyone else is looking for it. Encoded information includes: 
> dependency name, program name (if different from dependency),

Right, we have the common name of the program. We don't actually track
the actual name as it happens to be on any particular system except in
so far as we try to find the full path to the program when we configure
it.

The main point of the Program abstraction is about configuring and
running programs. As it happens some programs are provided by some
haskell packages (but not all, eg ld, ar, etc).

> option to get version info and code to extract it (with one apparently
> very special case being hsc2hs).

And ld.exe on windows (we find it in ghc's gcc-lib bin dir).

> Btw, most of the version extraction code looks like a regular 
> expression match - wouldn't that make the specification easier
> (and turn the comments into part of the spec)?

True, in most cases finding the name of the program involves running it
with some --version flag and matching some part of the output. However
that's not always the case. Some programs do silly things like produce
the version output on stderr instead of stdout. We figured the most
general thing was just a function

FilePath -> IO (Maybe Version)

which is what we've got. I'm not sure what the advantage would be to
make it more declarative by making it into data rather than a extraction
function.

Also, the Cabal lib cannot depend on any regular expression library
because they are not part of the bootstrapping library set.

> > If anyone has a godd suggestion I'm happy to hear it. Otherwise we can
> > just add a Maybe Dependency to the Program type to indicate that some
> > build tools have a corresponding haskell package.
> 
> I'm not sure what you're suggesting there (currently even those
> tools that can be built with Cabal do not register with Cabal), but 
> here are my suggestions:
>
> 1. Haskell tools should register with Cabal, whether built with it
>     (such as Alex, Happy, ..) or not (such as GHC, ..). That 
>     registration should include any build-relevant information
>     (versions/variants, ..).
> 
> 2. When checking a build-tools dependency, Cabal checks
>     (a) whether the tool is registered with Cabal

I'm not sure this helps. We want to know what to install when it's
missing. We can already tell if a program (not package) is available by
searching for it.

>     (b) whether the tool is registered with the system installation manager

This is hard.

>     (c) whether the tool can be found by other means (configure,
>             built-in rules, ..)
> 
> In other words, make tools look like packages (lifetime dependency
> management, not just build support), and make system packages look 
> like Cabal packages (Cabal as the interface to native managers), using 
> special treatment only if absolutely necessary. I thought those suggestions
> were clear from my earlier messages?-)

Sure, haskell executable tools built by haskell packages are really
packages.

So the problem currently is that build-tools refers to programs not
packages. One can list any known program in the build-tools field and
the list of programs is extensible in the Setup.hs script.

As they are used so far by current packages on hackage, they always
refer to haskell tools built by haskell packages (almost only used to
refer to alex, happy and c2hs) so perhaps we should just quietly
redefine the meaning on build-tools to be another kind of build-depends.
That is it specifies a haskell package.

If we have need to specify non-haskell build tools, perhaps we should do
that separately? eg "some-other-kind-of-build-tools: perl >= 5.8"

Duncan

From barsoap at web.de  Sun Jun 15 16:22:16 2008
From: barsoap at web.de (Achim Schneider)
Date: Sun Jun 15 16:14:34 2008
Subject: [Haskell-cafe] Re: Documenting the impossible
References: <485414BF.30307@btinternet.com>
Message-ID: <20080615222216.79be4ac8@solaris>

Andrew Coppin <andrewcoppin@btinternet.com> wrote:

> I have a small idea. I'm curios if anybody else thinks it's a good
> idea...
> 
> How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a 
> particular point in the program *should* be unreachable?
> 
I might support this in some way or the other _after_ we've got errors
that report source file and line number. Before that I will stay,
steadfast and stubborn, utterly ignorant of anything with less
importance.

Just use

assert s v = if debug then error s else v

in the mean time. -DHAVE_CONFIG_H ;)

-- 
(c) this sig last receiving data processing entity. Inspect headers for
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signature prohibited. 

From duncan.coutts at worc.ox.ac.uk  Sun Jun 15 17:17:56 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sun Jun 15 17:05:34 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
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Message-ID: <1213564676.15010.596.camel@localhost>


On Sat, 2008-06-14 at 19:21 +0100, Sebastian Sylvan wrote:

> I think that if GTK did use this system (rather than append the module
> name to the function and export them "flatly") a lot of people would
> resort to ugly hacks like putting the import statements in a file
> somewhere and using the C preprocessor to include it, yuck! (OTOH this
> may be just what's required to convince everyone that we need to
> improve the module system)...

Right. That's exactly why we've not done something like that. With 100+
modules in the Gtk package it's totally infeasible to do qualified
imports of them all.

If we get a proper way to export a non-flat namespace then Gtk2Hs will
certainly switch to using it. Using 'buttonBlah' is horrible but there
is currently nothing better.

There have been a few suggestions along these lines. Check the archives.
I'm not sure what is proposed for haskell', probably nothing since
nothing is currently implemented and we're only supposed to be
standardising existing practise.

Duncan

From duncan.coutts at worc.ox.ac.uk  Sun Jun 15 17:27:30 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sun Jun 15 17:15:08 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
Message-ID: <1213565250.15010.604.camel@localhost>


On Sat, 2008-06-14 at 18:18 +0200, Sebastiaan Visser wrote:
> Hi,
> 
> I've got a question about lazy IO in Haskell. The most well known
> function to do lazy IO is the `hGetContents', which lazily reads all the
> contents from a handle and returns this as a regular [Char].
> 
> The thing with hGetContents is that is puts the Handle in a semi-closed
> state, no one can use the handle anymore. This behaviour is
> understandable from the point of safety; it is not yet determined when
> the result of hGetContents will actually be computed, using the handle
> in the meantime is undesirable.
> 
> The point is, I think I really have a situation in which I want to use
> the handle again `after' a call to hGetContents. I think I can best
> explain this using a code example.
> 
>    readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
>    readHttpMessage = do
>      myStream <- <accept http connection from client>
>      request <- hGetContents myStream
>      header <- parseHttpHeader request
>      bs <- Data.ByteString.Lazy.hGetContents myStream
>      return (header, body)

Can you get the contents as a bytestring, then unpack that to a String
for the purpose of parsing a prefix of the input as the headers. Since
unpacking to a String is lazy it means you should only end up using
String for the headers and not for the payload.

As others have pointed out it's not clear from the above how you
separate the headers and the body. Returning the length of the headers
might work and then drop that amount from the bytestring would give the
body as a bytestring.

Duncan

From duncan.coutts at worc.ox.ac.uk  Sun Jun 15 17:38:07 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Sun Jun 15 17:25:46 2008
Subject: [Haskell-cafe] External query interface to HackageDB?
In-Reply-To: <bcba51a0806140726i358d4746vd69034bb9d026102@mail.gmail.com>
References: <bcba51a0806140726i358d4746vd69034bb9d026102@mail.gmail.com>
Message-ID: <1213565887.15010.613.camel@localhost>


On Sat, 2008-06-14 at 10:26 -0400, Dimitry Golubovsky wrote:
> Hi,
> 
> Is there any way to query the latest version of a particular package
> stored on Hackage, that was successfully built?

It is certainly part of the plan. There is currently no convenient way
to get at the information. I've been working on the client side of
things, actually generating decent build reports. That step is now done
and it's included in cabal-install-0.5.0. The next step is letting
people upload build reports to hackage and collating the data and
extracting useful information from the data. Included in that would be
some way for external clients to get at the data and summaries both via
human readable info on the package page and something machine readable.

> I mean, not _how_ to do that (I have some ideas that I have to
> download directory listings, looking for failure logs, etc.), but is
> there any tool or interface already available that does similar
> things?

In the mean time, using the current system, you can get at stuff by
knowing what urls to look at. eg:

http://hackage.haskell.org/packages/archive/pureMD5/0.2.0/logs/failure/ghc-6.8

So most recent packages have a logs subdir and either a success or
failure dir with a log file for a particular version of ghc, which at
the moment is 6.6 or 6.8.

> Unfortunately, tarfiles provided on Hackage (like 00-index.tar.gz) do
> not help, e. g. BerkeleyDB failed to build in all three versions, yet
> its all cabal files are included in the tarball:

Yes, the archive is complete. We do not remove anything. In future we
may augment the index with extra meta-data on what works, what is
obsolete or what is recommended.


Duncan

From pieter at laeremans.org  Sun Jun 15 18:34:00 2008
From: pieter at laeremans.org (Pieter Laeremans)
Date: Sun Jun 15 18:26:00 2008
Subject: [Haskell-cafe] Memory profiling
Message-ID: <ddacd4a70806151534w4754da06mf78e50b8e196c61f@mail.gmail.com>

Hi,

Which tools do you recommand for memory profiling   haskell programs
on a *nix system.
I'm using haskell to develop a CGI program/script.

The application has to be deployed on shared hosting infrastructure.
Since I would like to be a good citizen ,
I would need to meassure the maximum amount of memory allocated to the
program during execution.
The best I can do now is look at top but that 's not satisfactory.

thanks,

Pieter



-- 
Pieter Laeremans <pieter@laeremans.org>
From qdunkan at gmail.com  Sun Jun 15 21:42:08 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Sun Jun 15 21:34:09 2008
Subject: [Haskell-cafe] Documenting the impossible
In-Reply-To: <4854CFB5.6010009@btinternet.com>
References: <485414BF.30307@btinternet.com>
	<Pine.LNX.4.64.0806142144400.17143@anubis.informatik.uni-halle.de>
	<4854CFB5.6010009@btinternet.com>
Message-ID: <2518b95d0806151842s68c0670x50a0d3f93a7ab704@mail.gmail.com>

> Hmm, this gives me a new idea for a feature request - how about a function
> that evaluates to the source code line number it was called from? ;-)

Well, that wouldn't be a function, but one of the other "-hc"s (j? n?)
has srcloc_annotate which is a macro that does that.  It would be nice
if ghc had it.  Meanwhile, I use -pgmF to replace certain functions
with *_srcloc ones that pass a SrcLoc argument, and it works mostly
ok.  I don't know what other people do, but having file:line in logs
and test failures is pretty handy.

Only "mostly" because it replaces things in strings, because I can't
use cpp because it doesn't understand dots in identifiers, and can't
use Language.Haskell.Parser because it *also* doesn't understand dots
in identifiers, so it's Regex.subRegex (speaking of not being designed
for qualified import...) until I get around to doing it with parsec.
From magicloud.magiclouds at gmail.com  Sun Jun 15 22:31:22 2008
From: magicloud.magiclouds at gmail.com (Magicloud Magiclouds)
Date: Sun Jun 15 22:23:22 2008
Subject: [Haskell-cafe] How to do this in FP way?
Message-ID: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>

Hello,
    I am getting familiar with FP now, and I have a "program design" kind of
question.
    Say I have something like this in C:
static int old;
int diff (int now) { /* this would be called once a second */
  int ret = now - old;
  old = now;
  return ret;
}
    Because there is no "variable" in Haskell. So how to do this in a FP
way?

Thanks.
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From thomas.dubuisson at gmail.com  Sun Jun 15 23:00:03 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Sun Jun 15 22:53:26 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <1213585203.3291.9.camel@localhost.localdomain>

Magicloud Magiclouds wrote:
>     Say I have something like this in C:
> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }
>     Because there is no "variable" in Haskell. So how to do this in a
> FP way?

So you have a global time count that is updated every second - I presume
for the rest of the process to use, avoiding syscalls due to expense.
Am I getting this right?

You can use mutable variables in Haskell, though some people will frown,
but it might fit your need.  See MVar, STM, or IO Refs.  At any rate, if
what you are doing needs to check the clock time then this code isn't
going to be pure.

Perhaps you just want something in particular to be triggered every
second then use control-timeout, event-list, or control-event.

Tom
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From skynare at gmail.com  Sun Jun 15 23:10:09 2008
From: skynare at gmail.com (sam lee)
Date: Sun Jun 15 23:02:09 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <4e7aa0f80806152010w4e79aef7je4f84e99a4ea3cb7@mail.gmail.com>

I can think of 2 ways.

    > module Main where
    >
    > import Control.Monad.State

First, normal way:

    > diff (now, old) = (now - old, now)

diff takes now and old and returns result (now - old) and modified old (now).
For example,
diff (diff (1,0))
==> diff (1 - 0, 1)
==> diff (1, 1)
==> (1 - 1, 1)
==> (0, 1)

I think people use the word "threaded" to describe what diff is doing:
the variable "old" is threaded through many calls to diff.

    > testDiff = diff . diff . diff . diff . diff . diff $ (2, 1)

testDiff returns (2,1)

Second way is using monads:

    > diff' now = do
    >     old <- get
    >     put now
    >     return (now - old)


diff' uses State monad.
If you're not familiar with monads, State monad does similar to what
diff function does (it threads the variable "old").
But, being a monadic action, diff' looks like imperative version
syntactically. It gives illusion of having global variable (old).


    > testDiff' = do
    >     result <- diff' 2
    >     result <- diff' result
    >     result <- diff' result
    >     result <- diff' result
    >     result <- diff' result
    >     result <- diff' result
    >     return result
    >
    > runTestDiff' = runState testDiff' 1

runTestDiff' also returns (2,1)

2008/6/15 Magicloud Magiclouds <magicloud.magiclouds@gmail.com>:
> Hello,
>     I am getting familiar with FP now, and I have a "program design" kind of
> question.
>     Say I have something like this in C:
> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }
>     Because there is no "variable" in Haskell. So how to do this in a FP
> way?
>
> Thanks.
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
From barsoap at web.de  Mon Jun 16 00:00:33 2008
From: barsoap at web.de (Achim Schneider)
Date: Sun Jun 15 23:52:40 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <20080616060033.396f1e5c@solaris>

"Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> wrote:

> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }
>
You do it with variables, of course. This is out of some GLUT code,
using IORef's:

idle :: State -> IdleCallback
idle state = do
    t0 <- get $ t state
    t1 <- get elapsedTime
    t state $= t1
    let td = fromIntegral t1 - fromIntegral t0
    fps state $= 1/td * 1000

    angle' state $~! (+2)
    
    (bpx, bpy) <- get $ ballPos state
    (bvx, bvy) <- get $ ballVel state
    
    ballPos state $= (bpx + bvx*td, bpy + bvy*td)   
    postRedisplay Nothing

One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too. 

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From tom.davie at gmail.com  Mon Jun 16 03:42:45 2008
From: tom.davie at gmail.com (Thomas Davie)
Date: Mon Jun 16 03:34:48 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
In-Reply-To: <20080616060033.396f1e5c@solaris>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
Message-ID: <9A3A3243-08F0-42DD-80BC-6FFD6BB73274@gmail.com>

>
> One half of all Haskell coders will tell you that mutable state  
> isn't a
> good starting point to learn Haskell, the other half will tell you the
> same because they want to be cool kids, too.

And the one left over will point out that he asked how to do this the  
FP way, not the imperative way?

If it was me btw, I'd take a stab at the problem being that each time  
we do something a time gets updated and we want to know how much time  
has passed since we last did "something".

I'd approach this by generating a lazy list of times at which we  
started doing "something", and then generating a lazy list of time  
differences.

Bob
From chaddai.fouche at gmail.com  Mon Jun 16 04:11:55 2008
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Mon Jun 16 04:03:56 2008
Subject: [Haskell-cafe] Memory profiling
In-Reply-To: <ddacd4a70806151534w4754da06mf78e50b8e196c61f@mail.gmail.com>
References: <ddacd4a70806151534w4754da06mf78e50b8e196c61f@mail.gmail.com>
Message-ID: <e9350eaf0806160111q409bac10t2e58f7df90a41e30@mail.gmail.com>

2008/6/16 Pieter Laeremans <pieter@laeremans.org>:
> Hi,
>
> Which tools do you recommand for memory profiling   haskell programs
> on a *nix system.
> I'm using haskell to develop a CGI program/script.
>
> The application has to be deployed on shared hosting infrastructure.
> Since I would like to be a good citizen ,
> I would need to meassure the maximum amount of memory allocated to the
> program during execution.
> The best I can do now is look at top but that 's not satisfactory.

Are you aware that by calling the program with the correct RTS options
you can have memory profiling ?
http://www.haskell.org/ghc/docs/latest/html/users_guide/runtime-control.html
(see option -s for simple statistics)
http://www.haskell.org/ghc/docs/latest/html/users_guide/prof-heap.html

-- 
Jeda?
From ketil at malde.org  Mon Jun 16 04:19:16 2008
From: ketil at malde.org (Ketil Malde)
Date: Mon Jun 16 04:10:48 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	(Magicloud Magiclouds's message of "Mon\,
	16 Jun 2008 10\:31\:22 +0800")
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <87skvdzta3.fsf@malde.org>

"Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> writes:

> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }

>     Because there is no "variable" in Haskell. So how to do this in a FP way?

I would claim the FP way is like this:

  -- | Repeatedly subtract values from a baseline, returning a list
  --   containing each intermediate result
  diff :: Int -> [Int] -> [Int]
  diff = scanl (-)

  Prelude> diff 100 [1..10]
  [100,99,97,94,90,85,79,72,64,55,45]

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From g9ks157k at acme.softbase.org  Mon Jun 16 05:55:45 2008
From: g9ks157k at acme.softbase.org (Wolfgang Jeltsch)
Date: Mon Jun 16 05:47:53 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <1213564676.15010.596.camel@localhost>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
	<1213564676.15010.596.camel@localhost>
Message-ID: <200806161155.46039.g9ks157k@acme.softbase.org>

Am Sonntag, 15. Juni 2008 23:17 schrieb Duncan Coutts:
> [?]

> If we get a proper way to export a non-flat namespace then Gtk2Hs will
> certainly switch to using it. Using 'buttonBlah' is horrible but there
> is currently nothing better.

So is there anyone who wants to file a feature request?

> [?]

Best wishes,
Wolfgang
From michal.palka at poczta.fm  Mon Jun 16 06:48:38 2008
From: michal.palka at poczta.fm (=?UTF-8?Q?Micha=C5=82_Pa=C5=82ka?=)
Date: Mon Jun 16 06:40:43 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <87skvdzta3.fsf@malde.org>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<87skvdzta3.fsf@malde.org>
Message-ID: <1213613318.4200.6.camel@localhost>

On Mon, 2008-06-16 at 10:19 +0200, Ketil Malde wrote:
> "Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> writes:
> 
> > static int old;
> > int diff (int now) { /* this would be called once a second */
> >   int ret = now - old;
> >   old = now;
> >   return ret;
> > }
> 
> >     Because there is no "variable" in Haskell. So how to do this in a FP way?
> 
> I would claim the FP way is like this:
> 
>   -- | Repeatedly subtract values from a baseline, returning a list
>   --   containing each intermediate result
>   diff :: Int -> [Int] -> [Int]
>   diff = scanl (-)
> 
>   Prelude> diff 100 [1..10]
>   [100,99,97,94,90,85,79,72,64,55,45]

Better yet, you could create a recursive type that reflects what you are
actually doing:
newtype Step a = Step (a -> (a, Step a))

diff' :: Int -> Step Int
diff' x = Step (\a -> let r = a - x in (r, diff' r))

This way it will be easier to resume previous diff computations.

Best,
Micha?

From abhay.parvate at gmail.com  Mon Jun 16 06:50:13 2008
From: abhay.parvate at gmail.com (Abhay Parvate)
Date: Mon Jun 16 06:42:14 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
Message-ID: <3c4d5adf0806160350h5b74d3f9p4847da987712f14a@mail.gmail.com>

hGetContents reads the entire contents of the stream till the end (although
lazily). The return value of hGetContents is logically the entire contents
of the stream. That it has not read it completely is only a part of its
laziness, so the result does not depend upon when the caller stops consuming
the result. That is why the handle is semi-closed; logically the handle is
already at the end of the stream.

A complete parser to parse the header and the body has to be used on the
entire contents, or some function which knows how to find the header end and
stop there has to be used.

Regards,
Abhay

On Sat, Jun 14, 2008 at 9:48 PM, Sebastiaan Visser <sfvisser@cs.uu.nl>
wrote:

> Hi,
>
> I've got a question about lazy IO in Haskell. The most well known
> function to do lazy IO is the `hGetContents', which lazily reads all the
> contents from a handle and returns this as a regular [Char].
>
> The thing with hGetContents is that is puts the Handle in a semi-closed
> state, no one can use the handle anymore. This behaviour is
> understandable from the point of safety; it is not yet determined when
> the result of hGetContents will actually be computed, using the handle
> in the meantime is undesirable.
>
> The point is, I think I really have a situation in which I want to use
> the handle again `after' a call to hGetContents. I think I can best
> explain this using a code example.
>
>  readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString)
>  readHttpMessage = do
>    myStream <- <accept http connection from client>
>    request <- hGetContents myStream
>    header <- parseHttpHeader request
>    bs <- Data.ByteString.Lazy.hGetContents myStream
>    return (header, body)
>
> The Data.ByteString.Lazy.hGetContents in the example above obviously
> fails because the handle is semi-closed.
>
> So, what I am trying to do here is apply a parser (on that consumes
> Char's) to the input stream until it has succeeded. After this I want to
> collect the remainings of the stream in a lazy ByteString, or maybe even
> something else.
>
> I tried to open the handler again using some internal handle hackery,
> but this failed (luckily). In the module GHC.IO there is a function
> `lazyRead' that more or less seems to do what I want. But I'll guess
> there is a good reason for not exporting it.
>
> Does anyone know a pattern in which I can do this easily?
>
> Thanks,
>
> --
> Sebastiaan
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
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From isaacdupree at charter.net  Mon Jun 16 07:43:07 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Mon Jun 16 07:35:05 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <Pine.LNX.4.64.0806141542200.15299@anubis.informatik.uni-halle.de>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>	<200806061412.23585.g9ks157k@acme.softbase.org>	<A1EF016C-DD6B-4BAD-93D1-AB5761CC9BE5@alum.mit.edu>	<20080607024543.52z9hkmgz4s8o4g8-nwo@webmail.spamcop.net>	<87ve0ibt6n.fsf@malde.org>
	<1213036865.15010.448.camel@localhost>
	<Pine.LNX.4.64.0806141542200.15299@anubis.informatik.uni-halle.de>
Message-ID: <485651CB.4000904@charter.net>

Henning Thielemann wrote:
> 
> On Mon, 9 Jun 2008, Duncan Coutts wrote:
> 
>> On Mon, 2008-06-09 at 16:04 +0200, Ketil Malde wrote:
>>
>>> And - is there a way to make GHCi use aliased qualification?  I find
>>> my self typing detailed taxonomies all the time there.
>>
>> The ghci syntax currently is:
>> :m Data.Set
>> wouldn't it be much nicer as:
>> import Data.Set
>> then we could have the obvious:
>> import Data.Set as Set
> 
> This would be nice! Feature request?

feature request filed for this, 
http://hackage.haskell.org/trac/ghc/ticket/2362 .  For extending the 
import syntax in general, I wasn't sure we knew quite what we wanted 
yet, so it seemed a little premature for a feature request. (the first 
step in "implementing" the feature request would have to be specifying 
an exact design and probably asking for community feedback).  So let's 
talk about what we do or don't want for that one some more, perhaps.

From isaacdupree at charter.net  Mon Jun 16 08:02:10 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Mon Jun 16 07:54:08 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <1213564676.15010.596.camel@localhost>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>	<Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>	<3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
	<1213564676.15010.596.camel@localhost>
Message-ID: <48565642.2040403@charter.net>

Duncan Coutts wrote:
> Right. That's exactly why we've not done something like that. With 100+
> modules in the Gtk package it's totally infeasible to do qualified
> imports of them all.
> 
> If we get a proper way to export a non-flat namespace then Gtk2Hs will
> certainly switch to using it. Using 'buttonBlah' is horrible but there
> is currently nothing better.

okay, it's horrible!  It's no more manually-traceable than anything else 
either, if you just import Gtk2Hs unqualified.  Is there any way it 
could possibly be acceptably concise *and* traceable? let's see

If "GTK" appears in every usage (e.g. GTK.buttonBlah, gtkButtonBlah...), 
probably not at all concise enough for GUI code!  But if it doesn't, 
then we would need at minimum to list each of those ones that we used 
(probably not all 100 of them).  It couldn't get any more concise than 
this to use Button.blah etc.:

import GTK.modules (Button, Window, ...)

never mind the exact syntax yet -- is listing them acceptable? (and if 
there are so many, is it practically traceable by humans anyway? 
Perhaps we're assuming that these humans at least have "search this 
file" editor-capabilities?)

Are there multiple "blah" functions among the GTK modules? I.e. would 
GTK.blah be unambiguous, not mentioning that it's a button function. 
(And would it be too confusing not to mention that it's a button 
function...)  If it would be ambiguous, would typeclasses work to fix 
that (or renaming functions that have no good reason to have the same 
name, or occasionally including blahButton sort of names)?

If 100 modules is too much, would it be a reasonable compromise between 
clarity and conciseness to export coarser-grained, so there are only 
maybe half a dozen GTK modules that your typical program imports?

> There have been a few suggestions along these lines. Check the archives.
> I'm not sure what is proposed for haskell', probably nothing since
> nothing is currently implemented and we're only supposed to be
> standardising existing practise.

I had trouble in my first attempt to search the archives... Googling for 
"import" in haskell-cafe found too much code, and my personal e-mail 
records back to March 2007 found nothing else relevant with "import" in 
the title.

-Isaac
From bulat.ziganshin at gmail.com  Mon Jun 16 08:12:45 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Mon Jun 16 08:05:00 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <48565642.2040403@charter.net>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>
	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>
	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>
	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>
	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>
	<Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>
	<3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
	<1213564676.15010.596.camel@localhost>
	<48565642.2040403@charter.net>
Message-ID: <1483943909.20080616161245@gmail.com>

Hello Isaac,

Monday, June 16, 2008, 4:02:10 PM, you wrote:

> Are there multiple "blah" functions among the GTK modules? I.e. would
> GTK.blah be unambiguous, not mentioning that it's a button function. 

yes. actually, gtk2hs uses typeclasses to overload functions over
various types


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From claus.reinke at talk21.com  Mon Jun 16 08:25:42 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Mon Jun 16 08:17:44 2008
Subject: [Haskell-cafe] cabal-install failure
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com><1213392126.15010.547.camel@localhost>
	<20080614021052.GA8862@craft><1213430194.15010.556.camel@localhost><008501c8ce05$ec0ef260$f82b8351@cr3lt>
	<1213559354.15010.580.camel@localhost>
Message-ID: <006201c8cfac$1920be80$3a448351@cr3lt>

> The main point of the Program abstraction is about configuring and
> running programs. As it happens some programs are provided by some
> haskell packages (but not all, eg ld, ar, etc).
> 
>> option to get version info and code to extract it (with one apparently
>> very special case being hsc2hs).
> 
> And ld.exe on windows (we find it in ghc's gcc-lib bin dir).

I didn't notice this special case in Program.hs - are my sources
just out of date, or is this special handling encoded elsewhere?
 
>> Btw, most of the version extraction code looks like a regular 
>> expression match - wouldn't that make the specification easier
>> (and turn the comments into part of the spec)?
> 
> True, in most cases finding the name of the program involves running it
> with some --version flag and matching some part of the output. However
> that's not always the case. Some programs do silly things like produce
> the version output on stderr instead of stdout. We figured the most
> general thing was just a function
> 
> FilePath -> IO (Maybe Version)
> 
> which is what we've got. I'm not sure what the advantage would be to
> make it more declarative by making it into data rather than a extraction
> function.

Usually, the most general approach for this kind of problem is
good as a default/backup, but not so good for maintenance. The
more cases can be handled with dedicated declarative specs, the
smaller the risk of accidental/hidden breakage (eg, moving the 
comments into regex patterns), the more compact and understandable 
the specs (a line per tool, with option and regex, all in one place
would be easier to comprehend than the current free-coding style).

More importantly, concise declarative specs are easier to update
and extend (could be done by users rather than Cabal maintainers,
and preferably outside of Cabal sources).

> Also, the Cabal lib cannot depend on any regular expression library
> because they are not part of the bootstrapping library set.

Sigh. I've heard that one before, and the ghc-pkg bulk queries are
not as flexible as they could be because I had to use less expressive
functions instead of regexes. Since Haskell-only regex packages
exist, perhaps one should just be added to the bootlib set? After
all, we bother with regexes because they are so frequently useful.

>> 1. Haskell tools should register with Cabal, whether built with it
>>     (such as Alex, Happy, ..) or not (such as GHC, ..). That 
>>     registration should include any build-relevant information
>>     (versions/variants, ..).
>> 
>> 2. When checking a build-tools dependency, Cabal checks
>>     (a) whether the tool is registered with Cabal
> 
> I'm not sure this helps. We want to know what to install when it's
> missing. We can already tell if a program (not package) is available by
> searching for it.

But that means either configure or a subset of special configure
rules baked into Cabal's sources, combined with fragile Setup.hs
extensions to that subset. IMHO, the less of configure/hardcoded
rules/Setup.hs, the better (simpler, less breakage with Cabal 
updates, etc.).

How about this: instead of baking rules for those tools into the
Cabal sources, why not have a single "known-tools" package?
On (re-)installing that package, its configure/Setup is run once,
to register availability and build-related information for all those
tools with Cabal (currently, that would mean a package per
tool; later, the known-tools package itself could expose multiple
tools, but Cabal would still need to be able to check which of 
the "exposed-tools" have been found).

That way, the known-tools could be updated independently,
instead of requring Cabal source hacking and releases, and
instead of spreading special configure rules for common tools
over all packages, they'd be located in a single package 
(easier to maintain and improve, and improvements are shared).
 
>>     (b) whether the tool is registered with the system installation manager
> 
> This is hard.

Why? Because there are more installation managers than OSs,
or because so many program installs bypass them? Querying
an installation manager shouldn't be any more difficult than
querying ghc-pkg, say.

If a program is registered with, eg. Windows Add/Remove
Programs, I can use "reg query <key>" to find its registration
info, and if I don't know the key, I can use

reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall /s

to list all registered programs, or

reg export HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall <file>

to get all registration info dumped to a file, and look for
DisplayNames of the tools I'm interested in:

>reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall /s | 
    find "DisplayName" | find "Opera"
    DisplayName REG_SZ  Opera 9.50

>reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall /s | 
    find "DisplayName" | find "Hugs"
    DisplayName REG_SZ  WinHugs

>reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall /s | 
    find "DisplayName" | find "Haskell"
    DisplayName REG_SZ  Glasgow Haskell Compiler, version 6.4.1

Of course, the tools I'm interested in very often bypass the 
Windows installer (eg, I prefer tarballs for GHC, and GHC comes
with its own internally used set of tools, or Cygwin handles its own
tools itself, and so on) and so won't appear in that output.. 
 
Claus


>>     (c) whether the tool can be found by other means (configure,
>>             built-in rules, ..)
>> 
>> In other words, make tools look like packages (lifetime dependency
>> management, not just build support), and make system packages look 
>> like Cabal packages (Cabal as the interface to native managers), using 
>> special treatment only if absolutely necessary. I thought those suggestions
>> were clear from my earlier messages?-)
> 
> Sure, haskell executable tools built by haskell packages are really
> packages.
> 
> So the problem currently is that build-tools refers to programs not
> packages. One can list any known program in the build-tools field and
> the list of programs is extensible in the Setup.hs script.
> 
> As they are used so far by current packages on hackage, they always
> refer to haskell tools built by haskell packages (almost only used to
> refer to alex, happy and c2hs) so perhaps we should just quietly
> redefine the meaning on build-tools to be another kind of build-depends.
> That is it specifies a haskell package.
> 
> If we have need to specify non-haskell build tools, perhaps we should do
> that separately? eg "some-other-kind-of-build-tools: perl >= 5.8"
> 
> Duncan
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From jules at jellybean.co.uk  Mon Jun 16 08:51:14 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Mon Jun 16 08:43:14 2008
Subject: [Haskell-cafe] Design your modules for qualified import
In-Reply-To: <1213564676.15010.596.camel@localhost>
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>	<Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>	<3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com>
	<1213564676.15010.596.camel@localhost>
Message-ID: <485661C2.6070701@jellybean.co.uk>

Duncan Coutts wrote:
> If we get a proper way to export a non-flat namespace then Gtk2Hs will
> certainly switch to using it. Using 'buttonBlah' is horrible but there
> is currently nothing better.

Whilst I'm sure anyone who's used deep module structures has wondered 
about this feature, I've seen no serious proposal of any kind.

Does anyone know what this should look like?

Jules
From jules at jellybean.co.uk  Mon Jun 16 08:58:28 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Mon Jun 16 08:50:24 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
Message-ID: <48566374.7070803@jellybean.co.uk>

Sebastiaan Visser wrote:
> Does anyone know a pattern in which I can do this easily?

Don't use hGetContents on a socket. That's asking for trouble.

Use hGetContents either NEVER (easy option) or only on throwaway 
handles/files which won't be used again.

Jules

From claus.reinke at talk21.com  Mon Jun 16 09:01:20 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Mon Jun 16 08:53:29 2008
Subject: [Haskell-cafe] Design your modules for qualified import
References: <90889fe70806050819x44313662s9c48ecb77d776f3@mail.gmail.com>	<3d96ac180806091353q6fd8cyc78eb513c8a6c4c5@mail.gmail.com>	<Pine.LNX.4.64.0806141546540.15299@anubis.informatik.uni-halle.de>	<3d96ac180806140728m1061e1bdr43f3a4759554b0b2@mail.gmail.com>	<Pine.LNX.4.64.0806141631280.15299@anubis.informatik.uni-halle.de>	<3d96ac180806141038k46ea8058v60f8d78f59bc6a81@mail.gmail.com>	<Pine.LNX.4.64.0806141942110.16752@anubis.informatik.uni-halle.de>	<3d96ac180806141121k2c388ed4pd9f960bda540d45f@mail.gmail.com><1213564676.15010.596.camel@localhost>
	<485661C2.6070701@jellybean.co.uk>
Message-ID: <00db01c8cfb1$174b48f0$3a448351@cr3lt>

> Duncan Coutts wrote:
>> If we get a proper way to export a non-flat namespace then Gtk2Hs will
>> certainly switch to using it. Using 'buttonBlah' is horrible but there
>> is currently nothing better.
> 
> Whilst I'm sure anyone who's used deep module structures has wondered 
> about this feature, I've seen no serious proposal of any kind.

google for "haskell package mounting" or "haskell package grafting".
Perhaps the discussion has appeared under other keywords, but
those are the ones that spring to mind.

Claus


From sfvisser at cs.uu.nl  Mon Jun 16 09:11:03 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Mon Jun 16 09:03:13 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <48566374.7070803@jellybean.co.uk>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<48566374.7070803@jellybean.co.uk>
Message-ID: <7C297066-C27B-456E-B2C3-C526A09CD5B8@cs.uu.nl>

On Jun 16, 2008, at 2:58 PM, Jules Bean wrote:

> Sebastiaan Visser wrote:
>> Does anyone know a pattern in which I can do this easily?
>
> Don't use hGetContents on a socket. That's asking for trouble.

Can you please explain why?

What is a more easier method to spool your HTTP post data to a file  
than:

   Bs.hGetContens sock >>= Bs.hPut fd

?

> Use hGetContents either NEVER (easy option) or only on throwaway  
> handles/files which won't be used again.

My sockets will be thrown away eventually. Isn't anything? I can  
imagine that this can be a problem when using Keep-Alive connections  
- or alike - but that is a whole different story.

> Jules

Thanks,
Sebas.
From jules at jellybean.co.uk  Mon Jun 16 09:14:18 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Mon Jun 16 09:06:14 2008
Subject: [Haskell-cafe] Lazy IO.
In-Reply-To: <7C297066-C27B-456E-B2C3-C526A09CD5B8@cs.uu.nl>
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<48566374.7070803@jellybean.co.uk>
	<7C297066-C27B-456E-B2C3-C526A09CD5B8@cs.uu.nl>
Message-ID: <4856672A.4020509@jellybean.co.uk>

Sebastiaan Visser wrote:
> On Jun 16, 2008, at 2:58 PM, Jules Bean wrote:
> 
>> Sebastiaan Visser wrote:
>>> Does anyone know a pattern in which I can do this easily?
>>
>> Don't use hGetContents on a socket. That's asking for trouble.
> 
> Can you please explain why?

Because it's a broken abstraction.

It's only correct if all you will ever do is read all the data into one 
String and don't care about it after that.

In my experience this is almost never true of sockets : there is always 
protocol overhead, handshaking, and the "next request".

It might be fine for unusually simple socket setups.

> 
> What is a more easier method to spool your HTTP post data to a file than:
> 
>   Bs.hGetContens sock >>= Bs.hPut fd
> 
> ?

Yes, that's fine.
From barsoap at web.de  Mon Jun 16 12:28:39 2008
From: barsoap at web.de (Achim Schneider)
Date: Mon Jun 16 12:21:08 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
	<9A3A3243-08F0-42DD-80BC-6FFD6BB73274@gmail.com>
Message-ID: <20080616182839.61db51cc@solaris>

Thomas Davie <tom.davie@gmail.com> wrote:

> >
> > One half of all Haskell coders will tell you that mutable state  
> > isn't a
> > good starting point to learn Haskell, the other half will tell you
> > the same because they want to be cool kids, too.
> 
> And the one left over will point out that he asked how to do this
> the FP way, not the imperative way?
> 
There's no difference, as you can't do time-accounting non-strict and
still expect it to give meaningful results: I'm merely trying to be
helpful. None of the other solutions allow for the IO Monad. 

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From barsoap at web.de  Mon Jun 16 12:31:48 2008
From: barsoap at web.de (Achim Schneider)
Date: Mon Jun 16 12:27:04 2008
Subject: [Haskell-cafe] Re: Lazy IO.
References: <C47903CB-BDD9-4B22-829B-4E407E5949E8@cs.uu.nl>
	<48566374.7070803@jellybean.co.uk>
	<7C297066-C27B-456E-B2C3-C526A09CD5B8@cs.uu.nl>
	<4856672A.4020509@jellybean.co.uk>
Message-ID: <20080616183148.558e0047@solaris>

Jules Bean <jules@jellybean.co.uk> wrote:

> Sebastiaan Visser wrote:
> > On Jun 16, 2008, at 2:58 PM, Jules Bean wrote:
> > 
> >> Sebastiaan Visser wrote:
> >>> Does anyone know a pattern in which I can do this easily?
> >>
> >> Don't use hGetContents on a socket. That's asking for trouble.
> > 
> > Can you please explain why?
> 
> Because it's a broken abstraction.
> 
> It's only correct if all you will ever do is read all the data into
> one String and don't care about it after that.
> 
> In my experience this is almost never true of sockets : there is
> always protocol overhead, handshaking, and the "next request".
> 
It works for HTTP, as all responses MUST be in the same order as the
requests.



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past copyright information. All rights reserved. Unauthorised copying,
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From ndmitchell at gmail.com  Mon Jun 16 12:43:04 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Mon Jun 16 12:35:01 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
Message-ID: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>

Hi,

I'm in the process of updating the Deferred Binary library,
http://www-users.cs.york.ac.uk/~ndm/binarydefer/. The idea is that its
does serialisation, but certain elements can be marked as deferred -
instead of being written in the current file stream, they are merely
pointed at and if needed, that pointer will be followed.

Example:("hello","world"), where the first field is marked as deferred
would write out:

[6]"world""hello"

i.e. [skip 6 characters if you want hello], the "world" data, the
"hello" data we previously promised to put here. When reading, the
"hello" would only be seeked to and read if necessary.

So, its like binary, but some fields are lazy. The question is how to
indicate which fields are lazy. There are three schemes I can think
of:

== Simple Instances ==

put (a,b) = putDefer a >> put b
get = do a <- getDefer; b <- get; return (a,b)

If the put/get and putDefer/getDefer items do not line up perfectly it
will go very wrong at runtime - probably resulting in random values
being created. You also can't derive the instances automatically, with
something like Derive or DrIFT.

== Complex Instances ==

This is the current scheme, based on lazy pattern matching and
exceptions - very confusing, probably low performance.

deferBoth = [\~(a,b) -> unit (,) <<~ a << b]

Where <<~ a means write out the a field lazily, and << b means write
out the b field strictly. The advantage over the simple instances is
that a field being deferred is declared once.

== Lazy Data Type ==

Instead of customizing the instance, you can write a data Defer a =
Defer a type, and then instead of the original tuple write:

(Defer "hello","world")

But now the code must unwrap the Defer before accessing "hello", but
the instance becomes much simpler, and can be derived.

== The Question ==

Is there a simple way of tagging fields in a constructor as deferred,
just once for reading and writing, and ideally outside the instance
definition and not requiring additional code to unwrap? I can't think
of any, but there may be something I have missed.

Thanks

Neil
From tom.davie at gmail.com  Mon Jun 16 13:06:21 2008
From: tom.davie at gmail.com (Thomas Davie)
Date: Mon Jun 16 12:58:24 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
In-Reply-To: <20080616182839.61db51cc@solaris>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
	<9A3A3243-08F0-42DD-80BC-6FFD6BB73274@gmail.com>
	<20080616182839.61db51cc@solaris>
Message-ID: <3A5E5DA6-62B3-44E0-9012-883E098CBEFB@gmail.com>


On 16 Jun 2008, at 18:28, Achim Schneider wrote:

> Thomas Davie <tom.davie@gmail.com> wrote:
>
>>>
>>> One half of all Haskell coders will tell you that mutable state
>>> isn't a
>>> good starting point to learn Haskell, the other half will tell you
>>> the same because they want to be cool kids, too.
>>
>> And the one left over will point out that he asked how to do this
>> the FP way, not the imperative way?
>>
> There's no difference, as you can't do time-accounting non-strict and
> still expect it to give meaningful results: I'm merely trying to be
> helpful. None of the other solutions allow for the IO Monad.

Firstly, I'd phrase that differently -- the IO Monad doesn't allow for  
the other solutions -- the other solutions are the truly functional  
ones.  Secondly, I'm curious as to why you think that the two are  
incompatible, are you saying that for any meaningful kind of  
computation we need to resort to IORefs?  I'd strongly contest that  
idea.

Bob
From daveroundy at gmail.com  Mon Jun 16 13:17:02 2008
From: daveroundy at gmail.com (David Roundy)
Date: Mon Jun 16 13:09:01 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>

2008/6/15 Magicloud Magiclouds <magicloud.magiclouds@gmail.com>:
> Hello,
>     I am getting familiar with FP now, and I have a "program design" kind of
> question.
>     Say I have something like this in C:
> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }
>     Because there is no "variable" in Haskell. So how to do this in a FP
> way?

A better question would be to think about what you are trying to
accomplish, and then ask how to achieve that through functional
programming.

David
From barsoap at web.de  Mon Jun 16 13:24:06 2008
From: barsoap at web.de (Achim Schneider)
Date: Mon Jun 16 13:16:12 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
	<9A3A3243-08F0-42DD-80BC-6FFD6BB73274@gmail.com>
	<20080616182839.61db51cc@solaris>
	<3A5E5DA6-62B3-44E0-9012-883E098CBEFB@gmail.com>
Message-ID: <20080616192406.114c1a88@solaris>

Thomas Davie <tom.davie@gmail.com> wrote:

> 
> On 16 Jun 2008, at 18:28, Achim Schneider wrote:
> 
> > Thomas Davie <tom.davie@gmail.com> wrote:
> >
> >>>
> >>> One half of all Haskell coders will tell you that mutable state
> >>> isn't a
> >>> good starting point to learn Haskell, the other half will tell you
> >>> the same because they want to be cool kids, too.
> >>
> >> And the one left over will point out that he asked how to do this
> >> the FP way, not the imperative way?
> >>
> > There's no difference, as you can't do time-accounting non-strict
> > and still expect it to give meaningful results: I'm merely trying
> > to be helpful. None of the other solutions allow for the IO Monad.
> 
> Firstly, I'd phrase that differently -- the IO Monad doesn't allow
> for the other solutions -- the other solutions are the truly
> functional ones.  Secondly, I'm curious as to why you think that the
> two are incompatible, are you saying that for any meaningful kind of  
> computation we need to resort to IORefs?  I'd strongly contest that  
> idea.
> 
We have to resort to IO actions to get the time, and to IORefs because
we need to chain up different calls to getCurrentTime using the IO
Monad. The rest of the program can work with whatever you like best.


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From k.pierre.k at gmail.com  Mon Jun 16 13:54:44 2008
From: k.pierre.k at gmail.com (pierre)
Date: Mon Jun 16 13:46:54 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <20080616175444.GC11246@localdomain>

On Mon, Jun 16, 2008 at 10:31:22AM +0800, Magicloud Magiclouds wrote:
> Hello,
>     I am getting familiar with FP now, and I have a "program design" kind of
> question.
>     Say I have something like this in C:
> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }
>     Because there is no "variable" in Haskell. So how to do this in a FP
> way?
> 
> Thanks.

I think that "called once a second" suggests that you perhaps should
not do that in a FP way.

A state-changing function called frequently suggests that you are
perhaps doing something with a notion of time, maybe a game? Then FRP
is your FP approach. 

Or I would recommend you to explain your problem, because FP approach
could lie on much more higher level than one can figure out looking at
your short snippet.

> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe


-- 
pierre
From lemming at henning-thielemann.de  Mon Jun 16 14:59:23 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Mon Jun 16 14:51:21 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
In-Reply-To: <20080616192406.114c1a88@solaris>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
	<9A3A3243-08F0-42DD-80BC-6FFD6BB73274@gmail.com>
	<20080616182839.61db51cc@solaris>
	<3A5E5DA6-62B3-44E0-9012-883E098CBEFB@gmail.com>
	<20080616192406.114c1a88@solaris>
Message-ID: <Pine.LNX.4.64.0806162058160.16520@anubis.informatik.uni-halle.de>


On Mon, 16 Jun 2008, Achim Schneider wrote:

> We have to resort to IO actions to get the time, and to IORefs because
> we need to chain up different calls to getCurrentTime using the IO
> Monad. The rest of the program can work with whatever you like best.

Isn't  (StateT s IO a)  the cleaner alternative to IORef?
From barsoap at web.de  Mon Jun 16 15:11:11 2008
From: barsoap at web.de (Achim Schneider)
Date: Mon Jun 16 15:03:21 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
	<9A3A3243-08F0-42DD-80BC-6FFD6BB73274@gmail.com>
	<20080616182839.61db51cc@solaris>
	<3A5E5DA6-62B3-44E0-9012-883E098CBEFB@gmail.com>
	<20080616192406.114c1a88@solaris>
	<Pine.LNX.4.64.0806162058160.16520@anubis.informatik.uni-halle.de>
Message-ID: <20080616211111.1b20f7b9@solaris>

Henning Thielemann <lemming@henning-thielemann.de> wrote:

> 
> On Mon, 16 Jun 2008, Achim Schneider wrote:
> 
> > We have to resort to IO actions to get the time, and to IORefs
> > because we need to chain up different calls to getCurrentTime using
> > the IO Monad. The rest of the program can work with whatever you
> > like best.
> 
> Isn't  (StateT s IO a)  the cleaner alternative to IORef?
>
Yes. But then using one IORef in one place won't make your program
harder to understand, using Monad transformers quite certainly will.
Admittedly, I'm becoming dodgy.

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From sebastian.sylvan at gmail.com  Mon Jun 16 15:14:48 2008
From: sebastian.sylvan at gmail.com (Sebastian Sylvan)
Date: Mon Jun 16 15:06:47 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
Message-ID: <3d96ac180806161214o7c6b7fd8q77e8811dd4803fd0@mail.gmail.com>

On 6/16/08, Magicloud Magiclouds <magicloud.magiclouds@gmail.com> wrote:
>
> Hello,
>     I am getting familiar with FP now, and I have a "program design" kind
> of question.
>     Say I have something like this in C:
> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret = now - old;
>   old = now;
>   return ret;
> }
>     Because there is no "variable" in Haskell. So how to do this in a FP
> way?

The short answer is that your question amounts to "How do I do imperative
programming in an FP way", to which the answer is "you really should try to
avoid it".

Longer answer:

I think you'll be bette served if you describe your problem on a much higher
level than this. Chances are that if you write your program in an FP way,
you wouldn't need a function like your diff.

That said, Haskell do have variables (in this case an IORef would do what
you want), but again, you probably don't want that, so if you post what
problem you're trying to solve using "diff", then it will be easier to help
you design it in an FP way. Doing things in an FP way tend to impact your
program a lot more than just some minor changes to the functions at the
"bottom", it will change the whole design.

--
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862
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From ryani.spam at gmail.com  Mon Jun 16 17:22:55 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun 16 17:14:53 2008
Subject: [Haskell-cafe] monomorphism restriction
In-Reply-To: <1213242536.6353.6.camel@jonathans-macbook>
References: <Pine.LNX.4.62.0806112213360.20854@localhost.localdomain>
	<20080612032402.GA25431@scytale.galois.com>
	<1213242536.6353.6.camel@jonathans-macbook>
Message-ID: <2f9b2d30806161422m1278062eob0885aaf124c453d@mail.gmail.com>

On 6/11/08, Jonathan Cast <jonathanccast@fastmail.fm> wrote:
> This doesn't apply to f, though --- it has a function type, so the user
> presumably already knows it won't be subject to updating, no?
> Distinguishing functions from variables by the form of declaration,
> rather than the type, seems somewhat questionable to me.

Not necessarily, contrast these two definitions:

f = foldr (+) 0
f_expensive = let n = head $ drop 100000 $ fibs 1 1 in foldr (+) n

With the monomorphism restriction in place, f_expensive only
calculates n once.  Without, it gets calculated each time f is
instantiated.

  -- ryan
From andrewcoppin at btinternet.com  Mon Jun 16 15:46:16 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Mon Jun 16 17:28:33 2008
Subject: [Haskell-cafe] How to do this in FP way?
In-Reply-To: <117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
Message-ID: <4856C308.4050506@btinternet.com>

David Roundy wrote:
>
> A better question would be to think about what you are trying to
> accomplish, and then ask how to achieve that through functional
> programming.
>   

Amen!

I was waiting for somebody to say that...

There are a dozen situations in an imperative language where you'd write 
a loop. But in Haskell, you might well do something entirely different 
for each situation. So it really pays to focus on what the end result 
you're after is, rather than how to translate imperative code 
line-for-line into Haskell.

From ryani.spam at gmail.com  Mon Jun 16 17:40:07 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun 16 17:32:04 2008
Subject: [Haskell-cafe] FunPtr error?
In-Reply-To: <5ae4f2ba0806132340w39031820q3e1e86723760469@mail.gmail.com>
References: <5ae4f2ba0806081917u3cbeada0ge4968bb5183c888e@mail.gmail.com>
	<1097402345.20080609095428@gmail.com>
	<5ae4f2ba0806082324t53691b06se7efa48f5df7c379@mail.gmail.com>
	<5ae4f2ba0806091118y922e881nbcb1a945cc765bb3@mail.gmail.com>
	<2f9b2d30806091216j137abcbbj34761d6f7861c5f4@mail.gmail.com>
	<5ae4f2ba0806092054q75176dc0h1d9da81d4eacf877@mail.gmail.com>
	<6d74b0d20806092125n31df313ex483f42fc0557b06e@mail.gmail.com>
	<5ae4f2ba0806092301p2b5e9530r828abf6436e4d07d@mail.gmail.com>
	<5ae4f2ba0806132259o26632f1bsa159839029529fc@mail.gmail.com>
	<5ae4f2ba0806132340w39031820q3e1e86723760469@mail.gmail.com>
Message-ID: <2f9b2d30806161440m2385529co3e49e7f2c7ca1f5d@mail.gmail.com>

The simple explanation is "because the FFI standard says so";
primitive types wrapped in newtypes automatically get wrapped and
unwrapped during FFI calls.  See
http://www.cse.unsw.edu.au/~chak/haskell/ffi/ffi/ffise3.html#x6-120003.2
; the FFI uses "renamed datatype" to mean newtype.

Consider the following declarations translated to C:

> type Weak = Word32
> {- typedef HsWord32 Weak; }

Weak is just a type alias; you can use Word32 and Weak interchangeably
in your code after delcaring this type.

> newtype Strong = Strong Word32
> {- doesn't really exist in C; google for "c strong typedef" -}

Strong behaves exactly like a Word32 at runtime, in terms of storage,
but the typechecker can distinguish it from Word32.

> data Holder = Holder Word32
> {- typedef struct { HsWord32 x; } Holder; -}

Holder, on the other hand, is entirely separate from Word32; in fact,
there are strictly more values in Haskell of type Holder than there
are of type Word32:

> ha, hb, hc :: Holder  -- can all be distinguished at runtime
> ha = undefined
> hb = Holder undefined
> hc = Holder 0

> sa, sb :: Strong -- cannot be distinguished
> sa = undefined
> sb = Strong undefined
From robert.t.taepke at medtronic.com  Mon Jun 16 17:51:24 2008
From: robert.t.taepke at medtronic.com (Taepke, Bob)
Date: Mon Jun 16 17:43:22 2008
Subject: [Haskell-cafe] C-program calling Haskell program?
Message-ID: <B477629A5584724C9F8EE739B4F5B84B0D84386C9C@MSPM1BMSGM101.ent.core.medtronic.com>

Hello,

I am very new to Haskell, and I work in Windows XP.
Can anyone please point me to a working C / Haskell program pair that does the following:

1) The C routine passes one or more scalars, arrays, or matrices to the Haskell routine.
2) The Haskell routine reads a comma-delimited, ASCII file from the path, C:\my_directory\input_data\.
3) The Haskell routine writes a comma-delimited, ASCII file to the path, C:\my_directory\output_data\.
4) The Haskell routine returns to the C routine one or more scalars, arrays, or matrices.
5) For what it's worth, I'm only using the C-routine as an interface between MATLAB and Haskell, because MATLAB can call C-routines.

Has anyone written C / Haskell code that does the above tasks?  If so, would you please be willing to pass it along to me?

Thank you!

Bob



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From derek.a.elkins at gmail.com  Mon Jun 16 18:40:24 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Mon Jun 16 18:32:31 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
In-Reply-To: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
References: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
Message-ID: <1213656024.5557.23.camel@derek-laptop>

On Mon, 2008-06-16 at 17:43 +0100, Neil Mitchell wrote:
> Hi,
> 
> I'm in the process of updating the Deferred Binary library,
> http://www-users.cs.york.ac.uk/~ndm/binarydefer/. The idea is that its
> does serialisation, but certain elements can be marked as deferred -
> instead of being written in the current file stream, they are merely
> pointed at and if needed, that pointer will be followed.
> 
> Example:("hello","world"), where the first field is marked as deferred
> would write out:
> 
> [6]"world""hello"
> 
> i.e. [skip 6 characters if you want hello], the "world" data, the
> "hello" data we previously promised to put here. When reading, the
> "hello" would only be seeked to and read if necessary.
> 
> So, its like binary, but some fields are lazy. The question is how to
> indicate which fields are lazy. There are three schemes I can think
> of:
> 
> == Simple Instances ==
> 
> put (a,b) = putDefer a >> put b
> get = do a <- getDefer; b <- get; return (a,b)
> 
> If the put/get and putDefer/getDefer items do not line up perfectly it
> will go very wrong at runtime - probably resulting in random values
> being created. You also can't derive the instances automatically, with
> something like Derive or DrIFT.
> 
> == Complex Instances ==
> 
> This is the current scheme, based on lazy pattern matching and
> exceptions - very confusing, probably low performance.
> 
> deferBoth = [\~(a,b) -> unit (,) <<~ a << b]
> 
> Where <<~ a means write out the a field lazily, and << b means write
> out the b field strictly. The advantage over the simple instances is
> that a field being deferred is declared once.
> 
> == Lazy Data Type ==
> 
> Instead of customizing the instance, you can write a data Defer a =
> Defer a type, and then instead of the original tuple write:
> 
> (Defer "hello","world")
> 
> But now the code must unwrap the Defer before accessing "hello", but
> the instance becomes much simpler, and can be derived.
> 
> == The Question ==
> 
> Is there a simple way of tagging fields in a constructor as deferred,
> just once for reading and writing, and ideally outside the instance
> definition and not requiring additional code to unwrap? I can't think
> of any, but there may be something I have missed.

This isn't an answer to your question. This is just my opinion based on
my values.

I'd just immediately do option three.  It seems the simplest, most
composable and most flexible, and I like having things reflected in my
types.  It seems easy enough to code up the first option given the last.
I don't really understand what you are getting at with the second
option, but I suspect it too is easy to do on top of the third option.

From qdunkan at gmail.com  Mon Jun 16 19:07:33 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Mon Jun 16 18:59:30 2008
Subject: [Haskell-cafe] 1/0
Message-ID: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>

So, I know this has been discussed before, but:

> 1/0
Infinity
> 0/0
NaN

... so I see from the archives that Infinity is mandated by ieee754
even though my intuition says both should be NaN.

Every other language throws an exception, even C will crash the
program, so I'm guessing it's telling the processor / OS to turn these
into signals, while GHC is turning that off.  Or something.  But then
what about this note in Control.Exception:

(NOTE: GHC currently does not throw ArithExceptions except for DivideByZero)

Doesn't this imply GHC should be throwing DivideByZero?  Why is it in
the stdlib if it's turned off?  And why would it be turned off?

I suppose I could accept the above since Infinity *is* an exceptional
value meant to represent things like 1/0, and it can be nice to see
NaNs in your output instead of crashing everything (this is, I assume,
why ieee754 has these modes in the first place), but how about this:

> round (0/0) :: Integer
(huge negative number)

Ok, so integral types don't have that exceptional value.  Shouldn't
trying to convert NaN or Infinity to an Integral throw something?  Is
it a performance thing?  I'd think if you're converting to Integer you
don't really need hardware level performance anyway, so a couple of
checks wouldn't kill anyone.
From daveroundy at gmail.com  Mon Jun 16 19:12:52 2008
From: daveroundy at gmail.com (David Roundy)
Date: Mon Jun 16 19:04:50 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
In-Reply-To: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
References: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
Message-ID: <117f2cc80806161612oe3f2033q187cbf5c22592f03@mail.gmail.com>

On Mon, Jun 16, 2008 at 9:43 AM, Neil Mitchell <ndmitchell@gmail.com> wrote:
> == The Question ==
>
> Is there a simple way of tagging fields in a constructor as deferred,
> just once for reading and writing, and ideally outside the instance
> definition and not requiring additional code to unwrap? I can't think
> of any, but there may be something I have missed.

Is there any reason not to just write all lazy fields of variable size
in a deferred manner? That would seem like the best option to me, but
maybe that's just because I don't see any downside besides the
requirement that one use some space to write the size.  But that seems
like it would almost always be a trivial issue, as any small data
element will have a fixed size (so that the deferred/non-deferred
distinction doesn't exist).

David
From daveroundy at gmail.com  Mon Jun 16 19:18:01 2008
From: daveroundy at gmail.com (David Roundy)
Date: Mon Jun 16 19:09:58 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
Message-ID: <117f2cc80806161618x5c2a717bo551b8e4ff384633@mail.gmail.com>

On Mon, Jun 16, 2008 at 4:07 PM, Evan Laforge <qdunkan@gmail.com> wrote:
> So, I know this has been discussed before, but:
>
>> 1/0
> Infinity
>> 0/0
> NaN
>
> ... so I see from the archives that Infinity is mandated by ieee754
> even though my intuition says both should be NaN.

There is a good reason for 1/0 being infinity, as it allows correct
programs to give correct answers even in the presence of underflow and
overflow.

> Every other language throws an exception, even C will crash the
> program, so I'm guessing it's telling the processor / OS to turn these
> into signals, while GHC is turning that off.  Or something.  But then
> what about this note in Control.Exception:

That's just not true.  It depends on how your system (compiler?) is
configured, but the default on most systems that I've used is to
return NaNs.

David
From daveroundy at gmail.com  Mon Jun 16 19:21:24 2008
From: daveroundy at gmail.com (David Roundy)
Date: Mon Jun 16 19:13:20 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <117f2cc80806161618x5c2a717bo551b8e4ff384633@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<117f2cc80806161618x5c2a717bo551b8e4ff384633@mail.gmail.com>
Message-ID: <117f2cc80806161621h1e4d9eb2j7e52d6973c307995@mail.gmail.com>

On Mon, Jun 16, 2008 at 4:18 PM, David Roundy <daveroundy@gmail.com> wrote:
> On Mon, Jun 16, 2008 at 4:07 PM, Evan Laforge <qdunkan@gmail.com> wrote:
>> Every other language throws an exception, even C will crash the
>> program, so I'm guessing it's telling the processor / OS to turn these
>> into signals, while GHC is turning that off.  Or something.  But then
>> what about this note in Control.Exception:
>
> That's just not true.  It depends on how your system (compiler?) is
> configured, but the default on most systems that I've used is to
> return NaNs.

Sorry, I just read my post, and realized I quoted too much.  I was
responding to the first sentence about other languages, thinking of
octave, C and C++.

David
From john at repetae.net  Mon Jun 16 19:28:26 2008
From: john at repetae.net (John Meacham)
Date: Mon Jun 16 19:20:23 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
Message-ID: <20080616232826.GB12977@sliver.repetae.net>

On Mon, Jun 16, 2008 at 04:07:33PM -0700, Evan Laforge wrote:
> So, I know this has been discussed before, but:
> Every other language throws an exception, even C will crash the
> program, so I'm guessing it's telling the processor / OS to turn these
> into signals, while GHC is turning that off.  Or something.  But then
> what about this note in Control.Exception:

No, The issue is that '/' is always floating point division in haskell,
for integer division, use `div`.

1 `div` 0 throws an exception like you expect. 

GHC behaves exactly the same as C here. But in C whether '/' means
floating point or integral division depends on the types of its
arguments, in haskell they are separate operators.

        John


-- 
John Meacham - ?repetae.net?john?
From xj2106 at columbia.edu  Mon Jun 16 19:35:24 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Mon Jun 16 19:33:06 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	(Evan Laforge's message of "Mon, 16 Jun 2008 16:07:33 -0700")
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
Message-ID: <87r6axvtqb.fsf@columbia.edu>

"Evan Laforge" <qdunkan@gmail.com> writes:

> So, I know this has been discussed before, but:
>
>> 1/0
> Infinity
>> 0/0
> NaN
>
> ... so I see from the archives that Infinity is mandated by ieee754
> even though my intuition says both should be NaN.
>
> Every other language throws an exception, even C will crash the
> program, so I'm guessing it's telling the processor / OS to turn these
> into signals, while GHC is turning that off. [...]

No, C will not, with floating point type.  The following
program prints out a string "inf\n".

#include <stdio.h>
int main (void) 
{ 
    double a=1, b=0; 
    double i; 
    i = a / b; 
    printf ("%g\n",i);
    return 0;
}

I believe Haskell is behaving rationally.

Cheers,
Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From qdunkan at gmail.com  Mon Jun 16 19:41:23 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Mon Jun 16 19:33:26 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080616232826.GB12977@sliver.repetae.net>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
Message-ID: <2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>

> No, The issue is that '/' is always floating point division in haskell,
> for integer division, use `div`.
>
> 1 `div` 0 throws an exception like you expect.
>
> GHC behaves exactly the same as C here. But in C whether '/' means
> floating point or integral division depends on the types of its
> arguments, in haskell they are separate operators.

Aha, I was missing something.  Indeed, 1.0/0.0 gives me infinity with
C.  Thanks for the clarification.  Python does throw for 1.0/0.0, but
I think there's a (not very commonly used) module to turn that off.
It might be nice for GHC to have a some way to turn exceptions on, but
I can accept getting NaNs, and doing the ieee754 thing by default
seems entirely reasonable.


But what about that NaN->Integer conversion thing?
From dan.doel at gmail.com  Mon Jun 16 19:45:30 2008
From: dan.doel at gmail.com (Dan Doel)
Date: Mon Jun 16 19:37:59 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
Message-ID: <200806161945.30976.dan.doel@gmail.com>

On Monday 16 June 2008, Evan Laforge wrote:
> So, I know this has been discussed before, but:
> > 1/0
>
> Infinity
>
> > 0/0
>
> NaN
>
> ... so I see from the archives that Infinity is mandated by ieee754
> even though my intuition says both should be NaN.
>
> Every other language throws an exception, even C will crash the
> program, so I'm guessing it's telling the processor / OS to turn these
> into signals, while GHC is turning that off.  Or something.  But then
> what about this note in Control.Exception:

#include <stdio.h>
#include <stdlib.h>

int main (int argc, char **argv)
{
  float f1 = 1.0/0.0;
  float f2 = 0.0/0.0;

  printf("%f\n%f\n", f1, f2);

  return EXIT_SUCCESS;
}

% ./Inf
inf
nan

In a Haskell program, 1/0 is floating point division. In C, 1/0 is integer 
division, which may get implicitly converted to a floating point if you 
say "float f = 1/0;". That's why you get the exception in C.

> but how about this:
> > round (0/0) :: Integer
>
> (huge negative number)
>
> Ok, so integral types don't have that exceptional value.  Shouldn't
> trying to convert NaN or Infinity to an Integral throw something?  Is
> it a performance thing?  I'd think if you're converting to Integer you
> don't really need hardware level performance anyway, so a couple of
> checks wouldn't kill anyone.

This is a (known by some) bug of sorts in the various floating point -> 
integral transformations (which ultimately boil down to decodeFloat or 
something like that at some point). It apparently doesn't know about the 
various exceptional values in the IEEE representation, so it just treats the 
representation like any other value. Infinity and NaN look like various huge 
numbers if you interpret them like any other value, so that's what you get 
out of round/ceiling/floor/etc.

It's not ideal, but I guess no one's bothered to fix it. Might be something to 
bring up on the libraries mailing list.

-- Dan
From john at repetae.net  Mon Jun 16 19:50:05 2008
From: john at repetae.net (John Meacham)
Date: Mon Jun 16 19:42:02 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
Message-ID: <20080616235005.GC12977@sliver.repetae.net>

On Mon, Jun 16, 2008 at 04:41:23PM -0700, Evan Laforge wrote:
> But what about that NaN->Integer conversion thing?

I think that may be a bug or at least a misfeature. The standard is
somewhat vauge on a lot of issues dealing with floating point since
it is such a tricky subject and depends a lot on the environment. The
various rounding funcitons are particularly ugly IMHO. I added varients
of them that preserved the floating point type and properly implemented
IEEE behavior for jhc.

        John

-- 
John Meacham - ?repetae.net?john?
From droundy at darcs.net  Mon Jun 16 20:05:03 2008
From: droundy at darcs.net (David Roundy)
Date: Mon Jun 16 19:57:00 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080616235005.GC12977@sliver.repetae.net>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
	<20080616235005.GC12977@sliver.repetae.net>
Message-ID: <20080617000502.GZ32397@darcs.net>

On Mon, Jun 16, 2008 at 04:50:05PM -0700, John Meacham wrote:
> On Mon, Jun 16, 2008 at 04:41:23PM -0700, Evan Laforge wrote:
> > But what about that NaN->Integer conversion thing?
> 
> I think that may be a bug or at least a misfeature. The standard is
> somewhat vauge on a lot of issues dealing with floating point since
> it is such a tricky subject and depends a lot on the environment. The
> various rounding funcitons are particularly ugly IMHO. I added varients
> of them that preserved the floating point type and properly implemented
> IEEE behavior for jhc.

I think the Data.Binary guys think it's a feature, since they rely in
this behavior (well, they rely on the equivalently-foolish behavior of
toRational).  I think it's a bug.

David
From dons at galois.com  Mon Jun 16 20:08:36 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun 16 20:00:34 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080617000502.GZ32397@darcs.net>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
	<20080616235005.GC12977@sliver.repetae.net>
	<20080617000502.GZ32397@darcs.net>
Message-ID: <20080617000836.GC9848@scytale.galois.com>

droundy:
> On Mon, Jun 16, 2008 at 04:50:05PM -0700, John Meacham wrote:
> > On Mon, Jun 16, 2008 at 04:41:23PM -0700, Evan Laforge wrote:
> > > But what about that NaN->Integer conversion thing?
> > 
> > I think that may be a bug or at least a misfeature. The standard is
> > somewhat vauge on a lot of issues dealing with floating point since
> > it is such a tricky subject and depends a lot on the environment. The
> > various rounding funcitons are particularly ugly IMHO. I added varients
> > of them that preserved the floating point type and properly implemented
> > IEEE behavior for jhc.
> 
> I think the Data.Binary guys think it's a feature, since they rely in
> this behavior (well, they rely on the equivalently-foolish behavior of
> toRational).  I think it's a bug.

You mean:

    instance Binary Double where
        put d = put (decodeFloat d)
        get   = liftM2 encodeFloat get get

?

if you've a portable Double decoding that works in GHC and Hugs, I'm
accepting patches.

-- Don
From droundy at darcs.net  Mon Jun 16 20:31:22 2008
From: droundy at darcs.net (David Roundy)
Date: Mon Jun 16 20:23:19 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080617000836.GC9848@scytale.galois.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
	<20080616235005.GC12977@sliver.repetae.net>
	<20080617000502.GZ32397@darcs.net>
	<20080617000836.GC9848@scytale.galois.com>
Message-ID: <20080617003121.GA32397@darcs.net>

On Mon, Jun 16, 2008 at 05:08:36PM -0700, Don Stewart wrote:
> droundy:
> > On Mon, Jun 16, 2008 at 04:50:05PM -0700, John Meacham wrote:
> > > On Mon, Jun 16, 2008 at 04:41:23PM -0700, Evan Laforge wrote:
> > > > But what about that NaN->Integer conversion thing?
> > > 
> > > I think that may be a bug or at least a misfeature. The standard is
> > > somewhat vauge on a lot of issues dealing with floating point since
> > > it is such a tricky subject and depends a lot on the environment. The
> > > various rounding funcitons are particularly ugly IMHO. I added varients
> > > of them that preserved the floating point type and properly implemented
> > > IEEE behavior for jhc.
> > 
> > I think the Data.Binary guys think it's a feature, since they rely in
> > this behavior (well, they rely on the equivalently-foolish behavior of
> > toRational).  I think it's a bug.
> 
> You mean:
> 
>     instance Binary Double where
>         put d = put (decodeFloat d)
>         get   = liftM2 encodeFloat get get
> 
> ?
> 
> if you've a portable Double decoding that works in GHC and Hugs, I'm
> accepting patches.

I really don't understand why being portable is such an issue.  Is it
really better to behave wrong on every platform rather than behaving
wrong on a very small minority of platforms?

Anyhow, I've not hacked on binary, because I've not used it, and have
trouble seeing when I would use it.  So maybe I shouldn't have brought
the subject up, except that this use of decodeFloat/encodeFloat is a
particularly egregious misuse of floating point numbers.  decodeFloat
really ought to be a partial function, and this should be a crashing
bug, if the standard libraries were better-written.

David
From dons at galois.com  Mon Jun 16 20:39:39 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun 16 20:31:44 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080617003121.GA32397@darcs.net>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
	<20080616235005.GC12977@sliver.repetae.net>
	<20080617000502.GZ32397@darcs.net>
	<20080617000836.GC9848@scytale.galois.com>
	<20080617003121.GA32397@darcs.net>
Message-ID: <20080617003939.GE9848@scytale.galois.com>

droundy:
> On Mon, Jun 16, 2008 at 05:08:36PM -0700, Don Stewart wrote:
> > droundy:
> > > On Mon, Jun 16, 2008 at 04:50:05PM -0700, John Meacham wrote:
> > > > On Mon, Jun 16, 2008 at 04:41:23PM -0700, Evan Laforge wrote:
> > > > > But what about that NaN->Integer conversion thing?
> > > > 
> > > > I think that may be a bug or at least a misfeature. The standard is
> > > > somewhat vauge on a lot of issues dealing with floating point since
> > > > it is such a tricky subject and depends a lot on the environment. The
> > > > various rounding funcitons are particularly ugly IMHO. I added varients
> > > > of them that preserved the floating point type and properly implemented
> > > > IEEE behavior for jhc.
> > > 
> > > I think the Data.Binary guys think it's a feature, since they rely in
> > > this behavior (well, they rely on the equivalently-foolish behavior of
> > > toRational).  I think it's a bug.
> > 
> > You mean:
> > 
> >     instance Binary Double where
> >         put d = put (decodeFloat d)
> >         get   = liftM2 encodeFloat get get
> > 
> > ?
> > 
> > if you've a portable Double decoding that works in GHC and Hugs, I'm
> > accepting patches.
> 
> I really don't understand why being portable is such an issue.  Is it
> really better to behave wrong on every platform rather than behaving
> wrong on a very small minority of platforms?

The Binary instances are required to be portable, as that's the part
of the definition of Binary's mandate: a portable binary encoding.
  
> Anyhow, I've not hacked on binary, because I've not used it, and have
> trouble seeing when I would use it.  So maybe I shouldn't have brought
> the subject up, except that this use of decodeFloat/encodeFloat is a
> particularly egregious misuse of floating point numbers.  

> decodeFloat
> really ought to be a partial function, and this should be a crashing
> bug, if the standard libraries were better-written.

It's a bug in the H98 report then:

    Section 6.4.6:

    "The function decodeFloat applied to a real floating-point number returns
    the significand expressed as an Integer and an appropriately scaled
    exponent (an Int). If decodeFloat x yields (m,n), then x is equal in value
    to mb^n, where b is the floating-point radix, and furthermore, either m
    and n are both zero or else b^d-1<=m<b^d, where d is the value of
    floatDigits x.  encodeFloat performs the inverse of this transformation.
    "

-- Don
From avatar at hot.ee  Mon Jun 16 20:50:16 2008
From: avatar at hot.ee (Misha Aizatulin)
Date: Mon Jun 16 20:43:09 2008
Subject: [Haskell-cafe] ANN: Haddock Trac
In-Reply-To: <bb52000e0806131507x6ad904e0n4aa27b9d978ba5b2@mail.gmail.com>
References: <bb52000e0806131507x6ad904e0n4aa27b9d978ba5b2@mail.gmail.com>
Message-ID: <48570A48.1060702@hot.ee>

hi,

   I wasn't able to add an attachment to a ticket, is something wrong 
with permissions?

Python Traceback

Traceback (most recent call last):
   File "/var/lib/python-support/python2.4/trac/web/main.py", line 387, 
in dispatch_request
     dispatcher.dispatch(req)
   File "/var/lib/python-support/python2.4/trac/web/main.py", line 237, 
in dispatch
     resp = chosen_handler.process_request(req)
   File "/var/lib/python-support/python2.4/trac/attachment.py", line 
361, in process_request
     self._do_save(req, attachment)
   File "/var/lib/python-support/python2.4/trac/attachment.py", line 
494, in _do_save
     attachment.insert(filename, upload.file, size)
   File "/var/lib/python-support/python2.4/trac/attachment.py", line 
180, in insert
     os.makedirs(self.path)
   File "os.py", line 156, in makedirs
     makedirs(head, mode)
   File "os.py", line 159, in makedirs
     mkdir(name, mode)
OSError: [Errno 13] Permission denied: 
'/srv/trac/haddock/attachments/ticket'

Cheers,
   Misha
From john at repetae.net  Mon Jun 16 21:11:27 2008
From: john at repetae.net (John Meacham)
Date: Mon Jun 16 21:03:22 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080617003939.GE9848@scytale.galois.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
	<20080616235005.GC12977@sliver.repetae.net>
	<20080617000502.GZ32397@darcs.net>
	<20080617000836.GC9848@scytale.galois.com>
	<20080617003121.GA32397@darcs.net>
	<20080617003939.GE9848@scytale.galois.com>
Message-ID: <20080617011126.GD12977@sliver.repetae.net>

On Mon, Jun 16, 2008 at 05:39:39PM -0700, Don Stewart wrote:
> It's a bug in the H98 report then:

Yes, I consider a whole lot of the floating point stuff in the report a
bug of sorts IMHO :) It is certainly something that I hope to work on for
Haskell'. 

        John

-- 
John Meacham - ?repetae.net?john?
From droundy at darcs.net  Mon Jun 16 21:32:19 2008
From: droundy at darcs.net (David Roundy)
Date: Mon Jun 16 21:24:15 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <20080617003939.GE9848@scytale.galois.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<20080616232826.GB12977@sliver.repetae.net>
	<2518b95d0806161641p72f7543cm72faf33b6b0700e4@mail.gmail.com>
	<20080616235005.GC12977@sliver.repetae.net>
	<20080617000502.GZ32397@darcs.net>
	<20080617000836.GC9848@scytale.galois.com>
	<20080617003121.GA32397@darcs.net>
	<20080617003939.GE9848@scytale.galois.com>
Message-ID: <20080617013219.GB32397@darcs.net>

On Mon, Jun 16, 2008 at 05:39:39PM -0700, Don Stewart wrote:
> > decodeFloat really ought to be a partial function, and this should
> > be a crashing bug, if the standard libraries were better-written.
> 
> It's a bug in the H98 report then:
> 
>     Section 6.4.6:
> 
>     "The function decodeFloat applied to a real floating-point number returns
>     the significand expressed as an Integer and an appropriately scaled
>     exponent (an Int). If decodeFloat x yields (m,n), then x is equal in value
>     to mb^n, where b is the floating-point radix, and furthermore, either m
>     and n are both zero or else b^d-1<=m<b^d, where d is the value of
>     floatDigits x.  encodeFloat performs the inverse of this transformation.
>     "

Yes, it is a bug in the report, that it doesn't fully specify the
behavior this function when given a NaN or infinity.  There's also a
bug in the standard libraries, which is that they don't conform to the
report.

let x = 0/0
let (m,n) = decodeFloat x
Prelude> (m,n)
(-6755399441055744,972)
Prelude> let x = 0/0
Prelude> x
NaN
Prelude> let d = floatDigits x
Prelude> let (m,n) = decodeFloat x
Prelude> let x' = (fromInteger m :: Double)*2^n
Prelude> x'
-Infinity
Prelude> 2^d-1<=m
False
Prelude> m<2^d
True

So for the ghc decodeFloat, when operating on a NaN, the
specifications of decodeFloat are almost completely unsatisfied.  On
the plus side, at least it's true that m<b^d, so that's one out of
three.  I suppose the problem is that quickcheck was developed only
after the standard was written...

David
From tom.davie at gmail.com  Mon Jun 16 21:36:44 2008
From: tom.davie at gmail.com (Thomas Davie)
Date: Mon Jun 16 21:28:47 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
Message-ID: <92E5131B-C13A-401E-BE76-1447A6E40FBF@gmail.com>


On 16 Jun 2008, at 19:24, Achim Schneider wrote:

> Thomas Davie <tom.davie@gmail.com> wrote:
>
>>
>> On 16 Jun 2008, at 18:28, Achim Schneider wrote:
>>
>>> Thomas Davie <tom.davie@gmail.com> wrote:
>>>
>>>>>
>>>>> One half of all Haskell coders will tell you that mutable state
>>>>> isn't a
>>>>> good starting point to learn Haskell, the other half will tell you
>>>>> the same because they want to be cool kids, too.
>>>>
>>>> And the one left over will point out that he asked how to do this
>>>> the FP way, not the imperative way?
>>>>
>>> There's no difference, as you can't do time-accounting non-strict
>>> and still expect it to give meaningful results: I'm merely trying
>>> to be helpful. None of the other solutions allow for the IO Monad.
>>
>> Firstly, I'd phrase that differently -- the IO Monad doesn't allow
>> for the other solutions -- the other solutions are the truly
>> functional ones.  Secondly, I'm curious as to why you think that the
>> two are incompatible, are you saying that for any meaningful kind of
>> computation we need to resort to IORefs?  I'd strongly contest that
>> idea.
>>
> We have to resort to IO actions to get the time, and to IORefs because
> we need to chain up different calls to getCurrentTime using the IO
> Monad. The rest of the program can work with whatever you like best.

And in what way is this incompatible with either FRP as pierre  
suggested, or with generating an infinite list of times at which we  
call the function, and scanning it to find the differences?

Bob

From allbery at ece.cmu.edu  Mon Jun 16 21:53:32 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Mon Jun 16 21:45:30 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <117f2cc80806161618x5c2a717bo551b8e4ff384633@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<117f2cc80806161618x5c2a717bo551b8e4ff384633@mail.gmail.com>
Message-ID: <CA0BFF19-BFE6-4F28-844C-FC765C5E5881@ece.cmu.edu>


On 2008 Jun 16, at 19:18, David Roundy wrote:

> On Mon, Jun 16, 2008 at 4:07 PM, Evan Laforge <qdunkan@gmail.com>  
> wrote:
>> Every other language throws an exception, even C will crash the
>> program, so I'm guessing it's telling the processor / OS to turn  
>> these
>> into signals, while GHC is turning that off.  Or something.  But then
>> what about this note in Control.Exception:
>
> That's just not true.  It depends on how your system (compiler?) is
> configured, but the default on most systems that I've used is to
> return NaNs.


It's how the system FPU is configured; most FPU hardware on Unixlike  
systems let you configure the FPU behavior on a per-process basis,  
although the amount of configurability may vary.

That said, the divide by zero exception you get in both C and Haskell  
is *integer* divide-by-zero.  Floating is mandated by IEEE standard to  
produce Inf (but as said above, can usually be configured).

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From ok at cs.otago.ac.nz  Mon Jun 16 21:54:46 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Mon Jun 16 21:46:46 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
Message-ID: <480BB455-0E66-4BFF-97D3-AF0A003FD3E7@cs.otago.ac.nz>


On 17 Jun 2008, at 11:07 am, Evan Laforge wrote:

> So, I know this has been discussed before, but:
>
>> 1/0
> Infinity
>> 0/0
> NaN
>
> ... so I see from the archives that Infinity is mandated by ieee754
> even though my intuition says both should be NaN.

Other people have other intuitions.  It may be that your intuition
is telling you that neither result should be an ordinary number,
and if that's what it's really telling you, it's right: the C
function isfinite(x) is true of all signed zero, subnormal, or
normal x, false of signed infinities and NaNs.

 > Every other language throws an exception, even C will crash the
> program,

Not true.  C99 *definitely* allows both infinities and NaNs (see
Annex F of the C99 standard) and C89 practice also allowed it.
Some C89 systems required you to use signal() with SIGFPE to
turn IEEE extended results into exceptions; others required you
to use signal() to disable this; others used yet other means.

The Scheme systems I tried turn (/ 1.0 0.0) into a printed
representation of IEEE infinity.  Of the Prolog systems I checked,
some did and some didn't.  The Standard ML system I tried gave
"inf" as the response to 1.0/0.0.

Basically, with any programming language implementation that
truthfully claims conformance to IEEE 754 or a successor standard,
x/0 MUST NOT crash unless your program explicitly asks for such
behaviour.  As for programming language implementations that do
not make such a claim, who knows what they will do?

Since integers do not have the special IEEE values, conversion
of IEEE values to integral values really ought to be checked.
(Of course, in C what you typically get is garbage, but that can
be put more generally...)


From qdunkan at gmail.com  Mon Jun 16 22:29:05 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Mon Jun 16 22:21:03 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <480BB455-0E66-4BFF-97D3-AF0A003FD3E7@cs.otago.ac.nz>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<480BB455-0E66-4BFF-97D3-AF0A003FD3E7@cs.otago.ac.nz>
Message-ID: <2518b95d0806161929n4532a948s6cf60a4d66c3b558@mail.gmail.com>

>> ... so I see from the archives that Infinity is mandated by ieee754
>> even though my intuition says both should be NaN.
>
> Other people have other intuitions.  It may be that your intuition
> is telling you that neither result should be an ordinary number,
> and if that's what it's really telling you, it's right: the C
> function isfinite(x) is true of all signed zero, subnormal, or
> normal x, false of signed infinities and NaNs.

Yeah, on reflection, I think my "intuition" derives from me asking a
math teacher back in high school "isn't n/0 infinity?" after looking
at a graph, to which he said "no, it's undefined, you can only say it
approaches infinity in the limit, but it isn't infinity".

>> Every other language throws an exception, even C will crash the
>>
>> program,
>
> Not true.  C99 *definitely* allows both infinities and NaNs (see
> Annex F of the C99 standard) and C89 practice also allowed it.
> Some C89 systems required you to use signal() with SIGFPE to
> turn IEEE extended results into exceptions; others required you
> to use signal() to disable this; others used yet other means.

Yes, I was mistaken here, as has been pointed out.

And I should definitely know better than to make some generalization
about "every other language" among this crowd :)

> (Of course, in C what you typically get is garbage, but that can
> be put more generally...)

Heh, one for the C-bashing quotes file...
From barsoap at web.de  Mon Jun 16 23:08:36 2008
From: barsoap at web.de (Achim Schneider)
Date: Mon Jun 16 23:00:43 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
References: <92E5131B-C13A-401E-BE76-1447A6E40FBF@gmail.com>
Message-ID: <20080617050836.408039cb@solaris>

Thomas Davie <tom.davie@gmail.com> wrote:

> 
> On 16 Jun 2008, at 19:24, Achim Schneider wrote:
> 
> > Thomas Davie <tom.davie@gmail.com> wrote:
> >
> >>
> >> On 16 Jun 2008, at 18:28, Achim Schneider wrote:
> >>
> >>> Thomas Davie <tom.davie@gmail.com> wrote:
> >>>
> >>>>>
> >>>>> One half of all Haskell coders will tell you that mutable state
> >>>>> isn't a
> >>>>> good starting point to learn Haskell, the other half will tell
> >>>>> you the same because they want to be cool kids, too.
> >>>>
> >>>> And the one left over will point out that he asked how to do this
> >>>> the FP way, not the imperative way?
> >>>>
> >>> There's no difference, as you can't do time-accounting non-strict
> >>> and still expect it to give meaningful results: I'm merely trying
> >>> to be helpful. None of the other solutions allow for the IO Monad.
> >>
> >> Firstly, I'd phrase that differently -- the IO Monad doesn't allow
> >> for the other solutions -- the other solutions are the truly
> >> functional ones.  Secondly, I'm curious as to why you think that
> >> the two are incompatible, are you saying that for any meaningful
> >> kind of computation we need to resort to IORefs?  I'd strongly
> >> contest that idea.
> >>
> > We have to resort to IO actions to get the time, and to IORefs
> > because we need to chain up different calls to getCurrentTime using
> > the IO Monad. The rest of the program can work with whatever you
> > like best.
> 
> And in what way is this incompatible with either FRP as pierre  
> suggested, or with generating an infinite list of times at which we  
> call the function, and scanning it to find the differences?
> 
Argh. I should not have copypasted that GLUT code, as it introduces
IORefs not because they're 100% necessary but because that code is
called back from C. My main point is that his task, if it is as simple
as he described it, will stay imperative. My point also depends on that
code being part of a main driver loop, as you see it in games: It's
just the thing I instantly recognised in his code.

Consider this:

update :: MyState -> Int -> MyState
draw :: MyState -> IO ()

mainLoop :: MyState -> Int -> IO ()
mainLoop st old = do
	now <- getTimeOfDay
	let td = now - old
	    st' = update st td
	draw st'
	mainLoop st' now

This, to my understanding of things, is imperative, although there's no
IORef to be found. OTOH, recursing like this is "the FP way" to do it.
mainLoop's arguments are variables to my eyes.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From ok at cs.otago.ac.nz  Mon Jun 16 23:20:43 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Mon Jun 16 23:12:46 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <2518b95d0806161929n4532a948s6cf60a4d66c3b558@mail.gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<480BB455-0E66-4BFF-97D3-AF0A003FD3E7@cs.otago.ac.nz>
	<2518b95d0806161929n4532a948s6cf60a4d66c3b558@mail.gmail.com>
Message-ID: <C88E4CC5-E821-4032-8289-2AD1A94B8020@cs.otago.ac.nz>

Since Haskell-Caf? often strays into mathematics,
this may not be too far off topic.

On 17 Jun 2008, at 2:29 pm, Evan Laforge wrote:
> Yeah, on reflection, I think my "intuition" derives from me asking a
> math teacher back in high school "isn't n/0 infinity?" after looking
> at a graph, to which he said "no, it's undefined, you can only say it
> approaches infinity in the limit, but it isn't infinity".

Let's put this kindly:  it is POSSIBLE that your maths teacher knew
what he was talking about and was just telling what the "Science of
Discworld" authors call "lies-to-children".  It is certainly likely
that it didn't occur to him that you might transfer what he said
about the mathematical real numbers to a rather different algebraic
system, IEEE floats.

The usual "real numbers" R form an ordered field.
*In that structure*, n/0 is undefined.
But there is another algebraic structure which includes all
the real numbers plus one more: infinity.
It's call the real projective line.
See http://en.wikipedia.org/wiki/Real_projective_line
In that structure, n/0 is perfectly well defined, and is indeed
infinity.  That structure has all the properties you really need
to do calculus, but isn't a field and isn't ordered.  However,
whenever an operation on elements of R is defined, the
analogous operation on the corresponding elements of \hat R is
defined and has the corresponding value.

Basically, you can define operations any way you want as long as
you are willing to live with the consequences.  For example, it
turns out to be possible to define an alternative arithmetic in
which (-x)*(-y) = -(x*y) for positive x, y.  The price is that
it doesn't satisfy all the usual axioms, though it does satisfy
other possibly useful ones that the usual systems don't.

In an analogous way, the IEEE designers decided that it would be
useful to have +/- epsilon instead of 0 and +/- (1/epsilon)
instead of infinity, but then decided that the ordering operations
should identify -epsilon with +epsilon, so the result still isn't
quite a proper total order, even ignoring NaNs.  (What happens if
you sort a list of mixed +0.0 and -0.0?  What, if anything,
_should_ happen?)  They obtained the benefits they wanted, at the
price of making the resulting structure less like R.  But then,
floating point numbers never were _very_ much like R to start with.
It's not clear to me that *R offers anything more than a heuristic
analogy to IEEE arithmetic.  For one thing, *R is ordered.

From magicloud.magiclouds at gmail.com  Mon Jun 16 23:40:04 2008
From: magicloud.magiclouds at gmail.com (Magicloud)
Date: Mon Jun 16 23:32:05 2008
Subject: =?gb2312?B?tPC4tDogW0hhc2tlbGwtY2FmZV0gUmU6IEhvdyB0byBkbyB0aGlzIA==?=
	=?gb2312?B?aW4gRlAgd2F5Pw==?=
In-Reply-To: <20080616060033.396f1e5c@solaris>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
Message-ID: <48573218.034c6e0a.18f9.ffffabe5@mx.google.com>

Yes, that's it, State.
Thanks.

-----=D3=CA=BC=FE=D4=AD=BC=FE-----
=B7=A2=BC=FE=C8=CB: haskell-cafe-bounces@haskell.org
[mailto:haskell-cafe-bounces@haskell.org] =B4=FA=B1=ED Achim Schneider
=B7=A2=CB=CD=CA=B1=BC=E4: 2008=C4=EA6=D4=C216=C8=D5 12:01
=CA=D5=BC=FE=C8=CB: haskell-cafe@haskell.org
=D6=F7=CC=E2: [Haskell-cafe] Re: How to do this in FP way?

"Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> wrote:

> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret =3D now - old;
>   old =3D now;
>   return ret;
> }
>
You do it with variables, of course. This is out of some GLUT code,
using IORef's:

idle :: State -> IdleCallback
idle state =3D do
    t0 <- get $ t state
    t1 <- get elapsedTime
    t state $=3D t1
    let td =3D fromIntegral t1 - fromIntegral t0
    fps state $=3D 1/td * 1000

    angle' state $~! (+2)
   =20
    (bpx, bpy) <- get $ ballPos state
    (bvx, bvy) <- get $ ballVel state
   =20
    ballPos state $=3D (bpx + bvx*td, bpy + bvy*td)  =20
    postRedisplay Nothing

One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.=20

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From magicloud.magiclouds at gmail.com  Mon Jun 16 23:43:04 2008
From: magicloud.magiclouds at gmail.com (Magicloud)
Date: Mon Jun 16 23:35:05 2008
Subject: =?gb2312?B?tPC4tDogW0hhc2tlbGwtY2FmZV0gUmU6IEhvdyB0byBkbyB0aGlzIA==?=
	=?gb2312?B?aW4gRlAgd2F5Pw==?=
In-Reply-To: <20080616060033.396f1e5c@solaris>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
Message-ID: <485732cb.05886e0a.0bdb.ffff9a4e@mx.google.com>

I think if I do not use a state, and the function would be called for =
many
times, it would waste memory, if using something like loop, right?

-----=D3=CA=BC=FE=D4=AD=BC=FE-----
=B7=A2=BC=FE=C8=CB: haskell-cafe-bounces@haskell.org
[mailto:haskell-cafe-bounces@haskell.org] =B4=FA=B1=ED Achim Schneider
=B7=A2=CB=CD=CA=B1=BC=E4: 2008=C4=EA6=D4=C216=C8=D5 12:01
=CA=D5=BC=FE=C8=CB: haskell-cafe@haskell.org
=D6=F7=CC=E2: [Haskell-cafe] Re: How to do this in FP way?

"Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> wrote:

> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret =3D now - old;
>   old =3D now;
>   return ret;
> }
>
You do it with variables, of course. This is out of some GLUT code,
using IORef's:

idle :: State -> IdleCallback
idle state =3D do
    t0 <- get $ t state
    t1 <- get elapsedTime
    t state $=3D t1
    let td =3D fromIntegral t1 - fromIntegral t0
    fps state $=3D 1/td * 1000

    angle' state $~! (+2)
   =20
    (bpx, bpy) <- get $ ballPos state
    (bvx, bvy) <- get $ ballVel state
   =20
    ballPos state $=3D (bpx + bvx*td, bpy + bvy*td)  =20
    postRedisplay Nothing

One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.=20

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From barsoap at web.de  Mon Jun 16 23:48:54 2008
From: barsoap at web.de (Achim Schneider)
Date: Mon Jun 16 23:41:00 2008
Subject: [Haskell-cafe] Re: How to do this in FP way?
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
	<485732cb.05886e0a.0bdb.ffff9a4e@mx.google.com>
Message-ID: <20080617054854.47a5f8b6@solaris>

"Magicloud" <magicloud.magiclouds@gmail.com> wrote:

> I think if I do not use a state, and the function would be called for
> many times, it would waste memory, if using something like loop,
> right?
> 
nope, at least not in general.

update :: MyState -> Int -> MyState
draw :: MyState -> IO ()

mainLoop :: MyState -> Int -> IO ()
mainLoop st old = do
	now <- getTimeOfDay
	let td = now - old
	    st' = update st td
	draw st'
	mainLoop st' now

runs in constant space. Look up "tail recursion" in wikipedia.

> -----????-----
> ???: haskell-cafe-bounces@haskell.org
> [mailto:haskell-cafe-bounces@haskell.org] ?? Achim Schneider
> ????: 2008?6?16? 12:01
> ???: haskell-cafe@haskell.org
> ??: [Haskell-cafe] Re: How to do this in FP way?
> 
> "Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> wrote:
> 
> > static int old;
> > int diff (int now) { /* this would be called once a second */
> >   int ret = now - old;
> >   old = now;
> >   return ret;
> > }
> >
> You do it with variables, of course. This is out of some GLUT code,
> using IORef's:
> 
> idle :: State -> IdleCallback
> idle state = do
>     t0 <- get $ t state
>     t1 <- get elapsedTime
>     t state $= t1
>     let td = fromIntegral t1 - fromIntegral t0
>     fps state $= 1/td * 1000
> 
>     angle' state $~! (+2)
>     
>     (bpx, bpy) <- get $ ballPos state
>     (bvx, bvy) <- get $ ballVel state
>     
>     ballPos state $= (bpx + bvx*td, bpy + bvy*td)   
>     postRedisplay Nothing
> 
> One half of all Haskell coders will tell you that mutable state isn't
> a good starting point to learn Haskell, the other half will tell you
> the same because they want to be cool kids, too. 
> 


-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From magicloud.magiclouds at gmail.com  Mon Jun 16 23:52:35 2008
From: magicloud.magiclouds at gmail.com (Magicloud)
Date: Mon Jun 16 23:44:36 2008
Subject: =?gb2312?B?tPC4tDogW0hhc2tlbGwtY2FmZV0gUmU6IEhvdyB0byBkbyB0aGlzIA==?=
	=?gb2312?B?aW4gRlAgd2F5Pw==?=
In-Reply-To: <20080616060033.396f1e5c@solaris>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<20080616060033.396f1e5c@solaris>
Message-ID: <48573506.0e1b6e0a.7c01.7e87@mx.google.com>

But if there are some beautiful arithmetics that do not use something =
like
state, I won't say no to them.

-----=D3=CA=BC=FE=D4=AD=BC=FE-----
=B7=A2=BC=FE=C8=CB: haskell-cafe-bounces@haskell.org
[mailto:haskell-cafe-bounces@haskell.org] =B4=FA=B1=ED Achim Schneider
=B7=A2=CB=CD=CA=B1=BC=E4: 2008=C4=EA6=D4=C216=C8=D5 12:01
=CA=D5=BC=FE=C8=CB: haskell-cafe@haskell.org
=D6=F7=CC=E2: [Haskell-cafe] Re: How to do this in FP way?

"Magicloud Magiclouds" <magicloud.magiclouds@gmail.com> wrote:

> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret =3D now - old;
>   old =3D now;
>   return ret;
> }
>
You do it with variables, of course. This is out of some GLUT code,
using IORef's:

idle :: State -> IdleCallback
idle state =3D do
    t0 <- get $ t state
    t1 <- get elapsedTime
    t state $=3D t1
    let td =3D fromIntegral t1 - fromIntegral t0
    fps state $=3D 1/td * 1000

    angle' state $~! (+2)
   =20
    (bpx, bpy) <- get $ ballPos state
    (bvx, bvy) <- get $ ballVel state
   =20
    ballPos state $=3D (bpx + bvx*td, bpy + bvy*td)  =20
    postRedisplay Nothing

One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.=20

--=20
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past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited.=20

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From magicloud.magiclouds at gmail.com  Tue Jun 17 01:03:06 2008
From: magicloud.magiclouds at gmail.com (Magicloud)
Date: Tue Jun 17 00:55:10 2008
Subject: =?gb2312?B?tPC4tDogW0hhc2tlbGwtY2FmZV0gSG93IHRvIGRvIHRoaXMgaW4gRlAgd2E=?=
	=?gb2312?B?eT8=?=
In-Reply-To: <117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
Message-ID: <48574590.034c6e0a.18fd.ffffb68d@mx.google.com>

OK. Here it is.
I want to make a monitor tool for linux. It runs for a long time, and =
give
out a certain process's io stat per second. The way I get io stat is to =
read
from /proc/pid/io. But the data in this file is a total, I need to read =
it
first, then next second, read it again, and shows the difference, and go =
on.
So, what is your idea?

-----=D3=CA=BC=FE=D4=AD=BC=FE-----
=B7=A2=BC=FE=C8=CB: David Roundy [mailto:daveroundy@gmail.com]=20
=B7=A2=CB=CD=CA=B1=BC=E4: 2008=C4=EA6=D4=C217=C8=D5 1:17
=CA=D5=BC=FE=C8=CB: Magicloud Magiclouds
=B3=AD=CB=CD: haskell-cafe@haskell.org
=D6=F7=CC=E2: Re: [Haskell-cafe] How to do this in FP way?

2008/6/15 Magicloud Magiclouds <magicloud.magiclouds@gmail.com>:
> Hello,
>     I am getting familiar with FP now, and I have a "program design" =
kind
of
> question.
>     Say I have something like this in C:
> static int old;
> int diff (int now) { /* this would be called once a second */
>   int ret =3D now - old;
>   old =3D now;
>   return ret;
> }
>     Because there is no "variable" in Haskell. So how to do this in a =
FP
> way?

A better question would be to think about what you are trying to
accomplish, and then ask how to achieve that through functional
programming.

David

From valgarv at gmx.net  Tue Jun 17 01:51:22 2008
From: valgarv at gmx.net (Ariel J. Birnbaum)
Date: Tue Jun 17 01:43:20 2008
Subject: [Haskell-cafe] ANN: Topkata
In-Reply-To: <4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
Message-ID: <200806170851.22718.valgarv@gmx.net>

> In the mean time -- who knows enough to make ghc target ARM, and get
> this to link against the iPhone libraries?  This would be quite a coup
> if it could be made to run there!
For that matter, there's another ARM-based target in which I'm interested: 
Nintendo DS. Has anyone got any Haskell code to run on one of these?
PS: Maybe this discussion should be moved to a new "Haskell on ARM" thread?
-- 
Ariel J. Birnbaum
From lemming at henning-thielemann.de  Tue Jun 17 02:01:42 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue Jun 17 01:53:38 2008
Subject: [Haskell-cafe] 1/0
In-Reply-To: <200806161945.30976.dan.doel@gmail.com>
References: <2518b95d0806161607p207c20b1rcf083488d246efc5@mail.gmail.com>
	<200806161945.30976.dan.doel@gmail.com>
Message-ID: <Pine.LNX.4.64.0806170751170.28393@anubis.informatik.uni-halle.de>


On Mon, 16 Jun 2008, Dan Doel wrote:

> On Monday 16 June 2008, Evan Laforge wrote:
>
>> (huge negative number)
>>
>> Ok, so integral types don't have that exceptional value.  Shouldn't
>> trying to convert NaN or Infinity to an Integral throw something?  Is
>> it a performance thing?  I'd think if you're converting to Integer you
>> don't really need hardware level performance anyway, so a couple of
>> checks wouldn't kill anyone.
>
> This is a (known by some) bug of sorts in the various floating point ->
> integral transformations (which ultimately boil down to decodeFloat or
> something like that at some point). It apparently doesn't know about the
> various exceptional values in the IEEE representation, so it just treats the
> representation like any other value. Infinity and NaN look like various huge
> numbers if you interpret them like any other value, so that's what you get
> out of round/ceiling/floor/etc.
>
> It's not ideal, but I guess no one's bothered to fix it. Might be something to
> bring up on the libraries mailing list.

This could be combined with improving performance:
    http://hackage.haskell.org/trac/ghc/ticket/2281
    http://hackage.haskell.org/trac/ghc/ticket/2271
    http://hackage.haskell.org/trac/ghc/ticket/1434
From ndmitchell at gmail.com  Tue Jun 17 02:55:51 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Tue Jun 17 02:47:47 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
In-Reply-To: <117f2cc80806161612oe3f2033q187cbf5c22592f03@mail.gmail.com>
References: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
	<117f2cc80806161612oe3f2033q187cbf5c22592f03@mail.gmail.com>
Message-ID: <404396ef0806162355m1bf083f2pcebdbfa64e17e42b@mail.gmail.com>

Hi,

Derek: Yes, I was slowly coming round to the idea of the third option.
It does mean that if you want to change the deferredness of a field,
you have to change the type, which is a substantial alteration.


David:
> Is there any reason not to just write all lazy fields of variable size
>  in a deferred manner?

I completely hadn't though of this! You will loose a bit of time, for
example reading fields which were previously not deferred will require
a file seek, but the effort/thought/efficiency trade-off is good. I
think I will go with this.

Thanks

Neil
From hpacheco at gmail.com  Tue Jun 17 05:53:49 2008
From: hpacheco at gmail.com (Hugo Pacheco)
Date: Tue Jun 17 05:45:47 2008
Subject: [Haskell-cafe] Polymorphic QuickCheck arguments
Message-ID: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>

Hi all,
There is something about polymorphic tests in QuickCheck that I do not
understand.

If you write the simplest dummy test function

tst :: a -> Bool
tst _ = True

and evaluate it we get

> verboseCheck tst
0:
()
1:
()
...

How come did the polymorphic value a get instanciated to ()? Is this done
via the Testable type class?
Could someone please explain this to me? I'm not saying it does not make
sense, but I would like to understand how it works. Being possible to change
this behavior, this is, assign another "default type" whenever polymorphic
types occur, would be awesome.

Cheers,
hugo

-- 
www.di.uminho.pt/~hpacheco
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From dougal at dougalstanton.net  Tue Jun 17 06:05:01 2008
From: dougal at dougalstanton.net (Dougal Stanton)
Date: Tue Jun 17 05:57:08 2008
Subject: [Haskell-cafe] Polymorphic QuickCheck arguments
In-Reply-To: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>
References: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>
Message-ID: <2d3641330806170305s7a062031lf9672cd595648b29@mail.gmail.com>

2008/6/17 Hugo Pacheco <hpacheco@gmail.com>:
> Hi all,
> There is something about polymorphic tests in QuickCheck that I do not
> understand.
> If you write the simplest dummy test function
> tst :: a -> Bool
> tst _ = True
> and evaluate it we get
>> verboseCheck tst
> 0:
> ()
> 1:
> ()
> ...
> How come did the polymorphic value a get instanciated to ()? Is this done
> via the Testable type class?

I haven't got something here to check with, but from the formatting it
looks like every odd line is a randomly-chosen boolean value, and the
following line is the result? It might be just printing the result
value of IO (). Maybe try a more complete test to see how that looks?

Cheers,

D


-- 
Dougal Stanton
dougal@dougalstanton.net // http://www.dougalstanton.net
From hpacheco at gmail.com  Tue Jun 17 06:13:35 2008
From: hpacheco at gmail.com (Hugo Pacheco)
Date: Tue Jun 17 06:05:31 2008
Subject: [Haskell-cafe] Polymorphic QuickCheck arguments
In-Reply-To: <2d3641330806170305s7a062031lf9672cd595648b29@mail.gmail.com>
References: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>
	<2d3641330806170305s7a062031lf9672cd595648b29@mail.gmail.com>
Message-ID: <7b92c2840806170313j4df02951u6670370ec61ea210@mail.gmail.com>

It does not seem like printing the result value from IO (), because with a
more complicated example for lists.
t :: [a] -> Bool
t x = True

then it randomly generates values of type [()].

*Quick> verboseCheck t
0:
[]
1:
[()]
2:
[(),(),()]
3:
[]
4:
[()]
5:
[(),(),(),()]

I just wonder how the a got instantiated to ().

Thanks,
hugo


On Tue, Jun 17, 2008 at 11:05 AM, Dougal Stanton <dougal@dougalstanton.net>
wrote:

> 2008/6/17 Hugo Pacheco <hpacheco@gmail.com>:
> > Hi all,
> > There is something about polymorphic tests in QuickCheck that I do not
> > understand.
> > If you write the simplest dummy test function
> > tst :: a -> Bool
> > tst _ = True
> > and evaluate it we get
> >> verboseCheck tst
> > 0:
> > ()
> > 1:
> > ()
> > ...
> > How come did the polymorphic value a get instanciated to ()? Is this done
> > via the Testable type class?
>
> I haven't got something here to check with, but from the formatting it
> looks like every odd line is a randomly-chosen boolean value, and the
> following line is the result? It might be just printing the result
> value of IO (). Maybe try a more complete test to see how that looks?
>
> Cheers,
>
> D
>
>
> --
> Dougal Stanton
> dougal@dougalstanton.net // http://www.dougalstanton.net
>



-- 
www.di.uminho.pt/~hpacheco
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From sfvisser at cs.uu.nl  Tue Jun 17 07:17:07 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Tue Jun 17 07:09:14 2008
Subject: [Haskell-cafe] Polymorphic QuickCheck arguments
In-Reply-To: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>
References: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>
Message-ID: <2A22B918-BD68-4C0E-97D8-FACDC33CF6AD@cs.uu.nl>

On Jun 17, 2008, at 11:53 AM, Hugo Pacheco wrote:
> Hi all,
>
> There is something about polymorphic tests in QuickCheck that I do  
> not understand.
>
> If you write the simplest dummy test function
>
> tst :: a -> Bool
> tst _ = True
>
> and evaluate it we get
>
> > verboseCheck tst
> 0:
> ()
> 1:
> ()
> ...


> How come did the polymorphic value a get instanciated to ()? Is  
> this done via the Testable type class?
> Could someone please explain this to me? I'm not saying it does not  
> make sense, but I would like to understand how it works. Being  
> possible to change this behavior, this is, assign another "default  
> type" whenever polymorphic types occur, would be awesome.

I think it is GHCi that is instantiating the type with (). Try  
compiling the program, it will probably be rejected by the compiler  
when you do not specify a concrete type.

You can, for example, try this:

verboseCheck (tst :: [Int] -> Bool)

> Cheers,
> hugo
From xj2106 at columbia.edu  Tue Jun 17 08:09:29 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Tue Jun 17 08:07:12 2008
Subject: Haskell on ARM (was Re: [Haskell-cafe] ANN: Topkata)
In-Reply-To: <200806170851.22718.valgarv@gmx.net> (Ariel J. Birnbaum's message
	of "Tue, 17 Jun 2008 08:51:22 +0300")
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
Message-ID: <87ej6ww9dy.fsf_-_@columbia.edu>

"Ariel J. Birnbaum" <valgarv@gmx.net> writes:

>> In the mean time -- who knows enough to make ghc target
>> ARM, and get this to link against the iPhone libraries?
>> This would be quite a coup if it could be made to run
>> there!
> For that matter, there's another ARM-based target in which
> I'm interested: Nintendo DS. Has anyone got any Haskell
> code to run on one of these?  PS: Maybe this discussion
> should be moved to a new "Haskell on ARM" thread?

I would be interested to see ghc running on Nokia n8xx or
iRex iliad.  Both of them are quite open linux based
systems.
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From silva.samuel at gmail.com  Tue Jun 17 08:19:47 2008
From: silva.samuel at gmail.com (Samuel Silva)
Date: Tue Jun 17 08:11:41 2008
Subject: [Haskell-cafe] Compiling large code with old machine
Message-ID: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>

Hello

I'm using GHC to compile around 700K of Haskell Code generated by HaXml.
How I compile this code.
My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.

How much time it spend to compile this file?
I spent more than 1 hour and it doesn't finished.

What flags make compiling fast?
I try with -H500m but dont't expect.

It is possible GHC running endless cycle at compilation stage?

Thanks.

-- 
Don't hug that, Hugs ME!
Samuel Silva
From bulat.ziganshin at gmail.com  Tue Jun 17 08:27:50 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Tue Jun 17 08:20:22 2008
Subject: [Haskell-cafe] Compiling large code with old machine
In-Reply-To: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
Message-ID: <469977410.20080617162750@gmail.com>

Hello Samuel,

Tuesday, June 17, 2008, 4:19:47 PM, you wrote:

> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.
> What flags make compiling fast?
> I try with -H500m but dont't expect.

bad idea since OS needs memory too. -H400m would be much better



-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From aneumann at inf.fu-berlin.de  Tue Jun 17 10:23:27 2008
From: aneumann at inf.fu-berlin.de (Adrian Neumann)
Date: Tue Jun 17 10:15:37 2008
Subject: [Haskell-cafe] Compiling large code with old machine
In-Reply-To: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
Message-ID: <ADEC13C8-D1DF-4627-AA8D-D27675AEF2CB@inf.fu-berlin.de>

I would assume -O0, that is, turning off all optimizations, should  
make compilation faster

Adrian

Am 17.06.2008 um 14:19 schrieb Samuel Silva:

> Hello
>
> I'm using GHC to compile around 700K of Haskell Code generated by  
> HaXml.
> How I compile this code.
> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.
>
> How much time it spend to compile this file?
> I spent more than 1 hour and it doesn't finished.
>
> What flags make compiling fast?
> I try with -H500m but dont't expect.
>
> It is possible GHC running endless cycle at compilation stage?
>
> Thanks.
>
> -- 
> Don't hug that, Hugs ME!
> Samuel Silva
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

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From hoknamahn at gmail.com  Tue Jun 17 11:04:11 2008
From: hoknamahn at gmail.com (Olex P)
Date: Tue Jun 17 10:56:07 2008
Subject: [Haskell-cafe] Suggestion for implementation of vector library
Message-ID: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>

Hi guys,

Sorry for a silly questions but I didn't find a proper answer in Google.
I've started to learn Haskell and would like to implement a library for work
with vectors. I found different implementations of this stuff but all of
them made just for fun in a short as possible terms using lists or tuples. I
suppose there should be a better way to go. First idea came to my mind was
using of classes. Something like this:

[code]
-- Template Vector class

class Vector v where
    (<+>)     :: v -> v -> v
    (<->)     :: v -> v -> v
    (<*>)    :: v -> v -> v
    (*>)    :: v -> Float -> v
    -- other methods here

-- Vector3 instance

-- Declare new Vector3 type

data Vector3 = Vector3 (Float, Float, Float)

instance Vector Vector3 where
    (<+>) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 + x2,
y1 + y2, z1 + z2)
    (<->) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 - x2,
y1 - y2, z1 - z2)
    (<*>) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 * x2,
y1 * y2, z1 * z2)
    (*>) (Vector3 (x, y, z)) f = Vector3 (x * f, y * f, z * f)
    length (Vector3 (x, y, z)) = sqrt (x * x + y * y + z * z)
    -- the rest of methods
[/code]

What I don't like here is using of data type constructors when even simple
expression like v1 + v2 becomes too long (<+>) (Vector3 (1,2,3)) (Vector3
(4,5,6))
Do I really need a data type constructor (in this particular case)? Or
better to declare a vector3 type as: type Vector3 = (Float, Float, Float)?
Next question is how to make one instance which derives from several
classes? For example from Eq, Num and Vector (if I want to overload +, -, <,
>, == etc.)
Is it good idea to use classes and ad hoc polymorphism or better to use
parametric polymorphism? How you would implement such library? (not just for
educational purposes but for development of _very_good_extensible_ software)

Thank you,
Alex.
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From john at repetae.net  Tue Jun 17 11:24:58 2008
From: john at repetae.net (John Meacham)
Date: Tue Jun 17 11:16:51 2008
Subject: [Haskell-cafe] Suggestion for implementation of vector library
In-Reply-To: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
References: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
Message-ID: <20080617152458.GE12977@sliver.repetae.net>

On Tue, Jun 17, 2008 at 04:04:11PM +0100, Olex P wrote:
> Hi guys,
> 
> Sorry for a silly questions but I didn't find a proper answer in Google.
> I've started to learn Haskell and would like to implement a library for work
> with vectors. I found different implementations of this stuff but all of
> them made just for fun in a short as possible terms using lists or tuples. I
> suppose there should be a better way to go. First idea came to my mind was
> using of classes. Something like this:
> 
> [code]
> -- Template Vector class
> 
> class Vector v where
>     (<+>)     :: v -> v -> v
>     (<->)     :: v -> v -> v
>     (<*>)    :: v -> v -> v
>     (*>)    :: v -> Float -> v
>     -- other methods here
> 
> -- Vector3 instance
> 
> -- Declare new Vector3 type
> 
> data Vector3 = Vector3 (Float, Float, Float)
> 
> instance Vector Vector3 where
>     (<+>) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 + x2,
> y1 + y2, z1 + z2)
>     (<->) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 - x2,
> y1 - y2, z1 - z2)
>     (<*>) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 * x2,
> y1 * y2, z1 * z2)
>     (*>) (Vector3 (x, y, z)) f = Vector3 (x * f, y * f, z * f)
>     length (Vector3 (x, y, z)) = sqrt (x * x + y * y + z * z)
>     -- the rest of methods
> [/code]
> 
> What I don't like here is using of data type constructors when even simple
> expression like v1 + v2 becomes too long (<+>) (Vector3 (1,2,3)) (Vector3
> (4,5,6))
> Do I really need a data type constructor (in this particular case)? Or
> better to declare a vector3 type as: type Vector3 = (Float, Float, Float)?
> Next question is how to make one instance which derives from several
> classes? For example from Eq, Num and Vector (if I want to overload +, -, <,
> >, == etc.)
> Is it good idea to use classes and ad hoc polymorphism or better to use
> parametric polymorphism? How you would implement such library? (not just for
> educational purposes but for development of _very_good_extensible_ software)

Well, The type I would use for Vector3 is

data Vector3 = Vector3 !Float !Float !Float

That will give you 3 strict (and perhaps unboxed) floats and reduce your
need for parenthesis. In general, real types (declared with data or
newtype) are a good idea, they often allow compiler optimizations, make
your code more robust, and provide nice abstraction capabilities. The
'newtype deriving' extension is particularly useful.

You can also create helper functions like

v3 = Vector3

so you can do (v3 1 2 3 <+> v3 4 5 6)

        John        



-- 
John Meacham - ?repetae.net?john?
From dons at galois.com  Tue Jun 17 11:40:32 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 17 11:32:28 2008
Subject: [Haskell-cafe] Suggestion for implementation of vector library
In-Reply-To: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
References: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
Message-ID: <20080617154032.GB18127@scytale.galois.com>

hoknamahn:
>    Hi guys,
> 
>    Sorry for a silly questions but I didn't find a proper answer in Google.
>    I've started to learn Haskell and would like to implement a library for
>    work with vectors. I found different implementations of this stuff but all
>    of them made just for fun in a short as possible terms using lists or

The main serious implementation is probably hmatrix, blas or
numeric-prelude

    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix
    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas
    http://hackage.haskell.org/cgi-bin/hackage-scripts/package/numeric-prelude

>    tuples. I suppose there should be a better way to go. First idea came to
>    my mind was using of classes. Something like this:
> 
>    data Vector3 = Vector3 (Float, Float, Float)

data Vector3 =
        Vector3 {-# UNPACK #-} !Double
                {-# UNPACK #-} !Double
                {-# UNPACK #-} !Double

Compile with -O2 -fvia-C -optc-O2 and keep them in registers.

-- Don
From dons at galois.com  Tue Jun 17 11:48:58 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 17 11:41:41 2008
Subject: =?utf-8?B?562U5aSN?=
	=?utf-8?Q?=3A?= [Haskell-cafe] How to do this in FP way?
In-Reply-To: <48574590.034c6e0a.18fd.ffffb68d@mx.google.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
	<48574590.034c6e0a.18fd.ffffb68d@mx.google.com>
Message-ID: <20080617154858.GC18127@scytale.galois.com>

magicloud.magiclouds:
> OK. Here it is.
> I want to make a monitor tool for linux. It runs for a long time, and give
> out a certain process's io stat per second. The way I get io stat is to read
> from /proc/pid/io. But the data in this file is a total, I need to read it
> first, then next second, read it again, and shows the difference, and go on.
> So, what is your idea?

Easy,

    import Control.Concurrent
    import Control.Monad

    main = go 0
        where
            go st = forever $ do
                       n <- read `fmap` readFile "/proc/pid/io"
                       print (n - st) -- display difference
                       threadDelay (10^6)

-- Don
From dons at galois.com  Tue Jun 17 11:56:31 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 17 11:48:30 2008
Subject: =?utf-8?B?562U5aSN?=
	=?utf-8?Q?=3A?= [Haskell-cafe] How to do this in FP way?
In-Reply-To: <20080617154858.GC18127@scytale.galois.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
	<48574590.034c6e0a.18fd.ffffb68d@mx.google.com>
	<20080617154858.GC18127@scytale.galois.com>
Message-ID: <20080617155631.GD18127@scytale.galois.com>

dons:
> magicloud.magiclouds:
> > OK. Here it is.
> > I want to make a monitor tool for linux. It runs for a long time, and give
> > out a certain process's io stat per second. The way I get io stat is to read
> > from /proc/pid/io. But the data in this file is a total, I need to read it
> > first, then next second, read it again, and shows the difference, and go on.
> > So, what is your idea?
> 
> Easy,
> 
>     import Control.Concurrent
>     import Control.Monad
> 
>     main = go 0
>         where
>             go st = forever $ do
>                        n <- read `fmap` readFile "/proc/pid/io"
>                        print (n - st) -- display difference
>                        threadDelay (10^6)

Oops, not 'forever' :)

              go st = do
                    ...
                    go n
From karoly at negyesi.net  Tue Jun 17 12:45:09 2008
From: karoly at negyesi.net (Karoly Negyesi)
Date: Tue Jun 17 12:37:15 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
Message-ID: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>

Hi,

The PHP community is discussing the adding of closures and lambdas to
the language, see the proposal at http://wiki.php.net/rfc/closures

If someone with knowledge of both languages could take a quick look it
would be great.

Thanks a lot

Karoly Negyesi

Ps. I am not a member of the PHP internals team, I am just a PHP
developer but I am very very interested in getting these in my
favourite language.
From lemming at henning-thielemann.de  Tue Jun 17 11:30:34 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue Jun 17 13:25:52 2008
Subject: [Haskell-cafe] Suggestion for implementation of vector library
In-Reply-To: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
References: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806171728400.18714@anubis.informatik.uni-halle.de>


On Tue, 17 Jun 2008, Olex P wrote:

> Hi guys,
>
> Sorry for a silly questions but I didn't find a proper answer in Google.
> I've started to learn Haskell and would like to implement a library for work
> with vectors.

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vector-space
From prstanley at ntlworld.com  Tue Jun 17 13:46:51 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Tue Jun 17 13:38:46 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.co
 m>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
Message-ID: <20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>

Blimey! Talk about rearranging the deckchairs :-)
With respect, do you not think it'd be wiser for the community to 
deal with a total lack of proper type checking, the lack of any 
notion of the general concept of a function, or a whole range of 
other fundamental issues in PHP first before worrying about closures 
and lambda functions?  I'm no language purist but PHP really does 
take the biscuit.
My personal views and not in any way representing the list .
Paul

At 17:45 17/06/2008, you wrote:
>Hi,
>
>The PHP community is discussing the adding of closures and lambdas to
>the language, see the proposal at http://wiki.php.net/rfc/closures
>
>If someone with knowledge of both languages could take a quick look it
>would be great.
>
>Thanks a lot
>
>Karoly Negyesi
>
>Ps. I am not a member of the PHP internals team, I am just a PHP
>developer but I am very very interested in getting these in my
>favourite language.
>_______________________________________________
>Haskell-Cafe mailing list
>Haskell-Cafe@haskell.org
>http://www.haskell.org/mailman/listinfo/haskell-cafe

From hoknamahn at gmail.com  Tue Jun 17 13:50:25 2008
From: hoknamahn at gmail.com (Olex P)
Date: Tue Jun 17 13:42:31 2008
Subject: [Haskell-cafe] Suggestion for implementation of vector library
In-Reply-To: <Pine.LNX.4.64.0806171728400.18714@anubis.informatik.uni-halle.de>
References: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
	<Pine.LNX.4.64.0806171728400.18714@anubis.informatik.uni-halle.de>
Message-ID: <d7041fc20806171050r55c18ec6r470a2f1a88eab14e@mail.gmail.com>

Thank you guys, I'll check it.

On Tue, Jun 17, 2008 at 4:30 PM, Henning Thielemann <
lemming@henning-thielemann.de> wrote:

>
> On Tue, 17 Jun 2008, Olex P wrote:
>
>  Hi guys,
>>
>> Sorry for a silly questions but I didn't find a proper answer in Google.
>> I've started to learn Haskell and would like to implement a library for
>> work
>> with vectors.
>>
>
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vector-space
>
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From droundy at darcs.net  Tue Jun 17 14:27:01 2008
From: droundy at darcs.net (David Roundy)
Date: Tue Jun 17 14:18:57 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
In-Reply-To: <404396ef0806162355m1bf083f2pcebdbfa64e17e42b@mail.gmail.com>
References: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
	<117f2cc80806161612oe3f2033q187cbf5c22592f03@mail.gmail.com>
	<404396ef0806162355m1bf083f2pcebdbfa64e17e42b@mail.gmail.com>
Message-ID: <20080617182700.GD32397@darcs.net>

On Tue, Jun 17, 2008 at 07:55:51AM +0100, Neil Mitchell wrote:
> Hi,

Hello!

> David:
> > Is there any reason not to just write all lazy fields of variable size
> >  in a deferred manner?
> 
> I completely hadn't though of this! You will loose a bit of time, for
> example reading fields which were previously not deferred will require
> a file seek, but the effort/thought/efficiency trade-off is good. I
> think I will go with this.

Actually, you ought to be able to pretty easily remove this tradeoff
by introducing a strict read function as a new method in your class.
So anyone who wants to strictly read lazy data can use that function
instead of the lazy one.  The writing of data is unaffected... or
rather, it *is* affected, but only in the sense that writing deferred
data cannot be as lazy as the writing of undeferred data.  e.g. when
writing a deferred list, you can't output the first word until you've
already read through the entire list in order to find out how long it
is.  That could actually be quite a problem for code that relies on
laziness to handle massive amounts of data.  :( Lazy reading seems to
require strict writing, while lazy writing requires strict reading!

So perhaps you want a pair of read functions, one strict, one lazy,
and a pair of write functions.  That doesn't provide any sort of
fine-grained control, but at least allows streaming in either
direction.  You could use the same data format for either strictly or
lazily pickled data as long as you have a reserved value for the
length-to-be-skipped, so the lazy reader could tell if it reaches data
that whose length it doesn't know.

David
From droundy at darcs.net  Tue Jun 17 14:31:31 2008
From: droundy at darcs.net (David Roundy)
Date: Tue Jun 17 14:23:29 2008
Subject: [Haskell-cafe] Suggestion for implementation of vector library
In-Reply-To: <20080617152458.GE12977@sliver.repetae.net>
References: <d7041fc20806170804i43afb9eem9ef6540274fb8289@mail.gmail.com>
	<20080617152458.GE12977@sliver.repetae.net>
Message-ID: <20080617183130.GE32397@darcs.net>

On Tue, Jun 17, 2008 at 08:24:58AM -0700, John Meacham wrote:
> You can also create helper functions like
> 
> v3 = Vector3
> 
> so you can do (v3 1 2 3 <+> v3 4 5 6)

Or just use

data Vector3 = V3 !Float !Float !Float

and you've got compact pattern matching as well as constructing.

David
From droundy at darcs.net  Tue Jun 17 14:39:11 2008
From: droundy at darcs.net (David Roundy)
Date: Tue Jun 17 14:31:08 2008
Subject: =?utf-8?B?562U5aSN?=
	=?utf-8?Q?=3A?= [Haskell-cafe] How to do this in FP way?
In-Reply-To: <20080617155631.GD18127@scytale.galois.com>
References: <3bd412d40806151931s3cef9027x73d83943386f0cad@mail.gmail.com>
	<117f2cc80806161017w680f5c83p3165733e46256be0@mail.gmail.com>
	<48574590.034c6e0a.18fd.ffffb68d@mx.google.com>
	<20080617154858.GC18127@scytale.galois.com>
	<20080617155631.GD18127@scytale.galois.com>
Message-ID: <20080617183910.GF32397@darcs.net>

On Tue, Jun 17, 2008 at 08:56:31AM -0700, Don Stewart wrote:
> dons:
> > magicloud.magiclouds:
> > > OK. Here it is.
> > > I want to make a monitor tool for linux. It runs for a long time, and give
> > > out a certain process's io stat per second. The way I get io stat is to read
> > > from /proc/pid/io. But the data in this file is a total, I need to read it
> > > first, then next second, read it again, and shows the difference, and go on.
> > > So, what is your idea?
> > 
> > Easy,
> > 
> >     import Control.Concurrent
> >     import Control.Monad
> > 
> >     main = go 0
> >         where
> >             go st = forever $ do
> >                        n <- read `fmap` readFile "/proc/pid/io"
> >                        print (n - st) -- display difference
> >                        threadDelay (10^6)
> 
> Oops, not 'forever' :)
> 
>               go st = do
>                     ...
>                     go n


or

doEverySecond :: (a -> IO a) -> a -> IO ()
doEverySecond job n = do n' <- job n
                         threadDelay (10^6)
                         doEverySecond job n'

showChange :: Int -> IO Int
showChange n = do n' <- read `fmap` readFile "/proc/pid/io"
                  print (n' - n) -- display difference
                  return n'

main = doEverySecond showChange 0 -- note: prints bogus value first time

This demonstrates how you can abstract the ideas in Don's solution
just a bit, so that you could reuse these functions for somewhat
different purposes.  For such a simple function you'd probably be
better with Don's solution, but if your monitor tool is starting to
look more complicated than this, perhaps you're better off breaking
it into different functions.

David
From byorgey at gmail.com  Tue Jun 17 14:46:27 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Tue Jun 17 14:38:26 2008
Subject: [Haskell-cafe] send in material for the HWN!
Message-ID: <22fcbd520806171146q22d54029m7fbfe077ea9fefa3@mail.gmail.com>

Hi all,

Do you know of a blog post about Haskell that wasn't syndicated on Planet
Haskell?  Do you have a Haskell-related story to tell or announcement to
make?  Do you have a link to some great pictures from the latest
meetup/hackathon/talk/conference?  A funny story about Don Stewart?

If so, consider submitting it to the Haskell Weekly News.  The HWN isn't
really about Haskell so much as it is about the Haskell *community* -- and
that means you!

In addition to the above sorts of submissions, I am also thinking of adding
a "Community News" section with announcements of
(not-necessarily-Haskell-related) major events in the lives of community
members -- but obviously this depends on submissions, so if you get a new
job/move/start a new company/graduate/increment your age/have a comet named
after you/bring forth a new life (aka future Haskeller) into the world,
please share, and let the community celebrate with you!

Submissions can be sent to byorgey at seas dot upenn dot edu.  Be sure to
include "HWN" in the subject line.  For now I'm planning to put an issue out
every Wednesday afternoon, so the submission deadline is Wednesday at 11am
GMT (6am Eastern US).

-Brent
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From miguelimo38 at yandex.ru  Tue Jun 17 14:58:04 2008
From: miguelimo38 at yandex.ru (Miguel Mitrofanov)
Date: Tue Jun 17 14:50:44 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <C31F0D0C-01DD-46DB-9AB2-48966A4C8598@yandex.ru>

Calm down, PR, that's not so bad, all we're going to see is an example  
of closures done wrong, nothing more.

On 17 Jun 2008, at 21:46, PR Stanley wrote:

> Blimey! Talk about rearranging the deckchairs :-)
> With respect, do you not think it'd be wiser for the community to  
> deal with a total lack of proper type checking, the lack of any  
> notion of the general concept of a function, or a whole range of  
> other fundamental issues in PHP first before worrying about closures  
> and lambda functions?  I'm no language purist but PHP really does  
> take the biscuit.
> My personal views and not in any way representing the list .
> Paul
>
> At 17:45 17/06/2008, you wrote:
>> Hi,
>>
>> The PHP community is discussing the adding of closures and lambdas to
>> the language, see the proposal at http://wiki.php.net/rfc/closures
>>
>> If someone with knowledge of both languages could take a quick look  
>> it
>> would be great.
>>
>> Thanks a lot
>>
>> Karoly Negyesi
>>
>> Ps. I am not a member of the PHP internals team, I am just a PHP
>> developer but I am very very interested in getting these in my
>> favourite language.
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From barsoap at web.de  Tue Jun 17 15:31:23 2008
From: barsoap at web.de (Achim Schneider)
Date: Tue Jun 17 15:23:35 2008
Subject: [Haskell-cafe] Re: Lambda and closures in PHP -- could someone
	please comment?
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.co m>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <20080617213123.43e5e63b@solaris>

PR Stanley <prstanley@ntlworld.com> wrote:

> Blimey! Talk about rearranging the deckchairs :-)
> With respect, do you not think it'd be wiser for the community to 
> deal with a total lack of proper type checking, the lack of any 
> notion of the general concept of a function, or a whole range of 
> other fundamental issues in PHP first before worrying about closures 
> and lambda functions?  I'm no language purist but PHP really does 
> take the biscuit.
> My personal views and not in any way representing the list .
>
Oh yes they are. I'd rather smash my head repeatedly into a wall than
suffering the agony of using a hacked cat.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From lanny at cisco.com  Tue Jun 17 15:43:26 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Tue Jun 17 15:35:15 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <485813DE.1050706@cisco.com>

But all the cool kids have em!

Seriously though computer languages are about getting things done.
If this gets more things done for the PHP community in ways
easier/simpler/faster than before then it's a win.

They are after all /their/ deckchairs to play with.

  -ljr

PR Stanley wrote:
> Blimey! Talk about rearranging the deckchairs :-)
> With respect, do you not think it'd be wiser for the community to deal
> with a total lack of proper type checking, the lack of any notion of the
> general concept of a function, or a whole range of other fundamental
> issues in PHP first before worrying about closures and lambda
> functions?  I'm no language purist but PHP really does take the biscuit.
> My personal views and not in any way representing the list .
> Paul
> 
> At 17:45 17/06/2008, you wrote:
>> Hi,
>>
>> The PHP community is discussing the adding of closures and lambdas to
>> the language, see the proposal at http://wiki.php.net/rfc/closures
>>
>> If someone with knowledge of both languages could take a quick look it
>> would be great.
>>
>> Thanks a lot
>>
>> Karoly Negyesi
>>
>> Ps. I am not a member of the PHP internals team, I am just a PHP
>> developer but I am very very interested in getting these in my
>> favourite language.
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From hpacheco at gmail.com  Tue Jun 17 15:51:09 2008
From: hpacheco at gmail.com (Hugo Pacheco)
Date: Tue Jun 17 15:43:07 2008
Subject: [Haskell-cafe] Polymorphic QuickCheck arguments
In-Reply-To: <2A22B918-BD68-4C0E-97D8-FACDC33CF6AD@cs.uu.nl>
References: <7b92c2840806170253l7f53e07al7eedc1411934ca69@mail.gmail.com>
	<2A22B918-BD68-4C0E-97D8-FACDC33CF6AD@cs.uu.nl>
Message-ID: <7b92c2840806171251p7a27ff08w54dde46e208bfdf5@mail.gmail.com>

You are right!
If I try to compile it, then it complains about a Show instance for a, what
in fact forces a monomorphic type signature for t.

I have found under Test.Quickcheck.Poly a way to generate Int values for a
polymorphic type, but because it  requires an abstraction Poly a for some
type a I do not see how it can improve.

What it concretely states the module is

- This is the basic pseudo-polymorphic object.

- The idea is you can't cheat, and use the integer

- directly, but need to use the abstraction.

Is it possible to cheat? I would like to...

Thanks,

hugo


On Tue, Jun 17, 2008 at 12:17 PM, Sebastiaan Visser <sfvisser@cs.uu.nl>
wrote:

> On Jun 17, 2008, at 11:53 AM, Hugo Pacheco wrote:
>
>> Hi all,
>>
>> There is something about polymorphic tests in QuickCheck that I do not
>> understand.
>>
>> If you write the simplest dummy test function
>>
>> tst :: a -> Bool
>> tst _ = True
>>
>> and evaluate it we get
>>
>> > verboseCheck tst
>> 0:
>> ()
>> 1:
>> ()
>> ...
>>
>
>
>  How come did the polymorphic value a get instanciated to ()? Is this done
>> via the Testable type class?
>> Could someone please explain this to me? I'm not saying it does not make
>> sense, but I would like to understand how it works. Being possible to change
>> this behavior, this is, assign another "default type" whenever polymorphic
>> types occur, would be awesome.
>>
>
> I think it is GHCi that is instantiating the type with (). Try compiling
> the program, it will probably be rejected by the compiler when you do not
> specify a concrete type.
>
> You can, for example, try this:
>
> verboseCheck (tst :: [Int] -> Bool)
>
>  Cheers,
>> hugo
>>
>


-- 
www.di.uminho.pt/~hpacheco
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From dons at galois.com  Tue Jun 17 16:12:33 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 17 16:04:30 2008
Subject: Haskell on ARM (was Re: [Haskell-cafe] ANN: Topkata)
In-Reply-To: <87ej6ww9dy.fsf_-_@columbia.edu>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
	<87ej6ww9dy.fsf_-_@columbia.edu>
Message-ID: <20080617201233.GD19304@scytale.galois.com>

xj2106:
> "Ariel J. Birnbaum" <valgarv@gmx.net> writes:
> 
> >> In the mean time -- who knows enough to make ghc target
> >> ARM, and get this to link against the iPhone libraries?
> >> This would be quite a coup if it could be made to run
> >> there!
> > For that matter, there's another ARM-based target in which
> > I'm interested: Nintendo DS. Has anyone got any Haskell
> > code to run on one of these?  PS: Maybe this discussion
> > should be moved to a new "Haskell on ARM" thread?
> 
> I would be interested to see ghc running on Nokia n8xx or
> iRex iliad.  Both of them are quite open linux based
> systems.

Jeremy Shaw had ghc targeting the nokia last year, iirc.
Perhaps he'll have more info.

-- Don
From dons at galois.com  Tue Jun 17 16:16:15 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 17 16:08:13 2008
Subject: [Haskell-cafe] Compiling large code with old machine
In-Reply-To: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
Message-ID: <20080617201615.GE19304@scytale.galois.com>

silva.samuel:
> Hello
> 
> I'm using GHC to compile around 700K of Haskell Code generated by HaXml.
> How I compile this code.
> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.
> 
> How much time it spend to compile this file?
> I spent more than 1 hour and it doesn't finished.
> 
> What flags make compiling fast?
> I try with -H500m but dont't expect.
> 
> It is possible GHC running endless cycle at compilation stage?

Hmm. Try -Onot -fasm 

-- Don
From ronwalf at volus.net  Tue Jun 17 16:40:51 2008
From: ronwalf at volus.net (Ron Alford)
Date: Tue Jun 17 16:32:54 2008
Subject: [Haskell-cafe] Haskell's type system
Message-ID: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>

I'm trying to wrap my head around the theoretical aspects of haskell's
type system. Is there a discussion of the topic separate from the
language itself?

Since I come from a rather logic-y background, I have this
(far-fetched) hope that there is a translation from haskell's type
syntax to first order logic (or an extension there-of).  Is this done?
 Doable?

-Ron
From nicolas.pouillard at gmail.com  Tue Jun 17 16:47:10 2008
From: nicolas.pouillard at gmail.com (Nicolas Pouillard)
Date: Tue Jun 17 16:39:30 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
In-Reply-To: <20080617182700.GD32397@darcs.net>
References: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
	<117f2cc80806161612oe3f2033q187cbf5c22592f03@mail.gmail.com>
	<404396ef0806162355m1bf083f2pcebdbfa64e17e42b@mail.gmail.com>
	<20080617182700.GD32397@darcs.net>
Message-ID: <1213735407-sup-7909@ausone.local>

Excerpts from David Roundy's message of Tue Jun 17 20:27:01 +0200 2008:
> On Tue, Jun 17, 2008 at 07:55:51AM +0100, Neil Mitchell wrote:
> > Hi,
> 
> Hello!

Hello,

> :( Lazy reading seems to
> require strict writing, while lazy writing requires strict reading!

I'm wondering if it would be an option to read the file backward. If so
length annotations could be put at the end.

Reading  backward  seems  to  only fail with streamed data, which won't support
the "seek"ing required by a lazy reading anyway.

Regards,

-- 
Nicolas Pouillard aka Ertai
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From nielsadb at gmail.com  Tue Jun 17 17:24:11 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Tue Jun 17 17:16:06 2008
Subject: [Haskell-cafe] Compiling large code with old machine
In-Reply-To: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
Message-ID: <1213737851.19520.15.camel@porcupine>

On Tue, 2008-06-17 at 13:19 +0100, Samuel Silva wrote:
> 
> I'm using GHC to compile around 700K of Haskell Code generated by HaXml.
> How I compile this code.
> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.
> 
> How much time it spend to compile this file?
> I spent more than 1 hour and it doesn't finished.

Just out of curiosity, is all that 700K just one big file or did you
split it up into multiple files?

Are you using any "expensive" features? I'm not a GHC exert, but I'd
expect things like type manipulations (e.g. phantom types) to be
expensive (please correct me if this assumption is wrong).

Bottom line: if compiling is so slow consider changing the code
generator so the result is easier to process by GHC instead of fiddling
with command line switches. Since you've chosen to generate the code it
will probably change often and you'll run into this problem more than
once.

Regards,
Niels



From prstanley at ntlworld.com  Tue Jun 17 18:03:42 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Tue Jun 17 17:55:32 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could
	someone	please comment?
In-Reply-To: <485813DE.1050706@cisco.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<485813DE.1050706@cisco.com>
Message-ID: <20080617220921.UFRL16854.aamtaout01-winn.ispmail.ntl.com@pine.ntlworld.com>


>But all the cool kids have em!
>
>Seriously though computer languages are about getting things done.
>If this gets more things done for the PHP community in ways
>easier/simpler/faster than before then it's a win.

         nerve gas would sort out the problem with mice in our 
building too, easier simpler faster than the stupid traps.


>They are after all /their/ deckchairs to play with.

         Yes, playing with deckchairs while the ship sinks  with that 
bloody woman singing "my Heart Will Go on".


>   -ljr
>
>PR Stanley wrote:
> > Blimey! Talk about rearranging the deckchairs :-)
> > With respect, do you not think it'd be wiser for the community to deal
> > with a total lack of proper type checking, the lack of any notion of the
> > general concept of a function, or a whole range of other fundamental
> > issues in PHP first before worrying about closures and lambda
> > functions?  I'm no language purist but PHP really does take the biscuit.
> > My personal views and not in any way representing the list .
> > Paul
> >
> > At 17:45 17/06/2008, you wrote:
> >> Hi,
> >>
> >> The PHP community is discussing the adding of closures and lambdas to
> >> the language, see the proposal at http://wiki.php.net/rfc/closures
> >>
> >> If someone with knowledge of both languages could take a quick look it
> >> would be great.
> >>
> >> Thanks a lot
> >>
> >> Karoly Negyesi
> >>
> >> Ps. I am not a member of the PHP internals team, I am just a PHP
> >> developer but I am very very interested in getting these in my
> >> favourite language.
> >> _______________________________________________
> >> Haskell-Cafe mailing list
> >> Haskell-Cafe@haskell.org
> >> http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe@haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe

From loup.vaillant at gmail.com  Tue Jun 17 19:11:30 2008
From: loup.vaillant at gmail.com (Loup Vaillant)
Date: Tue Jun 17 19:03:24 2008
Subject: [Haskell-cafe] Re: Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <20080617213123.43e5e63b@solaris>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<20080617213123.43e5e63b@solaris>
Message-ID: <6f9f8f4a0806171611u3537da12x5f915517a1515927@mail.gmail.com>

2008/6/17 Achim Schneider <barsoap@web.de>:
> PR Stanley <prstanley@ntlworld.com> wrote:
>
>> Blimey! Talk about rearranging the deckchairs :-)
>> With respect, do you not think it'd be wiser for the community to
>> deal with a total lack of proper type checking, the lack of any
>> notion of the general concept of a function, or a whole range of
>> other fundamental issues in PHP first before worrying about closures
>> and lambda functions?  I'm no language purist but PHP really does
>> take the biscuit.
>> My personal views and not in any way representing the list .
>>
> Oh yes they are. I'd rather smash my head repeatedly into a wall than
> suffering the agony of using a hacked cat.

Well, it's not like they're going to turn python into Haskell :-) If
any flaw in a language is fundamental, fixing it is likely to cause
compatibility... issues.

And about closures done wrong, I think the biggest mistake (the only I
spotted, actually) is the keyword "lexical". It seems to add
unnecessary verbosity where plain lexical scope would suffice. It
would be OK if lexical scope is impossible (which I doubt), and plain
wrong if done for readability reasons. Is there any discussion about
this point? Concerning OOP, I didn't really pay attention.

My 2 cents. Take with a grain of salt, for I don't really know PHP
Loup
From dons at galois.com  Tue Jun 17 22:08:27 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 17 22:00:24 2008
Subject: [Haskell-cafe] Haskell's type system
In-Reply-To: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
References: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
Message-ID: <20080618020827.GB21778@scytale.galois.com>

ronwalf:
> I'm trying to wrap my head around the theoretical aspects of haskell's
> type system. Is there a discussion of the topic separate from the
> language itself?
> 
> Since I come from a rather logic-y background, I have this
> (far-fetched) hope that there is a translation from haskell's type
> syntax to first order logic (or an extension there-of).  Is this done?
>  Doable?

A quick link to get you started on the topic, I'm sure others will add
more material.

Haskell's type system is based on System F, the polymorphic lambda
calculus. By the Curry-Howard isomorphism, this corresponds to
second-order logic.

The GHC compiler itself implements Haskell and extensions by encoding
them in System Fc internally, "which extends System F with support for
non-syntactic type equality.".  JHC, I believe, encodes Haskell into a
pure type system internally, some sort of higher order dependently-typed
polymorphic lambda calculus.

-- Don
From jonathanccast at fastmail.fm  Tue Jun 17 22:26:21 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Tue Jun 17 22:17:54 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
Message-ID: <1213755981.3338.15.camel@jonathans-macbook>

On Tue, 2008-06-17 at 18:45 +0200, Karoly Negyesi wrote:
> Hi,
> 
> The PHP community is discussing the adding of closures and lambdas to
> the language, see the proposal at http://wiki.php.net/rfc/closures
> 
> If someone with knowledge of both languages could take a quick look it
> would be great.

I program in Perl for a living, so hopefully you'll understand when I
say

(a) I would *never* want to use an implementation of closures like that.
(b) Closures as proposed are *far* better than not having closures.

jcc


From gwern0 at gmail.com  Tue Jun 17 22:41:38 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Tue Jun 17 22:34:18 2008
Subject: [Haskell-cafe] ANN: Mueval 0.3
Message-ID: <20080618024138.GA30776@craft>

Hiya everyone. So I've uploaded Mueval 0.3 (release early, release often) <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval-0.3>.

What's new? Well, I changed the printing output to be cleaner, and I made printing the inferred type optional (through a --print-type flag). In addition, I've made sure it can run (for me, at least) under -N4, and the watchdog threads should be sturdier. (Plus extra tests.)

However, I've been hearing that a number of people (3 at last count) have been having a lot of trouble with the ResourceLimits stuff.

So, I have a few requests of people who install mueval:
* First, does it work out of the box, with no tweaking of the resource limits?
* Second, if it doesn't work out of the box, which resource limits did you need to disable or increase?
* Thirdly, if you changed the resource limits, could you run ./build.sh and tell me whether all the tests pass?

Finally, I've been pondering removing the rlimits entirely since they are both very unportable, empirically derived, and apparently don't even work consistently on Linux. Any thoughts?

--
gwern
PABX MEMEX 868 1* TSCI @ shelter Yukon el ASLET
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From aeyakovenko at gmail.com  Wed Jun 18 00:00:26 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Tue Jun 17 23:52:24 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
Message-ID: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>

here is the C:

#include <cblas.h>
#include <stdlib.h>

int main() {
   int size = 1024;
   int ii = 0;
   double* v1 = malloc(sizeof(double) * (size));
   double* v2 = malloc(sizeof(double) * (size));
   for(ii = 0; ii < size*size; ++ii) {
      double _dd = cblas_ddot(0, v1, size, v2, size);
   }
   free(v1);
   free(v2);
}

this is the haskell:

module Main where

import Data.Vector.Dense.IO

main = do
   let size = 1024
   v1::IOVector Int Double <- newListVector size [0..]
   v2::IOVector Int Double <- newListVector size [0..]
   mapM_ (\ ii -> do v1 `getDot` v2) [0..size*size]

time ./testdot

real    0m0.017s
user    0m0.010s
sys     0m0.010s

time ./htestdot

real    0m4.692s
user    0m4.670s
sys     0m0.030s

so like 250x difference

htestdot.prof is no help

   Tue Jun 17 20:46 2008 Time and Allocation Profiling Report  (Final)

      htestdot +RTS -p -RTS

   total time  =        3.92 secs   (196 ticks @ 20 ms)
   total alloc = 419,653,032 bytes  (excludes profiling overheads)

COST CENTRE                    MODULE               %time %alloc

main                           Main                  88.3   83.0
CAF                            Main                  11.7   17.0



                        individual    inherited
COST CENTRE              MODULE
       no.    entries  %time %alloc   %time %alloc

MAIN                     MAIN
         1           0   0.0    0.0   100.0  100.0
 CAF                     Main
       216           7  11.7   17.0   100.0  100.0
  main                   Main
       222           1  88.3   83.0    88.3   83.0
 CAF                     GHC.Float
       187           1   0.0    0.0     0.0    0.0
 CAF                     GHC.Handle
       168           3   0.0    0.0     0.0    0.0
From karoly at negyesi.net  Wed Jun 18 00:36:23 2008
From: karoly at negyesi.net (Karoly Negyesi)
Date: Wed Jun 18 00:28:23 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <1213755981.3338.15.camel@jonathans-macbook>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<1213755981.3338.15.camel@jonathans-macbook>
Message-ID: <7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>

>  (a) I would *never* want to use an implementation of closures like that.
>  (b) Closures as proposed are *far* better than not having closures.

Could you elaborate on a) ?
From lrpalmer at gmail.com  Wed Jun 18 01:00:36 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun 18 00:52:31 2008
Subject: [Haskell-cafe] Haskell's type system
In-Reply-To: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
References: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
Message-ID: <7ca3f0160806172200s2a7631eaub5453101c6713279@mail.gmail.com>

On Tue, Jun 17, 2008 at 2:40 PM, Ron Alford <ronwalf@volus.net> wrote:
> I'm trying to wrap my head around the theoretical aspects of haskell's
> type system. Is there a discussion of the topic separate from the
> language itself?
>
> Since I come from a rather logic-y background, I have this
> (far-fetched) hope that there is a translation from haskell's type
> syntax to first order logic (or an extension there-of).  Is this done?
>  Doable?

Sort of, via the Curry-Howard Correspondence.  Haskell's type system
corresponds to a constructive logic (no law of excluded middle).
Arbitrary quantifiers are also introduced via the RankNTypes (I think
that's what it's called) extension.

Haskell's type system is a straightforward polymorphic type system for
the lambda calculus, so researching the Curry-Howard Correspondence
will probably get you what you want.

Luke
From vigalchin at gmail.com  Wed Jun 18 01:12:28 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Wed Jun 18 01:04:21 2008
Subject: [Haskell-cafe] Haskell data types and Storable class
Message-ID: <5ae4f2ba0806172212ge0ea659paa2c767bb12700ed@mail.gmail.com>

Hello,

     I am reading the FFI spec. Something is unclear to me. Let's assume we
have

         data A = {b:B, .......}

    and

         data B ={ .............}

both of which belong to class Storable. In the A instance of Storable I want
to do a poke and peek of "b" into and out-of, respectively, B. How do I
write the poke and peek function of "b" in the "instance Storable A"?

thank you, Vasili
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From ok at cs.otago.ac.nz  Wed Jun 18 01:16:10 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Wed Jun 18 01:08:36 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <485813DE.1050706@cisco.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<485813DE.1050706@cisco.com>
Message-ID: <B7307581-13D6-4238-8E65-D11A33EFBD3E@cs.otago.ac.nz>

I believe C# already has lambdas, and Java is supposed to be getting
them.  PHP is playing catchup, is all.  (Oh, and Eiffel has 'agents',
and I think I saw something about C++ Next Degeneration, and ...)
Heck, the idea has only been around in computing since the 1950s...


From barsoap at web.de  Wed Jun 18 02:06:46 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun 18 01:58:53 2008
Subject: [Haskell-cafe] Something like scan1
Message-ID: <20080618080646.29abd52f@solaris>

Is there a generalisation of scan1, such that eg.

foo (+) [0,1] (1,2) = [0,1,1,2,3,5,8,13,...]

?

I came up with it while thinking about the equivalence of laziness and
strictness resp. pull and push.

To be more specific, I was thinking about ArrowLoop and how that beast
generalises over time-varying values. It's some kind of helixoid fixed
point (which might not help at all if your visualisation is
incompatible with mine).


-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From andrewcoppin at btinternet.com  Tue Jun 17 16:05:31 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun 18 02:38:50 2008
Subject: [Haskell-cafe] Bit streams
Message-ID: <4858190B.4090909@btinternet.com>

OK, so today I tried to write my first program using the Binary library. 
And I've hit a snag: It appears the library will only handle data that 
is byte-aligned. So if I try to write three Bool values, it uses three 
bytes, not three bits.

Before I sit down and spend 3 months designing my own library from 
scratch, does anybody know of an existing library that allows you to do 
what Binary does, but with single-bit precision? [I presume Binary is 
byte-aligned for efficiency...]

From jonathanccast at fastmail.fm  Wed Jun 18 03:11:19 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Wed Jun 18 03:03:12 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<1213755981.3338.15.camel@jonathans-macbook>
	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
Message-ID: <1213773079.7014.22.camel@jonathans-macbook>

On Wed, 2008-06-18 at 06:36 +0200, Karoly Negyesi wrote:
> >  (a) I would *never* want to use an implementation of closures like that.
> >  (b) Closures as proposed are *far* better than not having closures.
> 
> Could you elaborate on a) ?

I dislike the habit of implicit declaration --- strongly --- and the
consequent need for the lexical keyword (although at this point PHP's
stuck with it).  I can see myself forgetting to use lexical far more
often than accidentally leaving off a `my' in Perl I should have used (I
hardly ever shadow variable names anyway, so if I forget `my' is usually
a use strict 'vars' error).

I dislike curly braces.  Syntax that extends as far to the right as
possible tends to end up with fewer delimiters and a cleaner appearance.
It's basically a way to replace a bunch of closing braces with a
single ) or (in Haskell, implicit) ;

lintPat p0 $ \ ty0 -> lintPat p1 $ \ ty1 -> lint e

vs

lintPat($p0, sub { my ($ty0) = @_; lintPat($p1, sub { my ($ty1) = @_;
lint($e) })})

Four closing delimiters seems excessive.

Nit: `function' is verbose.  ML uses fun or fn (I forget which and am
too lazy to google).  Perl's regular keyword is sub, so they use that.

There are worse fates than duck typing (C++ comes to mind :), and given
a language with neither lexical closures/anonymous functions nor HM
typing, I'd complain about the lack of lambdas first.  But, still, no HM
means no type classes.  That ultimately becomes limiting.  (I still
haven't seen a decent implementation of monads in a dynamically typed
language).  But PHP is probably pretty much stuck with it.

Not to criticize, mind you --- the proposal looks excellent for what it
does.  But I like what Haskell does worlds better.

jcc


From dominic.steinitz at blueyonder.co.uk  Wed Jun 18 03:17:07 2008
From: dominic.steinitz at blueyonder.co.uk (Dominic Steinitz)
Date: Wed Jun 18 03:09:18 2008
Subject: [Haskell-cafe] Re: Compiling large code with old machine
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
Message-ID: <loom.20080618T071307-64@post.gmane.org>

Samuel Silva <silva.samuel <at> gmail.com> writes:

> 
> Hello
> 
> I'm using GHC to compile around 700K of Haskell Code generated by HaXml.
> How I compile this code.
> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.
> 

Samuel,

You may not want to take this approach. I'm assuming you are generating 
haskell types from a (large) DTD. I went this way (admittedly quite a few 
years ago) for svg. In the end it was much easier to hand generate a few 
combinators to produced the svg. I don't know what your application is but it 
may worth thinking about an alternative to 700k loc.

Dominic.

From dominic.steinitz at blueyonder.co.uk  Wed Jun 18 03:46:08 2008
From: dominic.steinitz at blueyonder.co.uk (Dominic Steinitz)
Date: Wed Jun 18 03:38:10 2008
Subject: [Haskell-cafe] Re: Bit Streams
Message-ID: <loom.20080618T073859-884@post.gmane.org>

OK, so today I tried to write my first program using the Binary library. 
And I've hit a snag: It appears the library will only handle data that 
is byte-aligned. So if I try to write three Bool values, it uses three 
bytes, not three bits.

Before I sit down and spend 3 months designing my own library from 
scratch, does anybody know of an existing library that allows you to do 
what Binary does, but with single-bit precision? [I presume Binary is 
byte-aligned for efficiency...]

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict




From karoly at negyesi.net  Wed Jun 18 04:19:13 2008
From: karoly at negyesi.net (Karoly Negyesi)
Date: Wed Jun 18 04:11:08 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <1213773079.7014.22.camel@jonathans-macbook>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<1213755981.3338.15.camel@jonathans-macbook>
	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
	<1213773079.7014.22.camel@jonathans-macbook>
Message-ID: <7e270cea0806180119y30c56184m9b16969f05b5517f@mail.gmail.com>

>  Not to criticize, mind you --- the proposal looks excellent for what it
>  does.  But I like what Haskell does worlds better.

Obviously you like Haskell better given this mailing list :) I am not
here to compare PHP and Haskell, I was just asking advice from people
who know closures and lambdas very well and it seems that I got it in
the words of "the proposal looks excellent for what it does".

Thanks a lot.

Karoly Negyesi
From jules at jellybean.co.uk  Wed Jun 18 04:46:30 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Wed Jun 18 04:38:22 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <4858CB66.1040605@jellybean.co.uk>

PR Stanley wrote:
> With respect, do you not think it'd be wiser for the community 

[snip]

*disgusted*

This is exactly the sort of message that haskell-cafe does not normally 
contain. Let's not start now.

This is a civilized mailing list. Either comment on the nice gentlemen's 
PHP closure proposal from a language point of view, or don't say anything.

Jules
From devriese at cs.tcd.ie  Wed Jun 18 05:32:02 2008
From: devriese at cs.tcd.ie (Edsko de Vries)
Date: Wed Jun 18 05:23:58 2008
Subject: [Haskell-cafe] Haskell's type system
In-Reply-To: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
References: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
Message-ID: <20080618093202.GA18893@netsoc.tcd.ie>

On Tue, Jun 17, 2008 at 04:40:51PM -0400, Ron Alford wrote:
> I'm trying to wrap my head around the theoretical aspects of haskell's
> type system. Is there a discussion of the topic separate from the
> language itself?
> 
> Since I come from a rather logic-y background, I have this
> (far-fetched) hope that there is a translation from haskell's type
> syntax to first order logic (or an extension there-of).  Is this done?
>  Doable?

I'll give you some terms to Google for.

The "ideal" type system for Haskell (ignoring type classes) is System F.
Haskell'98 doesn't quite get there, but recent extensions such as boxy
types and FPH do. System F corresponds to second order propositional
logic: types correspond to propositions in this logic, and Haskell
programs as the corresponding proofs (by the Curry-Howard isomorphism).

The type system of Haskell'98 is a bit weird from a logical perspective,
and sort of corresponds to the rank 1.5 predicative fragment of second
order propositional logic (I say rank 1.5 because although no
abstraction over rank 1 types is allowed normally, limited abstractions
over rank 1 types is allowed through let-polymorphism -- so this is
*almost* first order logic but not quite: slightly more powerful). 

Regarding type classes, I'm not 100% what the logical equivalent is,
although one can regard a type such as

  forall a. Eq a => a -> a

as requiring a proof (evidence) that equality on a is decidable. Where
this sits formally as a logic I'm not sure though.

Edsko
From prstanley at ntlworld.com  Wed Jun 18 06:38:00 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 06:29:45 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could
	someone	please comment?
In-Reply-To: <4858CB66.1040605@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
Message-ID: <20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>


>>With respect, do you not think it'd be wiser for the community
>
>[snip]
>
>*disgusted*
>
>This is exactly the sort of message that haskell-cafe does not 
>normally contain. Let's not start now.
>
>This is a civilized mailing list. Either comment on the nice 
>gentlemen's PHP closure proposal from a language point of view, or 
>don't say anything.
Paul: Uncivilised you say. Well, I would have thought the civilised 
thing would be to share your concerns discretely with the list 
moderator. Instead you've chosen to make a public show of it.
The Chinese have a saying, and I paraphrase - when you point the 
finger of accusation at someone/something you have three pointing 
back at yourself.

Paul

From sfvisser at cs.uu.nl  Wed Jun 18 06:45:54 2008
From: sfvisser at cs.uu.nl (Sebastiaan Visser)
Date: Wed Jun 18 06:38:01 2008
Subject: [Haskell-cafe] Bit streams
In-Reply-To: <4858190B.4090909@btinternet.com>
References: <4858190B.4090909@btinternet.com>
Message-ID: <6E0C8147-0075-4FFE-9AC8-7606392370C8@cs.uu.nl>

On Jun 17, 2008, at 10:05 PM, Andrew Coppin wrote:

> OK, so today I tried to write my first program using the Binary  
> library. And I've hit a snag: It appears the library will only  
> handle data that is byte-aligned. So if I try to write three Bool  
> values, it uses three bytes, not three bits.
>
> Before I sit down and spend 3 months designing my own library from  
> scratch, does anybody know of an existing library that allows you  
> to do what Binary does, but with single-bit precision? [I presume  
> Binary is byte-aligned for efficiency...]

Andrew,

Maybe you could look at the generic encode/decode in this paper:
people.cs.uu.nl/johanj/publications/ComparingGP.pdf

When you look at some more literature about generic programming the  
(bit-aligned) encode and decode are quite common examples. It  
shouldn't be that hard to de-generify them, if you even want that.

--
Sebastiaan.




From silva.samuel at gmail.com  Wed Jun 18 07:07:22 2008
From: silva.samuel at gmail.com (Samuel Silva)
Date: Wed Jun 18 06:59:14 2008
Subject: [Haskell-cafe] Compiling large code with old machine
In-Reply-To: <382ead9b0806180022i605d069y199d44e7330bebd2@mail.gmail.com>
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
	<1213737851.19520.15.camel@porcupine>
	<382ead9b0806180022i605d069y199d44e7330bebd2@mail.gmail.com>
Message-ID: <382ead9b0806180407o80ee94dmf51bcf235f271d11@mail.gmail.com>

Hello
On Tue, Jun 17, 2008 at 10:24 PM, Niels Aan de Brugh <nielsadb@gmail.com> wrote:
> On Tue, 2008-06-17 at 13:19 +0100, Samuel Silva wrote:
>>
>> I'm using GHC to compile around 700K of Haskell Code generated by HaXml.
>> How I compile this code.
>> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2.
>>
>> How much time it spend to compile this file?
>> I spent more than 1 hour and it doesn't finished.
>
> Just out of curiosity, is all that 700K just one big file or did you
> split it up into multiple files?

 It's just two big files with 700K each generated by DtdToHaskell from
 two big DTD files around 70K each.

> Are you using any "expensive" features? I'm not a GHC exert, but I'd
> expect things like type manipulations (e.g. phantom types) to be
> expensive (please correct me if this assumption is wrong).

 This large module only contains datatype declarations and instance classes
 for HTypeable, XmlContent, XmlAttributes and XmlAttrType.

> Bottom line: if compiling is so slow consider changing the code
> generator so the result is easier to process by GHC instead of fiddling
> with command line switches. Since you've chosen to generate the code it
> will probably change often and you'll run into this problem more than
> once.
>
> Regards,
> Niels
>
>

 Each Haskell file have almost 15000 lines. It is huge.
 It's compiling very fast(some minutes) using -H300m without cabal and
 -H200m with cabal.

 GHC it is amazing. This was a valuable help.

 --
 Don't hug that, Hugs ME!
 Samuel Silva
From duncan.coutts at worc.ox.ac.uk  Wed Jun 18 07:45:20 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun 18 07:32:56 2008
Subject: [Haskell-cafe] ANNOUNCE: cabal-install 0.5
Message-ID: <1213789520.15010.837.camel@localhost>

cabal-install 0.5
=================

cabal-install version 0.5 is out:
http://haskell.org/cabal/download.html

or get it from hackage:
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-install

If you are already using a cabal-install pre-release then you can just:
$ cabal update
$ cabal install cabal-install

New features in cabal-install
=============================

Command line improvements
-------------------------

The most immediately noticeable thing is that the command line interface
now has all the commands that runhaskell Setup.hs has. Of course it
still has the features to download and install packages from hackage. It
also gained an upload command. So it now provides a command line
interface to the whole Cabal/Hackage system. There?s no need to use
runhaskell Setup.hs ever again.

There is also bash command line completion support included which I find
is a great time saver.

Installing and upgrading
------------------------

The next big thing is that it includes a new package dependency
resolution system that finds correct and sensible solutions more of the
time and has better default behaviour. The new behaviour should be
similar to other package managers that people are used to.

For example, suppose you?ve got xmonad-0.5 installed and version 0.7 is
the latest on hackage, then

$ cabal install xmonad

will install xmonad-0.7. The older version, xmonad-0.5, will remain
installed.

The behaviour of install is to upgrade as little as possible to satisfy
your request, but sometimes you want to upgrade all the dependencies
too. Supposing now that we have xmonad-0.7 installed, but we?re still
using X11-1.4.1 and the latest version on hackage is X11-1.4.2, then

$ cabal upgrade xmonad

will install X11-1.4.2 and *re-install* xmonad-0.7, this time built
against the newer X11-1.4.2.

So in general, the install command will install the latest version of
things but will try and use any existing installed versions of
dependencies while the upgrade command will also try to use the latest
versions of all dependencies. As a special case, cabal upgrade on its
own will try to upgrade all the packages that you have installed.

For both command there is a --dry-run flag so you can see what would be
installed without actually doing it.

Hugs
----

Yes, it even works with hugs. That is, cabal-install built by ghc can
manage the installation of packages for hugs. In principle cabal-install
should be able to be run by hugs but currently the zlib binding is using
a function that hugs does not support.

Note that for hugs, Cabal does not know what packages are already
installed because there is no equivalent of the package database that
ghc has. So that means cabal-install cannot do very sensible
installation planning. It should work ok so long as all the dependencies
are already installed.

Windows
-------

Yes, it even works on Windows. The one caveat is that cabal-install
cannot currently upgrade itself because Windows makes it hard for a
process to overwrite its own executable file. It needs more complex
trickery with the Win32 API. In the meantime the workaround is to rename
the cabal.exe file first eg to cabal-foo.exe, then run cabal-foo install
cabal-install.

Build reporting
---------------

One feature that made it into this release is build reporting.
cabal-install keeps logs of all packages that you install (at least
packages from hackage, not local ones). It records a bit of information
about each package, in particular whether the outcome was successful or
not. You can see these build reports in
~/.cabal/packages/$server/build-reports.log.

For example, there is one from my machine for xmonad:

        package: xmonad-0.7
        os: linux
        arch: x86_64
        compiler: ghc-6.8.2
        client: cabal-install-0.5.1
        flags: -testing small_base
        dependencies: X11-1.4.2 base-3.0.1.0 containers-0.1.0.1
                      directory-1.0.0.0 mtl-1.1.0.0 process-1.0.0.0
                      unix-2.3.0.0
        install-outcome: InstallOk
        docs-outcome: NotTried
        tests-outcome: NotTried

The plan in the longer term is to let people upload these build reports
to hackage so we can get a wider range of testing data about the
packages on hackage.


Duncan

From daniel.is.fischer at web.de  Wed Jun 18 08:28:25 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Wed Jun 18 08:19:00 2008
Subject: [Haskell-cafe] Problem building GHC 6.8.3
Message-ID: <200806181428.25083.daniel.is.fischer@web.de>

Sorry, probably stupid questions for knowledgeable folks, but after having 
built for a couple of hours, make died with

if ifBuildable/ifBuildable base; then \
  cd base && setup/Setup haddock --html-location='../$pkg' \
                               --hyperlink-source; \
fi
Preprocessing library base-3.0.2.0...
Running hscolour for base-3.0.2.0...
Preprocessing library base-3.0.2.0...
Running Haddock for base-3.0.2.0...
Warning: The documentation for package rts-1.0 is not installed. No links to 
it will be generated.
Setup: Haddock's internal GHC version must match the configured GHC version
make[1]: *** [doc.library.base] Fehler 1
make[1]: Leaving directory `/home/dafis/HasCom/ghc-6.8.3/libraries'
make: *** [stage1] Fehler 2

So, what is Haddock's internal GHC version?
Is it the version, haddock was built with?

And what is the configured GHC version, is it the one I'm trying to build or 
the one I'm building with? 
If the former, I seem to have landed in a circulus vitiosus, if the latter, 
that is the GHC, haddock was built with, too.

For the record:
dafis@linux:~/HasCom/ghc-6.8.3> haddock --version
Haddock version 2.1.0, (c) Simon Marlow 2006
Ported to use the GHC API by David Waern 2006-2008

How should I proceed now?

Thanks,
Daniel
From Malcolm.Wallace at cs.york.ac.uk  Wed Jun 18 08:36:40 2008
From: Malcolm.Wallace at cs.york.ac.uk (Malcolm Wallace)
Date: Wed Jun 18 08:31:50 2008
Subject: [Haskell-cafe] Bit streams
In-Reply-To: <4858190B.4090909@btinternet.com>
References: <4858190B.4090909@btinternet.com>
Message-ID: <20080618133640.24b78310.Malcolm.Wallace@cs.york.ac.uk>

Andrew Coppin <andrewcoppin@btinternet.com> wrote:

> It appears the library will only handle
> data that  is byte-aligned. So if I try to write three Bool values, it
> uses three  bytes, not three bits.

The original Binary library, circa 1998, was based on bit-streams rather
than bytes.  You might be able to dig up a copy and bring it back to
life.

http://citeseer.ist.psu.edu/wallace98bits.html
ftp://ftp.cs.york.ac.uk/pub/malcolm/ismm98.html

Regards,
    Malcolm
From dgorin at dc.uba.ar  Wed Jun 18 08:44:30 2008
From: dgorin at dc.uba.ar (=?ISO-8859-1?Q?Daniel_Gor=EDn?=)
Date: Wed Jun 18 08:36:52 2008
Subject: [Haskell-cafe] Haskell's type system
In-Reply-To: <20080618020827.GB21778@scytale.galois.com>
References: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
	<20080618020827.GB21778@scytale.galois.com>
Message-ID: <5783CCE5-9C5B-4B03-A673-61867D9A37F9@dc.uba.ar>

On Jun 17, 2008, at 11:08 PM, Don Stewart wrote:

> Haskell's type system is based on System F, the polymorphic lambda
> calculus. By the Curry-Howard isomorphism, this corresponds to
> second-order logic.


just nitpicking a little.... this should read "second-order  
propositional logic", right?

daniel
From voigt at tcs.inf.tu-dresden.de  Wed Jun 18 09:09:12 2008
From: voigt at tcs.inf.tu-dresden.de (Janis Voigtlaender)
Date: Wed Jun 18 08:56:08 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could	someone	please
	comment?
In-Reply-To: <20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
	<20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <485908F8.4040001@tcs.inf.tu-dresden.de>

PR Stanley wrote:
> 
>>> With respect, do you not think it'd be wiser for the community
>>
>>
>> [snip]
>>
>> *disgusted*
>>
>> This is exactly the sort of message that haskell-cafe does not 
>> normally contain. Let's not start now.
>>
>> This is a civilized mailing list. Either comment on the nice 
>> gentlemen's PHP closure proposal from a language point of view, or 
>> don't say anything.
> 
> Paul: Uncivilised you say. Well, I would have thought the civilised 
> thing would be to share your concerns discretely with the list 
> moderator.

Hmm, I wonder who exactly this "list moderator" is supposed to be. We
are usually adult enough around here to not need someone to look after
us. I think Jules was well entitled to raise his objections about the
tone of your email in public.

> Instead you've chosen to make a public show of it.
> The Chinese have a saying, and I paraphrase - when you point the finger 
> of accusation at someone/something you have three pointing back at 
> yourself.

Well, at least not this finger...

-- 
Dr. Janis Voigtlaender
http://wwwtcs.inf.tu-dresden.de/~voigt/
mailto:voigt@tcs.inf.tu-dresden.de

From asandroq at gmail.com  Wed Jun 18 09:11:36 2008
From: asandroq at gmail.com (Alex Sandro Queiroz e Silva)
Date: Wed Jun 18 09:03:45 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <4858CB66.1040605@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
Message-ID: <48590988.1020100@gmail.com>

Hallo,

Jules Bean wrote:
> PR Stanley wrote:
>> With respect, do you not think it'd be wiser for the community 
> 
> [snip]
> 
> *disgusted*
> 
> This is exactly the sort of message that haskell-cafe does not normally 
> contain. Let's not start now.
> 
> This is a civilized mailing list. Either comment on the nice gentlemen's 
> PHP closure proposal from a language point of view, or don't say anything.
> 

      Thanks Jules, I was starting to worry about Haskell-caf?.

-alex
http://www.ventonegro.org/

From bulat.ziganshin at gmail.com  Wed Jun 18 09:08:53 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Wed Jun 18 09:09:17 2008
Subject: [Haskell-cafe] Bit streams
In-Reply-To: <4858190B.4090909@btinternet.com>
References: <4858190B.4090909@btinternet.com>
Message-ID: <1281584231.20080618170853@gmail.com>

Hello Andrew,

Wednesday, June 18, 2008, 12:05:31 AM, you wrote:

> what Binary does, but with single-bit precision? [I presume Binary is

http://haskell.org/haskellwiki/Library/AltBinary

it's not maintained, so consider it as "last hope" :)


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From bulat.ziganshin at gmail.com  Wed Jun 18 09:11:30 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Wed Jun 18 09:12:26 2008
Subject: [Haskell-cafe] Re: Compiling large code with old machine
In-Reply-To: <loom.20080618T071307-64@post.gmane.org>
References: <382ead9b0806170519w3c2377f8v1584a97117a0d4f9@mail.gmail.com>
	<loom.20080618T071307-64@post.gmane.org>
Message-ID: <1293573671.20080618171130@gmail.com>

Hello Dominic,

Wednesday, June 18, 2008, 11:17:07 AM, you wrote:

>> I'm using GHC to compile around 700K of Haskell Code generated by HaXml.
> may worth thinking about an alternative to 700k loc.

i think he means bytes, not lines :)


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From bulat.ziganshin at gmail.com  Wed Jun 18 09:19:15 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Wed Jun 18 09:19:19 2008
Subject: [Haskell-cafe] Bit streams
In-Reply-To: <20080618133640.24b78310.Malcolm.Wallace@cs.york.ac.uk>
References: <4858190B.4090909@btinternet.com>
	<20080618133640.24b78310.Malcolm.Wallace@cs.york.ac.uk>
Message-ID: <136220278.20080618171915@gmail.com>

Hello Malcolm,

Wednesday, June 18, 2008, 4:36:40 PM, you wrote:

> The original Binary library, circa 1998, was based on bit-streams rather
> than bytes.  You might be able to dig up a copy and bring it back to
> life.

> http://citeseer.ist.psu.edu/wallace98bits.html
> ftp://ftp.cs.york.ac.uk/pub/malcolm/ismm98.html

well, i've seen ghc-compatible Binary library flying around which
supported bit fields. it was in pre-hackage days, but it should be
pretty easy to find this module


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From prstanley at ntlworld.com  Wed Jun 18 09:42:23 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 09:34:12 2008
Subject: [Haskell-cafe] Lambda and closures in PHP --
	could	someone	please comment?
In-Reply-To: <485908F8.4040001@tcs.inf.tu-dresden.de>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
	<20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<485908F8.4040001@tcs.inf.tu-dresden.de>
Message-ID: <20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>

PR Stanley wrote:

With respect, do you not think it'd be wiser for the community


[snip]

*disgusted*

This is exactly the sort of message that haskell-cafe does not 
normally contain. Let's not start now.

This is a civilized mailing list. Either comment on the nice 
gentlemen's PHP closure proposal from a language point of view, or 
don't say anything.
Paul: Uncivilised you say. Well, I would have thought the civilised 
thing would be to share your concerns discretely with the list moderator.

Hmm, I wonder who exactly this "list moderator" is supposed to be. We
are usually adult enough around here to not need someone to look after
us. I think Jules was well entitled to raise his objections about the
tone of your email in public.

Paul: As you say, we "are adult enougharound here to not need someone 
to look after us". So I don't need you or any other interfearing 
busybody to tell me what I can and can't say on Haskell Cafe. I 
expressed an opinion in a tongue-in-cheek way and at the end of my 
message expressed in clear terms that those were merely my views.
Now, if you, Jules, Alex or some other  wannabe Hitler have a problem 
with my freedom of expression then your best solution is to saddle up 
and get the hell out yourselves. This is the wrong place for setting 
up your tinpot dictatorship, Doctor!
I am grateful for the help I've been getting from the list and my 
understanding of FP has vastly improved since my membership of this 
list but I refuse to tolerate bullies who use the list as a way of 
lifting themselves out of their own shitty lives. Now I am angry!

Instead you've chosen to make a public show of it.
The Chinese have a saying, and I paraphrase - when you point the 
finger of accusation at someone/something you have three pointing 
back at yourself.

Well, at least not this finger...

	Paul: you're not making sense.

From voigt at tcs.inf.tu-dresden.de  Wed Jun 18 09:52:33 2008
From: voigt at tcs.inf.tu-dresden.de (Janis Voigtlaender)
Date: Wed Jun 18 09:39:22 2008
Subject: [Haskell-cafe] Lambda and closures in PHP --	could	someone	please
	comment?
In-Reply-To: <20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
	<20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<485908F8.4040001@tcs.inf.tu-dresden.de>
	<20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <48591321.5040602@tcs.inf.tu-dresden.de>

With respect, I will not engage in further communication on that level.

PR Stanley wrote:
> PR Stanley wrote:
> 
> With respect, do you not think it'd be wiser for the community
> 
> 
> [snip]
> 
> *disgusted*
> 
> This is exactly the sort of message that haskell-cafe does not normally 
> contain. Let's not start now.
> 
> This is a civilized mailing list. Either comment on the nice gentlemen's 
> PHP closure proposal from a language point of view, or don't say anything.
> Paul: Uncivilised you say. Well, I would have thought the civilised 
> thing would be to share your concerns discretely with the list moderator.
> 
> Hmm, I wonder who exactly this "list moderator" is supposed to be. We
> are usually adult enough around here to not need someone to look after
> us. I think Jules was well entitled to raise his objections about the
> tone of your email in public.
> 
> Paul: As you say, we "are adult enougharound here to not need someone to 
> look after us". So I don't need you or any other interfearing busybody 
> to tell me what I can and can't say on Haskell Cafe. I expressed an 
> opinion in a tongue-in-cheek way and at the end of my message expressed 
> in clear terms that those were merely my views.
> Now, if you, Jules, Alex or some other  wannabe Hitler have a problem 
> with my freedom of expression then your best solution is to saddle up 
> and get the hell out yourselves. This is the wrong place for setting up 
> your tinpot dictatorship, Doctor!
> I am grateful for the help I've been getting from the list and my 
> understanding of FP has vastly improved since my membership of this list 
> but I refuse to tolerate bullies who use the list as a way of lifting 
> themselves out of their own shitty lives. Now I am angry!
> 
> Instead you've chosen to make a public show of it.
> The Chinese have a saying, and I paraphrase - when you point the finger 
> of accusation at someone/something you have three pointing back at 
> yourself.
> 
> Well, at least not this finger...
> 
>     Paul: you're not making sense.
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 

-- 
Dr. Janis Voigtlaender
http://wwwtcs.inf.tu-dresden.de/~voigt/
mailto:voigt@tcs.inf.tu-dresden.de


From lrpalmer at gmail.com  Wed Jun 18 09:57:14 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun 18 09:49:06 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
	<20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<485908F8.4040001@tcs.inf.tu-dresden.de>
	<20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <7ca3f0160806180657q3722e2bfv57967e6d66e8401a@mail.gmail.com>

On Wed, Jun 18, 2008 at 1:42 PM, PR Stanley <prstanley@ntlworld.com> wrote:
> Now, if you, Jules, Alex or some other  wannabe Hitler have a problem with
> my freedom of expression then your best solution is to saddle up and get the
> hell out yourselves. This is the wrong place for setting up your tinpot
> dictatorship, Doctor!

Just more evidence...

http://en.wikipedia.org/wiki/Godwin's_law

Luke
From prstanley at ntlworld.com  Wed Jun 18 10:14:49 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 10:06:36 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <7ca3f0160806180657q3722e2bfv57967e6d66e8401a@mail.gmail.co
 m>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
	<20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<485908F8.4040001@tcs.inf.tu-dresden.de>
	<20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<7ca3f0160806180657q3722e2bfv57967e6d66e8401a@mail.gmail.com>
Message-ID: <20080618141750.JXTS29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>


> > Now, if you, Jules, Alex or some other  wannabe Hitler have a problem with
> > my freedom of expression then your best solution is to saddle up 
> and get the
> > hell out yourselves. This is the wrong place for setting up your tinpot
> > dictatorship, Doctor!
>
>Just more evidence...
>
>http://en.wikipedia.org/wiki/Godwin's_law
>
>Paul: I think you're missing a big painfully obvious point here, Mr 
>smarty pants. No, actually, I think I'll leave it at that. I just 
>can't be bothered. However, I'll say this - anyone sticking his 
>bloody big hooter into my business in the future will get a similar reaction!
Paul


>Luke

From sethg at ropine.com  Wed Jun 18 10:19:50 2008
From: sethg at ropine.com (Seth Gordon)
Date: Wed Jun 18 10:11:43 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <48591986.1020304@ropine.com>

PR Stanley wrote:
> Blimey! Talk about rearranging the deckchairs :-)

Today's xkcd seems apropos: http://xkcd.com/438/

It seems to me that if a PHP developer sees the Haskell community as a 
resource for advice on programming language implementation, we should 
take this as a compliment to the Haskell community.  Repaying that 
compliment with "your language sucks rocks" strikes me as unwise.

I'm familiar with a lot of arguments for why PHP is a poorly-designed 
language, and have found them sufficiently persuasive that I haven't 
bothered to learn PHP.  But I don't see any point to repeating those 
arguments on this list.

From lemming at henning-thielemann.de  Wed Jun 18 10:30:05 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun 18 10:22:09 2008
Subject: [Haskell-cafe] Something like scan1
In-Reply-To: <20080618080646.29abd52f@solaris>
References: <20080618080646.29abd52f@solaris>
Message-ID: <Pine.LNX.4.64.0806181624180.23055@anubis.informatik.uni-halle.de>


On Wed, 18 Jun 2008, Achim Schneider wrote:

> Is there a generalisation of scan1, such that eg.
>
> foo (+) [0,1] (1,2) = [0,1,1,2,3,5,8,13,...]
>
> ?

What is the (1,2) for? I could think of


foo f = List.unfoldr (\ xt@(x:xs) -> Just (x, xs ++ [f xt]))

foo sum [0,1]  =  [0,1,1,2,3,5,8,13,21,34,...
From lemming at henning-thielemann.de  Wed Jun 18 10:33:25 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun 18 10:25:57 2008
Subject: [Haskell-cafe] Haskell data types and Storable class
In-Reply-To: <5ae4f2ba0806172212ge0ea659paa2c767bb12700ed@mail.gmail.com>
References: <5ae4f2ba0806172212ge0ea659paa2c767bb12700ed@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806181632410.23055@anubis.informatik.uni-halle.de>


On Wed, 18 Jun 2008, Galchin, Vasili wrote:

> Hello,
>
>     I am reading the FFI spec. Something is unclear to me. Let's assume we
> have
>
>         data A = {b:B, .......}
>
>    and
>
>         data B ={ .............}
>
> both of which belong to class Storable. In the A instance of Storable I want
> to do a poke and peek of "b" into and out-of, respectively, B. How do I
> write the poke and peek function of "b" in the "instance Storable A"?

You will write a Storable instance for B and then just use the class 
methods 'poke' and 'peek' in the instance for A.
From prstanley at ntlworld.com  Wed Jun 18 10:40:06 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 10:31:51 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <48591986.1020304@ropine.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
Message-ID: <20080618144004.HOQC18637.aamtaout04-winn.ispmail.ntl.com@pine.ntlworld.com>


>It seems to me that if a PHP developer sees the Haskell community as 
>a resource for advice on programming language implementation, we 
>should take this as a compliment to the Haskell community.  Repaying 
>that compliment with "your language sucks rocks"


>  strikes me as unwise.
>
>I'm familiar with a lot of arguments for why PHP is a 
>poorly-designed language, and have found them sufficiently 
>persuasive that I haven't bothered to learn PHP.  But I don't see 
>any point to repeating those arguments on this list.

         Paul: So, you've never bothered to learn PHP. Well, I happen 
to know the language very well and therefore feel I am in a good 
position to express my views about it. Unlike you, I don't base my 
judgment on rumours and hearsay. It is true that PHP fails to capture 
the spirit of the classical concept of a function. Type checking in 
PHP is equally poor. These are not just my opinions. Are we not to 
say anything critical about a programming language even if it happens 
to be substantively relevant  lestwe should offend someone? God, if 
you want to stick up for your mates here at least come up with  a 
convincing cover.
Paul

>_______________________________________________
>Haskell-Cafe mailing list
>Haskell-Cafe@haskell.org
>http://www.haskell.org/mailman/listinfo/haskell-cafe

From lrpalmer at gmail.com  Wed Jun 18 10:50:00 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun 18 10:41:53 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
Message-ID: <7ca3f0160806180750m7d2ab838s1db4bd07b9bf4b6e@mail.gmail.com>

On Tue, Jun 17, 2008 at 4:45 PM, Karoly Negyesi <karoly@negyesi.net> wrote:
> Hi,
>
> The PHP community is discussing the adding of closures and lambdas to
> the language, see the proposal at http://wiki.php.net/rfc/closures
>
> If someone with knowledge of both languages could take a quick look it
> would be great.
>
> Thanks a lot
>
> Karoly Negyesi
>
> Ps. I am not a member of the PHP internals team, I am just a PHP
> developer but I am very very interested in getting these in my
> favourite language.

Whew.  Well I suspect you weren't expecting that kind of reaction.  Or
maybe you were... I used to be a Perl developer, and it didn't take
long before I got a level 12 resistence to flame...

Anyway, the proposal looks mostly okay.  I don't know that much PHP,
but I find the "lexical" keyword to be a nuisance.  What are the
semantics if the lexical keyword is omitted?    (i.e. does the
variable become function-local, global, what?)  If it is consistent
with the rest of the language, it'll do.

There is a much more important point with closures:  their
implementation cannot be half-assed!  I'm not claiming that the patch
is--I have not reviewed it--but there is nothing worse than coming up
with a design that relies on a language feature you only later find
out has been nerfed in some way.  Story of my life in C#.  And nerfed
closures are especially bad, because it's so hard to predict the code
path.

What I mean by this is the following must all be supported:

* A closure must only keep alive the varables it references, not the
whole pad on which they are allocated (Python messed up here)
* A closure must be able to call itself recursively (via a
higher-order function typically)  (Squeak messed up here IIRC)
* Multiple references to the same body of code with different bindings
must be able to exist at the same time (duh, that's kinda what makes
it a closure)
* Closures must be nestable.

Looking over the "Zend internal perspective" section, it looks like
that implementation will mostly work.  There are a couple of red
flags, though:

* I would recommend only saving $this in the op_array structure if the
closure actually references $this -- if that is possible to deduce at
the time.  Otherwise you might run into unexpected poor memory
performances in certain cases.  (This kind of thing can make an
*asymptotic* difference in memory performance; i.e. bringing the
memory usage of an algorithm from O(1) to O(n), for example)
* I'm worried that nested closures do not work properly with this
implementation sketch.  Here's a test case:

$f = function ($y) {
        return function ($z) {
            return $y + $z;
        }
     };
$f(1)(2) # should give 3

And congratulations, PHP, for adopting a most essential and powerful feature!

Luke
From barsoap at web.de  Wed Jun 18 10:54:07 2008
From: barsoap at web.de (Achim Schneider)
Date: Wed Jun 18 10:46:14 2008
Subject: [Haskell-cafe] Re: Something like scan1
References: <20080618080646.29abd52f@solaris>
	<Pine.LNX.4.64.0806181624180.23055@anubis.informatik.uni-halle.de>
Message-ID: <20080618165407.4760bdc9@solaris>

Henning Thielemann <lemming@henning-thielemann.de> wrote:

> 
> On Wed, 18 Jun 2008, Achim Schneider wrote:
> 
> > Is there a generalisation of scan1, such that eg.
> >
> > foo (+) [0,1] (1,2) = [0,1,1,2,3,5,8,13,...]
> >
> > ?
> 
> What is the (1,2) for? 
> 
Specifying the relative indexes an element depends on. Ideally, it
should be generalised for n-ary functions.

> I could think of
> foo f = List.unfoldr (\ xt@(x:xs) -> Just (x, xs ++ [f xt]))
> 
> foo sum [0,1]  =  [0,1,1,2,3,5,8,13,21,34,...
>
I should elaborate:

foo (+) [0,1,4] (1,2) = _|_, as 4 isn't 0+1
foo (+) [0,1] (2,3) = [0,1,_|_,1,_|_,_|_]
foo (+) [0,1,1,2,3,5] (1,2) = [0,1,1,2,3,5,8,13,...]
foo (+) [1] (1,1) = [1,2,4,8,16,32,...]


If you allow for inverse functions, you could even say

foo (+-) [0,...,3,..] (1,2) = [0,0,0,...,0,0,1,1,2,3,5,...]


It seems like I'm searching for some primitive that lets me combine
lists and currying. Think of passing a matrix, with each column (or row,
if you prefer) separately uniquely typed, into a function.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From miguelimo38 at yandex.ru  Wed Jun 18 10:54:19 2008
From: miguelimo38 at yandex.ru (Miguel Mitrofanov)
Date: Wed Jun 18 10:46:32 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <48591986.1020304@ropine.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
Message-ID: <2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>


On 18 Jun 2008, at 18:19, Seth Gordon wrote:

> It seems to me that if a PHP developer sees the Haskell community as  
> a resource for advice on programming language implementation, we  
> should take this as a compliment to the Haskell community.  Repaying  
> that compliment with "your language sucks rocks" strikes me as unwise.

Not necessarily. It can be that they'd implement closures in PHP, make  
a dog's dinner of it (as they always do), and then we would be blamed  
for giving them wrong advises.

Anyway, it seems that PR Stanley was forced to use PHP, no wonder he's  
a little mad at it.
From prstanley at ntlworld.com  Wed Jun 18 11:00:29 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 10:52:24 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
Message-ID: <20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>


>>It seems to me that if a PHP developer sees the Haskell community as
>>a resource for advice on programming language implementation, we
>>should take this as a compliment to the Haskell community.  Repaying
>>that compliment with "your language sucks rocks" strikes me as unwise.
>
>Not necessarily. It can be that they'd implement closures in PHP, make
>a dog's dinner of it (as they always do), and then we would be blamed
>for giving them bad advice.
>
>Anyway, it seems that PR Stanley was forced to use PHP, no wonder he's
>a little mad at it.

Paul: How did you know? :-)
You know, the funny thing is that all these so-called civilised 
people can find time and energy to have a go at me but can't be 
bothered to help the chap with the original query.

>_______________________________________________
>Haskell-Cafe mailing list
>Haskell-Cafe@haskell.org
>http://www.haskell.org/mailman/listinfo/haskell-cafe

From lemming at henning-thielemann.de  Wed Jun 18 11:06:13 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun 18 10:58:04 2008
Subject: [Haskell-cafe] Re: Something like scan1
In-Reply-To: <20080618165407.4760bdc9@solaris>
References: <20080618080646.29abd52f@solaris>
	<Pine.LNX.4.64.0806181624180.23055@anubis.informatik.uni-halle.de>
	<20080618165407.4760bdc9@solaris>
Message-ID: <Pine.LNX.4.64.0806181659550.23055@anubis.informatik.uni-halle.de>


On Wed, 18 Jun 2008, Achim Schneider wrote:

> Henning Thielemann <lemming@henning-thielemann.de> wrote:
>
>> On Wed, 18 Jun 2008, Achim Schneider wrote:
>>
>>> Is there a generalisation of scan1, such that eg.
>>>
>>> foo (+) [0,1] (1,2) = [0,1,1,2,3,5,8,13,...]
>>>
>>> ?
>>
>> What is the (1,2) for?
>>
> Specifying the relative indexes an element depends on. Ideally, it
> should be generalised for n-ary functions.

foo f prefix (n,m) =
    let k = length prefix
        xs = prefix ++ zipWith f (xss!!(k-n)) (xss!!(k-m))
        xss = List.tails xs
    in  xs

From jonathanccast at fastmail.fm  Wed Jun 18 11:07:59 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Wed Jun 18 10:59:55 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
	<20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <1213801679.7014.25.camel@jonathans-macbook>

On Wed, 2008-06-18 at 16:00 +0100, PR Stanley wrote:
> >>It seems to me that if a PHP developer sees the Haskell community as
> >>a resource for advice on programming language implementation, we
> >>should take this as a compliment to the Haskell community.  Repaying
> >>that compliment with "your language sucks rocks" strikes me as unwise.
> >
> >Not necessarily. It can be that they'd implement closures in PHP, make
> >a dog's dinner of it (as they always do), and then we would be blamed
> >for giving them bad advice.
> >
> >Anyway, it seems that PR Stanley was forced to use PHP, no wonder he's
> >a little mad at it.
> 
> Paul: How did you know? :-)
> You know, the funny thing is that all these so-called civilised 
> people can find time and energy to have a go at me but can't be 
> bothered to help the chap with the original query.

I could, and I think you're full of it, too.

So there.

jcc


From bos at serpentine.com  Wed Jun 18 11:11:14 2008
From: bos at serpentine.com (Bryan O'Sullivan)
Date: Wed Jun 18 11:03:17 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
Message-ID: <c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>

On Tue, Jun 17, 2008 at 9:00 PM, Anatoly Yakovenko
<aeyakovenko@gmail.com> wrote:
> here is the C:
>
> #include <cblas.h>
> #include <stdlib.h>
>
> int main() {
>   int size = 1024;
>   int ii = 0;
>   double* v1 = malloc(sizeof(double) * (size));
>   double* v2 = malloc(sizeof(double) * (size));
>   for(ii = 0; ii < size*size; ++ii) {
>      double _dd = cblas_ddot(0, v1, size, v2, size);
>   }
>   free(v1);
>   free(v2);
> }

Your C compiler sees that you're not using the result of cblas_ddot,
so it doesn't even bother to call it. That loop never gets run. All
your program does at runtime is call malloc and free twice, which is
very fast :-)
From bos at serpentine.com  Wed Jun 18 11:14:57 2008
From: bos at serpentine.com (Bryan O'Sullivan)
Date: Wed Jun 18 11:06:55 2008
Subject: [Haskell-cafe] Bit streams
In-Reply-To: <4858190B.4090909@btinternet.com>
References: <4858190B.4090909@btinternet.com>
Message-ID: <c290c4f20806180814i2bb44a67vfd8e592523a735a0@mail.gmail.com>

On Tue, Jun 17, 2008 at 1:05 PM, Andrew Coppin
<andrewcoppin@btinternet.com> wrote:

> Before I sit down and spend 3 months designing my own library from scratch,
> does anybody know of an existing library that allows you to do what Binary
> does, but with single-bit precision?

The binary-strict library includes this functionality. It also has
several other useful pieces of functionality. It's rather a shame the
binary and binary-strict developers haven't merged their efforts :-(
From bos at serpentine.com  Wed Jun 18 11:19:57 2008
From: bos at serpentine.com (Bryan O'Sullivan)
Date: Wed Jun 18 11:11:52 2008
Subject: [Haskell-cafe] Problem building GHC 6.8.3
In-Reply-To: <200806181428.25083.daniel.is.fischer@web.de>
References: <200806181428.25083.daniel.is.fischer@web.de>
Message-ID: <c290c4f20806180819t48157bccv197eedca6a153423@mail.gmail.com>

On Wed, Jun 18, 2008 at 5:28 AM, Daniel Fischer
<daniel.is.fischer@web.de> wrote:
> Sorry, probably stupid questions for knowledgeable folks

Not stupid at all, but possibly the wrong mailing list.
glasgow-haskell-users would usually be a better place to ask.

> Setup: Haddock's internal GHC version must match the configured GHC version

You're using Haddock 2.0 or newer. It's not actually possible to build
GHC with it; you must use Haddock 0.9.

Many other packages apparently break with Haddock 2, but GHC is
certainly rather visible :-)  It is possible to have Haddock 0.9 and
2.0 installed simultaneously under different names or in different
locations, but you'll have to patch GHC's sources in order to specify
which Haddock to use. It's a small patch; look on Trac for it.
From prstanley at ntlworld.com  Wed Jun 18 11:24:35 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 11:16:18 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <1213801679.7014.25.camel@jonathans-macbook>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
	<20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<1213801679.7014.25.camel@jonathans-macbook>
Message-ID: <20080618153359.DETZ8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>


> > >>It seems to me that if a PHP developer sees the Haskell community as
> > >>a resource for advice on programming language implementation, we
> > >>should take this as a compliment to the Haskell community.  Repaying
> > >>that compliment with "your language sucks rocks" strikes me as unwise.
> > >
> > >Not necessarily. It can be that they'd implement closures in PHP, make
> > >a dog's dinner of it (as they always do), and then we would be blamed
> > >for giving them bad advice.
> > >
> > >Anyway, it seems that PR Stanley was forced to use PHP, no wonder he's
> > >a little mad at it.
> >
> > Paul: How did you know? :-)
> > You know, the funny thing is that all these so-called civilised
> > people can find time and energy to have a go at me but can't be
> > bothered to help the chap with the original query.
>
>I could, and I think you're full of it, too.
>
>So there.

Paul: I rest my case! :-)
you cowardly hypocrit!

From iainspeed at gmail.com  Wed Jun 18 11:26:55 2008
From: iainspeed at gmail.com (Iain Barnett)
Date: Wed Jun 18 11:18:51 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <4858CB66.1040605@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
Message-ID: <F6AF5A5A-A496-439B-BAFA-6B041C08CBEC@gmail.com>

On 18 Jun 2008, at 9:46 am, Jules Bean wrote:

> This is exactly the sort of message that haskell-cafe does not  
> normally contain. Let's not start now.



Reactions/arguments like the ones on this thread are perfect for  
Haskell - recursive and exponential.

:)

Could we have closure too? :-) Sorry, couldn't resist that one!


Iain
frequent firestarter and purveyor of bad puns

From dons at galois.com  Wed Jun 18 11:36:25 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 18 11:28:32 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <loom.20080618T073859-884@post.gmane.org>
References: <loom.20080618T073859-884@post.gmane.org>
Message-ID: <20080618153625.GB23761@scytale.galois.com>

dominic.steinitz:
> OK, so today I tried to write my first program using the Binary library. 
> And I've hit a snag: It appears the library will only handle data that 
> is byte-aligned. So if I try to write three Bool values, it uses three 
> bytes, not three bits.
> 
> Before I sit down and spend 3 months designing my own library from 
> scratch, does anybody know of an existing library that allows you to do 
> what Binary does, but with single-bit precision? [I presume Binary is 
> byte-aligned for efficiency...]
> 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict

The bitsyntax library perhaps? or a StateT over Binary for carrying
arround the bit packet to write.

-- Don
From aeyakovenko at gmail.com  Wed Jun 18 12:16:24 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Wed Jun 18 12:08:20 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
Message-ID: <e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>

>> #include <cblas.h>
>> #include <stdlib.h>
>>
>> int main() {
>>   int size = 1024;
>>   int ii = 0;
>>   double* v1 = malloc(sizeof(double) * (size));
>>   double* v2 = malloc(sizeof(double) * (size));
>>   for(ii = 0; ii < size*size; ++ii) {
>>      double _dd = cblas_ddot(0, v1, size, v2, size);
>>   }
>>   free(v1);
>>   free(v2);
>> }
>
> Your C compiler sees that you're not using the result of cblas_ddot,
> so it doesn't even bother to call it. That loop never gets run. All
> your program does at runtime is call malloc and free twice, which is
> very fast :-)

C doesn't work like that :).  functions always get called.  but i did
find a problem with my C code, i am incorrectly calling the dot
production function:

#include <cblas.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main() {
   int size = 1024;
   int ii = 0;
   double dd = 0.0;
   double* v1 = malloc(sizeof(double) * (size));
   double* v2 = malloc(sizeof(double) * (size));
   for(ii = 0; ii < size; ++ii) {
      v1[ii] = 0.1;
      v2[ii] = 0.1;
   }
   for(ii = 0; ii < size*size; ++ii) {
      dd += cblas_ddot(size, v1, 0, v2, 0);
   }
   free(v1);
   free(v2);
   printf("%f\n", dd);
   return 0;
}

time ./testdot
10737418.240187

real    0m2.200s
user    0m2.190s
sys     0m0.010s

So C is about twice as fast.  I can live with that.
From qdunkan at gmail.com  Wed Jun 18 12:18:29 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Wed Jun 18 12:10:23 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <7ca3f0160806180750m7d2ab838s1db4bd07b9bf4b6e@mail.gmail.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<7ca3f0160806180750m7d2ab838s1db4bd07b9bf4b6e@mail.gmail.com>
Message-ID: <2518b95d0806180918n40001d40i1b4f77ff7ee8d88f@mail.gmail.com>

> * A closure must only keep alive the varables it references, not the
> whole pad on which they are allocated (Python messed up here)

Getting off subject, but I didn't know this about python.  I'm not
saying you're incorrect, but my experimentation shows:

% cat t.py
class A(object):
    def __init__(self, name): self.name = name
    def __del__(self): print self.name, 'gone'

def f():
    x = A('x')
    y = A('y')
    def g():
        print x.name, 'alive'
    return g

% python
Python 2.5.1 (r251:54869, Apr 18 2007, 22:08:04)
[GCC 4.0.1 (Apple Computer, Inc. build 5367)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
import t
g = t.f()
y gone
g()
x alive
g.func_closure
#-> (<cell at 0xefb50: A object at 0xefb90>,)
del g

x gone
%

So it looks to me like 'y' is not preserved by the closure returned by
'f', and you can see that in its func_closure which keeps the
reference to one A object, but not two.

Python closures do have a "unique" quirk, which is that variables
bound in a nested function are read-only.  This is something that a
schemer might take issue with, but a haskeller probably wouldn't
notice :)  And for the longest time python had its "two space"
namespace thing going on, so it wasn't even really lexically scoped,
but that's many years ago now.
From jim at sdf-eu.org  Wed Jun 18 12:34:33 2008
From: jim at sdf-eu.org (Jim Burton)
Date: Wed Jun 18 12:26:24 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <20080618153359.DETZ8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
	<20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<1213801679.7014.25.camel@jonathans-macbook>
	<20080618153359.DETZ8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <17986275.post@talk.nabble.com>




PR Stanley wrote:
> 
> [...]
> 
> Paul: I rest my case! :-)
> you cowardly hypocrit!
> 
Please take your own advice now, and rest your case. Like it or not (I think
most people do like it), haskell-cafe has norms of behaviour that make it
different to many pl mailing lists. Your sarky comments would have gone
unnoticed if they had been accompanied with something constructive. Name
calling is out.

Jim


> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
> 

-- 
View this message in context: http://www.nabble.com/Lambda-and-closures-in-PHP----could-someone-please-comment--tp17918732p17986275.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From agl at imperialviolet.org  Wed Jun 18 12:49:26 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Wed Jun 18 12:41:18 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <loom.20080618T073859-884@post.gmane.org>
References: <loom.20080618T073859-884@post.gmane.org>
Message-ID: <396556a20806180949u1542b803l895d8967f0762c5f@mail.gmail.com>

On Wed, Jun 18, 2008 at 12:46 AM, Dominic Steinitz
<dominic.steinitz@blueyonder.co.uk> wrote:
> OK, so today I tried to write my first program using the Binary library.
> And I've hit a snag: It appears the library will only handle data that
> is byte-aligned. So if I try to write three Bool values, it uses three
> bytes, not three bits.

There's a BitGet[1] and BitPut in the Hackage version of
binary-strict. However, these versions work on strict ByteStrings.
Putting, for one, is pretty inefficient. In the darcs version[2] of
binary-strict, there's a fully lazy BitPut[3].

There was a request for a lazy BitGet, but I never wrote it. Most of
the time, bit fields are small and you can use the lazy Get from
binary to extract a ByteString and parse that with strict BitGet.
However, the BitPut should be just fine (including doing things like
writing ByteStrings by shifting each byte etc).

If it's missing anything obvious, ping me and I'll see what I can do.

Cheers,


[1] http://darcs.imperialviolet.org/darcsweb.cgi?r=binary-strict;a=headblob;f=/src/Data/Binary/Strict/BitGet.hs
[2] http://darcs.imperialviolet.org/binary-strict/
[3] http://darcs.imperialviolet.org/darcsweb.cgi?r=binary-strict;a=headblob;f=/src/Data/Binary/BitPut.hs

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From hthiel.char at zonnet.nl  Wed Jun 18 12:48:18 2008
From: hthiel.char at zonnet.nl (Hans van Thiel)
Date: Wed Jun 18 12:42:12 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could
	someone	please comment?
In-Reply-To: <4858CB66.1040605@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
Message-ID: <1213807698.6937.30.camel@localhost.localdomain>


On Wed, 2008-06-18 at 09:46 +0100, Jules Bean wrote:
> PR Stanley wrote:
> > With respect, do you not think it'd be wiser for the community 
> 
> [snip]
> 
> *disgusted*
> 
> This is exactly the sort of message that haskell-cafe does not normally 
> contain. Let's not start now.
> 
> This is a civilized mailing list. Either comment on the nice gentlemen's 
> PHP closure proposal from a language point of view, or don't say anything.
> 
> Jules
Hear, hear...

Hans van Thiel
> 

From agl at imperialviolet.org  Wed Jun 18 12:51:45 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Wed Jun 18 12:43:35 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
	<e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
Message-ID: <396556a20806180951w57599c6fj4b70b3c57e776fa8@mail.gmail.com>

On Wed, Jun 18, 2008 at 9:16 AM, Anatoly Yakovenko
<aeyakovenko@gmail.com> wrote:
> C doesn't work like that :)

Yes it can. You would have to check the disassembly to be sure, but C
compilers can, and do, perform dead code elimination.


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From prstanley at ntlworld.com  Wed Jun 18 12:52:42 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 12:44:24 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <17986275.post@talk.nabble.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
	<20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<1213801679.7014.25.camel@jonathans-macbook>
	<20080618153359.DETZ8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<17986275.post@talk.nabble.com>
Message-ID: <20080618165819.HFYI16854.aamtaout01-winn.ispmail.ntl.com@pine.ntlworld.com>


>PR Stanley wrote:
> >
> > [...]
> >
> > Paul: I rest my case! :-)
> > you cowardly hypocrit!

Paul: Why did you remove Jonathan Cast's message? Afraid somebody 
might understand why I responded the way I did?

> >
>Please take your own advice now, and rest your case. Like it or not (I think
>most people do like it), haskell-cafe has norms of behaviour that make it
>different to many pl mailing lists. Your sarky comments would have gone
>unnoticed if they had been accompanied with something constructive. Name
>calling is out.
Paul: and who the bloody hell are you to tell me what's in or out? If 
you want the matter to rest then shut up yourself. I'm getting sick 
of you hypocrites who allow yourselves the audacity to attack me, 
totally gratuitously, yet when I try to defend myself you take the 
moral high ground. Tell me, why did you remove Jonathan Cast's 
message? Is he too big for you? Why don't you tell all the other 
people who have been busy attacking me to modify their language? Are 
you afraid of upsetting the Haskell Cafe Mafia?
Well, guess what, you damn thugs, I 'aint taking this lying down.
You come back with more and I'll give you even more!

From prstanley at ntlworld.com  Wed Jun 18 13:01:07 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 12:52:49 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could
	someone	please comment?
In-Reply-To: <1213807698.6937.30.camel@localhost.localdomain>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<4858CB66.1040605@jellybean.co.uk>
	<1213807698.6937.30.camel@localhost.localdomain>
Message-ID: <20080618170644.HKAV16854.aamtaout01-winn.ispmail.ntl.com@pine.ntlworld.com>


> > PR Stanley wrote:
> > > With respect, do you not think it'd be wiser for the community
> >
> > [snip]
> >
> > *disgusted*
> >
> > This is exactly the sort of message that haskell-cafe does not normally
> > contain. Let's not start now.
> >
> > This is a civilized mailing list. Either comment on the nice gentlemen's
> > PHP closure proposal from a language point of view, or don't say anything.
> >
> > Jules
>Hear, hear...
Paul: You can shut up too, you bloody troll!  

From jules at jellybean.co.uk  Wed Jun 18 13:03:42 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Wed Jun 18 12:55:36 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
	<e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
Message-ID: <48593FEE.70907@jellybean.co.uk>

Anatoly Yakovenko wrote:
>>> #include <cblas.h>
>>> #include <stdlib.h>
>>>
>>> int main() {
>>>   int size = 1024;
>>>   int ii = 0;
>>>   double* v1 = malloc(sizeof(double) * (size));
>>>   double* v2 = malloc(sizeof(double) * (size));
>>>   for(ii = 0; ii < size*size; ++ii) {
>>>      double _dd = cblas_ddot(0, v1, size, v2, size);
>>>   }
>>>   free(v1);
>>>   free(v2);
>>> }
>> Your C compiler sees that you're not using the result of cblas_ddot,
>> so it doesn't even bother to call it. That loop never gets run. All
>> your program does at runtime is call malloc and free twice, which is
>> very fast :-)
> 
> C doesn't work like that :). 

C compilers can do what they like ;)

GCC in particular is pretty good at removing dead code, including entire 
loops. However it shouldn't eliminate the call to cblas_ddot unless it 
thinks cblas_ddot has no side effects at all, which would be surprising 
unless it's inlined somehow.

Jules
From droundy at darcs.net  Wed Jun 18 13:05:44 2008
From: droundy at darcs.net (David Roundy)
Date: Wed Jun 18 12:57:36 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
	<e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
Message-ID: <20080618170543.GK32397@darcs.net>

On Wed, Jun 18, 2008 at 09:16:24AM -0700, Anatoly Yakovenko wrote:
> >> #include <cblas.h>
> >> #include <stdlib.h>
> >>
> >> int main() {
> >>   int size = 1024;
> >>   int ii = 0;
> >>   double* v1 = malloc(sizeof(double) * (size));
> >>   double* v2 = malloc(sizeof(double) * (size));
> >>   for(ii = 0; ii < size*size; ++ii) {
> >>      double _dd = cblas_ddot(0, v1, size, v2, size);
> >>   }
> >>   free(v1);
> >>   free(v2);
> >> }
> >
> > Your C compiler sees that you're not using the result of cblas_ddot,
> > so it doesn't even bother to call it. That loop never gets run. All
> > your program does at runtime is call malloc and free twice, which is
> > very fast :-)
> 
> C doesn't work like that :).  functions always get called.  but i did
> find a problem with my C code, i am incorrectly calling the dot
> production function:

See a recent article in lwn on pure and const functions to see how gcc
is able to perform dead code elimination and CSE, provided its given
annotations on the relevant functions.  I'd certainly hope that your
blas library is properly annotated!

> #include <cblas.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> 
> int main() {
>    int size = 1024;
>    int ii = 0;
>    double dd = 0.0;
>    double* v1 = malloc(sizeof(double) * (size));
>    double* v2 = malloc(sizeof(double) * (size));
>    for(ii = 0; ii < size; ++ii) {
>       v1[ii] = 0.1;
>       v2[ii] = 0.1;
>    }
>    for(ii = 0; ii < size*size; ++ii) {
>       dd += cblas_ddot(size, v1, 0, v2, 0);
>    }
>    free(v1);
>    free(v2);
>    printf("%f\n", dd);
>    return 0;
> }
> 
> time ./testdot
> 10737418.240187
> 
> real    0m2.200s
> user    0m2.190s
> sys     0m0.010s
> 
> So C is about twice as fast.  I can live with that.

I suspect that it is your initialization that is the difference.  For
one thing, you've initialized the arrays to different values, and in
your C code you've fused what are two separate loops in your Haskell
code.  So you've not only given the C compiler an easier loop to run
(since you're initializing the array to a constant rather than to a
sequence of numbers), but you've also manually optimized that
initialization.  In fact, this fusion could be precisely the factor of
two.  Why not see what happens in Haskell if you create just one
vector and dot it with itself? (of course, that'll also make the blas
call faster, so you'll need to be careful in your interpretation of
your results.)

David
From droundy at darcs.net  Wed Jun 18 13:06:17 2008
From: droundy at darcs.net (David Roundy)
Date: Wed Jun 18 12:58:08 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <48593FEE.70907@jellybean.co.uk>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
	<e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
	<48593FEE.70907@jellybean.co.uk>
Message-ID: <20080618170616.GL32397@darcs.net>

On Wed, Jun 18, 2008 at 06:03:42PM +0100, Jules Bean wrote:
> Anatoly Yakovenko wrote:
> >>>#include <cblas.h>
> >>>#include <stdlib.h>
> >>>
> >>>int main() {
> >>>  int size = 1024;
> >>>  int ii = 0;
> >>>  double* v1 = malloc(sizeof(double) * (size));
> >>>  double* v2 = malloc(sizeof(double) * (size));
> >>>  for(ii = 0; ii < size*size; ++ii) {
> >>>     double _dd = cblas_ddot(0, v1, size, v2, size);
> >>>  }
> >>>  free(v1);
> >>>  free(v2);
> >>>}
> >>Your C compiler sees that you're not using the result of cblas_ddot,
> >>so it doesn't even bother to call it. That loop never gets run. All
> >>your program does at runtime is call malloc and free twice, which is
> >>very fast :-)
> >
> >C doesn't work like that :). 
> 
> C compilers can do what they like ;)
> 
> GCC in particular is pretty good at removing dead code, including entire 
> loops. However it shouldn't eliminate the call to cblas_ddot unless it 
> thinks cblas_ddot has no side effects at all, which would be surprising 
> unless it's inlined somehow.

Or unless it's been annotated as pure, which it should be.

David
From jim at sdf-eu.org  Wed Jun 18 13:17:09 2008
From: jim at sdf-eu.org (Jim Burton)
Date: Wed Jun 18 13:09:00 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <20080618165819.HFYI16854.aamtaout01-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
	<20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<1213801679.7014.25.camel@jonathans-macbook>
	<20080618153359.DETZ8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<17986275.post@talk.nabble.com>
	<20080618165819.HFYI16854.aamtaout01-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <17987734.post@talk.nabble.com>



PR Stanley wrote:
> 
> 
>>PR Stanley wrote:
>> >
>> > [...]
>> >
>> > Paul: I rest my case! :-)
>> > you cowardly hypocrit!
> 
> Paul: Why did you remove Jonathan Cast's message? Afraid somebody 
> might understand why I responded the way I did?
> 
>> >
>>Please take your own advice now, and rest your case. Like it or not (I
think
>>most people do like it), haskell-cafe has norms of behaviour that make it
>>different to many pl mailing lists. Your sarky comments would have gone
>>unnoticed if they had been accompanied with something constructive. Name
>>calling is out.
> Paul: and who the bloody hell are you to tell me what's in or out? If 
> you want the matter to rest then shut up yourself. I'm getting sick 
> of you hypocrites who allow yourselves the audacity to attack me, 
> totally gratuitously, yet when I try to defend myself you take the 
> moral high ground. Tell me, why did you remove Jonathan Cast's 
> message? Is he too big for you? Why don't you tell all the other 
> people who have been busy attacking me to modify their language? Are 
> you afraid of upsetting the Haskell Cafe Mafia?
> Well, guess what, you damn thugs, I 'aint taking this lying down.
> You come back with more and I'll give you even more!
> 
I snipped Jonathan's message just because I was commenting on the tone of
your response. Sorry if you think I presented your reply out of context, but
my point is that I don't think there is any need for this in any context
here. I do have a right to say that, even as someone who hardly ever posts
but prefers to read the list...it's owned by everybody. This isn't the same
thing as censorship and you'll notice I said norms, not rules of behaviour.
No one's going to stop you making yourself look silly if you insist on doing
it. As for Jonathan being too big for me, erm, who is he again? :-)


> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
> 

-- 
View this message in context: http://www.nabble.com/Lambda-and-closures-in-PHP----could-someone-please-comment--tp17918732p17987734.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From prstanley at ntlworld.com  Wed Jun 18 13:28:39 2008
From: prstanley at ntlworld.com (PR Stanley)
Date: Wed Jun 18 13:20:36 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <17987734.post@talk.nabble.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
	<48591986.1020304@ropine.com>
	<2AA970B8-05C6-47D1-B3A9-DE2C5FA2B3FF@yandex.ru>
	<20080618150957.CRUB8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<1213801679.7014.25.camel@jonathans-macbook>
	<20080618153359.DETZ8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>
	<17986275.post@talk.nabble.com>
	<20080618165819.HFYI16854.aamtaout01-winn.ispmail.ntl.com@pine.ntlworld.com>
	<17987734.post@talk.nabble.com>
Message-ID: <20080618173140.NIPX29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>

         At 18:17 18/06/2008, you wrote:


>PR Stanley wrote:
> >
> >
> >>PR Stanley wrote:
> >> >
> >> > [...]
> >> >
> >> > Paul: I rest my case! :-)
> >> > you cowardly hypocrit!
> >
> > Paul: Why did you remove Jonathan Cast's message? Afraid somebody
> > might understand why I responded the way I did?
> >
> >> >
> >>Please take your own advice now, and rest your case. Like it or not (I
>think
> >>most people do like it), haskell-cafe has norms of behaviour that make it
> >>different to many pl mailing lists. Your sarky comments would have gone
> >>unnoticed if they had been accompanied with something constructive. Name
> >>calling is out.
> > Paul: and who the bloody hell are you to tell me what's in or out? If
> > you want the matter to rest then shut up yourself. I'm getting sick
> > of you hypocrites who allow yourselves the audacity to attack me,
> > totally gratuitously, yet when I try to defend myself you take the
> > moral high ground. Tell me, why did you remove Jonathan Cast's
> > message? Is he too big for you? Why don't you tell all the other
> > people who have been busy attacking me to modify their language? Are
> > you afraid of upsetting the Haskell Cafe Mafia?
> > Well, guess what, you damn thugs, I 'aint taking this lying down.
> > You come back with more and I'll give you even more!
> >
>I snipped Jonathan's message just because I was commenting on the tone of
>your response. Sorry if you think I presented your reply out of context, but
>my point is that I don't think there is any need for this in any context
>here. I do have a right to say that, even as someone who hardly ever posts
>but prefers to read the list...it's owned by everybody. This isn't the same
>thing as censorship and you'll notice I said norms, not rules of behaviour.
>No one's going to stop you making yourself look silly if you insist on doing
>it. As for Jonathan being too big for me, erm, who is he again? :-)
Paul: So, now I am silly! I'd still prefer that to a coward and a hypocrite

From andrewcoppin at btinternet.com  Wed Jun 18 13:43:25 2008
From: andrewcoppin at btinternet.com (Andrew Coppin)
Date: Wed Jun 18 13:37:17 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <loom.20080618T073859-884@post.gmane.org>
References: <loom.20080618T073859-884@post.gmane.org>
Message-ID: <4859493D.7070609@btinternet.com>

Dominic Steinitz wrote:
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict
>   

Ooo... looks interesting. Pity I can't look at any documentation for it. 
(Is that *really* Haddoc failing with a parse error on a pragma? Surely 
not...) I'll take a look at this.

Thanks.
Andrew.

From dons at galois.com  Wed Jun 18 13:52:07 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 18 13:44:06 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <396556a20806180949u1542b803l895d8967f0762c5f@mail.gmail.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<396556a20806180949u1542b803l895d8967f0762c5f@mail.gmail.com>
Message-ID: <20080618175207.GB24043@scytale.galois.com>

agl:
> On Wed, Jun 18, 2008 at 12:46 AM, Dominic Steinitz
> <dominic.steinitz@blueyonder.co.uk> wrote:
> > OK, so today I tried to write my first program using the Binary library.
> > And I've hit a snag: It appears the library will only handle data that
> > is byte-aligned. So if I try to write three Bool values, it uses three
> > bytes, not three bits.
> 
> There's a BitGet[1] and BitPut in the Hackage version of
> binary-strict. However, these versions work on strict ByteStrings.
> Putting, for one, is pretty inefficient. In the darcs version[2] of
> binary-strict, there's a fully lazy BitPut[3].
> 
> There was a request for a lazy BitGet, but I never wrote it. Most of
> the time, bit fields are small and you can use the lazy Get from
> binary to extract a ByteString and parse that with strict BitGet.
> However, the BitPut should be just fine (including doing things like
> writing ByteStrings by shifting each byte etc).
> 
> If it's missing anything obvious, ping me and I'll see what I can do.
> 
> Cheers,
> 
> 
> [1] http://darcs.imperialviolet.org/darcsweb.cgi?r=binary-strict;a=headblob;f=/src/Data/Binary/Strict/BitGet.hs
> [2] http://darcs.imperialviolet.org/binary-strict/
> [3] http://darcs.imperialviolet.org/darcsweb.cgi?r=binary-strict;a=headblob;f=/src/Data/Binary/BitPut.hs

Adam,

Would you recommend binary-strict over bitsyntax now?
Or are none yet entirely satisfactory

-- Don
From asandroq at gmail.com  Wed Jun 18 13:51:16 2008
From: asandroq at gmail.com (Alex Sandro Queiroz e Silva)
Date: Wed Jun 18 13:44:30 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could	someone	please
	comment?
In-Reply-To: <20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<20080617174953.WVJK29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>	<4858CB66.1040605@jellybean.co.uk>	<20080618104723.YEKX8797.aamtaout03-winn.ispmail.ntl.com@pine.ntlworld.com>	<485908F8.4040001@tcs.inf.tu-dresden.de>
	<20080618134525.JKIM29365.aamtaout02-winn.ispmail.ntl.com@pine.ntlworld.com>
Message-ID: <48594B14.1090202@gmail.com>

Hallo,

PR Stanley wrote:
> Now, if you, Jules, Alex or some other  wannabe Hitler have a problem 
> with my freedom of expression then your best solution is to saddle up 
> and get the hell out yourselves. This is the wrong place for setting up 
> your tinpot dictatorship, Doctor!
> I am grateful for the help I've been getting from the list and my 
> understanding of FP has vastly improved since my membership of this list 
> but I refuse to tolerate bullies who use the list as a way of lifting 
> themselves out of their own shitty lives. Now I am angry!
> 

      Wow, Godwin's in record time. Please don't confuse freedom of 
speech with name-calling, or distasteful, non-constructive comments 
about someone else's programming language.
      Stop making yourself look like a fool.

-alex
http://www.ventonegro.org/

From agl at imperialviolet.org  Wed Jun 18 14:00:20 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Wed Jun 18 13:52:12 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <20080618175207.GB24043@scytale.galois.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<396556a20806180949u1542b803l895d8967f0762c5f@mail.gmail.com>
	<20080618175207.GB24043@scytale.galois.com>
Message-ID: <396556a20806181100jdeeb0c8x98c56cfdaf734112@mail.gmail.com>

On Wed, Jun 18, 2008 at 10:52 AM, Don Stewart <dons@galois.com> wrote:
> Would you recommend binary-strict over bitsyntax now?
> Or are none yet entirely satisfactory

Probably, yes. Bitsyntax was, after all, the first Haskell code I ever
wrote :) It works, but I think the monad style of binary-strict is
better.


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From qdunkan at gmail.com  Wed Jun 18 14:00:58 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Wed Jun 18 13:52:49 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <4859493D.7070609@btinternet.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<4859493D.7070609@btinternet.com>
Message-ID: <2518b95d0806181100p4168bc22neb46dafdc3262e6e@mail.gmail.com>

On Wed, Jun 18, 2008 at 10:43 AM, Andrew Coppin
<andrewcoppin@btinternet.com> wrote:
> Dominic Steinitz wrote:
>>
>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict
>>
>
> Ooo... looks interesting. Pity I can't look at any documentation for it. (Is
> that *really* Haddoc failing with a parse error on a pragma? Surely not...)
> I'll take a look at this.

Yeah, I just ran into that myself, and "solved" it by removing the
haddock comments for those types.

I think Haddock is a bit oversensitive when it comes to parsing.  It
would be nice if it would at least try to continue when it failed to
parse something.  Of course, that might be easier said than done!

While I'm on the subject, what is the future for binary-strict?  I
recently wanted it since I wanted to catch parse errors, but didn't
wind up using it because I would have had to rewrite a whole bunch of
Binary instances to be separate Binary.Put Binary.Strict.Get
instances, and I'm lazy.  So I did 'length (show result) `seq` return
result" which doesn't win any beauty contests but seems to work.

Inclusion in the official Data.Binary would be nice, especially if it
could be a drop-in replacement, say by changing the Data.Binary
instance definitions to Strict.Binary or something.
From bos at serpentine.com  Wed Jun 18 14:07:09 2008
From: bos at serpentine.com (Bryan O'Sullivan)
Date: Wed Jun 18 13:59:00 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <396556a20806181100jdeeb0c8x98c56cfdaf734112@mail.gmail.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<396556a20806180949u1542b803l895d8967f0762c5f@mail.gmail.com>
	<20080618175207.GB24043@scytale.galois.com>
	<396556a20806181100jdeeb0c8x98c56cfdaf734112@mail.gmail.com>
Message-ID: <c290c4f20806181107l5df1f619sfbb9aa6f35fb7765@mail.gmail.com>

On Wed, Jun 18, 2008 at 11:00 AM, Adam Langley <agl@imperialviolet.org> wrote:
> On Wed, Jun 18, 2008 at 10:52 AM, Don Stewart <dons@galois.com> wrote:
>> Would you recommend binary-strict over bitsyntax now?
>> Or are none yet entirely satisfactory
>
> Probably, yes. Bitsyntax was, after all, the first Haskell code I ever
> wrote :) It works, but I think the monad style of binary-strict is
> better.

If you provide Applicative and Alternative instances for your getter
monads (perhaps you already do?), that will get us very close to the
kind of notational succinctness that Erlang's bit-level pattern
matching gives, using entirely general Haskell mechanisms, and without
the fuglitude of TH. That, I think, would be just lovely.
From gsauthof at TechFak.Uni-Bielefeld.DE  Wed Jun 18 14:19:10 2008
From: gsauthof at TechFak.Uni-Bielefeld.DE (Georg Sauthoff)
Date: Wed Jun 18 14:11:02 2008
Subject: [Haskell-cafe] Fast sorting with Bytestring
Message-ID: <20080618181910.GB25272@TechFak.Uni-Bielefeld.DE>

Hi,

I played a bit around with the nice bytestring package. At some point I
implemented a simple sorting program, because I needed line-sorting a file
with a custom line-compare function. I was a bit surprised, that the
resulting code is very fast. A lot of faster than sorting via GNU sort
(with the standard line-compare function).

Then I got suspicious and tested standard GNU sort against a trivial
standard sort implementation in Haskell using bytestring. The Haskell
implementation looks like:

> module Main
> where

> import qualified Data.ByteString.Lazy.Char8 as B
> import Data.List


> main = do
>          c <- B.getContents
>          let l = B.lines c
>          let r = sort l
>          B.putStr $ B.unlines r

Sorting a file of '[]'-strings I get:

time ./sort < brackets > /dev/null  # ~  0.01 s
time sort < brackets > /dev/null    # ~ 14    s

Ok, strane ... Well, let's test with some 'normal' text:

time ./sort < bible > /dev/null       # ~  0.4   s
time sort < bible > /dev/null         # ~  0.56  s

Ok, not that different. But with Haskell you often expect to get very
slow code compared to an implementation in C.

And I am surprised, that the Haskell is fast _and_ nice to read - because
for example the ultra fast 'wc -l' Haskell implementation from the
Haskell-Wiki uses some insider-knowledge about bytestring, and looks to
a beginner not that intuitive, I guess.

./sort is the shown Haskell implementation. I used ghc 6.8.2, installed
bytestring 0.9.1.0 as a user-local package (don't now I this superseeds
the global bytestring package), compiled via ghc -O2. The tests are run at a
Pentium M 1.3 GHz computer. As GNU sort I tested the version from
coreutils 6.9.

You can get the test files from:
http://www.techfak.uni-bielefeld.de/~gsauthof/stuff/brackets.gz
http://www.techfak.uni-bielefeld.de/~gsauthof/stuff/bible.gz
(obviously, you have to gunzip them after downloading ...)

Of course, the naive Haskell implementation doesn't care about locales
(i.e. collating locale sequences), but this shouldn't explain the
observed differences sorting the brackets file.

Best regards
Georg Sauthoff
-- 
Fortune : 'Real programmers don't comment their code.
           It was hard to write, it should be hard to understand.' ;)
From stefanor at cox.net  Wed Jun 18 14:23:00 2008
From: stefanor at cox.net (Stefan O'Rear)
Date: Wed Jun 18 14:14:52 2008
Subject: [Haskell-cafe] Fast sorting with Bytestring
In-Reply-To: <20080618181910.GB25272@TechFak.Uni-Bielefeld.DE>
References: <20080618181910.GB25272@TechFak.Uni-Bielefeld.DE>
Message-ID: <20080618182300.GA3585@localhost.localdomain>

On Wed, Jun 18, 2008 at 08:19:10PM +0200, Georg Sauthoff wrote:
> Hi,
> 
> I played a bit around with the nice bytestring package. At some point I
> implemented a simple sorting program, because I needed line-sorting a file
> with a custom line-compare function. I was a bit surprised, that the
> resulting code is very fast. A lot of faster than sorting via GNU sort
> (with the standard line-compare function).
> 
> Then I got suspicious and tested standard GNU sort against a trivial
> standard sort implementation in Haskell using bytestring. The Haskell
> implementation looks like:
> 
[snip]
> Ok, strane ... Well, let's test with some 'normal' text:
> 
> time ./sort < bible > /dev/null       # ~  0.4   s
> time sort < bible > /dev/null         # ~  0.56  s
> 
> Ok, not that different. But with Haskell you often expect to get very
> slow code compared to an implementation in C.
> 
> And I am surprised, that the Haskell is fast _and_ nice to read - because
> for example the ultra fast 'wc -l' Haskell implementation from the
> Haskell-Wiki uses some insider-knowledge about bytestring, and looks to
> a beginner not that intuitive, I guess.
> 
> ./sort is the shown Haskell implementation. I used ghc 6.8.2, installed
> bytestring 0.9.1.0 as a user-local package (don't now I this superseeds
> the global bytestring package), compiled via ghc -O2. The tests are run at a
> Pentium M 1.3 GHz computer. As GNU sort I tested the version from
> coreutils 6.9.
> 
> You can get the test files from:
> http://www.techfak.uni-bielefeld.de/~gsauthof/stuff/brackets.gz
> http://www.techfak.uni-bielefeld.de/~gsauthof/stuff/bible.gz
> (obviously, you have to gunzip them after downloading ...)
> 
> Of course, the naive Haskell implementation doesn't care about locales
> (i.e. collating locale sequences), but this shouldn't explain the
> observed differences sorting the brackets file.

GNU 'sort' uses an external sort algorithm.  You can, with 200M of
memory, give it a 50G input file, and it will work.  This might explain
the difference..

Stefan
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From gsauthof at TechFak.Uni-Bielefeld.DE  Wed Jun 18 14:38:34 2008
From: gsauthof at TechFak.Uni-Bielefeld.DE (Georg Sauthoff)
Date: Wed Jun 18 14:30:27 2008
Subject: [Haskell-cafe] Fast sorting with Bytestring
In-Reply-To: <20080618182300.GA3585@localhost.localdomain>
References: <20080618181910.GB25272@TechFak.Uni-Bielefeld.DE>
	<20080618182300.GA3585@localhost.localdomain>
Message-ID: <20080618183834.GC25272@TechFak.Uni-Bielefeld.DE>

On Wed, Jun 18, 2008 at 11:23:00AM -0700, Stefan O'Rear wrote:
> GNU 'sort' uses an external sort algorithm.  You can, with 200M of
> memory, give it a 50G input file, and it will work.  This might explain
> the difference..

But the input files are both < 10 mb ...

If I create a 'big_bible' file like 'cat bible bible | dd
of=big_bible count=1 bs=SIZE_OF_BRACKETS' then the timings are:

time sort < big_bible > /dev/null     #  ~ 1.2 s
time ./sort < big_bible > /dev/null   #  ~ 0.8 s

I.e. the difference here is like a low constant factor, and not like a factor
of 1000 with the brackets.

Best regards
Georg Sauthoff
-- 
Fortune : 'Real programmers don't comment their code.
           It was hard to write, it should be hard to understand.' ;)
From ketil at malde.org  Wed Jun 18 14:56:43 2008
From: ketil at malde.org (Ketil Malde)
Date: Wed Jun 18 14:48:18 2008
Subject: [Haskell-cafe] Fast sorting with Bytestring
In-Reply-To: <20080618182300.GA3585@localhost.localdomain> (Stefan O'Rear's
	message of "Wed\, 18 Jun 2008 11\:23\:00 -0700")
References: <20080618181910.GB25272@TechFak.Uni-Bielefeld.DE>
	<20080618182300.GA3585@localhost.localdomain>
Message-ID: <87wskmk1w4.fsf@malde.org>

Stefan O'Rear <stefanor@cox.net> writes:

>> Ok, strane ... Well, let's test with some 'normal' text:
>> 
>> time ./sort < bible > /dev/null       # ~  0.4   s
>> time sort < bible > /dev/null         # ~  0.56  s

>> Ok, not that different. But with Haskell you often expect to get very
>> slow code compared to an implementation in C.

> GNU 'sort' uses an external sort algorithm.  You can, with 200M of
> memory, give it a 50G input file, and it will work.  This might explain
> the difference..

GNU sort also handles locale-based comparison, which I suspect
explains more of the difference.  Try with LC_ALL=C.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From stephen at enterity.com  Wed Jun 18 15:31:18 2008
From: stephen at enterity.com (Stephen Howard)
Date: Wed Jun 18 15:22:30 2008
Subject: [Haskell-cafe] type constructor confusion
Message-ID: <48596286.6050201@enterity.com>

hello list,

loading the code below into ghci gives me this error:

HttpMessage.hs:36:20: Not in scope: type constructor or class `HttpRequest'

The troublesome line is the definition of the cookie function at the end 
of the code.  I've made HttpRequest and HttpResponse constructors of 
HttpMessage as I've sketched out an action that might return either 
one.  Given that I thought what I was doing below was defining these as 
type constructors (maybe I have my vocabulary mixed up) I don't know why 
ghci is returning this error.


module HttpMessage ( HttpMessage(..), HttpRequestMethod(..), cookie ) where

import Data.Map as M

data HttpHeaders = HttpHeaders !(M.Map String String )
data HttpMessage =
    HttpRequest {
        headers        :: HttpHeaders,
        body           :: String,
        request_method :: HttpRequestMethod,
        uri            :: URI,
        http_version   :: Float,
        cookies        :: !(M.Map String String)
    }
    | HttpResponse {
        headers        :: HttpHeaders,
        body           :: String,
        status         :: HttpStatus
    }

data HttpRequestMethod = Get | Head | Post | Put | Delete | Unsupported 
String
data HttpStatus = OK | NotFound | NotAuthorized | ServerError

data URI = URI {
    protocol :: String,
    domain   :: String,
    port     :: String,
    path     :: String,
    query    :: !(M.Map String String),
    anchor   :: String
}

cookie :: String -> HttpRequest -> Maybe String
cookie n request = M.lookup n (cookies request)

From allbery at ece.cmu.edu  Wed Jun 18 15:38:15 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Wed Jun 18 15:30:03 2008
Subject: [Haskell-cafe] type constructor confusion
In-Reply-To: <48596286.6050201@enterity.com>
References: <48596286.6050201@enterity.com>
Message-ID: <D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>


On Jun 18, 2008, at 15:31 , Stephen Howard wrote:

> HttpMessage.hs:36:20: Not in scope: type constructor or class  
> `HttpRequest'
>
> The troublesome line is the definition of the cookie function at  
> the end of the code.  I've made

Right.  "HttpRequest" is a data constructor associated with the type  
constructor "HttpMessage".
(Data constructors are effectively functions; you used it in the  
context of a type, not a function name.)

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From stephen at enterity.com  Wed Jun 18 15:39:02 2008
From: stephen at enterity.com (Stephen Howard)
Date: Wed Jun 18 15:30:17 2008
Subject: [Haskell-cafe] Re: working with Random.randoms
In-Reply-To: <wfskvgcnqp.fsf@calligramme.charmers>
References: <4852A281.8000508@enterity.com>
	<wfskvgcnqp.fsf@calligramme.charmers>
Message-ID: <48596456.6000108@enterity.com>

Thanks for the replies.  This was my solution:

module RandomTest ( random_test ) where

import Random

random_test :: Int -> IO String
random_test n = do
    g <- newStdGen
    return $ take n (randomRs printable_ascii g)
  where printable_ascii = ('!','~')

The "struggling with the type system" was supposed to be 
tongue-in-cheek.  I trust it, it just takes some time to get used to 
it.  And I appreciate Dan's comments about separating the pure code from 
the non-pure, but in this case the code was succinct enough that one 
more layer of functions seemed to do more harm than good when it came to 
legibility.

- Stephen

Jon Fairbairn wrote:
> Stephen Howard <stephen@enterity.com> writes:
>
>   
>> I am a newcomer doing my obligatory struggling with
>> Haskell's type system, 
>>     
>
> That's your mistake. Don't struggle with the type system,
> the type system is your friend; when it tells you you are
> doing something wrong, it's usually right.
>
>   
>> and I've got a nut I've not been able to crack.  Given:
>>
>> import Random
>>
>> random_test :: Int -> String
>> random_test n = do
>>    g <- getStdGen
>>    take n (randoms g)::String
>>     
>
> My immediate reaction on seeing this is that "do" is for
> manipulating monads, but the only monad you've indicated in
> the type is [] (from String = [Char]), and that's probably
> an accident.
>
> In GHCi:
>
> Prelude> :t Random.getStdGen
> Random.getStdGen :: IO System.Random.StdGen
>
> What this says is that getStdGen isn't a function, which is
> to say it doesn't always return the same value (ie it isn't
> pure -- it wouldn't be much use if it were!). In effect it
> uses the real world to get a new value, and such things are
> kept safely in the IO monad. In C, everything is in the IO
> monad; there's no way of telling from the type whether
> something is pure or not?. In Haskell (apart from some
> ugliness that's supposed to stay hidden) you have to
> distinguish between pure and impure, and the type checker
> keeps track of all this for you.
>
>   
>> And yet, when I run these lines in GHCI by hand,
>>     
>
> The top level of GHCi is IO (which shouldn't come as a
> surprise!)
>
>   
>> things seem to work (though the string is the same set of
>> random characters each time, another bit that I need to
>> solve
>>     
>
> That's a somewhat obscure aspect of GHCi, I think, to do
> with "not reverting top-level expressions".  If you do this:
>
> Prelude> :set +r
> Prelude> g <- Random.getStdGen -- what's the type?
> 1954047482 7573
> Prelude> g <- Random.getStdGen -- what's the type?
> 1626678354 7697
> Prelude> 
>
> you see that you get a different StdGen each time.
>
>   
>> I'm guessing that randoms is returning an IO type but I'm
>> not sure how to go about extracting the String to return to
>> the calling action.  Changing the type signature to Int ->
>> IO  String only gives me a different error.
>>     
>
> If you do any IO, you've done some IO! So you need to lift
> out the StdGen and pass that to the functions that you want
> to use it.
>
> main :: IO()
>    do gen <- getStdGen
>       the_list <- real_programme gen
>       print the_list
>
> You should be able to deduce from the fact that the first
> argument of real_programme here is of type StdGen (not IO
> anything) and its result type is [something] that
> real_programme is pure, and gen has only one value
> throughout. So if you want more than one random list out of
> it, you either need to use Random.split or pass more than
> one gen in.
>
>
> [1] Were you truly perverse, you could define your own
> libraries in Haskell so that YourInt = IO Int; YourDouble =
> IO Double etc, and make appropriate classes in place of Num
> &c (hiding the proper ones), so that
>
> + :: YourInt -> YourInt -> YourInt
>
> and so on (you'd have to define your own Bool and if, too,
> but Haskell can do that). Then the type checker would
> overlook all sorts of mistakes that it could otherwise have
> caught.
>
>
>   
From gsauthof at TechFak.Uni-Bielefeld.DE  Wed Jun 18 15:43:23 2008
From: gsauthof at TechFak.Uni-Bielefeld.DE (Georg Sauthoff)
Date: Wed Jun 18 15:35:14 2008
Subject: [Haskell-cafe] Fast sorting with Bytestring
In-Reply-To: <87wskmk1w4.fsf@malde.org>
References: <20080618181910.GB25272@TechFak.Uni-Bielefeld.DE>
	<20080618182300.GA3585@localhost.localdomain>
	<87wskmk1w4.fsf@malde.org>
Message-ID: <20080618194323.GD25272@TechFak.Uni-Bielefeld.DE>

On Wed, Jun 18, 2008 at 08:56:43PM +0200, Ketil Malde wrote:
> Stefan O'Rear <stefanor@cox.net> writes:
> > GNU 'sort' uses an external sort algorithm.  You can, with 200M of
> > memory, give it a 50G input file, and it will work.  This might explain
> > the difference..
 
> GNU sort also handles locale-based comparison, which I suspect
> explains more of the difference.  Try with LC_ALL=C.

Well, for input 'bible' with locale en_US.utf8 GNU sort is ~ 6 times
slower than with locale C. But for input 'brackets' it is ~ 433 times
slower ...

Best regards
Georg Sauthoff
-- 
Fortune : 'Real programmers don't comment their code.
           It was hard to write, it should be hard to understand.' ;)
From alfonso.acosta at gmail.com  Wed Jun 18 16:13:13 2008
From: alfonso.acosta at gmail.com (Alfonso Acosta)
Date: Wed Jun 18 16:05:04 2008
Subject: [Haskell-cafe] Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
Message-ID: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>

Hi,

Can anyone give a good explanation of what ribbonsPerLine means?

Maybe it would be better to simply ask for the meaning of ribbon in
this context. The documentation is totally meaningless to me:
"reibbonsPerLine: Ratio of ribbon length to line length".

I asked at #haskell and frankly, I was surprised by the answer:

fons: can anyone tell me what the heck does ribbonsPerLine mean in
Text.PrettyPrint.HughesPJ?
fons: > renderStyle style{lineLength=10, ribbonsPerLine=1} $ sep [text
"foo" ,text "bar"]
lambdabot:  "foo bar"
fons: > renderStyle style{lineLength=10, ribbonsPerLine=2} $ sep [text
"foo" ,text "bar"]
lambdabot:  "foo\nbar"
fons: ok, somehow it affects the line width ...
byorgey: fons: I can't explain it, all I know is that you must set it
to 1 or else it does bizarre things
fons: hahah, ok
fons: byorgey: that's funny considering its default value is 1.5
byorgey: if you set it to 1 then lineLength means what you think it should
byorgey: fons: EXACTLY

Cheers,

Fons
From byorgey at seas.upenn.edu  Wed Jun 18 16:43:36 2008
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Wed Jun 18 16:35:26 2008
Subject: [Haskell-cafe] Haskell Weekly News: Issue 73 - June 18, 2008
Message-ID: <20080618204336.GA1701@plus.seas.upenn.edu>

---------------------------------------------------------------------------
Haskell Weekly News
http://sequence.complete.org/hwn/20080618
Issue 73 - June 18, 2008
---------------------------------------------------------------------------

   Welcome to issue 73 of HWN, a newsletter covering developments in the
   [1]Haskell community.

   The Google Summer of Code is in full swing, preparations are underway
   for ICFP and the eleventh ICFP Programming Contest, and cabal-install
   is oh-so-sexy. It's an exciting time to be a part of the Haskell
   community!

Community News

   Andy Gill has completed his move from Portland, OR to Kansas.

   Luke Palmer (luqui) has [2]begun work for [3]Anygma, Peter
   Verswyvelen's startup using Haskell (among other languages) to
   ``generate easy-to-use tools for creating audio-visual 2D/3D content.''

   Congrats to Andy and Luke on their new beginnings!

Announcements

   Final CFP: 2008 Haskell Symposium. Andy Gill [4]announced the final
   call for papers for the [5]2008 Haskell Symposium. The deadline is the
   23rd of this month; please submit a paper!

   cabal-install. Duncan Coutts [6]announced the release of
   [7]cabal-install-0.5, along with the release of Cabal-1.4 to support
   it. It features an improved command line interface, smarter upgrading,
   and is made of win. If you are still stuck in the dark ages of
   runhaskell Setup configure blah blah, then the imperative monkeys have
   already won.

   ICFP programming contest. Tim Chevalier [8]announced the eleventh
   annual [9]ICFP programming contest, to be held from Friday, July 11,
   2008 to Monday, July 14, 2008. Are you ready?

   c.h.o trac. Ian Lynagh [10]announced that it is now possible for
   projects on [11]community.haskell.org to [12]create themselves a trac,
   providing a bug tracking system and wiki.

   random-access-list. Stephan Friedrichs [13]announced an
   [14]implementation of Chris Okasaki's random-access lists, providing
   typical list operations (cons, head, tail) in O(1) and indexed
   random-access in O(log n).

   GHC version 6.8.3. Ian Lynagh [15]announced a [16]new patchlevel
   release of [17]GHC, containing a number of bugfixes relative to 6.8.2.

   Printf-TH. Marc Weber [18]announced that he has taken over maintenance
   of the [19]Printf-TH library, which implements a printf function via
   [20]Template Haskell, in order to guarantee that wrong argument types
   or the wrong number of arguments will result in compile time errors.

   Mueval. Gwern Branwen [21]announced the release of the [22]mueval
   package, providing a standalone executable for evaluating Haskell
   expressions based on the GHC API.

   Topkata. Christoph Bauer [23]announced the release of [24]Topkata, a
   simple OpenGL game written in Haskell. The goal is to guide a ball
   through a labyrinth to the opposite corner.

   Haddock Trac. David Waern [25]announced a new [26]bug-tracker and wiki
   for the [27]Haddock project.

   Fortress talk. Jeff Polakow [28]announced that a [29]talk on
   [30]Fortress, a new OO/functional language from Sun, will take place on
   Wednesday, June 25 at 6:30pm in Manhattan, New York, USA.

   ieee-0.2. Patrick Perry [31]announced the release of [32]ieee, a
   library that provides approximate comparison of floating point numbers
   based, NaN-aware minimum and maximum, and a type class for approximate
   comparisons.

Google Summer of Code

   Hoogle 4. Neil Mitchell (ndm) is [33]working on Hoogle 4, recently
   adding support for generating Hoogle databases to [34]Haddock, using
   the GHC API. This week he plans to work on database creation and text
   searches.

   DPH physics engine. Roman Cheplyaka (Feuerbach) is [35]working on a
   physics engine using [36]Data Parallel Haskell, recently adding
   rotations, represented by quaternions. Next he plans to handle
   collisions properly with respect to rotation, and to add documentation.

   Generic tries. Jamie Brandon is writing a library for efficient maps
   using generalized tries. He has come up with a preliminary API and is
   [37]asking for feedback.

   Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a
   make-like dependency analysis framework for Cabal, recently refining
   the core model, that has built its first sources in the testing
   environment. The next step will be dealing with preprocessor chaining.

   Language.C. Benedikt Huber (visq) is working on Language.C, a
   standalone parser/pretty printer library for C99. The test suite is
   finished, the parser and pretty printer support most GNU extensions,
   and all failing tests of gcc.dg are documented.

   GHC API. Thomas Schilling (nominolo) is working on improvements to the
   GHC API.

   GHC plugins. Maximilian Conroy Bolingbroke is working on dynamically
   loaded plugins for GHC.

Discussion

   Low-level array performance. Dan Doel began a [38]discussion about the
   [39]fannkuch benchmark and the current state of Haskell support for
   fast low-level array operations.

   1/0. Evan Laforge began a lively [40]discussion about Infinity, NaN,
   and Haskell's support for the IEEE floating-point standard.

   Documenting the impossible. Andrew Coppin began a [41]discussion on the
   relative merits of {-# IMPOSSIBLE #-} pragmas, calls to 'error' and
   'assert', the use of tools like [42]Catch, and other methods of
   annotating impossible cases.

Blog noise

   [43]Haskell news from the [44]blogosphere.
     * [45]PE Problem #1 in Haskell
     * [46]osfameron: Countdown words game solver in Haskell
     * [47]Algebraic Data Types in JavaScript
     * [48]Finance and Haskell
     * [49]Well-Typed.Com: New Cabal and cabal-install releases
     * [50]Neil Mitchell: GSoC Hoogle: Week 3
     * [51]Max Bolingbroke: Compiler Plugins For GHC: The First Week
     * [52]Dan Piponi (sigfpe): Categories of polynomials and comonadic
       plumbing
     * [53]Roman Cheplyaka: Status report: week 3
     * [54]Thomas DuBuisson (TomMD): Static Buffers Considered Harmful

Quotes of the Week

     * ddarius: Here's the short guide to Haskell for OO programmers:
       Haskell isn't at all an OO language.
     * swalters: I'm starting to believe that learning haskell is mostly
       about carefully crafting small and clever functions and then
       finding out that they are already part of the standard library.

About the Haskell Weekly News

   New editions are posted to [55]the Haskell mailing list as well as to
   [56]the Haskell Sequence and [57]Planet Haskell. [58]RSS is also
   available, and headlines appear on [59]haskell.org. Headlines are
   available as [60]PDF.

   To help create new editions of this newsletter, please see the
   information on [61]how to contribute. Send stories to byorgey at seas
   dot upenn dot edu. The darcs repository is available at darcs get
   [62]http://code.haskell.org/~byorgey/code/hwn/ .

References

   1. http://haskell.org/
   2. http://luqui.org/blog/archives/2008/06/18/new-job/
   3. http://anygma.com/
   4. http://article.gmane.org/gmane.comp.lang.haskell.general/16249
   5. http://haskell.org/haskell-symposium/2008
   6. http://article.gmane.org/gmane.comp.lang.haskell.cabal.devel/3267
   7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-install
   8. http://article.gmane.org/gmane.comp.lang.haskell.general/16238
   9. http://icfpcontest.org/
  10. http://article.gmane.org/gmane.comp.lang.haskell.general/16241
  11. http://community.haskell.org/
  12. http://community.haskell.org/admin/using_project.html#trac
  13. http://article.gmane.org/gmane.comp.lang.haskell.general/16237
  14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/random-access-list
  15. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14645
  16. http://haskell.org/ghc/docs/6.8.3/html/users_guide/release-6-8-3.html
  17. http://www.haskell.org/ghc/
  18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41293
  19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Printf-TH
  20. http://www.haskell.org/th/
  21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41265
  22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval
  23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41263
  24. http://home.arcor.de/chr_bauer/topkata.html
  25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41249
  26. http://trac.haskell.org/haddock
  27. http://www.haskell.org/haddock/
  28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41235
  29. http://lisp.meetup.com/59
  30. http://research.sun.com/projects/plrg/
  31. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41201
  32. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ieee
  33. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-3.html
  34. http://www.haskell.org/haddock/
  35. http://physics-dph.blogspot.com/2008/06/status-report-week-3.html
  36. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell
  37. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9259
  38. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14637
  39. http://shootout.alioth.debian.org/gp4/benchmark.php?test=fannkuch
  40. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41368
  41. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41295
  42. http://www-users.cs.york.ac.uk/~ndm/catch/
  43. http://planet.haskell.org/
  44. http://haskell.org/haskellwiki/Blog_articles
  45. http://jdfrens.blogspot.com/2008/06/pe-problem-1-in-haskell.html
  46. http://osfameron.vox.com/library/post/countdown-words-game-solver-in-haskell.html
  47. http://w3future.com/weblog/stories/2008/06/16/adtinjs.xml
  48. http://blog.gmosx.com/2008/06/finance-and-haskell.html
  49. http://blog.well-typed.com/2008/06/new-cabal-and-cabal-install-releases/
  50. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-3.html
  51. http://blog.omega-prime.co.uk/2008/06/15/compiler-plugins-for-ghc-the-first-week/
  52. http://sigfpe.blogspot.com/2008/06/categories-of-polynomials-and-comonadic.html
  53. http://physics-dph.blogspot.com/2008/06/status-report-week-3.html
  54. http://tommd.wordpress.com/2008/05/25/static-buffers-considered-harmful/
  55. http://www.haskell.org/mailman/listinfo/haskell
  56. http://sequence.complete.org/
  57. http://planet.haskell.org/
  58. http://sequence.complete.org/node/feed
  59. http://haskell.org/
  60. http://code.haskell.org/~byorgey/code/hwn/archives/20080618.pdf
  61. http://haskell.org/haskellwiki/HWN
  62. http://code.haskell.org/~byorgey/code/hwn/
From daniel.is.fischer at web.de  Wed Jun 18 16:44:52 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Wed Jun 18 16:36:13 2008
Subject: [Haskell-cafe] Using cabal-install
Message-ID: <200806182244.52183.daniel.is.fischer@web.de>

Is there a tutorial/user's guide for cabal-install somewhere?
My limited google skills haven't found one and I really need it, because there 
MUST be a better way to get a package and its dependencies built and the 
haddock documentation generated, installed and hyperlinked than manually 
unpacking each .tar.gz and running cabal haddock there.

Thanks,
Daniel
From qdunkan at gmail.com  Wed Jun 18 16:55:32 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Wed Jun 18 16:47:22 2008
Subject: [Haskell-cafe] Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
Message-ID: <2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>

> byorgey: fons: I can't explain it, all I know is that you must set it
> to 1 or else it does bizarre things
> fons: hahah, ok
> fons: byorgey: that's funny considering its default value is 1.5
> byorgey: if you set it to 1 then lineLength means what you think it should
> byorgey: fons: EXACTLY

Excellent, thanks for solving a nagging problem I couldn't be bothered
to track down.  I was wondering why my pretty printing was a little
messed up and slightly too wide.

And isn't 100 columns a bit non-standard for a default?  I thought 80
columns had more traction?  I know that's what my terminals are at...
From dons at galois.com  Wed Jun 18 16:57:46 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 18 16:49:38 2008
Subject: [Haskell-cafe] Using cabal-install
In-Reply-To: <200806182244.52183.daniel.is.fischer@web.de>
References: <200806182244.52183.daniel.is.fischer@web.de>
Message-ID: <20080618205746.GL24043@scytale.galois.com>


http://blog.well-typed.com/2008/06/new-cabal-and-cabal-install-releases/

Basically, build and install cabal-install, then let have it.

daniel.is.fischer:
> Is there a tutorial/user's guide for cabal-install somewhere?
> My limited google skills haven't found one and I really need it, because there 
> MUST be a better way to get a package and its dependencies built and the 
> haddock documentation generated, installed and hyperlinked than manually 
> unpacking each .tar.gz and running cabal haddock there.
> 
> Thanks,
> Daniel
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From david.waern at gmail.com  Wed Jun 18 17:11:46 2008
From: david.waern at gmail.com (David Waern)
Date: Wed Jun 18 17:03:37 2008
Subject: [Haskell-cafe] Problem building GHC 6.8.3
In-Reply-To: <c290c4f20806180819t48157bccv197eedca6a153423@mail.gmail.com>
References: <200806181428.25083.daniel.is.fischer@web.de>
	<c290c4f20806180819t48157bccv197eedca6a153423@mail.gmail.com>
Message-ID: <bb52000e0806181411s4b411469n94b3eb7740940b18@mail.gmail.com>

2008/6/18 Bryan O'Sullivan <bos@serpentine.com>:
> On Wed, Jun 18, 2008 at 5:28 AM, Daniel Fischer
> <daniel.is.fischer@web.de> wrote:
>> Sorry, probably stupid questions for knowledgeable folks
>
> Not stupid at all, but possibly the wrong mailing list.
> glasgow-haskell-users would usually be a better place to ask.
>
>> Setup: Haddock's internal GHC version must match the configured GHC version
>
> You're using Haddock 2.0 or newer. It's not actually possible to build
> GHC with it; you must use Haddock 0.9.

We're discussing how to fix this problem in future releases of GHC and
Haddock. In the meantime, it is actually possible to build GHC with
Haddock 2.1.0 by first building GHC without docs, then installing
Haddock with this GHC, and then building the GHC documentation.

David
From daniel.is.fischer at web.de  Wed Jun 18 17:17:06 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Wed Jun 18 17:06:56 2008
Subject: [Haskell-cafe] Using cabal-install
In-Reply-To: <20080618205746.GL24043@scytale.galois.com>
References: <200806182244.52183.daniel.is.fischer@web.de>
	<20080618205746.GL24043@scytale.galois.com>
Message-ID: <200806182317.06321.daniel.is.fischer@web.de>

Am Mittwoch, 18. Juni 2008 22:57 schrieb Don Stewart:
> http://blog.well-typed.com/2008/06/new-cabal-and-cabal-install-releases/
>
> Basically, build and install cabal-install, then let have it.

I have cabal-install installed, and I'm thankful for it.
My problem is, when I do
cabal install foo
it downloads foo and its dependencies, builds and installs, but it doesn't 
generate the documentation.
How do I get it to build, install and link the documentation for all packages 
automatically, too?

>
> daniel.is.fischer:
> > Is there a tutorial/user's guide for cabal-install somewhere?
> > My limited google skills haven't found one and I really need it, because
> > there MUST be a better way to get a package and its dependencies built
> > and the haddock documentation generated, installed and hyperlinked than
> > manually unpacking each .tar.gz and running cabal haddock there.
> >
> > Thanks,
> > Daniel

From jeremy at n-heptane.com  Wed Jun 18 17:35:28 2008
From: jeremy at n-heptane.com (Jeremy Shaw)
Date: Wed Jun 18 17:25:16 2008
Subject: [Haskell-cafe] Bit streams
In-Reply-To: <20080618133640.24b78310.Malcolm.Wallace@cs.york.ac.uk>
References: <4858190B.4090909@btinternet.com>
	<20080618133640.24b78310.Malcolm.Wallace@cs.york.ac.uk>
Message-ID: <87wskmifz3.wl%jeremy@n-heptane.com>

Malcolm Wallace wrote:

> The original Binary library, circa 1998, was based on bit-streams rather
> than bytes.  You might be able to dig up a copy and bring it back to
> life.

This derivative (by Hal Daume III) works with GHC 6.8.2 (I haven't tried 6.8.3):

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/NewBinary

Not sure how to compares to the original version. It does appear to
still support bit-oriented I/O though.

j.

(Note: I just fixed the cabal stuff to work with 6.8.2 minutes ago, so if have tried it before, it should work now).
From duncan.coutts at worc.ox.ac.uk  Wed Jun 18 17:40:07 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun 18 17:27:22 2008
Subject: [Haskell-cafe] Using cabal-install
In-Reply-To: <200806182244.52183.daniel.is.fischer@web.de>
References: <200806182244.52183.daniel.is.fischer@web.de>
Message-ID: <1213825207.15010.857.camel@localhost>


On Wed, 2008-06-18 at 22:44 +0200, Daniel Fischer wrote:
> Is there a tutorial/user's guide for cabal-install somewhere?
> My limited google skills haven't found one and I really need it, because there 
> MUST be a better way to get a package and its dependencies built and the 
> haddock documentation generated, installed and hyperlinked than manually 
> unpacking each .tar.gz and running cabal haddock there.

The feature you are looking for is not implemented yet.

        "cabal-install should be able to generate haddock docs"
        http://hackage.haskell.org/trac/hackage/ticket/206

Go add your comments to that ticket and tell us how you think it should
work. I mean what command would you expect to run to have it work and
what would it do exactly?

A closely related feature and one it probably overlaps with is this
one: 

        "allow installing just specific bits, like just docs"
        http://hackage.haskell.org/trac/hackage/ticket/225

so we should also think about what the user interface / mode of
interaction of this feature should be.

The issue is that previously we had separate commands for each phase so
it was obvious where to put various phase-specific flags. Now with
cabal-install's install command it does all the phases in one go.
Currently it takes just the flags that the configure command takes (plus
one or two others). So do we just make the install command take the
union of the flags of the other phases? And how to say that we want
optional phases like docs and tests.

That's basically the issue, how do we expect to interact with it? If it
can be relatively consistent and memorable then that's all the better.

We also want all flags that you can pass on the command line to be able
to be set as defaults in the ~/.cabal/config file. Currently there's
just a subset but we want to have it cover everything.


In general, adding yourself to the cc list of a ticket counts as a vote
for the importance of that ticket and commenting on why it's important
even more so (eg how painful and time consuming the alternative is).

Duncan

From duncan.coutts at worc.ox.ac.uk  Wed Jun 18 17:41:52 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun 18 17:29:03 2008
Subject: [Haskell-cafe] Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
	<2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
Message-ID: <1213825312.15010.858.camel@localhost>


On Wed, 2008-06-18 at 13:55 -0700, Evan Laforge wrote:
> > byorgey: fons: I can't explain it, all I know is that you must set it
> > to 1 or else it does bizarre things
> > fons: hahah, ok
> > fons: byorgey: that's funny considering its default value is 1.5
> > byorgey: if you set it to 1 then lineLength means what you think it should
> > byorgey: fons: EXACTLY
> 
> Excellent, thanks for solving a nagging problem I couldn't be bothered
> to track down.  I was wondering why my pretty printing was a little
> messed up and slightly too wide.
> 
> And isn't 100 columns a bit non-standard for a default?  I thought 80
> columns had more traction?  I know that's what my terminals are at...

Yeah. I'd vote for 80. That's what we use in pretty printing messages in
Cabal.

Duncan

From pasalic at cs.rice.edu  Wed Jun 18 16:49:54 2008
From: pasalic at cs.rice.edu (Emir Pasalic)
Date: Wed Jun 18 17:39:11 2008
Subject: [Haskell-cafe] First Call for Papers: DSL WC
Message-ID: <A64BD465-4BC1-4ED4-A4EE-2AC4A5F93DE1@cs.rice.edu>

IFIP Working Conference on Domain Specific Languages (DSL WC)
July 15-17, 2009, Oxford

CALL FOR PAPERS

Domain-specific languages are emerging as a fundamental component of  
software engineering practice. DSLs are often introduced when new  
domains such as web-scripting or markup come into existence, but it is  
also common to see DSLs being introduced and adopted for traditional  
domains such as parsing and data description. Developing software  
using DSLs has many benefits. DSLs are often designed based on  
existing notations that are already in use by experts in a given  
domain. As such, successful DSLs often reduce or eliminate the effort  
needed to transform the concept or innovation produced by the domain  
expert into an executable artifact or even a deliverable software  
product. DSL implementations can capture and mechanize a significant  
portion of the repetitive and mechanical tasks that a domain expert  
traditionally needed to perform in order to produce an executable.  
DSLs can in many cases capture and make widely available special  
expertise that only top specialists in a given domain might have. By  
capturing expert knowledge and reducing repetitive tasks, DSLs often  
also lead to software that is significantly more portable, more  
reliable and more understandable than it would otherwise be.

DSLs can be viewed as having a dual role to general-purpose languages:  
whereas general purpose languages try to do everything as well as  
possible, DSLs are designed to find a domain where they can solve some  
class of problems -- no matter how small -- in the best possible way.  
Widely known examples of DSLs include Matlab, Verilog, SQL, LINQ,  
JavaScript, PERL, HTML, Open GL, Tcl/Tk, Macromedia Director,  
Mathematica/Maple, AutoLisp/AutoCAD, XSLT, RPM, Make, lex/yacc, LaTeX,  
PostScript, Excel, among many others. But while these tools have been  
widely successful, they still fall short of realizing the full idea  
behind them. The goal of this conference is to explore the extent to  
which incorporating modern principles of language design and software  
engineering can benefit existing and future domain-specific languages.

The ultimate goal of using DSLs is to improve programmer productivity  
and software quality. Often, this is achieved by reducing the cost of  
initial software development as well as maintenance costs. These  
improvements - programs being easier to write and maintain -  
materialize as a result of domain-specific guarantees, analyses,  
testing techniques, verification techniques, and optimizations.

    * Paper Criteria
Papers are sought addressing the research problems, fundamental  
principles, and practical techniques of DSLs, including but not  
limited to:
       - Foundations, including semantics, formal methods, type  
theory, and complexity theory
       - Language design, ranging from concrete syntax to semantic and  
typing issues
       - Software engineering, including domain analysis, software  
design, and round-trip         engineering
       - Software processes, including metrics for software and  
language evaluation
       - Implementation techniques, including parsing, compiling, and  
program generation
       - Program analysis and automated transformation
       - Reverse engineering, re-engineering, design discovery,  
automated refactoring
       - Hardware/software codesign
       - Programming environments, including visual languages,  
debuggers, and testing infrastructure
       - Teaching DSLs and the use of DSLs in teaching
       - Case studies, including engineering, bioinformatics, hardware  
specification languages, parallel computing languages, real-time and  
embedded systems, and networked and distributed domains

Papers will be judged on the depth of their insight and the extent to  
which they translate specific experience into general lessons for  
domain-specific language designers and implementers, and software  
engineers. Papers can range from the practical to the theoretical;  
where appropriate, they should refer to actual languages, tools, and  
techniques, provide pointers to full definitions and implementations,  
and include empirical data on results.

    * Important Dates
       - December 14th, 2008: Abstract submission due. Firm, will not  
have any extensions
       - December 21st, 2008: Paper submission deadline. Firm, will  
not have any extensions
       - February 23rd, 2009: Author notification of decisions
       - March 22nd, 2009: Camera ready manuscripts due

    * Program Committee
       - Jon Bentley, Avayalabs
       - Martin Erwig, Oregon State University
       - Jeff Gray, University of Alabama at Birmingham
       - Robert Grimm, New York University
       - Jim Grundy, Intel Strategic CAD Labs
       - Tom Henzinger, EPFL
       - Sam Kamin, UIUC
       - Dick Kieburtz, Portland State University
       - Ralf L?mmel, University of Koblenz
       - Julia Lawall, University of Copenhagen
       - Benjamin Pierce, University of Pennsylvania
       - Vivek Sarkar, Rice University
       - Jeremy Siek, University of Colorado at Boulder
       - Jos? Nuno Oliveira, University of Minho
       - Doaitse Swierstra, Utrecht University
       - Walid Taha (Chair), Rice University
       - Eelco Visser, Delft University
       - William Waite, University of Colorado at Boulder
       - Stephanie Weirich, University of Pennsylvania

    * Organizers
       - General Chair: Jeremy Gibbons, Oxford University
       - Publicity Chair: Emir Pasalic, LogicBlox
From dominic.steinitz at blueyonder.co.uk  Wed Jun 18 17:56:32 2008
From: dominic.steinitz at blueyonder.co.uk (Dominic Steinitz)
Date: Wed Jun 18 17:47:29 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <20080618153625.GB23761@scytale.galois.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<20080618153625.GB23761@scytale.galois.com>
Message-ID: <48598490.5070403@blueyonder.co.uk>

Don Stewart wrote:
> dominic.steinitz:
>> OK, so today I tried to write my first program using the Binary library. 
>> And I've hit a snag: It appears the library will only handle data that 
>> is byte-aligned. So if I try to write three Bool values, it uses three 
>> bytes, not three bits.
>>
>> Before I sit down and spend 3 months designing my own library from 
>> scratch, does anybody know of an existing library that allows you to do 
>> what Binary does, but with single-bit precision? [I presume Binary is 
>> byte-aligned for efficiency...]
>>
>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict
> 
> The bitsyntax library perhaps? or a StateT over Binary for carrying
> arround the bit packet to write.
> 
> -- Don
> 
> 
The vagaries of gmane have made it appear that I asked the question. In
fact, Andrew Coppin asked the question and I responded with a pointer to
 the library Adam Langley pulled together.

Dominic.

From ok at cs.otago.ac.nz  Wed Jun 18 19:19:37 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Wed Jun 18 19:11:35 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<1213755981.3338.15.camel@jonathans-macbook>
	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
Message-ID: <CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>


On 18 Jun 2008, at 4:36 pm, Karoly Negyesi wrote:
>> (a) I would *never* want to use an implementation of closures like  
>> that.
>> Could you elaborate on a) ?

It wasn't me who wrote it, but consider
- non-local variables are *not* captured unless you explicitly
   hoist them into the lambda expression using the 'lexical' keyword.
- references to non-local variables that are not so hoisted are
   not syntax errors, they just quietly do something else.
- ordinary functions do not act as if defined by lambda expressions;
   'lexical' is required in lambdas and forbidden in functions.
- ordinary functions do not act as if defined by lambda expressions;
   the latter can outlive their lexical scope, the former can't.
- what you get is a reference to a variable (as you do in Scheme)
   but loop variables really are variables, not names for values,
   so lambdas created in different iterations of the same loop point
   so the same loop variable, and do not remember the value it had
   when they were created.  The proposal explains how to work around  
this.

All of this boils down to something in which you *can* with care do
the things you expect to do with closures, but the language gently
leads you to the edge of the Pit and the compiler just smiles quietly
as you fall over.






From ok at cs.otago.ac.nz  Wed Jun 18 20:17:58 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Wed Jun 18 20:09:51 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
	<e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
Message-ID: <C0D150EF-BE4A-43A3-B910-61E297098B24@cs.otago.ac.nz>


On 19 Jun 2008, at 4:16 am, Anatoly Yakovenko wrote:
> C doesn't work like that :).  functions always get called.

Not true.  A C compiler must produce the same *effect* as if
the function had been called, but if by some means the compiler
knows that the function has no effect, it is entitled to skip
the call.  In particular, the C compiler I normally use offers
these pragmas, amongst others:

#pragma does_not_write_global_data (funcname [, funcname])
#pragma no_side_effect(funcname[, funcname])

So with a declaration like

	extern double cblas_ddot(
			int,
		        double const *, int,
                         double const *, int);
	#pragma no_side_effect (cblas_ddot)
>
the compiler would be completely within its rights to discard
any call to cblas_ddot() whose result was not used.  (As it
happens, it didn't, but it would have been allowed to.)
If using gcc,

	extern double cblas_ddot( ... as before ...)
		__attribute__ ((const));

seems to have the same effect, certainly the test case I tried
did in fact completely eliminate a call to cblas_ddot() when
so declared.

Since the malloc() results pointed to uninitialised memory,
the C compiler was entitled to do anything it pleased anyway.

From stephen at enterity.com  Wed Jun 18 22:02:27 2008
From: stephen at enterity.com (Stephen Howard)
Date: Wed Jun 18 21:53:40 2008
Subject: [Haskell-cafe] type constructor confusion
In-Reply-To: <D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>
References: <48596286.6050201@enterity.com>
	<D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>
Message-ID: <4859BE33.2040008@enterity.com>

Thanks Brandon, forgot to send my reply to the list:

Ok, so I am confusing things.  Good to know.  So my question is how do I 
fulfill this scenario?

- I have an action that might return either an HttpResponse or an 
HttpRequest, depending on if the IO in the action determined more work 
needed doing.  It's here, though I doubt it's "correct" yet:

requestHandler :: HttpRequest -> IO HttpResponse
requestHandler request = do
   session <- sessionHandler request
   ret     <- uriHandler     request
   case ret of
       HttpResponse -> ret
       HttpRequest  -> resourceHandler session ret

uriHandler :: HttpRequest -> IO HttpMessage
sessionHandler :: HttpRequest -> IO HttpSession

I've given the uriHandler a signature of IO HttpMessage because the 
HttpMessage might be either an HttpResponse or an HttpRequest, and I 
don't know how I should be specifying that.  Ideas?

- Stephen

Brandon S. Allbery KF8NH wrote:
>
> On Jun 18, 2008, at 15:31 , Stephen Howard wrote:
>
>> HttpMessage.hs:36:20: Not in scope: type constructor or class 
>> `HttpRequest'
>>
>> The troublesome line is the definition of the cookie function at the 
>> end of the code.  I've made
>
> Right.  "HttpRequest" is a data constructor associated with the type 
> constructor "HttpMessage".
> (Data constructors are effectively functions; you used it in the 
> context of a type, not a function name.)
>
From ryani.spam at gmail.com  Wed Jun 18 22:46:57 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Wed Jun 18 22:38:48 2008
Subject: [Haskell-cafe] Haskell's type system
In-Reply-To: <20080618093202.GA18893@netsoc.tcd.ie>
References: <d9b7ed750806171340yb04c336i658db913b32084a9@mail.gmail.com>
	<20080618093202.GA18893@netsoc.tcd.ie>
Message-ID: <2f9b2d30806181946gc809426p7a65ccea89a73982@mail.gmail.com>

On 6/18/08, Edsko de Vries <devriese@cs.tcd.ie> wrote:
> Regarding type classes, I'm not 100% what the logical equivalent is,
> although one can regard a type such as
>
>  forall a. Eq a => a -> a
>
> as requiring a proof (evidence) that equality on a is decidable. Where
> this sits formally as a logic I'm not sure though.

You can take the minimalist view and treat a typeclass parameter as an
explicitly passed dictionary; that is:
   (Eq a => a -> a)
is isomorphic to
   (a -> a -> Bool, a -> a -> Bool) -> a -> a

In fact, this is basically what GHC does.

You then treat an instance declaration:
   instance Eq Int where
      (==) = eqInt#
      (/=) = neqInt#
as just a constant
   Eq_Int = (eqInt#, neqInt#)

  -- ryan
From ryani.spam at gmail.com  Wed Jun 18 23:04:24 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Wed Jun 18 22:56:15 2008
Subject: [Haskell-cafe] type constructor confusion
In-Reply-To: <4859BE33.2040008@enterity.com>
References: <48596286.6050201@enterity.com>
	<D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>
	<4859BE33.2040008@enterity.com>
Message-ID: <2f9b2d30806182004g6b60bb72w9a57fa5e0a9f1401@mail.gmail.com>

It sounds like you need to split up your types a bit more.

data HttpRequest = HttpRequest ...

data HttpResponse = HttpResponse ...

data HttpMessage = MsgRequest HttpRequest | MsgResponse HttpResponse
-- alternatively
-- type HttpMessage = Either HttpRequest HttpResponse

Now you can have functions that take/return just an HttpRequest or
just an HttpResponse, as well as functions that use either one via
HttpMessage.  In the latter case, you do need to pattern match to
decide which one you have.

  -- ryan


On 6/18/08, Stephen Howard <stephen@enterity.com> wrote:
> Thanks Brandon, forgot to send my reply to the list:
>
> Ok, so I am confusing things.  Good to know.  So my question is how do I
> fulfill this scenario?
>
> - I have an action that might return either an HttpResponse or an
> HttpRequest, depending on if the IO in the action determined more work
> needed doing.  It's here, though I doubt it's "correct" yet:
>
> requestHandler :: HttpRequest -> IO HttpResponse
> requestHandler request = do
>  session <- sessionHandler request
>  ret     <- uriHandler     request
>  case ret of
>      HttpResponse -> ret
>      HttpRequest  -> resourceHandler session ret
>
> uriHandler :: HttpRequest -> IO HttpMessage
> sessionHandler :: HttpRequest -> IO HttpSession
>
> I've given the uriHandler a signature of IO HttpMessage because the
> HttpMessage might be either an HttpResponse or an HttpRequest, and I don't
> know how I should be specifying that.  Ideas?
>
> - Stephen
>
> Brandon S. Allbery KF8NH wrote:
> >
> > On Jun 18, 2008, at 15:31 , Stephen Howard wrote:
> >
> >
> > > HttpMessage.hs:36:20: Not in scope: type constructor or class
> `HttpRequest'
> > >
> > > The troublesome line is the definition of the cookie function at the end
> of the code.  I've made
> > >
> >
> > Right.  "HttpRequest" is a data constructor associated with the type
> constructor "HttpMessage".
> > (Data constructors are effectively functions; you used it in the context
> of a type, not a function name.)
> >
> >
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From newsham at lava.net  Wed Jun 18 23:23:11 2008
From: newsham at lava.net (Tim Newsham)
Date: Wed Jun 18 23:15:02 2008
Subject: [Haskell-cafe] Gtk2Hs and GCs
Message-ID: <Pine.BSI.4.64.0806181720520.16752@malasada.lava.net>

I don't see a way to fetch an existing standard GC from a widget.
In other Gtk bindings I usually do this by fetching the widget's
style and then grabbing one of the gc's (such as fg_gc[STATE_NORMAL]).
In Gtk2Hs docs:
http://www.haskell.org/gtk2hs/docs/gtk2hs-docs-0.9.12/Graphics-UI-Gtk-General-Style.html
it looks like you can only get Colors, not the whole GC.
I can't seem to find any other way short of making a whole new GC
(as is done in Gtk2Hs/demos/graphic/Drawing.hs).  Am I missing
something?  Is there a reason the GC's arent retrievable?

Tim Newsham
http://www.thenewsh.com/~newsham/
From nfjinjing at gmail.com  Wed Jun 18 23:33:56 2008
From: nfjinjing at gmail.com (jinjing)
Date: Wed Jun 18 23:25:48 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
Message-ID: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>

Hi guys,

This is my second attempt to learn Haskell :)

Any way here's the code:

module Dot where
import Prelude hiding ( (.) )

(.) :: a -> (a -> b) -> b
a . f = f a

infixl 9 .


So for example, 99 questions: Problem 10
(*) Run-length encoding of a list.



comparing:

encode xs = map (\x -> (length x,head x)) (group xs)

to

encode xs = xs.group.map token where token x = (x.length, x.head)




I found starting with data and working my way to a solution seems to be
easier to think with, or maybe it's just me ...

What is your thought?

Jinjing
From levi.stephen at optusnet.com.au  Thu Jun 19 01:34:46 2008
From: levi.stephen at optusnet.com.au (Levi Stephen)
Date: Thu Jun 19 01:26:39 2008
Subject: [Haskell-cafe] (Lazy) SmallCheck and peano numbers
Message-ID: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>

Hi,

I have the following definitions

type Zero
type Succ a

so that I can muck around with a Vector type that includes its length
encoded in its type.

I was wondering whether it was possible to use SmallCheck (or
QuickCheck) to generate random Peano numbers? Is there an issue here
in that what I actually want to generate is a type rather than a
value?

I do have

reifyInt :: Int -> (forall a. ReflectNum a => a -> b) -> b

but, I'm not sure if this can help me when I need to generate other
values based upon that type (e.g., two vectors with the same size
type)

Thanks,
Levi
From jules at jellybean.co.uk  Thu Jun 19 01:53:47 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Thu Jun 19 01:45:39 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<1213755981.3338.15.camel@jonathans-macbook>	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
	<CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>
Message-ID: <4859F46B.5060602@jellybean.co.uk>

Richard A. O'Keefe wrote:

> - what you get is a reference to a variable (as you do in Scheme)
>   but loop variables really are variables, not names for values,
>   so lambdas created in different iterations of the same loop point
>   so the same loop variable, and do not remember the value it had
>   when they were created.  The proposal explains how to work around this.

This one trips everyone up in Javascript.

I think I'm of the opinion that variable capture from lambda formation 
should always be by value. However you can certainly make an argument 
that that's inconsistent in a language which generally has 
mutation/reference semantics. Whichever choice you make, though, 
document it loudly I predict it will be a source of confusion.

Jules
From ok at cs.otago.ac.nz  Thu Jun 19 02:05:56 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Thu Jun 19 01:57:49 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <4859F46B.5060602@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<1213755981.3338.15.camel@jonathans-macbook>	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
	<CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>
	<4859F46B.5060602@jellybean.co.uk>
Message-ID: <279D0571-7E22-41C1-8F46-8FF40E12506A@cs.otago.ac.nz>


On 19 Jun 2008, at 5:53 pm, Jules Bean wrote:

> Richard A. O'Keefe wrote:
>
>> - what you get is a reference to a variable (as you do in Scheme)
>>  but loop variables really are variables, not names for values,
>>  so lambdas created in different iterations of the same loop point
>>  so the same loop variable, and do not remember the value it had
>>  when they were created.  The proposal explains how to work around  
>> this.
>
> This one trips everyone up in Javascript.

What's going on here is a nasty interaction with the semantics of loops.
In Smalltalk and Scheme (to name two languages with closures and
mutable variables), each iteration of a loop in principle creates a new
variable binding.  Scheme example:
	(do ((i 0 (+ i 1))
              (l '() (cons (lambda (x) (* x i)) l)))
             ((>= i 10) l))
is equivalent to
	let f i l = if i >= 10 then l
                     else f (i + 1) ((\x -> x * i) : l)
         in f 0 []
except for i and l being potentially mutable in Scheme but not Haskell.
The Smalltalk equivalent would be
	(0 to: 9) collect: [:i | [:x | x*i]]
in which (a) each iteration creates a *new* i, and (b) method and
block parameters are *not* mutable, because they never are in Smalltalk.

Importing only values into closures would not work for Smalltalk.
Consider the usual implementation of Smalltalk's equivalent of 'fold:

	Collection>>
	inject: initial into: function
	  |r|
	  r := initial.
	  self do: [:each | r := function value: r value: each].
	  ^r

The mutablity of r here really isn't a problem.  Nor is the mutability
of variables _as such_ really the problem in the PHP proposal.
The problem is that it's the *same* variable every time.  If PHP
loops introduced new bindings on every iteration, this particular
problem would not exist.






From jules at jellybean.co.uk  Thu Jun 19 02:25:05 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Thu Jun 19 02:16:57 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <279D0571-7E22-41C1-8F46-8FF40E12506A@cs.otago.ac.nz>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<1213755981.3338.15.camel@jonathans-macbook>	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
	<CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>
	<4859F46B.5060602@jellybean.co.uk>
	<279D0571-7E22-41C1-8F46-8FF40E12506A@cs.otago.ac.nz>
Message-ID: <4859FBC1.2070102@jellybean.co.uk>

Richard A. O'Keefe wrote:
> The mutablity of r here really isn't a problem.  Nor is the mutability
> of variables _as such_ really the problem in the PHP proposal.
> The problem is that it's the *same* variable every time.  If PHP
> loops introduced new bindings on every iteration, this particular
> problem would not exist.

Well, arguably it's not only the loop variable that can be susceptible 
to this problem. There could be other variables in the loop body which 
change each time through (e.g. while loops). Consider this pseudo-code 
(sorry, my PHP is a bit rusty, this syntax is C really)

char c;

while (!eof(fp)) {
   c = getChar(fp);
   bind_event(... some lambda expression referencing c ...);
}

It's pretty surprising to the programmer if all that family of lambda 
expressions reference the *variable* c (and hence, in practice, its 
final value) rather than the *value* c.

Well, maybe that doesn't surprise everyone. It surprised me the first 
time I used closures in Javascript and judging by a few google searches 
I wasn't alone in that.

Jules
From alfonso.acosta at gmail.com  Thu Jun 19 02:39:29 2008
From: alfonso.acosta at gmail.com (Alfonso Acosta)
Date: Thu Jun 19 02:31:20 2008
Subject: [Haskell-cafe] Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <1213825312.15010.858.camel@localhost>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
	<2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
	<1213825312.15010.858.camel@localhost>
Message-ID: <6a7c66fc0806182339k1516fa98ue308cb6c2d94dd28@mail.gmail.com>

On Wed, Jun 18, 2008 at 5:41 PM, Duncan Coutts
<duncan.coutts@worc.ox.ac.uk> wrote:
>> And isn't 100 columns a bit non-standard for a default?  I thought 80
>> columns had more traction?  I know that's what my terminals are at...
>
> Yeah. I'd vote for 80. That's what we use in pretty printing messages in
> Cabal.

Yep, me too, I'm also using 80. I'd also vote for a default
ribbonsPerLine of 1 (whatever that is).
From naur at post11.tele.dk  Thu Jun 19 03:14:10 2008
From: naur at post11.tele.dk (Thorkil Naur)
Date: Thu Jun 19 03:08:14 2008
Subject: [Haskell-cafe] Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
Message-ID: <200806190914.10745.naur@post11.tele.dk>

Hello,

On Wednesday 18 June 2008 22:13, Alfonso Acosta wrote:
> Hi,
> 
> Can anyone give a good explanation of what ribbonsPerLine means?
> 
> Maybe it would be better to simply ask for the meaning of ribbon in
> this context. The documentation is totally meaningless to me:
> "reibbonsPerLine: Ratio of ribbon length to line length".

In the paper "The Design of a Pretty-printing Library" by John Hughes 
(http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps) that 
introduced this pretty printing library, the ribbon concept is introduced 
like this (apologies for the layout, please use the original .ps file for 
accuracy):

> 7.4 Choosing a Pretty Layout
>
> Now that we have designed combinators for constructing documents with many 
possible layouts, it is time to discuss choosing among those alternatives. 
Many prettyprinters aim simply to avoid exceeding a given page width. 
However, we found that using this criterion alone tends to produce layouts 
such as
>
> for i = 1 to 100 do for j = 1 to 100 do for k = 1 to 100 do a[i,j,k] := 0 
>
> which fits on a page, but cannot be described as pretty. We therefore impose 
an additional constraint limiting the number of characters on each line 
(excluding indentation) to a smaller number. The idea is to avoid placing too 
much information on a line -- even a line that begins at the left margin. 
Under this constraint the example above might instead be laid out as
>
> for i = 1 to 100 do
>   for j = 1 to 100 do
>     for k = 1 to 100 do a[i,j,k] := 0
>
> In general a pretty layout will consist of a ribbon of text snaking across 
the page. To see that this is reasonable, ask yourself: `is the prettiest 
layout on an infinitely wide page really to place everything on one line?'

So pretty printing is guided by two lengths: The line length and the (smaller) 
ribbon length.

The ribbons per line ratio that you can specify is simply a way of specifying 
the ribbon length relative to the line length. So, for example, if the line 
length is 80 and the ratio is 1.5, the ribbon length would be 80/1.5 which is 
rounded to 53.

> ...

Best regards
Thorkil
From ketil at malde.org  Thu Jun 19 03:35:08 2008
From: ketil at malde.org (Ketil Malde)
Date: Thu Jun 19 03:26:42 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	(jinjing's message of "Thu\, 19 Jun 2008 11\:33\:56 +0800")
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
Message-ID: <878wx1khcj.fsf@malde.org>

jinjing <nfjinjing@gmail.com> writes:

> Any way here's the code:

> module Dot where
> import Prelude hiding ( (.) )

> (.) :: a -> (a -> b) -> b
> a . f = f a

> infixl 9 .

Isn't this (roughly?) the same as flip ($)?

As a side note, may I advise you to use another symbol, and leave the
poor dot alone? Overloading it as a module separator is bad enough.
If you have a keyboard that allows greater-than-ascii input, there are
plenty of options: ? ? ? ? ? ? ? ? ?...

> comparing:

> encode xs = map (\x -> (length x,head x)) (group xs)

> encode xs = xs.group.map token where token x = (x.length, x.head)

To be fair, you could write the first line as:

   encode xs = map token (group xs) where token x = (length x, head x)

I'm not normally too enthusiastic about point-free style, but when the
left and right side of the = both end with the same term, there's
really no need to name them, so:

   encode = map token . group where token x = (length x, head x)
   -- using function composition (.), not your definition

I'm not sure that would work with left-to-right composition.

> I found starting with data and working my way to a solution seems to be
> easier to think with, or maybe it's just me ...

For monadic code, there "default" is >>= and >> which pass things
forward.  There's also =<< which goes the other way - so I guess
opinions differ.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From magnus at therning.org  Thu Jun 19 05:46:26 2008
From: magnus at therning.org (Magnus Therning)
Date: Thu Jun 19 05:38:19 2008
Subject: [Haskell-cafe] ANN: dataenc 0.11 and omnicodec 0.2
Message-ID: <e040b520806190246l7a5e65ecp634643137801974d@mail.gmail.com>

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

A few days ago I uploaded dataenc 0.11[1] and omnicode 0.2[2].

The short description of the (most visible) changes would be the added
support for Base85 encoding and decoding in dataenc.

The dataenc package (version 0.11)


Data encoding library currently providing Uuencode, Base64, Base64Url,
Base32, Base32Hex, Base16, and Base85.

Other versions0.9, 0.10.1, 0.10.2
Dependenciesbase
LicenseLGPL
CopyrightMagnus Therning, 2007
AuthorMagnus Therning
Maintainermagnus@therning.org
CategoryCodec
Exposed modulesCodec.Binary.DataEncoding, Codec.Binary.Base16,
Codec.Binary.Base32Hex, Codec.Binary.Base32, Codec.Binary.Uu,
Codec.Binary.Base64Url, Codec.Binary.Base64, Codec.Binary.Base85
Upload dateThu Jun 12 15:18:19 PDT 2008
Uploaded byMagnusTherning
Built onghc-6.8


The omnicodec package (version 0.2)

Two simply command line tools built on dataenc.

Other versions0.1
Dependenciesbase, dataenc (>=0.11), directory, filepath, haskell98
LicenseGPL
CopyrightMagnus Therning, 2007
AuthorMagnus Therning
Maintainermagnus@therning.org
CategoryCodec
Executablesodec, oenc
Upload dateThu Jun 12 15:19:07 PDT 2008
Uploaded byMagnusTherning
Built onghc-6.8


/M

[1]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc
[2]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/omnicodec
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Version: GnuPG v1.4.9 (GNU/Linux)

iEYEARECAAYFAkhaKtsACgkQiMWTaatN+6Ru6wCdFBrMfmFWbqTbkWhml8idgbb7
e8sAoN58Xil4ZnbFmSH7xPUtrPUCyZq9
=vlsA
-----END PGP SIGNATURE-----
From ndmitchell at gmail.com  Thu Jun 19 05:48:30 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Thu Jun 19 05:40:19 2008
Subject: [Haskell-cafe] Design suggestion for Data.Binary.Defer
In-Reply-To: <1213735407-sup-7909@ausone.local>
References: <404396ef0806160943r381f0b90ue418cb86bca0bc95@mail.gmail.com>
	<117f2cc80806161612oe3f2033q187cbf5c22592f03@mail.gmail.com>
	<404396ef0806162355m1bf083f2pcebdbfa64e17e42b@mail.gmail.com>
	<20080617182700.GD32397@darcs.net> <1213735407-sup-7909@ausone.local>
Message-ID: <404396ef0806190248g73a4441byfae1795770f362ad@mail.gmail.com>

Hi

> Actually, you ought to be able to pretty easily remove this tradeoff
> by introducing a strict read function as a new method in your class.
> So anyone who wants to strictly read lazy data can use that function
> instead of the lazy one.

Not quite, the library is written so that strict fields are at the
current file pointer while deferred fields require a position jump.

For example, two strict strings would be:

"hello""world"

But two lazy strings would be:

[ptr 5][ptr 10]"hello""world"

>  > :( Lazy reading seems to
>  > require strict writing, while lazy writing requires strict reading!

The library is all designed around making reading maximally efficient,
and minimizing file seeks, but writing can be totally inefficient. As
you mention, the lazy/strict IO trade off is very interesting, its
just fortunate that for my application (Hoogle) the files are written
once and read many many times.

> I'm wondering if it would be an option to read the file backward. If so
>  length annotations could be put at the end.
>
>  Reading  backward  seems  to  only fail with streamed data, which won't support
>  the "seek"ing required by a lazy reading anyway.

You still want to minimize seeking, even if it is possible. In my case
having length information at the front helps reading, and I don't care
about writing, so its an easy win.

I think I've got my design nailed down, and have most of it
implemented and used in Hoogle. These discussions and points were very
helpful!

Thanks

Neil
From duncan.coutts at worc.ox.ac.uk  Thu Jun 19 06:26:21 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Thu Jun 19 06:13:30 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
Message-ID: <1213871181.15010.863.camel@localhost>


On Thu, 2008-06-19 at 11:33 +0800, jinjing wrote:
> Hi guys,
> 
> This is my second attempt to learn Haskell :)
> 
> Any way here's the code:
> 
> module Dot where
> import Prelude hiding ( (.) )
> 
> (.) :: a -> (a -> b) -> b
> a . f = f a
> 
> infixl 9 .

Note that if you redefine (.) composition to be backward application
(flip ($)) then nobody will understand your programs. It's also quite
probably that after reading your own code for a while that you'll not
understand the code that everyone else writes either! :-)

If you want an operator like that, I suggest picking some other symbol.


Duncan

From barsoap at web.de  Thu Jun 19 08:10:00 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun 19 08:02:02 2008
Subject: [Haskell-cafe] News of the day: C fails to stay self-hosting
Message-ID: <20080619141001.01f36fe0@solaris>

http://article.gmane.org/gmane.comp.gcc.patches/165063

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From gwern0 at gmail.com  Thu Jun 19 08:29:25 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Thu Jun 19 08:22:07 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
Message-ID: <20080619122925.GA12077@craft>

On 2008.06.19 11:33:56 +0800, jinjing <nfjinjing@gmail.com> scribbled 0.5K characters:
> Hi guys,
>
> This is my second attempt to learn Haskell :)
>
> Any way here's the code:
>
> module Dot where
> import Prelude hiding ( (.) )
>
> (.) :: a -> (a -> b) -> b
> a . f = f a
>
> infixl 9 .
>
> So for example, 99 questions: Problem 10
> (*) Run-length encoding of a list.
>
> comparing:
>
> encode xs = map (\x -> (length x,head x)) (group xs)
>
> to
>
> encode xs = xs.group.map token where token x = (x.length, x.head)
>
> I found starting with data and working my way to a solution seems to be
> easier to think with, or maybe it's just me ...
>
> What is your thought?
>
> Jinjing

http://cgi.cse.unsw.edu.au/~dons/blog/2007/07 sez:

    encode = map (length &&& head) . group

    decode = concatMap (uncurry replicate)

for a different twist on your approach using arrows.

--
gwern
Kerry W NAVSVS industrial Parvus NAVWAN ISM 8182 NRC Reno
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From benjovi at gmx.net  Thu Jun 19 08:31:14 2008
From: benjovi at gmx.net (Benedikt Huber)
Date: Thu Jun 19 08:23:10 2008
Subject: [Haskell-cafe] Re: Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
	<2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
Message-ID: <485A5192.8030400@gmx.net>

Evan Laforge schrieb:
>> byorgey: fons: I can't explain it, all I know is that you must set it
>> to 1 or else it does bizarre things
>> fons: hahah, ok
>> fons: byorgey: that's funny considering its default value is 1.5
>> byorgey: if you set it to 1 then lineLength means what you think it should
>> byorgey: fons: EXACTLY
> 
> Excellent, thanks for solving a nagging problem I couldn't be bothered
> to track down.  I was wondering why my pretty printing was a little
> messed up and slightly too wide.
> 
> And isn't 100 columns a bit non-standard for a default?  I thought 80
> columns had more traction?  I know that's what my terminals are at...

Hi,

The "ribbon length" is used when choosing the most beautiful layout:
I'll just summarize the relevant section from John Hughes paper 
(http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps), which explains it 
very nicely:

"... Using [the criterion whether the text fits on the page] alone tends 
to produce layouts such as

 > for i = 1 to 100; for j=1 to 100; for k=1 to 100; a[i][j][k]:=0;

which fits on a page {==> line-width} but cannot be described as pretty. 
We therefore impose an additional constraint limiting the number of 
characters on each line [==> ribbon-width} [...]

 > for i = 1 to 100
 >     for j = 1 to 100
 > ...
"

So the pretty printer tries to avoid sequences (ribbons) of characters 
which are longer than ribbon_length, when using auto layout stuff like 
`sep'.

In the source code, we have (paraphrased)

 > ribbon_length = line_length / ribbonsPerLine

and

 > choose_nicest_layout indent p q =
 >   if p + indent fits into line_length and p fits into ribbon_length
 >    then p
 >    else q

Working example below.

I'm not sure 80 characters is still standard when _pretty_-printing - 
the longest line in Text.PrettyPrint.HughesPJ is 109 characters wide ;)

Setting the ribbon ratio to 1 essentially disables the ribbon feature.

Btw: while studying the source code, I also found the cat (and sep) can 
be implemented in a more space efficient way (currently, cat needs to 
evaluate every document in a list to yield some output). Does this make 
sense (see below) ?

cheers,

benedikt


-- * ribbon example

 > -- lineLength = 26, ribbonsPerLine = 1.5 ==> ribbonLength = 17
 > -- therefore, we have a line break if width-indent > 17 or width > 26
 > testStyle = Style { mode = PageMode,
 >                    lineLength = 26,
 >                    ribbonsPerLine = 1.5 }
 > ribbonTest = renderStyle testStyle $
 >
 >   -- use hsep as width == 17 <= ribbonLength
 >       sep [ txt 5, txt 11 ]
 >
 >   -- linebreak, as width-indent = width = 18 > ribbonLength
 >   $+$ sep [ txt 5, txt 12 ]
 >
 >   -- use hsep, as width - indent == 17, and width == 22 < lineLength
 >   $+$ sep (map (nest 5) $ [txt 5, txt 11] )
 >
 >   -- linebreak, as width would be 27 > lineLength
 >   $+$ sep (map (nest 10) $ [txt 5, txt 11] )
 >
 > txt :: Int -> Doc
 > txt 0 = text ""
 > txt k = text $
 >  let ks = show k in
 >   (replicate (k - (length ks)) '_') ++ ks


-- * lazy variants of vcat and hcat
--   you need the constructors from the HughesPJ module

 > vcat' = foldAbove . foldr vcomp2 empty
 > hcat' = foldBeside . foldr hcomp2 empty
 >
 > foldAbove :: Doc -> Doc
 > foldAbove (Above Empty _ d2) = d2
 > foldAbove (Above d1 f d2) = Above d1 f $ foldAbove d2
 > foldAbove doc = doc
 >
 > vcomp2 :: Doc -> Doc -> Doc
 > vcomp2 d1 Empty = d1
 > -- do not match `vcomp2 Empty d1' !
 > vcomp2 d1 d2 = Above d1 False d2
 >
 > foldBeside :: Doc -> Doc
 > foldBeside (Beside Empty _ d2) = d2
 > foldBeside (Beside d1 f d2) = Beside d1 f $ foldBeside d2
 > foldBeside doc = doc
 >
 > hcomp2 :: Doc  -> Doc -> Doc
 > hcomp2 p Empty = p
 > hcomp2 p q = Beside p False q

From benjovi at gmx.net  Thu Jun 19 08:31:14 2008
From: benjovi at gmx.net (Benedikt Huber)
Date: Thu Jun 19 08:23:18 2008
Subject: [Haskell-cafe] Re: Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
	<2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
Message-ID: <485A5192.8030400@gmx.net>

Evan Laforge schrieb:
>> byorgey: fons: I can't explain it, all I know is that you must set it
>> to 1 or else it does bizarre things
>> fons: hahah, ok
>> fons: byorgey: that's funny considering its default value is 1.5
>> byorgey: if you set it to 1 then lineLength means what you think it should
>> byorgey: fons: EXACTLY
> 
> Excellent, thanks for solving a nagging problem I couldn't be bothered
> to track down.  I was wondering why my pretty printing was a little
> messed up and slightly too wide.
> 
> And isn't 100 columns a bit non-standard for a default?  I thought 80
> columns had more traction?  I know that's what my terminals are at...

Hi,

The "ribbon length" is used when choosing the most beautiful layout:
I'll just summarize the relevant section from John Hughes paper 
(http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps), which explains it 
very nicely:

"... Using [the criterion whether the text fits on the page] alone tends 
to produce layouts such as

 > for i = 1 to 100; for j=1 to 100; for k=1 to 100; a[i][j][k]:=0;

which fits on a page {==> line-width} but cannot be described as pretty. 
We therefore impose an additional constraint limiting the number of 
characters on each line [==> ribbon-width} [...]

 > for i = 1 to 100
 >     for j = 1 to 100
 > ...
"

So the pretty printer tries to avoid sequences (ribbons) of characters 
which are longer than ribbon_length, when using auto layout stuff like 
`sep'.

In the source code, we have (paraphrased)

 > ribbon_length = line_length / ribbonsPerLine

and

 > choose_nicest_layout indent p q =
 >   if p + indent fits into line_length and p fits into ribbon_length
 >    then p
 >    else q

Working example below.

I'm not sure 80 characters is still standard when _pretty_-printing - 
the longest line in Text.PrettyPrint.HughesPJ is 109 characters wide ;)

Setting the ribbon ratio to 1 essentially disables the ribbon feature.

Btw: while studying the source code, I also found the cat (and sep) can 
be implemented in a more space efficient way (currently, cat needs to 
evaluate every document in a list to yield some output). Does this make 
sense (see below) ?

cheers,

benedikt


-- * ribbon example

 > -- lineLength = 26, ribbonsPerLine = 1.5 ==> ribbonLength = 17
 > -- therefore, we have a line break if width-indent > 17 or width > 26
 > testStyle = Style { mode = PageMode,
 >                    lineLength = 26,
 >                    ribbonsPerLine = 1.5 }
 > ribbonTest = renderStyle testStyle $
 >
 >   -- use hsep as width == 17 <= ribbonLength
 >       sep [ txt 5, txt 11 ]
 >
 >   -- linebreak, as width-indent = width = 18 > ribbonLength
 >   $+$ sep [ txt 5, txt 12 ]
 >
 >   -- use hsep, as width - indent == 17, and width == 22 < lineLength
 >   $+$ sep (map (nest 5) $ [txt 5, txt 11] )
 >
 >   -- linebreak, as width would be 27 > lineLength
 >   $+$ sep (map (nest 10) $ [txt 5, txt 11] )
 >
 > txt :: Int -> Doc
 > txt 0 = text ""
 > txt k = text $
 >  let ks = show k in
 >   (replicate (k - (length ks)) '_') ++ ks


-- * lazy variants of vcat and hcat
--   you need the constructors from the HughesPJ module

 > vcat' = foldAbove . foldr vcomp2 empty
 > hcat' = foldBeside . foldr hcomp2 empty
 >
 > foldAbove :: Doc -> Doc
 > foldAbove (Above Empty _ d2) = d2
 > foldAbove (Above d1 f d2) = Above d1 f $ foldAbove d2
 > foldAbove doc = doc
 >
 > vcomp2 :: Doc -> Doc -> Doc
 > vcomp2 d1 Empty = d1
 > -- do not match `vcomp2 Empty d1' !
 > vcomp2 d1 d2 = Above d1 False d2
 >
 > foldBeside :: Doc -> Doc
 > foldBeside (Beside Empty _ d2) = d2
 > foldBeside (Beside d1 f d2) = Beside d1 f $ foldBeside d2
 > foldBeside doc = doc
 >
 > hcomp2 :: Doc  -> Doc -> Doc
 > hcomp2 p Empty = p
 > hcomp2 p q = Beside p False q

From Malcolm.Wallace at cs.york.ac.uk  Thu Jun 19 08:44:47 2008
From: Malcolm.Wallace at cs.york.ac.uk (Malcolm Wallace)
Date: Thu Jun 19 08:37:06 2008
Subject: [Haskell-cafe] Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <6a7c66fc0806182339k1516fa98ue308cb6c2d94dd28@mail.gmail.com>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
	<2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
	<1213825312.15010.858.camel@localhost>
	<6a7c66fc0806182339k1516fa98ue308cb6c2d94dd28@mail.gmail.com>
Message-ID: <20080619134447.116a4837.Malcolm.Wallace@cs.york.ac.uk>

To answer the original question (in the subject line),

  "The ribbon ratio is the number of times the ribbon fits into a line.
   The ribbon is the number of characters on a line excluding leading
   and trailing white spaces.
  "
See also the original paper on which the Text.PrettyPrint.HughesPJ code
is based:
    http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps
section 7.4.

The idea is that the pretty-printer should not cram lots of text into a
single line, if it would look nicer split across two (shorter) lines.
The ribbonsPerLine ratio is the factor that determines this level of
"prettiness".  A ratio of 1.0 means to cram everything into the line if
you can.  A larger ratio means to go for more lines, but less text on
each.  Somewhere between 1.2 and 1.8 is likely to be more or less
pleasing: 1.0 will be ugly, 2.0 or above will look decidedly fragmented.

Regards,
    Malcolm
From lemming at henning-thielemann.de  Thu Jun 19 11:17:38 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 19 11:09:28 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
Message-ID: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>


Is there a way of accessing a remote Oracle database by one of the common 
Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get 
unixODBC and Oracle's Instant Client running on a Linux machine, but I'm 
trapped in the notorious error:

$ isql USER -v
[IM004][unixODBC][Driver Manager]Driver's SQLAllocHandle on SQL_HANDLE_HENV failed
[ISQL]ERROR: Could not SQLConnect

This error message is discussed in various web forums, but there seems to 
be no systematic way to track down the problem. So I wonder whether there 
is another way to access the Oracle data base from Haskell.
From byorgey at gmail.com  Thu Jun 19 12:00:00 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Thu Jun 19 11:51:50 2008
Subject: [Haskell-cafe] network-related segfaults
Message-ID: <22fcbd520806190900q7683be90x8de1d89a2e840c23@mail.gmail.com>

Hi all,

Has anyone else experienced segfaults related to network stuff?  Observe:

[11:50:56 brent@xenophon:~]$ ghci -ignore-dot-ghci
GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> :m +Text.HTML.Download
Prelude Text.HTML.Download> txt <- openURL "http://www.google.com"
Loading package bytestring-0.9.1.0 ... linking ... done.
Loading package mtl-1.1.0.0 ... linking ... done.
Loading package parsec-3.0.0 ... linking ... done.
Loading package network-2.1.0.0 ... linking ... done.
Loading package array-0.1.0.0 ... linking ... done.
Loading package containers-0.1.0.1 ... linking ... done.
Loading package tagsoup-0.6 ... linking ... done.
Segmentation fault (core dumped)

This just started happening yesterday.  I think I may have just upgraded
some packages via cabal-install but I'm not sure which ones.  Now is a time
when I wish all my terminal sessions were automatically logged. (Hmm,
perhaps I should look into that...)

-Brent
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From stephen at enterity.com  Thu Jun 19 12:28:22 2008
From: stephen at enterity.com (Stephen Howard)
Date: Thu Jun 19 12:19:32 2008
Subject: [Haskell-cafe] type constructor confusion
In-Reply-To: <2f9b2d30806182004g6b60bb72w9a57fa5e0a9f1401@mail.gmail.com>
References: <48596286.6050201@enterity.com>	
	<D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>	
	<4859BE33.2040008@enterity.com>
	<2f9b2d30806182004g6b60bb72w9a57fa5e0a9f1401@mail.gmail.com>
Message-ID: <485A8926.7010902@enterity.com>

Cool, "Either" looks like what I'm looking for.  I'll have to look into 
that.  What do I do about the fact that both HttpRequest and 
HttpResponse have some of the same named fields (headers and body, for 
example).  Seems a pain to drop them into separate modules just so I can 
keep the naming conventions consistent.

- Stephen

Ryan Ingram wrote:
> It sounds like you need to split up your types a bit more.
>
> data HttpRequest = HttpRequest ...
>
> data HttpResponse = HttpResponse ...
>
> data HttpMessage = MsgRequest HttpRequest | MsgResponse HttpResponse
> -- alternatively
> -- type HttpMessage = Either HttpRequest HttpResponse
>
> Now you can have functions that take/return just an HttpRequest or
> just an HttpResponse, as well as functions that use either one via
> HttpMessage.  In the latter case, you do need to pattern match to
> decide which one you have.
>
>   -- ryan
>
>
> On 6/18/08, Stephen Howard <stephen@enterity.com> wrote:
>   
>> Thanks Brandon, forgot to send my reply to the list:
>>
>> Ok, so I am confusing things.  Good to know.  So my question is how do I
>> fulfill this scenario?
>>
>> - I have an action that might return either an HttpResponse or an
>> HttpRequest, depending on if the IO in the action determined more work
>> needed doing.  It's here, though I doubt it's "correct" yet:
>>
>> requestHandler :: HttpRequest -> IO HttpResponse
>> requestHandler request = do
>>  session <- sessionHandler request
>>  ret     <- uriHandler     request
>>  case ret of
>>      HttpResponse -> ret
>>      HttpRequest  -> resourceHandler session ret
>>
>> uriHandler :: HttpRequest -> IO HttpMessage
>> sessionHandler :: HttpRequest -> IO HttpSession
>>
>> I've given the uriHandler a signature of IO HttpMessage because the
>> HttpMessage might be either an HttpResponse or an HttpRequest, and I don't
>> know how I should be specifying that.  Ideas?
>>
>> - Stephen
>>
>> Brandon S. Allbery KF8NH wrote:
>>     
>>> On Jun 18, 2008, at 15:31 , Stephen Howard wrote:
>>>
>>>
>>>       
>>>> HttpMessage.hs:36:20: Not in scope: type constructor or class
>>>>         
>> `HttpRequest'
>>     
>>>> The troublesome line is the definition of the cookie function at the end
>>>>         
>> of the code.  I've made
>>     
>>> Right.  "HttpRequest" is a data constructor associated with the type
>>>       
>> constructor "HttpMessage".
>>     
>>> (Data constructors are effectively functions; you used it in the context
>>>       
>> of a type, not a function name.)
>>     
>>>       
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>     
From gwern0 at gmail.com  Thu Jun 19 12:30:56 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Thu Jun 19 12:24:16 2008
Subject: [Haskell-cafe] cabal-install failure
In-Reply-To: <1213430194.15010.556.camel@localhost>
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
	<1213392126.15010.547.camel@localhost>
	<20080614021052.GA8862@craft>
	<1213430194.15010.556.camel@localhost>
Message-ID: <20080619163056.GD28192@craft>

On 2008.06.14 08:56:34 +0100, Duncan Coutts <duncan.coutts@worc.ox.ac.uk> scribbled 1.3K characters:
>
> On Fri, 2008-06-13 at 22:10 -0400, Gwern Branwen wrote:
>
> > I think this may be Cabal's fault anyway. The yi.cabal includes the line:
> >          build-tools:   alex >= 2.0.1 && < 3
> >
> > in the 'executable yi' section, right after the build-depends, so Yi
> > is being straightforward and upfront about its needs. Now, Cabal is
> > obviously checking that the build-depends is satisfied first, but why
> > isn't it checking that alex is available when it has the information
> > it needs to check, presumably anything in build-tools is *required*,
> > and the field name suggests that it would be checked?
>
> Yes, you're right. This is the ticket you filed last time:
>
> http://hackage.haskell.org/trac/hackage/ticket/227
>
> and my comment:
>
>         One problem is that not all build-tools correspond to haskell
>         packages. Some do some don't. We have a hard coded list of them
>         at the moment (which can be extended in Setup.hs files) so we
>         could extend that with what haskell package if any the tools
>         correspond to. Any better suggestions to make it a tad more
>         generic?
>
> If anyone has a godd suggestion I'm happy to hear it. Otherwise we can
> just add a Maybe Dependency to the Program type to indicate that some
> build tools have a corresponding haskell package.
>
> Duncan

Well, one work-around would be to have everyone do a library/executable split for their tools. This exposes a library module and allows it to be listed in build-depends:.

(This is something of a hack, but I think it has some nice effects - it's polite to allow people access to the core logic so they can try to improve on your version, and it encourages you to make the executable more of a wrapper around a library.)

--
gwern
benelux EIP Red CISD LUK on botux Bletchley 2E781 Connections
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From agl at imperialviolet.org  Thu Jun 19 12:34:06 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Thu Jun 19 12:25:56 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <2518b95d0806181100p4168bc22neb46dafdc3262e6e@mail.gmail.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<4859493D.7070609@btinternet.com>
	<2518b95d0806181100p4168bc22neb46dafdc3262e6e@mail.gmail.com>
Message-ID: <396556a20806190934t384e16e2je53f336f94ab32be@mail.gmail.com>

On Wed, Jun 18, 2008 at 11:00 AM, Evan Laforge <qdunkan@gmail.com> wrote:
> Inclusion in the official Data.Binary would be nice, especially if it
> could be a drop-in replacement, say by changing the Data.Binary
> instance definitions to Strict.Binary or something.

I have a class defined to abstract the various Get monads, i.e. you
can write generic code which will work over a strict get, or an
incremental (continuation based) get.

I don't have the same for put yet. The trick is to make it so that it
doesn't end up with any runtime cost. dons would not be happy if I
took his highly tuned binary library and made it slow :)

AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From agl at imperialviolet.org  Thu Jun 19 12:35:15 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Thu Jun 19 12:27:04 2008
Subject: [Haskell-cafe] Re: Bit Streams
In-Reply-To: <c290c4f20806181107l5df1f619sfbb9aa6f35fb7765@mail.gmail.com>
References: <loom.20080618T073859-884@post.gmane.org>
	<396556a20806180949u1542b803l895d8967f0762c5f@mail.gmail.com>
	<20080618175207.GB24043@scytale.galois.com>
	<396556a20806181100jdeeb0c8x98c56cfdaf734112@mail.gmail.com>
	<c290c4f20806181107l5df1f619sfbb9aa6f35fb7765@mail.gmail.com>
Message-ID: <396556a20806190935j7c0bf35anad1856dc55639ada@mail.gmail.com>

On Wed, Jun 18, 2008 at 11:07 AM, Bryan O'Sullivan <bos@serpentine.com> wrote:
> If you provide Applicative and Alternative instances for your getter
> monads (perhaps you already do?)

I have Alternative instances, and they're used a fair bit in my HTTP
parser (network-minihttp). You're right that I should add Applicative
too; maybe this weekend.


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From mfn-haskell-cafe at cs.york.ac.uk  Thu Jun 19 12:50:12 2008
From: mfn-haskell-cafe at cs.york.ac.uk (Matthew)
Date: Thu Jun 19 12:46:46 2008
Subject: [Haskell-cafe] (Lazy) SmallCheck and peano numbers
In-Reply-To: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>
References: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>
Message-ID: <20080619165012.GA7049@pc149.staff.cs.york.ac.uk>

Hi Levi,

> so that I can muck around with a Vector type that includes its length
> encoded in its type.

I suppose you have some operations over these vectors, such as

  nil  :: Vec Zero a
  (|>) :: a -> Vec n a -> Vec (Succ n) a

If so, you could write a SmallCheck Series instance as follows.

  instance Serial (Vec Zero a) where
    series = cons0 nil 

  instance (Serial a, Serial (Vec n a)) => Serial (Vec (Succ n) a) where
    series = cons2 (|>)

Let's assume the earlier ops are defined as

  data Vec n a = V [a]

  nil :: Vec Zero a
  nil = V []

  (|>) :: a -> Vec n a -> Vec (Succ n) a
  x |> V xs = V (x:xs)

If we have the property

  prop_vector :: Vec (Succ (Succ Zero)) Bool -> Bool
  prop_vector (V xs) = xs == xs

we can check it, and only 2 element vectors will be tested:

  *Main> smallCheck 4 prop_vector
  Depth 0:
    Completed 0 test(s) without failure.
  Depth 1:
    Completed 0 test(s) without failure.
  Depth 2:
    Completed 4 test(s) without failure.
  Depth 3:
    Completed 4 test(s) without failure.
  Depth 4:
    Completed 4 test(s) without failure.

Now, it seems what you really want to do is define polymorphic
properties like

  prop_poly :: Vec n Bool -> Vec n Bool -> Bool

and have SmallCheck check all equal-sized vectors.  If so, good
question! :-)

Anybody else?

Matt.
From byorgey at gmail.com  Thu Jun 19 13:12:59 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Thu Jun 19 13:04:49 2008
Subject: [Haskell-cafe] Re: network-related segfaults
In-Reply-To: <22fcbd520806190900q7683be90x8de1d89a2e840c23@mail.gmail.com>
References: <22fcbd520806190900q7683be90x8de1d89a2e840c23@mail.gmail.com>
Message-ID: <22fcbd520806191012n564c652alb2aaf75ba74c3f63@mail.gmail.com>

On Thu, Jun 19, 2008 at 12:00 PM, Brent Yorgey <byorgey@gmail.com> wrote:

> Hi all,
>
> Has anyone else experienced segfaults related to network stuff?  Observe:
>

Well, just to keep everyone updated, I suddenly remembered that
cabal-install now writes log information! =D  So I looked in the logs and
found that I had indeed recently installed network-2.1.0.0 when trying to
upgrade the urlcheck package.  So I upgraded to the latest version of
network (2.2.0.0) and now everything is peachy again.  So, it seems that
network-2.1.0.0 was the culprit...

-Brent
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From vogt.adam at gmail.com  Thu Jun 19 13:18:13 2008
From: vogt.adam at gmail.com (Adam Vogt)
Date: Thu Jun 19 13:10:06 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <878wx1khcj.fsf@malde.org>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	<878wx1khcj.fsf@malde.org>
Message-ID: <20080619171812.GA25606@dell>

* On Thursday, June 19 2008, Ketil Malde wrote:

>As a side note, may I advise you to use another symbol, and leave the
>poor dot alone? Overloading it as a module separator is bad enough.
>If you have a keyboard that allows greater-than-ascii input, there are
>plenty of options: ? ? ? ? ? ? ? ? ?...

And even if you have a plain us layout in hardware, you can use 
us-international layout (or whatever it is called).

So we can make haskell sort of like apl...

While we are kind of on this topic, what makes the characters ? ? prefix 
operator by default, while ? and most other odd ones infix?
From derek.a.elkins at gmail.com  Thu Jun 19 13:29:35 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Thu Jun 19 13:22:02 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone
	please comment?
In-Reply-To: <4859FBC1.2070102@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<1213755981.3338.15.camel@jonathans-macbook>
	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>
	<CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>
	<4859F46B.5060602@jellybean.co.uk>
	<279D0571-7E22-41C1-8F46-8FF40E12506A@cs.otago.ac.nz>
	<4859FBC1.2070102@jellybean.co.uk>
Message-ID: <1213896576.5557.55.camel@derek-laptop>

On Thu, 2008-06-19 at 07:25 +0100, Jules Bean wrote:
> Richard A. O'Keefe wrote:
> > The mutablity of r here really isn't a problem.  Nor is the mutability
> > of variables _as such_ really the problem in the PHP proposal.
> > The problem is that it's the *same* variable every time.  If PHP
> > loops introduced new bindings on every iteration, this particular
> > problem would not exist.
> 
> Well, arguably it's not only the loop variable that can be susceptible 
> to this problem. There could be other variables in the loop body which 
> change each time through (e.g. while loops). Consider this pseudo-code 
> (sorry, my PHP is a bit rusty, this syntax is C really)
> 
> char c;
> 
> while (!eof(fp)) {
>    c = getChar(fp);
>    bind_event(... some lambda expression referencing c ...);
> }
> 
> It's pretty surprising to the programmer if all that family of lambda 
> expressions reference the *variable* c (and hence, in practice, its 
> final value) rather than the *value* c.
> 
> Well, maybe that doesn't surprise everyone. It surprised me the first 
> time I used closures in Javascript and judging by a few google searches 
> I wasn't alone in that.

Lambda abstractions should close over bindings.  Full stop.

The first "surprising" behaviour is the correct one.  The latter would
be broken.

In my opinion, the reason this behaviour is "surprising" isn't
mutability, but -implicit- mutability.  Let's make bindings immutable,
but add ML-style references to your example.

char ref c = ref(undefined);
while(!eof(fp)) {
    c := getChar(fp);
    bind_event( ... print !c; ... );
}

compare this to

while(!eof(fp)) {
    char c = getChar(fp);
    bind_event( ... print c; ...);
}

or

while(!eof(fp)) {
    char ref c = ref(getChar(fp));
    bind_event( ... print !c; ...);
}

Each of these examples makes it clearer what is going on.  Admittedly,
if we write a 'foreachChar' HOF, the difference between the first
implementation and the last will not be apparent from the type.  That's
just the nature of the beast; there is simply more than one
implementation.

At any rate, as Richard O'Keefe stated, it's not the lambda's behaviour
that needs to be documented, it's the loop's (or HOFs in general), for
the iteration variables.  The ones you introduce are your own concern;
say what you mean.

From silva.samuel at gmail.com  Thu Jun 19 13:55:11 2008
From: silva.samuel at gmail.com (Samuel Silva)
Date: Thu Jun 19 13:47:28 2008
Subject: [Haskell-cafe] This is a bug?
Message-ID: <382ead9b0806191055k7aba616bh3ff1e527648037ca@mail.gmail.com>

Hello

I'm using HaXml library to handle XML.


How I solve this issue when call "readXml":
>in <score-partwise>, In a sequence:
>  in <part>, In a sequence:
>    in <measure>, Too many elements inside <measure> at
>    file ../../../parsers/elite2.xml  at line 75 col 15
>    Found excess:
>
>
>Done.

I don't understood this error.

I'm using HaXml-1.19.4 with GHC-6.8.2

-- 
Don't hug that, Hugs ME!
Samuel Silva
From benjovi at gmx.net  Thu Jun 19 14:00:50 2008
From: benjovi at gmx.net (Benedikt Huber)
Date: Thu Jun 19 13:52:41 2008
Subject: [Haskell-cafe] Re: (Lazy) SmallCheck and peano numbers
In-Reply-To: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>
References: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>
Message-ID: <485A9ED2.5050703@gmx.net>

Levi Stephen schrieb:
> Hi,
> 
> I have the following definitions
> 
> type Zero
> type Succ a
> 
> so that I can muck around with a Vector type that includes its length
> encoded in its type.
> 
> I was wondering whether it was possible to use SmallCheck (or
> QuickCheck) to generate random Peano numbers? Is there an issue here
> in that what I actually want to generate is a type rather than a
> value?
> 
> I do have
> 
> reifyInt :: Int -> (forall a. ReflectNum a => a -> b) -> b
> 
> but, I'm not sure if this can help me when I need to generate other
> values based upon that type (e.g., two vectors with the same size
> type)

Hi Levi,

For QuickCheck, I know it is possible as long as you do not need to use 
type level functions in your tests. For example, using Alfonso's 
type-level and parametrized-data packages, one can write:

 > instance (Nat n, Arbitrary a) => Arbitrary (FSVec n a) where
 >    arbitrary =
 >      liftM (unsafeVector (undefined :: n)) $
 >        mapM (const arbitrary) [1..toInt (undefined :: n)]

 > propLength :: forall n a. (Nat n) => FSVec n Integer -> Bool
 > propLength (FSVec xs) = P.length xs == toInt (undefined :: n)

 > propLengthEqual :: forall n a. (Nat n) =>
 >                    FSVec n Integer -> FSVec n Integer -> Bool
 > propLengthEqual v1 v2 = length v1 == length v2

 > tests1 = forM_ [0..100] $ \n -> reifyIntegral n $ \(t :: ty) ->
 >    quickCheck (propLength :: FSVec ty Integer -> Bool)
 > tests2 = forM_ [0..100] $ \n -> reifyIntegral n $ \(t :: ty) ->
 >    quickCheck (uncurry propLengthEqual ::
 >                     (FSVec ty Integer,FSVec ty Integer) -> Bool)

It is also possible to reify type-level numbers with more context; I 
managed to get as far as (iirc)

 > reifyPos :: Integer ->
 >       (forall n. (Pos n, Succ n n', DivMod10 n nd nm) =>
 >        n -> r) -> r

This way you can test head, tail e.g., but I found it to be a lot of 
work to write additional reifications.

I do not know if it is possible (I think it is not) to have a 
reification which allows you to use total type level functions such as 
Add, e.g.

 > tylvl = reifyIntegral? k $ \(n :: ty) -> toInt (m :: Add ty D9)
 > -- (D9 is the type level number 9)


I'm really curious what exactly would make this possible.

best regards,

benedikt
From jefferson.r.heard at gmail.com  Thu Jun 19 14:04:03 2008
From: jefferson.r.heard at gmail.com (Jefferson Heard)
Date: Thu Jun 19 13:55:53 2008
Subject: [Haskell-cafe] Wrapping FTGL in FFI calls
Message-ID: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>

I've been looking for awhile now for a simple way to get truetype fonts into
my visualizations so I can abandon the hideous GLUT fonts and make things
that look like they were developed in the 1990s instead of back in the days
of TRON.  I found FTGL, but I'm mostly a Haskell developer these days, and
resent having to go back to C just to write a simple application.

So I was wondering if anyone had ever wrapped the FTGL library in Haskel FFI
or whether those out there who are experts on the FFI think at first glance
it should be readily wrappable by a rank amateur at FFI such as myself.

http://ftgl.sourceforge.net/docs/html/

-- Jeff
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From sk at k-hornz.de  Thu Jun 19 14:08:46 2008
From: sk at k-hornz.de (stefan kersten)
Date: Thu Jun 19 14:01:10 2008
Subject: [Haskell-cafe] reactive and <<loop>>
Message-ID: <A237EBA9-2691-44A3-A127-67E00CD1C865@k-hornz.de>

hi,

i'm having problems with a very simple example using conal elliott's  
'reactive' library:

module Main where

import Control.Applicative
import Control.Concurrent
import Control.Monad
import Data.Reactive
import System.Random

main :: IO ()
main = do
     (e, snk) <- mkEvent
     forkIO $ forever ((getStdRandom random :: IO Double) >>= snk >>  
threadDelay 10000)
     runE (print `fmap` withPrevE e)
     return ()

which starts to output this after a while:

reactive_loop.hs: <<loop>>

this is with ghc 6.8.1 on osx 10.4. any ideas what might be going wrong?

many thanks,
<sk>

From chaddai.fouche at gmail.com  Thu Jun 19 14:36:05 2008
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Thu Jun 19 14:27:56 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
Message-ID: <e9350eaf0806191136p1e5d0aafwfc4b96ef7cf43b3@mail.gmail.com>

2008/6/19 jinjing <nfjinjing@gmail.com>:
> encode xs = xs.group.map token where token x = (x.length, x.head)

Working in this direction is a question of taste, but the choice of
the dot for the operator is a pretty bad idea...

On the other hand, my favourite would be :

encode = map (length &&& head) . group

-- 
Jeda?
From westondan at imageworks.com  Thu Jun 19 14:42:20 2008
From: westondan at imageworks.com (Dan Weston)
Date: Thu Jun 19 14:34:19 2008
Subject: [Haskell-cafe] type constructor confusion
In-Reply-To: <2f9b2d30806182004g6b60bb72w9a57fa5e0a9f1401@mail.gmail.com>
References: <48596286.6050201@enterity.com>	<D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>	<4859BE33.2040008@enterity.com>
	<2f9b2d30806182004g6b60bb72w9a57fa5e0a9f1401@mail.gmail.com>
Message-ID: <485AA88C.1000003@imageworks.com>

If it helps, feel free to use a different name for the data constructors 
and their data type until the difference is painfully clear to you 
(maybe suffix the constructor with a C or prefix by Mk).

Data types and constructors live in different namespaces and can happily 
use the same identifier. That doesn't mean you have to, if it means more 
work deciphering error messages.

Computers would be just as happy with identifiers like g2ch_Sw'K54h 
(just take a look at the GHC simple core dump!), so pick ones that you 
yourself find perspicuous.

Dan

Ryan Ingram wrote:
> It sounds like you need to split up your types a bit more.
> 
> data HttpRequest = HttpRequest ...
> 
> data HttpResponse = HttpResponse ...
> 
> data HttpMessage = MsgRequest HttpRequest | MsgResponse HttpResponse
> -- alternatively
> -- type HttpMessage = Either HttpRequest HttpResponse
> 
> Now you can have functions that take/return just an HttpRequest or
> just an HttpResponse, as well as functions that use either one via
> HttpMessage.  In the latter case, you do need to pattern match to
> decide which one you have.
> 
>   -- ryan
> 
> 
> On 6/18/08, Stephen Howard <stephen@enterity.com> wrote:
>> Thanks Brandon, forgot to send my reply to the list:
>>
>> Ok, so I am confusing things.  Good to know.  So my question is how do I
>> fulfill this scenario?
>>
>> - I have an action that might return either an HttpResponse or an
>> HttpRequest, depending on if the IO in the action determined more work
>> needed doing.  It's here, though I doubt it's "correct" yet:
>>
>> requestHandler :: HttpRequest -> IO HttpResponse
>> requestHandler request = do
>>  session <- sessionHandler request
>>  ret     <- uriHandler     request
>>  case ret of
>>      HttpResponse -> ret
>>      HttpRequest  -> resourceHandler session ret
>>
>> uriHandler :: HttpRequest -> IO HttpMessage
>> sessionHandler :: HttpRequest -> IO HttpSession
>>
>> I've given the uriHandler a signature of IO HttpMessage because the
>> HttpMessage might be either an HttpResponse or an HttpRequest, and I don't
>> know how I should be specifying that.  Ideas?
>>
>> - Stephen
>>
>> Brandon S. Allbery KF8NH wrote:
>>> On Jun 18, 2008, at 15:31 , Stephen Howard wrote:
>>>
>>>
>>>> HttpMessage.hs:36:20: Not in scope: type constructor or class
>> `HttpRequest'
>>>> The troublesome line is the definition of the cookie function at the end
>> of the code.  I've made
>>> Right.  "HttpRequest" is a data constructor associated with the type
>> constructor "HttpMessage".
>>> (Data constructors are effectively functions; you used it in the context
>> of a type, not a function name.)
>>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
> 


From george.moschovitis at gmail.com  Thu Jun 19 15:08:47 2008
From: george.moschovitis at gmail.com (George Moschovitis)
Date: Thu Jun 19 15:00:39 2008
Subject: [Haskell-cafe] HDBC converting a date sql value to UTCTime
Message-ID: <afd80b540806191208j38dced52g25357d510c79dbf3@mail.gmail.com>

Hello,

I am HDBC with the Postgres driver. I am trying to read a simple date column
from the DB:

stmt <- DB.prepare conn "SELECT date FROM my_table ORDER BY date DESC LIMIT
1"
DB.execute stmt []
DB.commit conn
rows <- fetchAllRows' stmt
let ((d:_):_) = rows

the d variable is of type:

SqlEpochTime 1213736400

I am wondering how to convert this value to an UTCTime value.

Any help appreciated (I am a newbie).

-g.



-- 
http://gmosx.me.gr
http://joy.gr
http://cull.gr
http://nitroproject.org
http://phidz.com
http://joyerz.com
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From jeff at renci.org  Thu Jun 19 15:10:41 2008
From: jeff at renci.org (Jefferson Heard)
Date: Thu Jun 19 15:02:30 2008
Subject: [Haskell-cafe] Wrapping FTGL in FFI calls
In-Reply-To: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>
Message-ID: <4165d3a70806191210t57f06235y55b068d98ce33429@mail.gmail.com>

I've been looking for awhile now for a simple way to get truetype fonts into
my visualizations so I can abandon the hideous GLUT fonts and make things
that look like they were developed in the 1990s instead of back in the days
of TRON.  I found FTGL, but I'm mostly a Haskell developer these days, and
resent having to go back to C just to write a simple application.

So I was wondering if anyone had ever wrapped the FTGL library in Haskel FFI
or whether those out there who are experts on the FFI think at first glance
it should be readily wrappable by a rank amateur at FFI such as myself.

http://ftgl.sourceforge.net/docs/html/

-- Jeff
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From byorgey at gmail.com  Thu Jun 19 15:24:19 2008
From: byorgey at gmail.com (Brent Yorgey)
Date: Thu Jun 19 15:16:08 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <878wx1khcj.fsf@malde.org>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	<878wx1khcj.fsf@malde.org>
Message-ID: <22fcbd520806191224n3145ef92xeb5fd79be7ff0ccb@mail.gmail.com>

On Thu, Jun 19, 2008 at 3:35 AM, Ketil Malde <ketil@malde.org> wrote:

> jinjing <nfjinjing@gmail.com> writes:
>
> > Any way here's the code:
>
> > module Dot where
> > import Prelude hiding ( (.) )
>
> > (.) :: a -> (a -> b) -> b
> > a . f = f a
>
> > infixl 9 .
>
> Isn't this (roughly?) the same as flip ($)?
>
> As a side note, may I advise you to use another symbol, and leave the
> poor dot alone? Overloading it as a module separator is bad enough.
> If you have a keyboard that allows greater-than-ascii input, there are
> plenty of options: ? ? ? ? ? ? ? (R) ?...
>

Note that there already is a standard symbol for this, (>>>) from
Control.Arrow.  Well, actually (>>>) is more general than backwards function
composition, so maybe making your own symbol is still a good idea while
you're learning.

-Brent
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From barsoap at web.de  Thu Jun 19 15:41:42 2008
From: barsoap at web.de (Achim Schneider)
Date: Thu Jun 19 15:33:42 2008
Subject: [Haskell-cafe] Burn ACM
Message-ID: <20080619214142.78370c4d@solaris>

for monetary reasons.

I just wanted my voice to be heard, you may pass on now.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From duncan.coutts at worc.ox.ac.uk  Thu Jun 19 15:56:46 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Thu Jun 19 15:43:51 2008
Subject: [Haskell-cafe] cabal-install failure
In-Reply-To: <006201c8cfac$1920be80$3a448351@cr3lt>
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
	<1213392126.15010.547.camel@localhost> <20080614021052.GA8862@craft>
	<1213430194.15010.556.camel@localhost>
	<008501c8ce05$ec0ef260$f82b8351@cr3lt>
	<1213559354.15010.580.camel@localhost>
	<006201c8cfac$1920be80$3a448351@cr3lt>
Message-ID: <1213905406.15010.908.camel@localhost>


On Mon, 2008-06-16 at 13:25 +0100, Claus Reinke wrote:
> > The main point of the Program abstraction is about configuring and
> > running programs. As it happens some programs are provided by some
> > haskell packages (but not all, eg ld, ar, etc).
> > 
> >> option to get version info and code to extract it (with one apparently
> >> very special case being hsc2hs).
> > 
> > And ld.exe on windows (we find it in ghc's gcc-lib bin dir).
> 
> I didn't notice this special case in Program.hs - are my sources
> just out of date, or is this special handling encoded elsewhere?

It's in the configuration code for ghc. If it's on windows then it tries
to find ld.exe relative to where ghc was found.

> >> Btw, most of the version extraction code looks like a regular 
> >> expression match - wouldn't that make the specification easier
> >> (and turn the comments into part of the spec)?
> > 
> > True, in most cases finding the name of the program involves running it
> > with some --version flag and matching some part of the output. However
> > that's not always the case. Some programs do silly things like produce
> > the version output on stderr instead of stdout. We figured the most
> > general thing was just a function
> > 
> > FilePath -> IO (Maybe Version)
> > 
> > which is what we've got. I'm not sure what the advantage would be to
> > make it more declarative by making it into data rather than a extraction
> > function.
> 
> Usually, the most general approach for this kind of problem is
> good as a default/backup, but not so good for maintenance. The
> more cases can be handled with dedicated declarative specs, the
> smaller the risk of accidental/hidden breakage (eg, moving the 
> comments into regex patterns), the more compact and understandable 
> the specs (a line per tool, with option and regex, all in one place
> would be easier to comprehend than the current free-coding style).

So we can provide a more compact helper function for the common case bu
since not all of them fit the common case we cannot change the general
interface.

> More importantly, concise declarative specs are easier to update
> and extend (could be done by users rather than Cabal maintainers,
> and preferably outside of Cabal sources).
> 
> > Also, the Cabal lib cannot depend on any regular expression library
> > because they are not part of the bootstrapping library set.
> 
> Sigh. I've heard that one before, and the ghc-pkg bulk queries are
> not as flexible as they could be because I had to use less expressive
> functions instead of regexes. Since Haskell-only regex packages
> exist, perhaps one should just be added to the bootlib set? After
> all, we bother with regexes because they are so frequently useful.

In the specific case of parsing --version strings, I'm not sure regexes
are any easier. Using words and then selecting the Nth word seems to do
pretty well.

> >> 1. Haskell tools should register with Cabal, whether built with it
> >>     (such as Alex, Happy, ..) or not (such as GHC, ..). That 
> >>     registration should include any build-relevant information
> >>     (versions/variants, ..).
> >> 
> >> 2. When checking a build-tools dependency, Cabal checks
> >>     (a) whether the tool is registered with Cabal
> > 
> > I'm not sure this helps. We want to know what to install when it's
> > missing. We can already tell if a program (not package) is available by
> > searching for it.
> 
> But that means either configure or a subset of special configure
> rules baked into Cabal's sources, combined with fragile Setup.hs
> extensions to that subset. IMHO, the less of configure/hardcoded
> rules/Setup.hs, the better (simpler, less breakage with Cabal 
> updates, etc.).
> 
> How about this: instead of baking rules for those tools into the
> Cabal sources, why not have a single "known-tools" package?
> On (re-)installing that package, its configure/Setup is run once,
> to register availability and build-related information for all those
> tools with Cabal (currently, that would mean a package per
> tool; later, the known-tools package itself could expose multiple
> tools, but Cabal would still need to be able to check which of 
> the "exposed-tools" have been found).
> 
> That way, the known-tools could be updated independently,
> instead of requring Cabal source hacking and releases, and
> instead of spreading special configure rules for common tools
> over all packages, they'd be located in a single package 
> (easier to maintain and improve, and improvements are shared).

Yeah this would be better. The same goes for things like pre-processors,
but their rules are harder to express.

> >>     (b) whether the tool is registered with the system installation manager
> > 
> > This is hard.
> 
> Why? Because there are more installation managers than OSs,
> or because so many program installs bypass them? Querying
> an installation manager shouldn't be any more difficult than
> querying ghc-pkg, say.

Both. There are many of them, each with their own quirks and things
installed in /usr/local.

Duncan



From monnier at iro.umontreal.ca  Thu Jun 19 17:07:13 2008
From: monnier at iro.umontreal.ca (Stefan Monnier)
Date: Thu Jun 19 16:59:07 2008
Subject: [Haskell-cafe] do and ifthenelse indentation in GHC
Message-ID: <jwvy751gmun.fsf-monnier+gmane.comp.lang.haskell.cafe@gnu.org>

http://hackage.haskell.org/trac/haskell-prime/wiki/DoAndIfThenElse says
(and my memory seems to agree) that GHC has been changed to accept
things like

   readnums f n = do eof <- hIsEOF f
                     if eof
                     then return n
                     else do l <- hGetLine f
                             readnums f (n + read l)

where the `then' and `else' are aligned with the `if' rather than being
slightly more indented as the Haskell 98 standard requires.
Yet, when I try it with GHCi 6.8.2 I get an error:

   Prelude> :load "/home/monnier/tmp/foo.hs"
   [1 of 1] Compiling Main      ( /home/monnier/tmp/foo.hs, interpreted )
   
   /home/monnier/tmp/foo.hs:6:18:
       parse error (possibly incorrect indentation)
   Failed, modules loaded: none.
   Prelude> 

Does anybody know what's up with that?


        Stefan

From allbery at ece.cmu.edu  Thu Jun 19 17:57:18 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Thu Jun 19 17:50:04 2008
Subject: [Haskell-cafe] Gtk2Hs and GCs
In-Reply-To: <Pine.BSI.4.64.0806181720520.16752@malasada.lava.net>
References: <Pine.BSI.4.64.0806181720520.16752@malasada.lava.net>
Message-ID: <5EA3C4E4-287D-4A98-B42D-D10D5A184A6C@ece.cmu.edu>


On 2008 Jun 18, at 23:23, Tim Newsham wrote:

> I can't seem to find any other way short of making a whole new GC
> (as is done in Gtk2Hs/demos/graphic/Drawing.hs).  Am I missing
> something?  Is there a reason the GC's arent retrievable?


Join the gtk2hs list ( https://lists.sourceforge.net/lists/listinfo/gtk2hs-users 
  ) and propose it?  Duncan has told me the interface is still  
evolving based on user feedback.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From allbery at ece.cmu.edu  Thu Jun 19 18:14:33 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Thu Jun 19 18:06:27 2008
Subject: [Haskell-cafe] type constructor confusion
In-Reply-To: <485A8926.7010902@enterity.com>
References: <48596286.6050201@enterity.com>	
	<D2C34D88-C126-4D63-ADCA-DA530F36F366@ece.cmu.edu>	
	<4859BE33.2040008@enterity.com>
	<2f9b2d30806182004g6b60bb72w9a57fa5e0a9f1401@mail.gmail.com>
	<485A8926.7010902@enterity.com>
Message-ID: <358A036F-BA04-491A-AC63-AC7735514985@ece.cmu.edu>


On 2008 Jun 19, at 12:28, Stephen Howard wrote:

> Cool, "Either" looks like what I'm looking for.  I'll have to look  
> into that.  What do I do about the fact that both HttpRequest and  
> HttpResponse have some of the same named fields (headers and body,  
> for example).  Seems a pain to drop them into separate modules just  
> so I can keep the naming conventions consistent.

IIRC as long as they have the same types you can use them in both.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From claus.reinke at talk21.com  Thu Jun 19 18:28:54 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Thu Jun 19 18:24:58 2008
Subject: [Haskell-cafe] cabal-install failure
References: <a2e649c70806130819y4e7d3885l60d39a780a31d134@mail.gmail.com>
	<1213392126.15010.547.camel@localhost>
	<20080614021052.GA8862@craft>
	<1213430194.15010.556.camel@localhost>
	<008501c8ce05$ec0ef260$f82b8351@cr3lt>
	<1213559354.15010.580.camel@localhost>
	<006201c8cfac$1920be80$3a448351@cr3lt>
	<1213905406.15010.908.camel@localhost>
Message-ID: <015401c8d25c$7224d5e0$5b057ad5@cr3lt>

> In the specific case of parsing --version strings, I'm not sure regexes
> are any easier. Using words and then selecting the Nth word seems to do
> pretty well.

for comparison, see the examples below:-) There's no reason
this can't be massaged further, but it already allows for IO if
necessary (I like that it is compact and self-documenting -the
comments have become part of the patterns, but if you don't 
want to match against the precise message format, you can use 
more of [^[:space:]]* - pity that \S* isn't posix..).

Claus

import Text.Regex
import System.Process(runInteractiveProcess)
import System.IO(hGetContents)

test = mapM_ ((print =<<) . getVersion) programs

getVersion (prg,flag,io,extract) = do
  (i,o,e,p) <- runInteractiveProcess prg [flag] Nothing Nothing
  version <- hGetContents ([o,e]!!(io-1)) >>= extract
  return (prg,version)

defaultMatch :: String -> String -> IO String
defaultMatch pattern = return . maybe "" head . (matchRegex (mkRegex pattern))

programs = [ghc,ghcPkg,happy,alex,haddock]

ghc = ("ghc","--numeric-version",1,
  defaultMatch "([^[:space:]]*)")
ghcPkg = ("ghc-pkg","--version",1,
  defaultMatch "GHC package manager version ([^[:space:]]*)")
happy = ("happy","--version",1,
  defaultMatch "Happy Version ([^[:space:]]*)")
alex = ("alex","--version",1,
  defaultMatch "Alex version ([.0-9]*)")
haddock = ("haddock","--version",1,
  defaultMatch "Haddock version ([.0-9]*)")


From waqner at gmx.net  Thu Jun 19 18:53:19 2008
From: waqner at gmx.net (Alexander Wagner)
Date: Thu Jun 19 18:45:10 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
Message-ID: <200806200053.19198.waqner@gmx.net>

On Wednesday 18 June 2008, Luke Palmer wrote:
> I don't know that much PHP, but I find the "lexical" keyword to be a
> nuisance.  What are the semantics if the lexical keyword is omitted? 

In PHP Variables are local by default, the keyword global defines them as 
references to the global namespace.
There are some exceptions, like the availability of $this in methods or a 
couple of predefined superglobal variables that are implicitly global in all 
functions.

<?php
$globalVar = 1;
$param = "notshared";
$localVar = "notshared";

function foo ($param) {
  global $globalVar;
  $localVar = (int) $param;
  return $localVar + $localVar;
}
?>

Given how much it works like "global", the keyword "lexical" seems quite 
consistent with the style of PHP.

Gesundheit
  Wag

-- 
There?s a phrase we live by in America: ?In God We Trust?. It?s right there 
where Jesus would want it: on our money.
 - Steven Colbert
From waqner at gmx.net  Thu Jun 19 18:54:51 2008
From: waqner at gmx.net (Alexander Wagner)
Date: Thu Jun 19 18:46:42 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone please
	comment?
In-Reply-To: <7ca3f0160806180750m7d2ab838s1db4bd07b9bf4b6e@mail.gmail.com>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>
	<7ca3f0160806180750m7d2ab838s1db4bd07b9bf4b6e@mail.gmail.com>
Message-ID: <200806200054.51714.waqner@gmx.net>

CC to Christian Seiler
http://www.haskell.org/pipermail/haskell-cafe/2008-June/044379.html
http://www.haskell.org/pipermail/haskell-cafe/2008-June/thread.html

On Wednesday 18 June 2008, Luke Palmer wrote:
> * A closure must be able to call itself recursively (via a
> higher-order function typically)

I see two ways a closure might get a hold of itself, in order it can call 
itself:

$f = function () {
  lexical $whatever;
  lexical $f; //get yourself by lexical scope
  return $f();
};
$f();

$g = function ($g) {  //get yourself by parameter
  lexical $whatever;
  return $g($g);
};
$g($g);

Getting the first version to work is somewhat tricky in a non-lazy language, 
but it would be nice to have. The second should definately work.
I guess I'll download the patch and try.

> * I would recommend only saving $this in the op_array structure if the
> closure actually references $this -- if that is possible to deduce at
> the time. Otherwise you might run into unexpected poor memory
> performances in certain cases.

Agreed. A closure created inside an object should be able to outlive the 
object by not holding a reference to it.
Since many PHP programmers put pretty much all of their functions into classes 
for style reasons, which would mean most closures are created in the context 
of an object, implicitly referencing $this might prevent a lot of objects 
from being garbage-collected. Also, doesn't that turn all lambdas defined 
inside an object into closures, which are heavier?

Between always referencing $this in a lamda and requiring "lexical $this", the 
latter seems like the smaller evil to me. 

Gesundheit
  Wag
From trebla at vex.net  Thu Jun 19 18:59:23 2008
From: trebla at vex.net (Albert Y. C. Lai)
Date: Thu Jun 19 18:51:15 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <20080619171812.GA25606@dell>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>	<878wx1khcj.fsf@malde.org>
	<20080619171812.GA25606@dell>
Message-ID: <485AE4CB.4080708@vex.net>

Adam Vogt wrote:
> While we are kind of on this topic, what makes the characters ? ? prefix 
> operator by default, while ? and most other odd ones infix?

alphanumeric vs non-alphanumeric


From levi.stephen at optusnet.com.au  Thu Jun 19 20:03:57 2008
From: levi.stephen at optusnet.com.au (Levi Stephen)
Date: Thu Jun 19 19:55:45 2008
Subject: [Haskell-cafe] Re: (Lazy) SmallCheck and peano numbers
In-Reply-To: <8341e4f40806191630o62ed9e35q863cb3261d8b5f1c@mail.gmail.com>
References: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>
	<20080619165012.GA7049@pc149.staff.cs.york.ac.uk>
	<8341e4f40806191630o62ed9e35q863cb3261d8b5f1c@mail.gmail.com>
Message-ID: <8341e4f40806191703t2623fb42m7a96100f6324744c@mail.gmail.com>

> If so, you could write a SmallCheck Series instance as follows.
>
>  instance Serial (Vec Zero a) where
>    series = cons0 nil
>
>  instance (Serial a, Serial (Vec n a)) => Serial (Vec (Succ n) a) where
>    series = cons2 (|>)

> If we have the property
>
>  prop_vector :: Vec (Succ (Succ Zero)) Bool -> Bool
>  prop_vector (V xs) = xs == xs
>
> we can check it, and only 2 element vectors will be tested

I have some code up now at http://hpaste.org/8420

It looks pretty much like what you've written above and is what I am
doing for the moment, but for various size vectors from zero to four.


> Now, it seems what you really want to do is define polymorphic
> properties like
>
>  prop_poly :: Vec n Bool -> Vec n Bool -> Bool
>
> and have SmallCheck check all equal-sized vectors.  If so, good
> question! :-)

Yep, this would be exactly what I'm after. Thanks for a better write
up and background on what I'm after than I gave :)

I'm thinking the property might be written as

prop_poly:: size -> Vec size Bool -> Vec size Bool -> Bool,

so that the size is generated randomly and the types take care of
ensuring the vectors generated are of the same size.

Levi
From levi.stephen at optusnet.com.au  Thu Jun 19 20:04:30 2008
From: levi.stephen at optusnet.com.au (Levi Stephen)
Date: Thu Jun 19 19:56:19 2008
Subject: [Haskell-cafe] Re: (Lazy) SmallCheck and peano numbers
In-Reply-To: <8341e4f40806191643h79e96cbav314ed7932f0eecee@mail.gmail.com>
References: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>
	<485A9ED2.5050703@gmx.net>
	<8341e4f40806191643h79e96cbav314ed7932f0eecee@mail.gmail.com>
Message-ID: <8341e4f40806191704y5e2f8f87v95e3805b6a3d1b85@mail.gmail.com>

On Fri, Jun 20, 2008 at 3:30 AM, Benedikt Huber <benjovi@gmx.net> wrote:
> Levi Stephen schrieb:
>>
>> Hi,
>>
>> I have the following definitions
>>
>> type Zero
>> type Succ a
>>
>> so that I can muck around with a Vector type that includes its length
>> encoded in its type.
>>
>> I was wondering whether it was possible to use SmallCheck (or
>> QuickCheck) to generate random Peano numbers? Is there an issue here
>> in that what I actually want to generate is a type rather than a
>> value?
>>
>> I do have
>>
>> reifyInt :: Int -> (forall a. ReflectNum a => a -> b) -> b
>>
>> but, I'm not sure if this can help me when I need to generate other
>> values based upon that type (e.g., two vectors with the same size
>> type)
>
> Hi Levi,
>
> For QuickCheck, I know it is possible as long as you do not need to use type
> level functions in your tests. For example, using Alfonso's type-level and
> parametrized-data packages, one can write:
>
>> instance (Nat n, Arbitrary a) => Arbitrary (FSVec n a) where
>>    arbitrary =
>>      liftM (unsafeVector (undefined :: n)) $
>>        mapM (const arbitrary) [1..toInt (undefined :: n)]
>
>> propLength :: forall n a. (Nat n) => FSVec n Integer -> Bool
>> propLength (FSVec xs) = P.length xs == toInt (undefined :: n)
>
>> propLengthEqual :: forall n a. (Nat n) =>
>>                    FSVec n Integer -> FSVec n Integer -> Bool
>> propLengthEqual v1 v2 = length v1 == length v2
>
>> tests1 = forM_ [0..100] $ \n -> reifyIntegral n $ \(t :: ty) ->
>>    quickCheck (propLength :: FSVec ty Integer -> Bool)
>> tests2 = forM_ [0..100] $ \n -> reifyIntegral n $ \(t :: ty) ->
>>    quickCheck (uncurry propLengthEqual ::
>>                     (FSVec ty Integer,FSVec ty Integer) -> Bool)

Thanks for the example code. Ideally it would be great to have n generated also.

Any thoughts on whether something like

propLengthEqual :: forall n a. (Nat n) => n -> FSVec n Integer ->
FSVec n Integer -> Bool
propLengthEqual _ v1 v 2 = length v1 == length v2

with an arbitrary instance for generate all Nat n's is possible?

Is something like instance (forall n. Nat n) => Arbitrary n
possible/legal haskell? and would it for the above test?

>
> best regards,
>
> benedikt
>

Thanks,
Levi
From derek.a.elkins at gmail.com  Thu Jun 19 21:53:54 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Thu Jun 19 21:47:08 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <22fcbd520806191224n3145ef92xeb5fd79be7ff0ccb@mail.gmail.com>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	<878wx1khcj.fsf@malde.org>
	<22fcbd520806191224n3145ef92xeb5fd79be7ff0ccb@mail.gmail.com>
Message-ID: <1213926834.26144.1.camel@derek-laptop>

On Thu, 2008-06-19 at 15:24 -0400, Brent Yorgey wrote:
> 
> On Thu, Jun 19, 2008 at 3:35 AM, Ketil Malde <ketil@malde.org> wrote:
>         jinjing <nfjinjing@gmail.com> writes:
>         
>         > Any way here's the code:
>         
>         > module Dot where
>         > import Prelude hiding ( (.) )
>         
>         > (.) :: a -> (a -> b) -> b
>         > a . f = f a
>         
>         > infixl 9 .
>         
>         
>         Isn't this (roughly?) the same as flip ($)?
>         
>         As a side note, may I advise you to use another symbol, and
>         leave the
>         poor dot alone? Overloading it as a module separator is bad
>         enough.
>         If you have a keyboard that allows greater-than-ascii input,
>         there are
>         plenty of options: ? ? ? ? ? ? ? ? ?...

> 
> Note that there already is a standard symbol for this, (>>>) from
> Control.Arrow.  Well, actually (>>>) is more general than backwards
> function composition, so maybe making your own symbol is still a good
> idea while you're learning.

Application, not composition.  Cont's return would work if it weren't
for the wrapping.  Similarly, (>>=) for the Id monad.
> 

From oddron at gmail.com  Thu Jun 19 22:45:19 2008
From: oddron at gmail.com (Ronald Guida)
Date: Thu Jun 19 22:37:08 2008
Subject: [Haskell-cafe] Haddock compilation problem
Message-ID: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>

I just upgraded to ghc-6.8.3, using a linux binary, and I am having a
problem compiling Haddock.  Haddock 2.1.0 and Haddock 2.0.0.0 both
fail to build under ghc-6.8.3, but they both build successfully with
ghc-6.8.2.  I don't know if this is a Haddock problem, or a GHC
problem, or perhaps something else entirely?

Here is the error I'm getting.  It is the same error for either
version of Haddock.

[15 of 24] Compiling Haddock.GHC.Typecheck (
src/Haddock/GHC/Typecheck.hs,
dist/build/haddock/haddock-tmp/Haddock/GHC/Typecheck.o )

src/Haddock/GHC/Typecheck.hs:82:4:
    Constructor `HsModule' should have 7 arguments, but has been given 8
    In the pattern: HsModule _ _ _ _ _ mbOpts _ _
    In a pattern binding: HsModule _ _ _ _ _ mbOpts _ _ = unLoc parsed
    In the definition of `mkGhcModule':
        mkGhcModule (mod, file, checkedMod) dynflags
                      = GhcModule
                          {ghcModule = mod, ghcFilename = file,
ghcMbDocOpts = mbOpts,
                           ghcHaddockModInfo = info, ghcMbDoc = mbDoc,
ghcGroup = group,
                           ghcMbExports = mbExports,
                           ghcExportedNames = modInfoExports modInfo,
                           ghcNamesInScope = fromJust $
modInfoTopLevelScope modInfo,
                           ghcInstances = modInfoInstances modInfo}
                      where
                          HsModule _ _ _ _ _ mbOpts _ _ = unLoc parsed
                          (group, _, mbExports, mbDoc, info) = renamed
                          (parsed, renamed, _, modInfo) = checkedMod
From alistair at abayley.org  Fri Jun 20 01:10:41 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Fri Jun 20 01:02:28 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
Message-ID: <79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>

> Is there a way of accessing a remote Oracle database by one of the common
> Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get
> unixODBC and Oracle's Instant Client running on a Linux machine, but I'm
> trapped in the notorious error:

Takusen's Oracle backend uses the Oracle Call Interface (OCI) library
directly. I think most Oracle client drivers (ODBC, ADO.Net, etc) use
the OCI. I don't know what the Oracle Instant Client is; I'll assume
that it includes an oci.so or liboci.so. On Windows, with which I am
most familiar, the Oracle client software is all installed in
$ORACLE_HOME, and the OCI library is $ORACLE_HOME/bin/oci.dll. If you
can locate that, then you ought to be able to use Takusen with it.

Alistair
From barsoap at web.de  Fri Jun 20 01:16:12 2008
From: barsoap at web.de (Achim Schneider)
Date: Fri Jun 20 01:08:07 2008
Subject: [Haskell-cafe] Re: Wrapping FTGL in FFI calls
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>
Message-ID: <20080620071612.12d7e6c2@solaris>

"Jefferson Heard" <jefferson.r.heard@gmail.com> wrote:

> I've been looking for awhile now for a simple way to get truetype
> fonts into my visualizations so I can abandon the hideous GLUT fonts
> and make things that look like they were developed in the 1990s
> instead of back in the days of TRON.  I found FTGL, but I'm mostly a
> Haskell developer these days, and resent having to go back to C just
> to write a simple application.
> 
> So I was wondering if anyone had ever wrapped the FTGL library in
> Haskel FFI or whether those out there who are experts on the FFI
> think at first glance it should be readily wrappable by a rank
> amateur at FFI such as myself.
> 
> http://ftgl.sourceforge.net/docs/html/
> 
Using the FFI is generally straight forward, as long as you can live
with using the IO monad and the C code uses objects (well,
pointers to structs passed as first argument, where's the
difference...).

Things only depend on the purity of the C code and how high-level you
want your interface to be. In this case, I estimate half an hour if
you're a fast typist. That includes the time needed to read the FFI
docs.

-- 
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited. 

From simonpj at microsoft.com  Fri Jun 20 01:50:58 2008
From: simonpj at microsoft.com (Simon Peyton-Jones)
Date: Fri Jun 20 01:42:37 2008
Subject: [Haskell-cafe] Re: Meaning of "ribbonsPerLine" at
	Text.PrettyPrint.HughesPJ ?
In-Reply-To: <485A5192.8030400@gmx.net>
References: <6a7c66fc0806181313o447839et23358d5ba0523ac0@mail.gmail.com>
	<2518b95d0806181355r5f301c41l3321ff3437222829@mail.gmail.com>
	<485A5192.8030400@gmx.net>
Message-ID: <638ABD0A29C8884A91BC5FB5C349B1C32AE6D38428@EA-EXMSG-C334.europe.corp.microsoft.com>

Benedikt

Despite the name, neither I nor John Hughes are actively maintaining this library, so if you have got some better implementations of 'cat' and 'sep', do please submit a patch. That's how it'll improve.

Do test carefully!  Preferably add some Quickcheck tests too.

Thanks

Simon

| -----Original Message-----
| From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-
| bounces@haskell.org] On Behalf Of Benedikt Huber
| Sent: 19 June 2008 13:31
| To: Evan Laforge
| Cc: haskell
| Subject: [Haskell-cafe] Re: Meaning of "ribbonsPerLine" at
| Text.PrettyPrint.HughesPJ ?
|
| Evan Laforge schrieb:
| >> byorgey: fons: I can't explain it, all I know is that you must set it
| >> to 1 or else it does bizarre things
| >> fons: hahah, ok
| >> fons: byorgey: that's funny considering its default value is 1.5
| >> byorgey: if you set it to 1 then lineLength means what you think it should
| >> byorgey: fons: EXACTLY
| >
| > Excellent, thanks for solving a nagging problem I couldn't be bothered
| > to track down.  I was wondering why my pretty printing was a little
| > messed up and slightly too wide.
| >
| > And isn't 100 columns a bit non-standard for a default?  I thought 80
| > columns had more traction?  I know that's what my terminals are at...
|
| Hi,
|
| The "ribbon length" is used when choosing the most beautiful layout:
| I'll just summarize the relevant section from John Hughes paper
| (http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps), which explains it
| very nicely:
|
| "... Using [the criterion whether the text fits on the page] alone tends
| to produce layouts such as
|
|  > for i = 1 to 100; for j=1 to 100; for k=1 to 100; a[i][j][k]:=0;
|
| which fits on a page {==> line-width} but cannot be described as pretty.
| We therefore impose an additional constraint limiting the number of
| characters on each line [==> ribbon-width} [...]
|
|  > for i = 1 to 100
|  >     for j = 1 to 100
|  > ...
| "
|
| So the pretty printer tries to avoid sequences (ribbons) of characters
| which are longer than ribbon_length, when using auto layout stuff like
| `sep'.
|
| In the source code, we have (paraphrased)
|
|  > ribbon_length = line_length / ribbonsPerLine
|
| and
|
|  > choose_nicest_layout indent p q =
|  >   if p + indent fits into line_length and p fits into ribbon_length
|  >    then p
|  >    else q
|
| Working example below.
|
| I'm not sure 80 characters is still standard when _pretty_-printing -
| the longest line in Text.PrettyPrint.HughesPJ is 109 characters wide ;)
|
| Setting the ribbon ratio to 1 essentially disables the ribbon feature.
|
| Btw: while studying the source code, I also found the cat (and sep) can
| be implemented in a more space efficient way (currently, cat needs to
| evaluate every document in a list to yield some output). Does this make
| sense (see below) ?
|
| cheers,
|
| benedikt
|
|
| -- * ribbon example
|
|  > -- lineLength = 26, ribbonsPerLine = 1.5 ==> ribbonLength = 17
|  > -- therefore, we have a line break if width-indent > 17 or width > 26
|  > testStyle = Style { mode = PageMode,
|  >                    lineLength = 26,
|  >                    ribbonsPerLine = 1.5 }
|  > ribbonTest = renderStyle testStyle $
|  >
|  >   -- use hsep as width == 17 <= ribbonLength
|  >       sep [ txt 5, txt 11 ]
|  >
|  >   -- linebreak, as width-indent = width = 18 > ribbonLength
|  >   $+$ sep [ txt 5, txt 12 ]
|  >
|  >   -- use hsep, as width - indent == 17, and width == 22 < lineLength
|  >   $+$ sep (map (nest 5) $ [txt 5, txt 11] )
|  >
|  >   -- linebreak, as width would be 27 > lineLength
|  >   $+$ sep (map (nest 10) $ [txt 5, txt 11] )
|  >
|  > txt :: Int -> Doc
|  > txt 0 = text ""
|  > txt k = text $
|  >  let ks = show k in
|  >   (replicate (k - (length ks)) '_') ++ ks
|
|
| -- * lazy variants of vcat and hcat
| --   you need the constructors from the HughesPJ module
|
|  > vcat' = foldAbove . foldr vcomp2 empty
|  > hcat' = foldBeside . foldr hcomp2 empty
|  >
|  > foldAbove :: Doc -> Doc
|  > foldAbove (Above Empty _ d2) = d2
|  > foldAbove (Above d1 f d2) = Above d1 f $ foldAbove d2
|  > foldAbove doc = doc
|  >
|  > vcomp2 :: Doc -> Doc -> Doc
|  > vcomp2 d1 Empty = d1
|  > -- do not match `vcomp2 Empty d1' !
|  > vcomp2 d1 d2 = Above d1 False d2
|  >
|  > foldBeside :: Doc -> Doc
|  > foldBeside (Beside Empty _ d2) = d2
|  > foldBeside (Beside d1 f d2) = Beside d1 f $ foldBeside d2
|  > foldBeside doc = doc
|  >
|  > hcomp2 :: Doc  -> Doc -> Doc
|  > hcomp2 p Empty = p
|  > hcomp2 p q = Beside p False q
|
| _______________________________________________
| Haskell-Cafe mailing list
| Haskell-Cafe@haskell.org
| http://www.haskell.org/mailman/listinfo/haskell-cafe

From ketil at malde.org  Fri Jun 20 01:57:58 2008
From: ketil at malde.org (Ketil Malde)
Date: Fri Jun 20 01:49:20 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <485AE4CB.4080708@vex.net> (Albert Y. C. Lai's message of "Thu\,
	19 Jun 2008 18\:59\:23 -0400")
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	<878wx1khcj.fsf@malde.org> <20080619171812.GA25606@dell>
	<485AE4CB.4080708@vex.net>
Message-ID: <874p7ops0p.fsf@malde.org>

"Albert Y. C. Lai" <trebla@vex.net> writes:

>> While we are kind of on this topic, what makes the characters ? ?
>> prefix operator by default, while ? and most other odd ones infix?

> alphanumeric vs non-alphanumeric

Testing this, I find that isAlpha is True also for '?', but as the OP
claims, Haskell will use it as a(n infix) symbol.  Neither does
isSymbol (all False), isLetter (all True), isMark (False), nor
isPunctuation (Fals) help to separate these.

The HR defines 

    uniSymbol 	 -> 	 any Unicode symbol or punctuation 

but I couldn't find any clear way to identify of these.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants
From benjovi at gmx.net  Fri Jun 20 03:37:41 2008
From: benjovi at gmx.net (Benedikt Huber)
Date: Fri Jun 20 03:29:29 2008
Subject: [Haskell-cafe] Re: (Lazy) SmallCheck and peano numbers
In-Reply-To: <8341e4f40806191704y5e2f8f87v95e3805b6a3d1b85@mail.gmail.com>
References: <8341e4f40806182234w43cd1c99l64b9c2bf7e784f2@mail.gmail.com>	<485A9ED2.5050703@gmx.net>	<8341e4f40806191643h79e96cbav314ed7932f0eecee@mail.gmail.com>
	<8341e4f40806191704y5e2f8f87v95e3805b6a3d1b85@mail.gmail.com>
Message-ID: <485B5E45.2020202@gmx.net>

Levi Stephen schrieb:
> On Fri, Jun 20, 2008 at 3:30 AM, Benedikt Huber <benjovi@gmx.net> wrote:
>> Levi Stephen schrieb:
>>> Hi,
>>>
>>> I have the following definitions
>>>
>>> type Zero
>>> type Succ a
>>>
>>> so that I can muck around with a Vector type that includes its length
>>> encoded in its type.
>>>
>>> I was wondering whether it was possible to use SmallCheck (or
>>> QuickCheck) to generate random Peano numbers? Is there an issue here
>>> in that what I actually want to generate is a type rather than a
>>> value?
>>>
>>> I do have
>>>
>>> reifyInt :: Int -> (forall a. ReflectNum a => a -> b) -> b
>>>
>>> but, I'm not sure if this can help me when I need to generate other
>>> values based upon that type (e.g., two vectors with the same size
>>> type)
>> Hi Levi,
>>
>> For QuickCheck, I know it is possible as long as you do not need to use type
>> level functions in your tests. For example, using Alfonso's type-level and
>> parametrized-data packages, one can write:
>>
>>> instance (Nat n, Arbitrary a) => Arbitrary (FSVec n a) where
>>>    arbitrary =
>>>      liftM (unsafeVector (undefined :: n)) $
>>>        mapM (const arbitrary) [1..toInt (undefined :: n)]
>>> propLength :: forall n a. (Nat n) => FSVec n Integer -> Bool
>>> propLength (FSVec xs) = P.length xs == toInt (undefined :: n)
>>> propLengthEqual :: forall n a. (Nat n) =>
>>>                    FSVec n Integer -> FSVec n Integer -> Bool
>>> propLengthEqual v1 v2 = length v1 == length v2
>>> tests1 = forM_ [0..100] $ \n -> reifyIntegral n $ \(t :: ty) ->
>>>    quickCheck (propLength :: FSVec ty Integer -> Bool)
>>> tests2 = forM_ [0..100] $ \n -> reifyIntegral n $ \(t :: ty) ->
>>>    quickCheck (uncurry propLengthEqual ::
>>>                     (FSVec ty Integer,FSVec ty Integer) -> Bool)
> 
> Thanks for the example code. Ideally it would be great to have n generated also.

Generating n isn't hard, in IO above you could just use Random.
But I assume you want to use QuickCheck, so see below.

> Any thoughts on whether something like
> 
> propLengthEqual :: forall n a. (Nat n) => n -> FSVec n Integer ->
> FSVec n Integer -> Bool
> propLengthEqual _ v1 v 2 = length v1 == length v2
> 
> with an arbitrary instance for generate all Nat n's is possible?

propLengthEqual is exactly the same as propLength, I just left out the 
first argument (it is redundant).

You cannot use an `Arbitrary' instance to generate some type level 
number, at least not in the same way as for ordinary numbers.

What you can do is introduce an existential type

 > data SomeNat = forall n. (Nat n) => SomeNat Int n
 > instance Show SomeNat where show (SomeNat value typ) = show value

 > instance Arbitrary SomeNat where
 >    arbitrary = sized $ \n -> reifyIntegral n (return . SomeNat n)


If you look into the QuickCheck source, you'll find that a property
is a result generator: newtype Property = Prop (Gen Result)

So a property can be written as a result generator:

 > propLength' :: SomeNat -> Gen Result
 > propLength' (SomeNat vn (n :: t)) = do
 >    (vector :: FSVec t Integer) <- arbitrary
 >    buildResult [show vn , show vec] $ propLength vector

--
What follows next is the neccessary boilerplate to have a working example
----
 > buildResult :: [String] -> Bool -> Gen Result
 > buildResult args b = evaluate b >>= \r ->
 >    return $ r { arguments = show args : arguments r}
 > natProp :: (SomeNat -> Gen Result) -> Property
 > natProp f = flip forAll id $ do
 >    (k::Int) <- choose (0,10)
 >    n <- resize k arbitrary
 >    f n
 > deriving instance Show Result
----

Finally, run the tests

 > tests = verboseCheck (natProp propLength')

Hope that helps.


best regards, benedikt
From malcolm.wallace at cs.york.ac.uk  Fri Jun 20 03:56:53 2008
From: malcolm.wallace at cs.york.ac.uk (Malcolm Wallace)
Date: Fri Jun 20 03:48:46 2008
Subject: [Haskell-cafe] This is a bug?
In-Reply-To: <382ead9b0806191055k7aba616bh3ff1e527648037ca@mail.gmail.com>
References: <382ead9b0806191055k7aba616bh3ff1e527648037ca@mail.gmail.com>
Message-ID: <2C3FBC33-8658-403C-BF88-8B557167B26B@cs.york.ac.uk>

> How I solve this issue when call "readXml":
>> in <score-partwise>, In a sequence:
>> in <part>, In a sequence:
>>   in <measure>, Too many elements inside <measure> at
>>   file ../../../parsers/elite2.xml  at line 75 col 15
>>   Found excess:

So, your XML document contains a <score-partwise>, which contains a  
sequence of <part>, at least one of which contains a sequence of  
<measure>.  But the <measure> at line 75 does not match the declared  
DTD.  The non-conforming text appears to be pure whitespace, which  
does seem a little odd.  This could be a bug in the HaXml parser, but  
it is hard to know for sure without seeing both the DTD and the  
failing file.  Can you send them to me (not to the list)?

Regards,
     Malcolm

From david.waern at gmail.com  Fri Jun 20 04:02:24 2008
From: david.waern at gmail.com (David Waern)
Date: Fri Jun 20 03:54:10 2008
Subject: [Haskell-cafe] Haddock compilation problem
In-Reply-To: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>
References: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>
Message-ID: <bb52000e0806200102r544d5cddw276e5d7c6b25613a@mail.gmail.com>

2008/6/20 Ronald Guida <oddron@gmail.com>:
> I just upgraded to ghc-6.8.3, using a linux binary, and I am having a
> problem compiling Haddock.  Haddock 2.1.0 and Haddock 2.0.0.0 both
> fail to build under ghc-6.8.3, but they both build successfully with
> ghc-6.8.2.  I don't know if this is a Haddock problem, or a GHC
> problem, or perhaps something else entirely?

The current Haddock isn't compatible with GHC 6.8.3, but I think the
next release will be.

David
From alistair at abayley.org  Fri Jun 20 05:51:01 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Fri Jun 20 05:42:46 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
Message-ID: <79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>

2008/6/20 Alistair Bayley <alistair@abayley.org>:
>> Is there a way of accessing a remote Oracle database by one of the common
>> Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get
>> unixODBC and Oracle's Instant Client running on a Linux machine, but I'm
>> trapped in the notorious error:
>
> Takusen's Oracle backend uses the Oracle Call Interface (OCI) library
> directly. I think most Oracle client drivers (ODBC, ADO.Net, etc) use
> the OCI. I don't know what the Oracle Instant Client is; I'll assume
> that it includes an oci.so or liboci.so. On Windows, with which I am
> most familiar, the Oracle client software is all installed in
> $ORACLE_HOME, and the OCI library is $ORACLE_HOME/bin/oci.dll. If you
> can locate that, then you ought to be able to use Takusen with it.

Having just taken a closer took at what Oracle Instant Client is, I
suspect that you might have some trouble getting Takusen to compile
against it. The Instant Client lacks header files, while Takusen's FFI
imports specify oci.h. I don't know what happens if ghc can't find the
header files. Oracle do state that the Instant Client is for
deployment only; developers (that means you) will need the full client
installation.

Another problem is that the Oracle installation process assumes that,
for all platforms, the library is called oci i.e. the linker option
-loci is used. For Unix clients, the OCI library seems to be
libclnstsh.so, so I guess it should pass -lclnstsh. This highlights
the lack of testing on non-Windows platforms. If you'd like to help
get this working better, perhaps we can discuss off-list.

Alistair
From jules at jellybean.co.uk  Fri Jun 20 07:34:01 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Fri Jun 20 07:25:49 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <1213896576.5557.55.camel@derek-laptop>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<1213755981.3338.15.camel@jonathans-macbook>	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>	<CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>	<4859F46B.5060602@jellybean.co.uk>	<279D0571-7E22-41C1-8F46-8FF40E12506A@cs.otago.ac.nz>	<4859FBC1.2070102@jellybean.co.uk>
	<1213896576.5557.55.camel@derek-laptop>
Message-ID: <485B95A9.2090002@jellybean.co.uk>

Derek Elkins wrote:
> Lambda abstractions should close over bindings.  Full stop.

Interesting. I agree with your analysis. I don't think I agree with your 
conclusion.

> 
> The first "surprising" behaviour is the correct one.  The latter would
> be broken.
> 
> In my opinion, the reason this behaviour is "surprising" isn't
> mutability, but -implicit- mutability.  Let's make bindings immutable,
> but add ML-style references to your example.
> 
> char ref c = ref(undefined);
> while(!eof(fp)) {
>     c := getChar(fp);
>     bind_event( ... print !c; ... );
> }
> 
> compare this to
> 
> while(!eof(fp)) {
>     char c = getChar(fp);
>     bind_event( ... print c; ...);
> }
> 
> or
> 
> while(!eof(fp)) {
>     char ref c = ref(getChar(fp));
>     bind_event( ... print !c; ...);
> }
> 
> Each of these examples makes it clearer what is going on. 

Agreed.

I think where I differ on you is how to map the semantics of a C-like 
language to explicit references.

I would argue that the glyph "c" in a C-like language denotes the value 
of C, not the reference to it. C-like languages have, for the most part, 
value semantics, and call-by-value.

The exception of course is what C-like languages called "lvalues", but 
lvalues are only really on the left of the = sign and a few other 
special positions. I think that's the exception and not the rule. I 
think the rule is that "c" denotes the value of c, and that's why I 
expect a closure to capture the value, not the reference.

In C, of course, if you want to capture the reference you do it 
explicitly with "&c".

Jules
From harald.rotter at sagem.com  Fri Jun 20 08:01:13 2008
From: harald.rotter at sagem.com (Harald ROTTER)
Date: Fri Jun 20 07:54:10 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
Message-ID: <OF9A1B2713.7561B55B-ONC125746E.004183E0-C125746E.004207DE@sagem.com>


Dear Haskellers,

after reading Oleg Kiselyov's paper on number-parameterized types I started
to play around with
the class Digits that encodes decimal numbers in types. The "typed number"
10 would e.g. be defined as

      D1 $ D0 $ Sz

I wondered if it would be possible replace the expression above by a
heterogeneous list like

      [D1,D0]

so I tried to define

      data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)

Loading this into ghci yields:

:t Digit D0

<interactive>:1:0:
    Ambiguous type variable `a' in the constraint:
      `Digits a' arising from a use of `Digit' at <interactive>:1:0-7
    Probable fix: add a type signature that fixes these type variable(s)

Removing the type constraints in the definition of "Digit":

      data Digit = forall a b.Digit (a -> b a)

makes it work like this:

      :t Digit D0
      Digit D0 :: Digit

      :t [Digit D0, Digit D1]
      [Digit D0, Digit D1] :: [Digit]

"Digit", however, is far too general (it also includes e.g. \x -> [x]), but
I would like it to be restricted to the Digit class.

Any help is appreciated.

Thanks

Harald.


CODE:

module Test where

data D0 a = D0 a
data D1 a = D1 a
data D2 a = D2 a
data D3 a = D3 a
data D4 a = D4 a
data D5 a = D5 a
data D6 a = D6 a
data D7 a = D7 a
data D8 a = D8 a
data D9 a = D9 a

class Digits ds where
    d2num :: Num a => ds -> a -> a

data Sz = Sz    -- zero size
instance Digits Sz where
    d2num _ acc = acc

instance Digits ds => Digits (D0 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc)
instance Digits ds => Digits (D1 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+1)
instance Digits ds => Digits (D2 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+2)
instance Digits ds => Digits (D3 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+3)
instance Digits ds => Digits (D4 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+4)
instance Digits ds => Digits (D5 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+5)
instance Digits ds => Digits (D6 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+6)
instance Digits ds => Digits (D7 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+7)
instance Digits ds => Digits (D8 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+8)
instance Digits ds => Digits (D9 ds) where
    d2num dds acc = d2num (t22 dds) (10*acc+9)

t22 :: f x -> x
t22 = undefined

--data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
data Digit = forall a b.Digit (a -> b a)

-------------------------------------------------------------------------------------------------



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From anton.tayanovskyy at gmail.com  Fri Jun 20 09:19:01 2008
From: anton.tayanovskyy at gmail.com (Anton Tayanovskyy)
Date: Fri Jun 20 09:10:47 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
In-Reply-To: <OF9A1B2713.7561B55B-ONC125746E.004183E0-C125746E.004207DE@sagem.com>
References: <OF9A1B2713.7561B55B-ONC125746E.004183E0-C125746E.004207DE@sagem.com>
Message-ID: <ab7bd6010806200619n147aefc3i24d56dbff053e3f2@mail.gmail.com>

Hi Harald,

Can you give a link to the paper? Interesting stuff. Thanks.

This is stretching my abilities a bit, but is this what you are after?

data Digit = forall b.(Digits (b Sz)) => Digit (Sz -> b Sz)

instance Digits [Digit] where
    d2num []           acc = acc
    d2num (Digit x:xs) acc = d2num xs (10*acc + d2num (x Sz) 0)

I assumed you only want D0..D9 as digits, maybe this is too narrow.

I've put this up on hpaste:

http://hpaste.org/8437#a1



Bests,

Anton



On Fri, Jun 20, 2008 at 3:01 PM, Harald ROTTER <harald.rotter@sagem.com> wrote:
>
> Dear Haskellers,
>
> after reading Oleg Kiselyov's paper on number-parameterized types I started
> to play around with
> the class Digits that encodes decimal numbers in types. The "typed number"
> 10 would e.g. be defined as
>
>      D1 $ D0 $ Sz
>
> I wondered if it would be possible replace the expression above by a
> heterogeneous list like
>
>      [D1,D0]
>
> so I tried to define
>
>      data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
>
> Loading this into ghci yields:
>
> :t Digit D0
>
> <interactive>:1:0:
>    Ambiguous type variable `a' in the constraint:
>      `Digits a' arising from a use of `Digit' at <interactive>:1:0-7
>    Probable fix: add a type signature that fixes these type variable(s)
>
> Removing the type constraints in the definition of "Digit":
>
>      data Digit = forall a b.Digit (a -> b a)
>
> makes it work like this:
>
>      :t Digit D0
>      Digit D0 :: Digit
>
>      :t [Digit D0, Digit D1]
>      [Digit D0, Digit D1] :: [Digit]
>
> "Digit", however, is far too general (it also includes e.g. \x -> [x]), but
> I would like it to be restricted to the Digit class.
>
> Any help is appreciated.
>
> Thanks
>
> Harald.
>
>
> CODE:
>
> module Test where
>
> data D0 a = D0 a
> data D1 a = D1 a
> data D2 a = D2 a
> data D3 a = D3 a
> data D4 a = D4 a
> data D5 a = D5 a
> data D6 a = D6 a
> data D7 a = D7 a
> data D8 a = D8 a
> data D9 a = D9 a
>
> class Digits ds where
>    d2num :: Num a => ds -> a -> a
>
> data Sz = Sz    -- zero size
> instance Digits Sz where
>    d2num _ acc = acc
>
> instance Digits ds => Digits (D0 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc)
> instance Digits ds => Digits (D1 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+1)
> instance Digits ds => Digits (D2 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+2)
> instance Digits ds => Digits (D3 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+3)
> instance Digits ds => Digits (D4 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+4)
> instance Digits ds => Digits (D5 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+5)
> instance Digits ds => Digits (D6 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+6)
> instance Digits ds => Digits (D7 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+7)
> instance Digits ds => Digits (D8 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+8)
> instance Digits ds => Digits (D9 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+9)
>
> t22 :: f x -> x
> t22 = undefined
>
> --data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
> data Digit = forall a b.Digit (a -> b a)
>
> -------------------------------------------------------------------------------------------------
>
>
>
> " Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes  pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel  ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite."
>
> " This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."
> _______________________________________________
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> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From neil.mehra at hutchinhill.com  Fri Jun 20 09:26:13 2008
From: neil.mehra at hutchinhill.com (Neil Mehra)
Date: Fri Jun 20 09:17:59 2008
Subject: [Haskell-cafe] Quantitative Trading Developer Position at Hutchin
	Hill Capital
Message-ID: <63D404D21F135440BFF6186D9059C6C1252A5071AC@EVS-PURPLE.coloflorida.com>


Job Description:

Quantitative Trading Developer

Description:

*         Newly formed multi-strategy hedge fund, Hutchin Hill Capital, located in midtown Manhattan, seeks a Quantitative Trading Developer;

*         Focus on building infrastructure, applications, and technical support for quantitative equity trading business;

*         Candidate should have demonstrated interest or passion for functional programming-with experience using Haskell, F#, Kdb+/q, OCaml, ML, and related technologies;

*         Position reports directly to portfolio manager, and will work closely with other technology and research professionals.


Responsibilities Include:

 *   Developing data management, quant research, and analytical tools for model-driven equity trading strategies;
 *   Building production environment for real-time content capture, trade generation, and risk management;
 *   Deploying equity trading technology, methods, and protocols, including electronic execution algorithms and market impact analysis;
 *   Conducting quantitative portfolio research using cutting-edge tools and techniques.

Required Experience/Education:

 *   2 - 5 years in IT development or quantitative analytics;
 *   Advanced degree or equivalent experience in a technical field such as computer science, mathematics, physics, or engineering;

Other Requirements:

 *   Exceptional technical and analytical problem-solving;
 *   Desire to master the latest technology, hardware, and quantitative methods;
 *   Willingness to work in a fast-paced, high pressure environment;
 *   Team-oriented and highly resourceful;
 *   Entrepreneurial drive.

Please contact quant2@hutchinhill.com<mailto:quant2@hutchinhill.com> with resume if interested.



__________
This communication, including any attachment(s), may contain confidential and/or privileged information. If you are not the intended recipient or have received this communication in error, please destroy/delete this email and any attachments. We do not waive confidentiality or privilege by mistransmission. This communication does not constitute an offer of employment, or an offer, or the solicitation of an offer, to buy or sell any security or investment advisory services, and is not an official confirmation of any transaction.
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From george.moschovitis at gmail.com  Fri Jun 20 09:44:38 2008
From: george.moschovitis at gmail.com (George Moschovitis)
Date: Fri Jun 20 09:36:24 2008
Subject: [Haskell-cafe] Re: HDBC converting a date sql value to UTCTime
In-Reply-To: <afd80b540806191208j38dced52g25357d510c79dbf3@mail.gmail.com>
References: <afd80b540806191208j38dced52g25357d510c79dbf3@mail.gmail.com>
Message-ID: <afd80b540806200644w23ba3463ma85608c5ef136a7c@mail.gmail.com>

Alternatively is there a way to create a UTCTime value from an epoch integer
(no of seconds since epoch).
I can't find a suitable constructor with Hoogle.

thank you in advance,
George.


On Thu, Jun 19, 2008 at 10:08 PM, George Moschovitis <
george.moschovitis@gmail.com> wrote:

> Hello,
>
> I am HDBC with the Postgres driver. I am trying to read a simple date
> column from the DB:
>
> stmt <- DB.prepare conn "SELECT date FROM my_table ORDER BY date DESC LIMIT
> 1"
> DB.execute stmt []
> DB.commit conn
> rows <- fetchAllRows' stmt
> let ((d:_):_) = rows
>
> the d variable is of type:
>
> SqlEpochTime 1213736400
>
> I am wondering how to convert this value to an UTCTime value.
>
> Any help appreciated (I am a newbie).
>
> -g.
>
>
>
> --
> http://gmosx.me.gr
> http://joy.gr
> http://cull.gr
> http://nitroproject.org
> http://phidz.com
> http://joyerz.com




-- 
Walt Disney  - "I love Mickey Mouse more than any woman I have ever known."
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From lemming at henning-thielemann.de  Fri Jun 20 11:43:04 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Fri Jun 20 11:34:51 2008
Subject: [Haskell-cafe] Checking packages before upload to Hackage
Message-ID: <Pine.LNX.4.64.0806201738130.31080@anubis.informatik.uni-halle.de>


Is there some command which tests a tar.gz created by 'Setup.lhs sdist' by 
unpacking the archive to say /tmp and compiling and documenting the 
sources? Hackage should recommend this tool before package upload.
From gwern0 at gmail.com  Fri Jun 20 12:12:05 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Fri Jun 20 12:03:49 2008
Subject: [Haskell-cafe] Checking packages before upload to Hackage
In-Reply-To: <Pine.LNX.4.64.0806201738130.31080@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806201738130.31080@anubis.informatik.uni-halle.de>
Message-ID: <cbf55b100806200912y64f05f9brec445eb3d4e462f3@mail.gmail.com>

On Fri, Jun 20, 2008 at 11:43 AM, Henning Thielemann
<lemming@henning-thielemann.de> wrote:
>
> Is there some command which tests a tar.gz created by 'Setup.lhs sdist' by
> unpacking the archive to say /tmp and compiling and documenting the sources?
> Hackage should recommend this tool before package upload.

There isn't. However, I do have some shell scripts which I use to the
same effect. They go like this:

function rh { nice runhaskell Setup "$@" --verbose; }
function build { rh build "$@"; }
function build_clean { rh clean && rh build "$@"; }
function build_sdist { clean_configure && sdist &&
    cd dist/ && untar *.tar.gz && cd `ls -t ./ | grep "/" | head -n 1` &&
    clean_configure && build && hinstall; haddock && hinstall; }
function clean { rh clean "$@"; }
function clean_configure { clean && configure; }
function configurenop { rh configure --enable-split-objs --user
--prefix=$HOME/bin "$@"; }
function configure { configurenop --enable-executable-profiling -p  "$@"; }
function haddock { rh haddock --executables "$@"; }
function hinstall { rh install --user "$@"; }
function sdist { rh sdist "$@"; }
function haskell { ( http_proxy="" pull ) & clean_configure && (build_sdist) & }

(Obviously you would either run 'haskell' or 'build_sdist' to test things out.)

If you're interested in a Haskell solution, there is an open Cabal bug
for this: <http://hackage.haskell.org/trac/hackage/ticket/274>.

--
gwern
From duncan.coutts at worc.ox.ac.uk  Fri Jun 20 14:25:44 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Fri Jun 20 14:12:42 2008
Subject: [Haskell-cafe] Checking packages before upload to Hackage
In-Reply-To: <cbf55b100806200912y64f05f9brec445eb3d4e462f3@mail.gmail.com>
References: <Pine.LNX.4.64.0806201738130.31080@anubis.informatik.uni-halle.de>
	<cbf55b100806200912y64f05f9brec445eb3d4e462f3@mail.gmail.com>
Message-ID: <1213986344.15010.980.camel@localhost>


On Fri, 2008-06-20 at 12:12 -0400, Gwern Branwen wrote:
> On Fri, Jun 20, 2008 at 11:43 AM, Henning Thielemann
> <lemming@henning-thielemann.de> wrote:
> >
> > Is there some command which tests a tar.gz created by 'Setup.lhs sdist' by
> > unpacking the archive to say /tmp and compiling and documenting the sources?
> > Hackage should recommend this tool before package upload.

> If you're interested in a Haskell solution, there is an open Cabal bug
> for this: <http://hackage.haskell.org/trac/hackage/ticket/274>.

This would indeed be a very useful feature.

If anyone wants to have a go at implementing it that would be great.
They can ask on cabal-devel for pointers and advice.

Duncan

From jefferson.r.heard at gmail.com  Fri Jun 20 14:25:42 2008
From: jefferson.r.heard at gmail.com (Jefferson Heard)
Date: Fri Jun 20 14:17:28 2008
Subject: [Haskell-cafe] Re: Wrapping FTGL in FFI calls
In-Reply-To: <20080620071612.12d7e6c2@solaris>
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>
	<20080620071612.12d7e6c2@solaris>
Message-ID: <4165d3a70806201125r59da2dfcla9467e61e9ae7876@mail.gmail.com>

Well, Achim you were almost exactly correct.  I have a functional function
interface in about half an hour's worth of work.  I have one question, which
is how to create a Ptr to four CFloats on the fly, pass them to the bounding
box functions, and then come back out with a [Float]

My prototype looks like this:
foreign import ccall unsafe "ftglGetFontBBox" fgetFontBBox :: Font ->
CString -> Ptr CFloat -> IO ()

the ptr to cfloat should be a float[4], which is modified inside the
original C function.

On Fri, Jun 20, 2008 at 1:16 AM, Achim Schneider <barsoap@web.de> wrote:

> "Jefferson Heard" <jefferson.r.heard@gmail.com> wrote:
>
> > I've been looking for awhile now for a simple way to get truetype
> > fonts into my visualizations so I can abandon the hideous GLUT fonts
> > and make things that look like they were developed in the 1990s
> > instead of back in the days of TRON.  I found FTGL, but I'm mostly a
> > Haskell developer these days, and resent having to go back to C just
> > to write a simple application.
> >
> > So I was wondering if anyone had ever wrapped the FTGL library in
> > Haskel FFI or whether those out there who are experts on the FFI
> > think at first glance it should be readily wrappable by a rank
> > amateur at FFI such as myself.
> >
> > http://ftgl.sourceforge.net/docs/html/
> >
> Using the FFI is generally straight forward, as long as you can live
> with using the IO monad and the C code uses objects (well,
> pointers to structs passed as first argument, where's the
> difference...).
>
> Things only depend on the purity of the C code and how high-level you
> want your interface to be. In this case, I estimate half an hour if
> you're a fast typist. That includes the time needed to read the FFI
> docs.
>
> --
> (c) this sig last receiving data processing entity. Inspect headers for
> past copyright information. All rights reserved. Unauthorised copying,
> hiring, renting, public performance and/or broadcasting of this
> signature prohibited.
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>



-- 
I try to take things like a crow; war and chaos don't always ruin a picnic,
they just mean you have to be careful what you swallow.

-- Jessica Edwards
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From jefferson.r.heard at gmail.com  Fri Jun 20 14:31:43 2008
From: jefferson.r.heard at gmail.com (Jefferson Heard)
Date: Fri Jun 20 14:23:30 2008
Subject: [Haskell-cafe] Re: Wrapping FTGL in FFI calls
In-Reply-To: <4165d3a70806201125r59da2dfcla9467e61e9ae7876@mail.gmail.com>
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>
	<20080620071612.12d7e6c2@solaris>
	<4165d3a70806201125r59da2dfcla9467e61e9ae7876@mail.gmail.com>
Message-ID: <4165d3a70806201131o4370aee7kd63d20cad5caab9@mail.gmail.com>

Oh, and I should say the function I want to implement is

getFontBBox :: Font -> String -> IO [Float]

I do know how to marhsal/unmarshal the String.  Just not the CFloat array to
Haskell [Float]

On Fri, Jun 20, 2008 at 2:25 PM, Jefferson Heard <
jefferson.r.heard@gmail.com> wrote:

> Well, Achim you were almost exactly correct.  I have a functional function
> interface in about half an hour's worth of work.  I have one question, which
> is how to create a Ptr to four CFloats on the fly, pass them to the bounding
> box functions, and then come back out with a [Float]
>
> My prototype looks like this:
> foreign import ccall unsafe "ftglGetFontBBox" fgetFontBBox :: Font ->
> CString -> Ptr CFloat -> IO ()
>
> the ptr to cfloat should be a float[4], which is modified inside the
> original C function.
>
>
> On Fri, Jun 20, 2008 at 1:16 AM, Achim Schneider <barsoap@web.de> wrote:
>
>> "Jefferson Heard" <jefferson.r.heard@gmail.com> wrote:
>>
>> > I've been looking for awhile now for a simple way to get truetype
>> > fonts into my visualizations so I can abandon the hideous GLUT fonts
>> > and make things that look like they were developed in the 1990s
>> > instead of back in the days of TRON.  I found FTGL, but I'm mostly a
>> > Haskell developer these days, and resent having to go back to C just
>> > to write a simple application.
>> >
>> > So I was wondering if anyone had ever wrapped the FTGL library in
>> > Haskel FFI or whether those out there who are experts on the FFI
>> > think at first glance it should be readily wrappable by a rank
>> > amateur at FFI such as myself.
>> >
>> > http://ftgl.sourceforge.net/docs/html/
>> >
>> Using the FFI is generally straight forward, as long as you can live
>> with using the IO monad and the C code uses objects (well,
>> pointers to structs passed as first argument, where's the
>> difference...).
>>
>> Things only depend on the purity of the C code and how high-level you
>> want your interface to be. In this case, I estimate half an hour if
>> you're a fast typist. That includes the time needed to read the FFI
>> docs.
>>
>> --
>> (c) this sig last receiving data processing entity. Inspect headers for
>> past copyright information. All rights reserved. Unauthorised copying,
>> hiring, renting, public performance and/or broadcasting of this
>> signature prohibited.
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
>
>
> --
> I try to take things like a crow; war and chaos don't always ruin a picnic,
> they just mean you have to be careful what you swallow.
>
> -- Jessica Edwards




-- 
I try to take things like a crow; war and chaos don't always ruin a picnic,
they just mean you have to be careful what you swallow.

-- Jessica Edwards
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From matti.niemenmaa+news at iki.fi  Fri Jun 20 14:56:47 2008
From: matti.niemenmaa+news at iki.fi (Matti Niemenmaa)
Date: Fri Jun 20 14:56:47 2008
Subject: [Haskell-cafe] Re: Haddock compilation problem
In-Reply-To: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>
References: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>
Message-ID: <g3guhg$qvq$1@ger.gmane.org>

Ronald Guida wrote:
> I just upgraded to ghc-6.8.3, using a linux binary, and I am having a
> problem compiling Haddock.  Haddock 2.1.0 and Haddock 2.0.0.0 both
> fail to build under ghc-6.8.3, but they both build successfully with
> ghc-6.8.2.  I don't know if this is a Haddock problem, or a GHC
> problem, or perhaps something else entirely?
> 
> Here is the error I'm getting.  It is the same error for either
> version of Haddock.
> 
> [15 of 24] Compiling Haddock.GHC.Typecheck (
> src/Haddock/GHC/Typecheck.hs,
> dist/build/haddock/haddock-tmp/Haddock/GHC/Typecheck.o )
> 
> src/Haddock/GHC/Typecheck.hs:82:4:
>     Constructor `HsModule' should have 7 arguments, but has been given 8
>     In the pattern: HsModule _ _ _ _ _ mbOpts _ _
>     In a pattern binding: HsModule _ _ _ _ _ mbOpts _ _ = unLoc parsed
<snip>

I managed to fix this with a bit of hacking:
1) add "import FastString" to the top of the file
2) remove one of the _'s before mbOpts on that line that gives the error
3) on line 72 of the original file (probably 73 after step 1), insert 'fmap 
unpackFS' before 'mbOpts'.

I now get some sort of System.Process-related link error, though. YMMV.

libHSghc.a(SysTools.o)(.text+0x7200):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcess_a6_closure'
libHSghc.a(SysTools.o)(.text+0x75c5):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcess_lvl1_closure'
libHSghc.a(SysTools.o)(.text+0xa6df):fake: undefined reference to 
`__stginit_processzm1zi0zi0zi1_SystemziProcess_'
libHSghc.a(SysTools.o)(.text+0x7215):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcessziInternals_a3_info'
libHSghc.a(SysTools.o)(.text+0x75d4):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcess_a8_info'
libHSghc.a(SysTools.o)(.data+0xcf8):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcess_lvl1_closure'
libHSghc.a(SysTools.o)(.data+0xcfc):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcess_a8_closure'
libHSghc.a(SysTools.o)(.data+0xd00):fake: undefined reference to 
`processzm1zi0zi0zi1_SystemziProcess_a6_closure'

From matti.niemenmaa+news at iki.fi  Fri Jun 20 15:19:54 2008
From: matti.niemenmaa+news at iki.fi (Matti Niemenmaa)
Date: Fri Jun 20 15:11:50 2008
Subject: [Haskell-cafe] Re: Haddock compilation problem
In-Reply-To: <g3guhg$qvq$1@ger.gmane.org>
References: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>
	<g3guhg$qvq$1@ger.gmane.org>
Message-ID: <g3gvsr$vgq$1@ger.gmane.org>

Matti Niemenmaa wrote:
> I now get some sort of System.Process-related link error, though. YMMV.

Audrey Tang gave me the fix for this on the IRC channel: passing 
--ghc-option="-package process-1.0.0.1" dealt with that.

It appears that it was all for naught, though: running the haddock binary on 
pretty much anything results in "Segmentation fault/access violation in 
generated code" or a downright crash.

I suppose I'll leave this to the Haddock developers, then. <g>

From vigalchin at gmail.com  Fri Jun 20 15:51:11 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Fri Jun 20 15:42:55 2008
Subject: [Haskell-cafe] another FFI question
Message-ID: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>

Hello,

    I am reading the FFI spec. The following is unclear to me. Say I have

data Bonzo = A | B |C

and I want to "poke" Bonzo to an Int

A -> 0

B -> 1

C -> 4

I have made  Bonzo an instance of Storable.

How do I write the poke functions and call them?

Thanks, Vasili
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From bulat.ziganshin at gmail.com  Fri Jun 20 16:20:16 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Fri Jun 20 16:13:33 2008
Subject: [Haskell-cafe] another FFI question
In-Reply-To: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
References: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
Message-ID: <1662913902.20080621002016@gmail.com>

Hello Vasili,

Friday, June 20, 2008, 11:51:11 PM, you wrote:
> data Bonzo = A | B |C

> How do I write the poke functions and call them?

instance Storable Bonzo
  poke A = poke 0
  poke B = poke 1
  poke C = poke 4

call as "poke x"

probably, you don't understand differences between OOP classes and
type classes. look at http://haskell.org/haskellwiki/OOP_vs_type_classes
and papers mentioned there


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From jules at jellybean.co.uk  Fri Jun 20 16:26:07 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Fri Jun 20 16:17:53 2008
Subject: [Haskell-cafe] Re: Wrapping FTGL in FFI calls
In-Reply-To: <4165d3a70806201131o4370aee7kd63d20cad5caab9@mail.gmail.com>
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>	<20080620071612.12d7e6c2@solaris>	<4165d3a70806201125r59da2dfcla9467e61e9ae7876@mail.gmail.com>
	<4165d3a70806201131o4370aee7kd63d20cad5caab9@mail.gmail.com>
Message-ID: <485C125F.3010401@jellybean.co.uk>

Jefferson Heard wrote:
> Oh, and I should say the function I want to implement is
> 
> getFontBBox :: Font -> String -> IO [Float]
> 
> I do know how to marhsal/unmarshal the String.  Just not the CFloat 
> array to Haskell [Float]

import Foreign.C
import Foreign.Ptr
import Foreign.Marshal.Array

import Control.Applicative((<$>))

oneway :: Ptr CFloat -> IO [Float]
oneway p = map real2Frac <$> peekArray 4 p

the other way you would probably want withArray, but I think this is the 
way you need?


From oddron at gmail.com  Fri Jun 20 16:39:15 2008
From: oddron at gmail.com (Ronald Guida)
Date: Fri Jun 20 16:31:06 2008
Subject: [Haskell-cafe] Re: Haddock compilation problem
In-Reply-To: <g3gvsr$vgq$1@ger.gmane.org>
References: <62728db30806191945n6e8d8835pd8bef91a658c2b7b@mail.gmail.com>
	<g3guhg$qvq$1@ger.gmane.org> <g3gvsr$vgq$1@ger.gmane.org>
Message-ID: <62728db30806201339v61706ff0v73260092b371c8b4@mail.gmail.com>

I have added ticket #18 to the Haddock Trac.
http://trac.haskell.org/haddock/wiki
From jefferson.r.heard at gmail.com  Fri Jun 20 16:42:43 2008
From: jefferson.r.heard at gmail.com (Jefferson Heard)
Date: Fri Jun 20 16:34:29 2008
Subject: [Haskell-cafe] Re: Wrapping FTGL in FFI calls
In-Reply-To: <485C125F.3010401@jellybean.co.uk>
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>
	<20080620071612.12d7e6c2@solaris>
	<4165d3a70806201125r59da2dfcla9467e61e9ae7876@mail.gmail.com>
	<4165d3a70806201131o4370aee7kd63d20cad5caab9@mail.gmail.com>
	<485C125F.3010401@jellybean.co.uk>
Message-ID: <4165d3a70806201342n41b745e4t81051089dce38fbf@mail.gmail.com>

Exactly.  thanks!

On Fri, Jun 20, 2008 at 4:26 PM, Jules Bean <jules@jellybean.co.uk> wrote:

> Jefferson Heard wrote:
>
>> Oh, and I should say the function I want to implement is
>>
>> getFontBBox :: Font -> String -> IO [Float]
>>
>> I do know how to marhsal/unmarshal the String.  Just not the CFloat array
>> to Haskell [Float]
>>
>
> import Foreign.C
> import Foreign.Ptr
> import Foreign.Marshal.Array
>
> import Control.Applicative((<$>))
>
> oneway :: Ptr CFloat -> IO [Float]
> oneway p = map real2Frac <$> peekArray 4 p
>
> the other way you would probably want withArray, but I think this is the
> way you need?
>
>
>


-- 
I try to take things like a crow; war and chaos don't always ruin a picnic,
they just mean you have to be careful what you swallow.

-- Jessica Edwards
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From jules at jellybean.co.uk  Fri Jun 20 16:43:51 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Fri Jun 20 16:35:35 2008
Subject: [Haskell-cafe] Re: Wrapping FTGL in FFI calls
In-Reply-To: <4165d3a70806201342n41b745e4t81051089dce38fbf@mail.gmail.com>
References: <4165d3a70806191104h5b8105cfo222058cba5518bc6@mail.gmail.com>	<20080620071612.12d7e6c2@solaris>	<4165d3a70806201125r59da2dfcla9467e61e9ae7876@mail.gmail.com>	<4165d3a70806201131o4370aee7kd63d20cad5caab9@mail.gmail.com>	<485C125F.3010401@jellybean.co.uk>
	<4165d3a70806201342n41b745e4t81051089dce38fbf@mail.gmail.com>
Message-ID: <485C1687.3070707@jellybean.co.uk>

Sorry, it's "realToFrac". Typo!

Jefferson Heard wrote:
> Exactly.  thanks!
> 
> On Fri, Jun 20, 2008 at 4:26 PM, Jules Bean <jules@jellybean.co.uk 
> <mailto:jules@jellybean.co.uk>> wrote:
> 
>     Jefferson Heard wrote:
> 
>         Oh, and I should say the function I want to implement is
> 
>         getFontBBox :: Font -> String -> IO [Float]
> 
>         I do know how to marhsal/unmarshal the String.  Just not the
>         CFloat array to Haskell [Float]
> 
> 
>     import Foreign.C
>     import Foreign.Ptr
>     import Foreign.Marshal.Array
> 
>     import Control.Applicative((<$>))
> 
>     oneway :: Ptr CFloat -> IO [Float]
>     oneway p = map real2Frac <$> peekArray 4 p
> 
>     the other way you would probably want withArray, but I think this is
>     the way you need?
> 
> 
> 
> 
> 
> -- 
> I try to take things like a crow; war and chaos don't always ruin a 
> picnic, they just mean you have to be careful what you swallow.
> 
> -- Jessica Edwards
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

From vigalchin at gmail.com  Fri Jun 20 17:55:00 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Fri Jun 20 17:46:45 2008
Subject: [Haskell-cafe] another FFI question
In-Reply-To: <1662913902.20080621002016@gmail.com>
References: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
	<1662913902.20080621002016@gmail.com>
Message-ID: <5ae4f2ba0806201455n20f6af46pa65adb664b2e78c8@mail.gmail.com>

Thanks Bulat!

Vasili

On Fri, Jun 20, 2008 at 3:20 PM, Bulat Ziganshin <bulat.ziganshin@gmail.com>
wrote:

> Hello Vasili,
>
> Friday, June 20, 2008, 11:51:11 PM, you wrote:
> > data Bonzo = A | B |C
>
> > How do I write the poke functions and call them?
>
> instance Storable Bonzo
>  poke A = poke 0
>  poke B = poke 1
>  poke C = poke 4
>
> call as "poke x"
>
> probably, you don't understand differences between OOP classes and
> type classes. look at http://haskell.org/haskellwiki/OOP_vs_type_classes
> and papers mentioned there
>
>
> --
> Best regards,
>  Bulat                            mailto:Bulat.Ziganshin@gmail.com
>
>
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From pieter at laeremans.org  Fri Jun 20 18:04:10 2008
From: pieter at laeremans.org (Pieter Laeremans)
Date: Fri Jun 20 17:55:54 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
Message-ID: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>

HI,

What 's wrong with this:

type Id = String

class Catalog a where
    listItems :: a -> IO [String]
    getItem :: a -> Id -> IO (Maybe String)

class Item a where
    getCatalog :: Catalog catalog => a -> catalog

data Catalog c => Content c = Content {auteur :: String, inhoud::
String, catalog::c}

instance Catalog c => Item (Content c) where
   getCatalog (Content  _ _ c) = c

I get this as error from ghci:

    Couldn't match expected type `catalog' against inferred type `c'
      `catalog' is a rigid type variable bound by
                the type signature for `getCatalog'
                  at
../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:16:26
      `c' is a rigid type variable bound by
          the instance declaration
            at ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:20:17
    In the expression: c
    In the definition of `getCatalog': getCatalog (Content _ _ c) = c
    In the definition for method `getCatalog'
Failed, modules loaded: none.

thanks in advance,

P

-- 
Pieter Laeremans <pieter@laeremans.org>

"The future is here. It's just not evenly distributed yet." W. Gibson
From bulat.ziganshin at gmail.com  Fri Jun 20 18:22:45 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Fri Jun 20 18:15:29 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
In-Reply-To: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
References: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
Message-ID: <1617672145.20080621022245@gmail.com>

Hello Pieter,

Saturday, June 21, 2008, 2:04:10 AM, you wrote:

for me, it seems just like you directly translated OOP classes into
Haskell that is the wrong way. you may look into
http://haskell.org/haskellwiki/OOP_vs_type_classes and
ghc user manual which discuss functional dependencies on the example
of collection classes


> HI,

> What 's wrong with this:

> type Id = String

> class Catalog a where
>     listItems :: a -> IO [String]
>     getItem :: a -> Id -> IO (Maybe String)

> class Item a where
>     getCatalog :: Catalog catalog => a -> catalog

data Catalog c =>> Content c = Content {auteur :: String, inhoud::
> String, catalog::c}

> instance Catalog c => Item (Content c) where
>    getCatalog (Content  _ _ c) = c

> I get this as error from ghci:

>     Couldn't match expected type `catalog' against inferred type `c'
>       `catalog' is a rigid type variable bound by
>                 the type signature for `getCatalog'
>                   at
> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:16:26
>       `c' is a rigid type variable bound by
>           the instance declaration
>             at
> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:20:17
>     In the expression: c
>     In the definition of `getCatalog': getCatalog (Content _ _ c) = c
>     In the definition for method `getCatalog'
> Failed, modules loaded: none.

> thanks in advance,

> P




-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From westondan at imageworks.com  Fri Jun 20 18:25:48 2008
From: westondan at imageworks.com (Dan Weston)
Date: Fri Jun 20 18:17:35 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
In-Reply-To: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
References: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
Message-ID: <485C2E6C.5060709@imageworks.com>

I think the problem is here:

 >     getCatalog :: Catalog catalog => a -> catalog

This wants to constrain the result of getCatalog to be an instance of 
Catalog, but this only works for function arguments, not results. The 
following code does typecheck, though I have no idea what is does or if 
it is what you want:


type Id = String

class Catalog a where
     listItems :: a -> IO [String]
     getItem :: a -> Id -> IO (Maybe String)

class Catalog q => Item q a where
     getCatalog :: a -> q

data Content d = MkContent {auteur  :: String,
                             inhoud  :: String,
                             catalog :: d}

instance Catalog c => Item c (Content c) where
    getCatalog (MkContent  _ _ e) = e



Pieter Laeremans wrote:
> HI,
> 
> What 's wrong with this:
> 
> type Id = String
> 
> class Catalog a where
>     listItems :: a -> IO [String]
>     getItem :: a -> Id -> IO (Maybe String)
> 
> class Item a where
>     getCatalog :: Catalog catalog => a -> catalog
> 
> data Catalog c => Content c = Content {auteur :: String, inhoud::
> String, catalog::c}
> 
> instance Catalog c => Item (Content c) where
>    getCatalog (Content  _ _ c) = c
> 
> I get this as error from ghci:
> 
>     Couldn't match expected type `catalog' against inferred type `c'
>       `catalog' is a rigid type variable bound by
>                 the type signature for `getCatalog'
>                   at
> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:16:26
>       `c' is a rigid type variable bound by
>           the instance declaration
>             at ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:20:17
>     In the expression: c
>     In the definition of `getCatalog': getCatalog (Content _ _ c) = c
>     In the definition for method `getCatalog'
> Failed, modules loaded: none.
> 
> thanks in advance,
> 
> P
> 


From dan.doel at gmail.com  Fri Jun 20 18:26:32 2008
From: dan.doel at gmail.com (Dan Doel)
Date: Fri Jun 20 18:18:26 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
In-Reply-To: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
References: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
Message-ID: <200806201826.33689.dan.doel@gmail.com>

On Friday 20 June 2008, Pieter Laeremans wrote:
> type Id = String
>
> class Catalog a where
>     listItems :: a -> IO [String]
>     getItem :: a -> Id -> IO (Maybe String)
>
> class Item a where
>     getCatalog :: Catalog catalog => a -> catalog
>
> data Catalog c => Content c = Content {auteur :: String, inhoud::
> String, catalog::c}
>
> instance Catalog c => Item (Content c) where
>    getCatalog (Content  _ _ c) = c
>
> I get this as error from ghci:
>
>     Couldn't match expected type `catalog' against inferred type `c'
>       `catalog' is a rigid type variable bound by
>                 the type signature for `getCatalog'
>                   at
> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:16:26
>       `c' is a rigid type variable bound by
>           the instance declaration
>             at
> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:20:17 In the
> expression: c
>     In the definition of `getCatalog': getCatalog (Content _ _ c) = c
>     In the definition for method `getCatalog'
> Failed, modules loaded: none.

The problem is in the type of getCatalog:

  (Item a, Catalog catalog) => a -> catalog

That type says that given the a, you can produce a value of any type 'catalog' 
so long as that type is an instance of Catalog.

What you probably meant it to say is that you can produce *some particular* 
type that belongs to catalog. There are a couple ways you could express this. 
For instance, using functional dependencies:

    class Catalog cat => HasCatalog a cat | a -> cat where
      getCatalog :: a -> cat

or the new type families:

    class (Catalog (Cat a)) => Item a where
      type Cat a :: *
      getCatalog :: a -> Cat a

Or you could wrap catalogues in an existential type:

    data SomeCatalog = forall c. Catalog c => Cat c

    class Item a where
      getCatalog :: a -> SomeCatalog

However, as just a word of warning, I'd say that when you run into something 
like this, it's probably an indication that you're structuring your program 
from an object oriented mindset, and that may not be the best fit for 
programming in Haskell (of course, it's possible an existential type or some 
such is the appropriate way to do things).

Cheers,
-- Dan
From derek.a.elkins at gmail.com  Fri Jun 20 18:37:23 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Fri Jun 20 18:29:16 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
In-Reply-To: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
References: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
Message-ID: <1214001443.26144.10.camel@derek-laptop>

On Sat, 2008-06-21 at 00:04 +0200, Pieter Laeremans wrote:
> HI,
> 
> What 's wrong with this:

It looks like you think Haskell is an OO language or want it to be.  It
is not.

> 
> type Id = String
> 
> class Catalog a where
>     listItems :: a -> IO [String]
>     getItem :: a -> Id -> IO (Maybe String)
> 
> class Item a where
>     getCatalog :: Catalog catalog => a -> catalog

This means 
class Item a where
    getCatalog :: forall catalog. Catalog catalog => a -> catalog

That means, given some Item a, I can create a value of -any- type that
is an instance of Catalog.  There is no well-defined function that could
do that.

> 
> data Catalog c => Content c = Content {auteur :: String, inhoud::
> String, catalog::c}
> 
> instance Catalog c => Item (Content c) where
>    getCatalog (Content  _ _ c) = c
> 
> I get this as error from ghci:
> 
>     Couldn't match expected type `catalog' against inferred type `c'
>       `catalog' is a rigid type variable bound by
>                 the type signature for `getCatalog'
>                   at
> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:16:26
>       `c' is a rigid type variable bound by
>           the instance declaration
>             at ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:20:17
>     In the expression: c
>     In the definition of `getCatalog': getCatalog (Content _ _ c) = c
>     In the definition for method `getCatalog'
> Failed, modules loaded: none.
> 
> thanks in advance,
> 
> P
> 

From pieter at laeremans.org  Fri Jun 20 18:44:13 2008
From: pieter at laeremans.org (Pieter Laeremans)
Date: Fri Jun 20 18:35:57 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
In-Reply-To: <200806201826.33689.dan.doel@gmail.com>
References: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
	<200806201826.33689.dan.doel@gmail.com>
Message-ID: <ddacd4a70806201544n2326c2fdidec4542ab1b1c737@mail.gmail.com>

Thanks all!

I have to admit, I have an OO mndset :-).

I think I have found a more "functional design" :

import Text.StringTemplate.Classes
import Text.StringTemplate

data (ToSElem a) => Item  a b = Item {cargo::a , catalog :: (Catalog a b)}

instance (ToSElem a) => ToSElem (Item a b) where
    toSElem = (toSElem . cargo)

type Id = String

type ItemToSelem a b = Item a b -> SElem b
type ItemParser a b = String -> Item a b

type AllItemReader a b = IO [Item a b]
type SingleItemReader a b = Id -> IO (Item a b)

data Catalog a b = Catalog  {reader:: (AllItemReader a b),
singleReader ::( SingleItemReader a b)}

data Content = Content {authort :: String, text:: String}

type ContentItem = Item Content String






What I want to express is that there exists differnet kinds of catalogs which,
depending on how they are configured can read from a file system or a database.
And each catalog can contain a specific type of Item.

For each Item I have to be able to produce the toSELem representation
that subsequently can be used by HStringTemplate

I thik that means I could declare

On Sat, Jun 21, 2008 at 12:26 AM, Dan Doel <dan.doel@gmail.com> wrote:
> On Friday 20 June 2008, Pieter Laeremans wrote:
>> type Id = String
>>
>> class Catalog a where
>>     listItems :: a -> IO [String]
>>     getItem :: a -> Id -> IO (Maybe String)
>>
>> class Item a where
>>     getCatalog :: Catalog catalog => a -> catalog
>>
>> data Catalog c => Content c = Content {auteur :: String, inhoud::
>> String, catalog::c}
>>
>> instance Catalog c => Item (Content c) where
>>    getCatalog (Content  _ _ c) = c
>>
>> I get this as error from ghci:
>>
>>     Couldn't match expected type `catalog' against inferred type `c'
>>       `catalog' is a rigid type variable bound by
>>                 the type signature for `getCatalog'
>>                   at
>> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:16:26
>>       `c' is a rigid type variable bound by
>>           the instance declaration
>>             at
>> ../Sites/liberaleswebsite/www.liberales.be/cgi-bin/Test.hs:20:17 In the
>> expression: c
>>     In the definition of `getCatalog': getCatalog (Content _ _ c) = c
>>     In the definition for method `getCatalog'
>> Failed, modules loaded: none.
>
> The problem is in the type of getCatalog:
>
>  (Item a, Catalog catalog) => a -> catalog
>
> That type says that given the a, you can produce a value of any type 'catalog'
> so long as that type is an instance of Catalog.
>
> What you probably meant it to say is that you can produce *some particular*
> type that belongs to catalog. There are a couple ways you could express this.
> For instance, using functional dependencies:
>
>    class Catalog cat => HasCatalog a cat | a -> cat where
>      getCatalog :: a -> cat
>
> or the new type families:
>
>    class (Catalog (Cat a)) => Item a where
>      type Cat a :: *
>      getCatalog :: a -> Cat a
>
> Or you could wrap catalogues in an existential type:
>
>    data SomeCatalog = forall c. Catalog c => Cat c
>
>    class Item a where
>      getCatalog :: a -> SomeCatalog
>
> However, as just a word of warning, I'd say that when you run into something
> like this, it's probably an indication that you're structuring your program
> from an object oriented mindset, and that may not be the best fit for
> programming in Haskell (of course, it's possible an existential type or some
> such is the appropriate way to do things).
>
> Cheers,
> -- Dan
>



-- 
Pieter Laeremans <pieter@laeremans.org>

"The future is here. It's just not evenly distributed yet." W. Gibson
From wren at freegeek.org  Fri Jun 20 18:49:17 2008
From: wren at freegeek.org (wren ng thornton)
Date: Fri Jun 20 18:41:04 2008
Subject: [Haskell-cafe] What's wrong with the classes/insances?
In-Reply-To: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
References: <ddacd4a70806201504s57ebbf17o22cb1af863be6520@mail.gmail.com>
Message-ID: <485C33ED.8010301@freegeek.org>

Pieter Laeremans wrote:
> HI,
> 
> What 's wrong with this:
> 
> [...]
> 
> class Item a where
>     getCatalog :: Catalog catalog => a -> catalog

This is a shorthand for

  > class Item a where
  >     getCatalog :: forall c. (Catalog c) => a -> c

That is, the class provides the contract that given some value of type a 
it will be able to return *any* type c which adheres to the contract of 
the class Catalog. This function is polymorphic in the return type.


> instance Catalog c => Item (Content c) where
>    getCatalog (Content  _ _ c) = c

The problem is, here you're returning a *specific* type c which adheres 
to Catalog. What happens if the caller of getCatalog is expecting some 
other type (Catalog c') => c' or (Catalog c'') => c'' etc?


There are a few different solutions you could take. The easiest one is 
to use multi-parameter type classes and functional dependencies to 
define Item like so:

  > class Item a c | a -> c where
  >     getCatalog :: (Catalog c) => a -> c

This says that for any given type a there is one particular type c which 
getCatalog returns. Depending on your goals this may be enough, but if 
you really want getCatalog to be polymorphic in c then it won't work. 
(If you only want to be, er, multimorphic in c then you can leave out 
the fundep and define instances for each a*c type pair. This can lead to 
needing to declare excessively many type signatures however.)


If you really want to be able to return any c then there are a couple of 
approaches you could take. First is to add a conversion function to the 
Catalog class:

  > class Catalog c where
  >     ...
  >     convertCatalog:: forall c'. (Catalog c') => c -> c'

Given the rest of the definition for Catalog, this looks to be eminently 
doable-- at least in as far as people don't try to access any other 
fiddly bits inside the value c'. Of course this gives no way of 
preventing them from trying to do that fiddling, which leads to...


The other common approach is to use existential types to wrap values up 
with their class dictionaries like so:

  > data CatalogWrapper = forall c. (Catalog c) => CatalogWrapper c

In this case you'd have getCatalog return a CatalogWrapper instead of a 
(Catalog c) => c. If you're not familiar with existential types they can 
be harder to think about since they loose information about what type 
you actually have inside; once wrapped they're only ever accessible by 
the methods of type classes restricting what we can wrap. But if you 
want to restrict people to only ever using the Catalog interface to 
manipulate them, then this is exactly what you want.


-- 
Live well,
~wren
From kangas at math.ku.edu  Fri Jun 20 19:15:20 2008
From: kangas at math.ku.edu (George Kangas)
Date: Fri Jun 20 19:07:03 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
Message-ID: <485C3A08.8070302@math.ku.edu>

Hi, Cafe,

   For no practical purpose, I wrote new definitions of list folds as 
chains of partially applied functions, joined by composition.  I took 
the liberty of rearranging the type signature.

 > foldright :: (a -> b -> b)) -> [a] -> b -> b
 > foldright f = chain where
 >     chain (a:as) = (f a).(chain as)
 >     chain _ = id

 > foldleft :: (a -> b -> b) -> [a] -> b -> b
 > foldleft f = chain where
 >     chain (a:as) = (chain as).(f a)
 >     chain _ = id

   These definitions are point free, with respect to the "initializer" 
argument (which is now the last argument).  Also, you can see how 
similar they are to each other, with the difference boiling down to the 
order of the composition, e.g.:

foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0


   We can also see the following identities:

foldright f as == foldright (.) (map f as) id
foldleft f as == foldright (flip (.)) (map f as) id

   I like that second one, after trying to read another definition of 
left fold in terms of right fold (in the web book "Real World Haskell").

   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
(b -> b)), suggests generalization to another type constructor C: (a -> 
(b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
sense?

   Okay, it goes without saying that this is useless dabbling, but have 
I entertained anyone?  Or have I just wasted your time?  I eagerly await 
comments on this, my first posting.

very truly yours,

George Kangas
From allbery at ece.cmu.edu  Fri Jun 20 19:21:25 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Fri Jun 20 19:13:14 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <485C3A08.8070302@math.ku.edu>
References: <485C3A08.8070302@math.ku.edu>
Message-ID: <555BB226-AF91-4EEA-B109-90702F3769D2@ece.cmu.edu>


On 2008 Jun 20, at 19:15, George Kangas wrote:

>  The type signature, which could be written (a -> (b -> b)) -> ([a] - 
> > (b -> b)), suggests generalization to another type constructor C:  
> (a -> (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass  
> make any sense?

http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Foldable.html

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From stevelihn at gmail.com  Fri Jun 20 20:44:16 2008
From: stevelihn at gmail.com (Steve Lihn)
Date: Fri Jun 20 20:36:00 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
Message-ID: <a66b8c070806201744v1e7d05d8jd0ab33efb395f553@mail.gmail.com>

You may want to check this out.

http://www.orafaq.com/wiki/ODBC_FAQ#Where_can_one_get_ODBC_drivers_for_Oracle_and_Rdb.3F

As Oracle is a commercial company who is not interested in open source
historically, it is little chance that you will get robust software
for free -- from someone with many years of Oracle DBA experience :-)


On 6/19/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>
> Is there a way of accessing a remote Oracle database by one of the common
> Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get
> unixODBC and Oracle's Instant Client running on a Linux machine, but I'm
> trapped in the notorious error:
>
> $ isql USER -v
> [IM004][unixODBC][Driver Manager]Driver's SQLAllocHandle on SQL_HANDLE_HENV
> failed
> [ISQL]ERROR: Could not SQLConnect
>
> This error message is discussed in various web forums, but there seems to be
> no systematic way to track down the problem. So I wonder whether there is
> another way to access the Oracle data base from Haskell.
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From byorgey at seas.upenn.edu  Fri Jun 20 22:31:17 2008
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Fri Jun 20 22:22:59 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <485C3A08.8070302@math.ku.edu>
References: <485C3A08.8070302@math.ku.edu>
Message-ID: <20080621023117.GA2741@minus.seas.upenn.edu>

On Fri, Jun 20, 2008 at 06:15:20PM -0500, George Kangas wrote:
> 
> foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
> foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0
> 

Hi George,

This is very cool!  I have never thought of folds in quite this way
before.  It makes a lot of things (such as the identities you point
out) obvious and elegant.

>   We can also see the following identities:
> 
> foldright f as == foldright (.) (map f as) id
> foldleft f as == foldright (flip (.)) (map f as) id
> 
>   I like that second one, after trying to read another definition of 
> left fold in terms of right fold (in the web book "Real World Haskell").
> 
>   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
> (b -> b)), suggests generalization to another type constructor C: (a -> 
> (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
> sense?

As Brandon points out, you have rediscovered Data.Foldable. =) There's
nothing wrong with that, congratulations on discovering it for
yourself!  But again, I like this way of organizing the type
signature: I had never thought of a fold as a sort of 'lift' before.
If f :: a -> b -> b, then foldright 'lifts' f to foldright f :: [a] ->
b -> b (or C a -> b -> b, more generally).  

>   Okay, it goes without saying that this is useless dabbling, but have 
> I entertained anyone?  Or have I just wasted your time?  I eagerly await 
> comments on this, my first posting.

Not at all!  Welcome, and thanks for posting.

-Brent
From derek.a.elkins at gmail.com  Fri Jun 20 22:52:36 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Fri Jun 20 22:44:23 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <20080621023117.GA2741@minus.seas.upenn.edu>
References: <485C3A08.8070302@math.ku.edu>
	<20080621023117.GA2741@minus.seas.upenn.edu>
Message-ID: <1214016756.26144.15.camel@derek-laptop>

On Fri, 2008-06-20 at 22:31 -0400, Brent Yorgey wrote:
> On Fri, Jun 20, 2008 at 06:15:20PM -0500, George Kangas wrote:
> > 
> > foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
> > foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0
> > 
> 
> Hi George,
> 
> This is very cool!  I have never thought of folds in quite this way
> before.  It makes a lot of things (such as the identities you point
> out) obvious and elegant.
> 
> >   We can also see the following identities:
> > 
> > foldright f as == foldright (.) (map f as) id
> > foldleft f as == foldright (flip (.)) (map f as) id
> > 
> >   I like that second one, after trying to read another definition of 
> > left fold in terms of right fold (in the web book "Real World Haskell").
> > 
> >   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
> > (b -> b)), suggests generalization to another type constructor C: (a -> 
> > (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
> > sense?
> 
> As Brandon points out, you have rediscovered Data.Foldable. =) There's
> nothing wrong with that, congratulations on discovering it for
> yourself!  But again, I like this way of organizing the type
> signature: I had never thought of a fold as a sort of 'lift' before.
> If f :: a -> b -> b, then foldright 'lifts' f to foldright f :: [a] ->
> b -> b (or C a -> b -> b, more generally).  
> 
> >   Okay, it goes without saying that this is useless dabbling, but have 
> > I entertained anyone?  Or have I just wasted your time?  I eagerly await 
> > comments on this, my first posting.
> 
> Not at all!  Welcome, and thanks for posting.

Look into the theory of monoids, monoid homomorphisms, M-sets and free
monoids.

From vigalchin at gmail.com  Fri Jun 20 23:52:06 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Fri Jun 20 23:43:50 2008
Subject: [Haskell-cafe] another FFI question
In-Reply-To: <1662913902.20080621002016@gmail.com>
References: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
	<1662913902.20080621002016@gmail.com>
Message-ID: <5ae4f2ba0806202052w143dc215x281a1faa4884ec@mail.gmail.com>

I am still reading the web pages. Here is what I tried:

data SigNotify = Signal | None | Thread | ThreadId


instance Storable SigNotify where

   sizeOf _ = (#const sizeof (int))

   alignment _ = 1

   poke Signal = (#const SIGEV_SIGNAL)

   poke None = poke (#const SIGEV_NONE)

   poke Thread = poke (#const SIGEV_THREAD)

   poke ThreadId = poke (#const SIGEV_THREAD_ID)


but I got ...

    Couldn't match expected type `Ptr SigNotify'
           against inferred type `SigNotify'
    In the pattern: Signal
    In the definition of `poke': poke Signal = poke (0)
    In the definition for method `poke'

Basically I want to marshall SigInfo constructors to CInt values. ??

Regards, Vasili


On Fri, Jun 20, 2008 at 3:20 PM, Bulat Ziganshin <bulat.ziganshin@gmail.com>
wrote:

> Hello Vasili,
>
> Friday, June 20, 2008, 11:51:11 PM, you wrote:
> > data Bonzo = A | B |C
>
> > How do I write the poke functions and call them?
>
> instance Storable Bonzo
>  poke A = poke 0
>  poke B = poke 1
>  poke C = poke 4
>
> call as "poke x"
>
> probably, you don't understand differences between OOP classes and
> type classes. look at http://haskell.org/haskellwiki/OOP_vs_type_classes
> and papers mentioned there
>
>
> --
> Best regards,
>  Bulat                            mailto:Bulat.Ziganshin@gmail.com
>
>
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From lanny at cisco.com  Sat Jun 21 01:42:25 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Sat Jun 21 01:33:48 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <a66b8c070806201744v1e7d05d8jd0ab33efb395f553@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<a66b8c070806201744v1e7d05d8jd0ab33efb395f553@mail.gmail.com>
Message-ID: <485C94C1.6030006@cisco.com>

I had luck with this the other day using Database.HDBC.ODBC.  For
Ubuntu's Hardy I found that Oracle's 10.2.0.3 worked best.
(10.2.0.4 and 11 seemed to have problems for me at least.)

http://www.oracle.com/technology/software/tech/oci/instantclient/htdocs/linuxsoft.html

Grab the basic (not basic-lite), odbc, and sqlplus (to test) zips.
The odbc_update_ini.sh should be run from inside the
instantclient_10_2 directory as root

  sudo /bin/sh odbc_update_ini.sh /

(assuming a standard unixODBC install.)  You'll also need a
tnsnames.ora file to describe your connection(s) to the DB(s).
You'll also need to define some environment variables to run against
all this.  I use a small script:

  #!/bin/sh
  oracle_home=/opt/lib/oracle/instantclient_10_2
  export TNS_ADMIN=$oracle_home
  export LD_LIBRARY_PATH=$oracle_home
  [ $# = 0 ] && exit 1
  exec "$@"

Best of luck,
  -ljr


Steve Lihn wrote:
> You may want to check this out.
> 
> http://www.orafaq.com/wiki/ODBC_FAQ#Where_can_one_get_ODBC_drivers_for_Oracle_and_Rdb.3F
> 
> As Oracle is a commercial company who is not interested in open source
> historically, it is little chance that you will get robust software
> for free -- from someone with many years of Oracle DBA experience :-)
> 
> 
> On 6/19/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>> Is there a way of accessing a remote Oracle database by one of the common
>> Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get
>> unixODBC and Oracle's Instant Client running on a Linux machine, but I'm
>> trapped in the notorious error:
>>
>> $ isql USER -v
>> [IM004][unixODBC][Driver Manager]Driver's SQLAllocHandle on SQL_HANDLE_HENV
>> failed
>> [ISQL]ERROR: Could not SQLConnect
>>
>> This error message is discussed in various web forums, but there seems to be
>> no systematic way to track down the problem. So I wonder whether there is
>> another way to access the Oracle data base from Haskell.
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From jules at jellybean.co.uk  Sat Jun 21 04:47:14 2008
From: jules at jellybean.co.uk (Jules Bean)
Date: Sat Jun 21 04:38:57 2008
Subject: [Haskell-cafe] Re: HDBC converting a date sql value to UTCTime
In-Reply-To: <afd80b540806200644w23ba3463ma85608c5ef136a7c@mail.gmail.com>
References: <afd80b540806191208j38dced52g25357d510c79dbf3@mail.gmail.com>
	<afd80b540806200644w23ba3463ma85608c5ef136a7c@mail.gmail.com>
Message-ID: <485CC012.4080906@jellybean.co.uk>

George Moschovitis wrote:
> Alternatively is there a way to create a UTCTime value from an epoch 
> integer (no of seconds since epoch).
> I can't find a suitable constructor with Hoogle.

http://www.haskell.org/ghc/docs/latest/html/libraries/time/Data-Time-Clock-POSIX.html

posixSecondsToUTCTime

probably in combination with fromIntegral

Jules
From p.f.moore at gmail.com  Sat Jun 21 07:18:29 2008
From: p.f.moore at gmail.com (Paul Moore)
Date: Sat Jun 21 07:10:11 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
Message-ID: <79990c6b0806210418r5376fc80j8eceef9f9663468d@mail.gmail.com>

2008/6/20 Alistair Bayley <alistair@abayley.org>:
> Having just taken a closer took at what Oracle Instant Client is, I
> suspect that you might have some trouble getting Takusen to compile
> against it. The Instant Client lacks header files, while Takusen's FFI
> imports specify oci.h. I don't know what happens if ghc can't find the
> header files. Oracle do state that the Instant Client is for
> deployment only; developers (that means you) will need the full client
> installation.

There's an additional download for the Instant Client which includes
the OCI headers.

Paul.
From stevelihn at gmail.com  Sat Jun 21 09:49:25 2008
From: stevelihn at gmail.com (Steve Lihn)
Date: Sat Jun 21 09:41:07 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79990c6b0806210418r5376fc80j8eceef9f9663468d@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<79990c6b0806210418r5376fc80j8eceef9f9663468d@mail.gmail.com>
Message-ID: <a66b8c070806210649q4394047eq3394aaf2e3a14513@mail.gmail.com>

Oracle OCI interface is quite different between 7/8 and 9/10. And 10
is different from 9 in some respect. I don't know much about 11.
Oracle 10.2.0.3 is a stable release, but there are some major server
bugs in it, that Oracle had to release 10.2.0.4. I'd recommend Haskell
community to focus on 10.2.0.x release. It should be good for another
2-3 years. It is too risky to venture into 11.

That said, there is a large enterprise user base that will find
Haskell useful if it works with Oracle DB (particularly on linux).

On 6/21/08, Paul Moore <p.f.moore@gmail.com> wrote:
> 2008/6/20 Alistair Bayley <alistair@abayley.org>:
> > Having just taken a closer took at what Oracle Instant Client is, I
> > suspect that you might have some trouble getting Takusen to compile
> > against it. The Instant Client lacks header files, while Takusen's FFI
> > imports specify oci.h. I don't know what happens if ghc can't find the
> > header files. Oracle do state that the Instant Client is for
> > deployment only; developers (that means you) will need the full client
> > installation.
>
> There's an additional download for the Instant Client which includes
> the OCI headers.
>
> Paul.
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From trifod at gmail.com  Sat Jun 21 11:38:37 2008
From: trifod at gmail.com (trifod@gmail.com)
Date: Sat Jun 21 11:30:19 2008
Subject: [Haskell-cafe] an example from YAHT doesn't run
In-Reply-To: <1e8d59210806181227x1e6f5d8and846421a9164b6dc@mail.gmail.com>
References: <1e8d59210806181227x1e6f5d8and846421a9164b6dc@mail.gmail.com>
Message-ID: <1e8d59210806210838i579bdfcfh789571b0089d1499@mail.gmail.com>

Hello,

On pdf page 43 of YAHT it provides a code example. I typed this into a file
named "Guess.hs" and tried unsuccessfully to load it into ghci. I am running
ghci version 6.8.2 This is the output it gave me:

" [1 of 1] Compiling Main ( Guess.hs, interpreted )

Guess.hs:19:12: parse error on input `doGuessing'

Failed, modules loaded: none. "

I've attached the code module. As far as I can tell it is identical to the
example in YAHT. Did I type it wrong, is the tutorial wrong, or something
else?

thanks again,

Jared Langson
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From tanimoto at arizona.edu  Sat Jun 21 11:48:41 2008
From: tanimoto at arizona.edu (Paulo Tanimoto)
Date: Sat Jun 21 11:40:23 2008
Subject: [Haskell-cafe] an example from YAHT doesn't run
In-Reply-To: <1e8d59210806210838i579bdfcfh789571b0089d1499@mail.gmail.com>
References: <1e8d59210806181227x1e6f5d8and846421a9164b6dc@mail.gmail.com>
	<1e8d59210806210838i579bdfcfh789571b0089d1499@mail.gmail.com>
Message-ID: <bfcc0ca60806210848y1515e132o49b7aea84f2bad27@mail.gmail.com>

Hi Jared,

2008/6/21  <trifod@gmail.com>:
> Guess.hs:19:12: parse error on input `doGuessing'
>
> Failed, modules loaded: none. "

That says there's something wrong at line 19.  In this case,
'doGuessing' is not properly aligned with 'putStrLn' of the previous
line.  The same happens at line 22.

See if that helps and double-check the rules of indentation.  : )

Paulo
From matti.niemenmaa+news at iki.fi  Sat Jun 21 12:08:57 2008
From: matti.niemenmaa+news at iki.fi (Matti Niemenmaa)
Date: Sat Jun 21 12:00:55 2008
Subject: [Haskell-cafe] ANNOUNCE: Pipe 1.0
Message-ID: <g3j92p$jh1$1@ger.gmane.org>

Greetings,

I hereby announce the release of the Pipe library, a library for piping data 
through a pipeline of processes.

A web page with (hopefully) all the necessary info and a simple example can be 
found at http://iki.fi/matti.niemenmaa/pipe/

The package is at Hackage: 
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Pipe

Feel free to comment on any part of it, either here or straight to my e-mail 
address.

I've tested it on Windows XP and Linux (Gentoo) and GHC 6.8.2 and 6.8.3. Since 
the code is rather low-level it'd be interesting to hear whether it works on 
other systems, say the BSDs or OS X.

-- 
Matti Niemenmaa

From igloo at earth.li  Sat Jun 21 13:10:28 2008
From: igloo at earth.li (Ian Lynagh)
Date: Sat Jun 21 13:02:13 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <874p7ops0p.fsf@malde.org>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	<878wx1khcj.fsf@malde.org> <20080619171812.GA25606@dell>
	<485AE4CB.4080708@vex.net> <874p7ops0p.fsf@malde.org>
Message-ID: <20080621171028.GA1077@matrix.chaos.earth.li>

On Fri, Jun 20, 2008 at 07:57:58AM +0200, Ketil Malde wrote:
> "Albert Y. C. Lai" <trebla@vex.net> writes:
> 
> >> While we are kind of on this topic, what makes the characters ? ?
> >> prefix operator by default, while ? and most other odd ones infix?
> 
> > alphanumeric vs non-alphanumeric
> 
> Testing this, I find that isAlpha is True also for '?', but as the OP
> claims, Haskell will use it as a(n infix) symbol.

This is a bug in GHC. The characters <= '\255' were done specially, but
incorrectly for many of those >= '\128'. I'll fix it, probably by just
removing the specialisation for them.


Thanks
Ian

From blais at furius.ca  Sat Jun 21 14:18:54 2008
From: blais at furius.ca (Martin Blais)
Date: Sat Jun 21 13:18:13 2008
Subject: [Haskell-cafe] Literal programming in Haskell with rst-literals
Message-ID: <20080621181854.184193C8002@banane.furius.ca>


Hello Haskell community!

I just did a marginally cool thing and I wanted to share it
with you.

"rst-literals" is a small program I wrote a while ago in
order to write documents in reStructuredText format that
would embed SQL code for data models in them, a form of
literal programming for SQL if you will; I would describe my
needs for the schema in prose, and reST literal-blocks were
used to embed SQL code, blocks that look like this::

  CLASS Employee (
     firstname VARCHAR,
     lastname VARCHAR
  )

I wrote the script to be entirely generic: it parses the
reST documents using the docutils code and outputs only the
literal-blocks, with indentation removed; you can then run
your favourite interpreter/compiler on the result (in that
case, psql to initialize a database).

Recently, while experimenting with Haskell, I started using
both the literal (.lhs) and non-literal (.hs) styles of
Haskell input, and I found the literal style a bit
unpleasant to use, in particular, I don't like to have to
prefix every line of code I write, despite the help that
Emacs' haskell-mode provides.

So I tried pulling a similar trick and embedding Haskell
code in literal-blocks within reST documents, extracting
that code using rst-literals, and it turns out that it works
like a charm. Here is an example makefile for doing this::

  .SUFFIXES: .rst .hs

  all: chap6

  .rst.hs:
          rst-literals $< > $@

  chap6: chap6.hs
          ghc --make chap6.hs

An example reST document with some embedded Haskell code
follows this email. Note that since rst-literals is using
the docutils parser, you can make use of all of the
recursive reST syntax, sections, bulleted items and much
more. Only the literal-blocks are extracted, anywhere they
appear. You can also easily process the reST source into
HTML pages or LaTeX documents using the tools that come with
docutils.

You can find rst-literals here:
http://furius.ca/pubcode/

Enjoy,




--
Martin

P.S. If there is a way to output cpp-like directives for
GHC, like "#line <filename> <lineno>", it would be easy to
modify rst-literals to generate those, so that compilation
errors could refer to the source reST document instead of
the extracted source.



chap6.hs:
----------------------------------------------------------------------

===========================================
   Exercises from Hutton book, Chapter 6
===========================================

.. contents::
..
    1  Introduction
    2  Exercise 1
    3  Exercise 2
    4  Exercise 3
    5  Exercise 4
    6  Exercise 5
    7  Exercise 6


Introduction
============

Bla bla bla blablablablablabla bla bla blabla. Bla bla bla
blablablablablabla bla bla blabla. Bla bla bla blablablablablabla bla
bla blabla. Bla bla bla blablablablablabla bla bla blabla. Bla bla bla
blablablablablabla bla bla blabla. Bla bla bla blablablablablabla bla
bla blabla.


Exercise 1
==========
::

  myexp :: Int -> Int -> Int
  myexp b 0 = 1
  myexp b (n+1) = b * (myexp b n)


Exercise 2
==========

(Exercise 2 consisted in derivations, so we mark the literal
blocks as another type of block with "#!example", so that
they don't get included in the output when only the
"default" literal blocks get extracted. See rst-literals
docstring for details.)

Length::

    #!example
    1 + (length [2, 3])
    1 + 1 + (length [3])
    1 + 1 + (1)
    3

Drop::

  #!example
  drop 3 [1, 2, 3, 4, 5]
  [] ++ drop 3 [2, 3, 4, 5]
  [] ++ [] ++ drop 3 [3, 4, 5]
  [] ++ [] ++ [] ++ [4, 5]
  [4, 5]

Init::

  #!example
  init [1, 2, 3]
  [1] ++ init [2, 3]
  [1] ++ [2] ++ init [3]
  [1] ++ [2] ++ []
  [1, 2]


Exercise 3
==========

These are alternate versions of the example functions defined in the
text::

  and' :: [Bool] -> Bool
  and' [x] = x
  and' (x:xs) = x && and' xs

  concat' :: [[a]] -> [a]
  concat' [] = []
  concat' (x:xs) = x ++ concat' xs

  replicate' :: Int -> a -> [a]
  replicate' 0 x = []
  replicate' (n+1) x = (x : replicate' n x)

  select' :: [a] -> Int -> a
  select' (x:xs) 0 = x
  select' (x:xs) (n+1) = select' xs n

  elem' :: Eq a => a -> [a] -> Bool
  elem' _ [] = False
  elem' y (x:xs) | x == y = True
                 | otherwise = elem' y xs

Exercise 4
==========

The exercise asked to implement a function to merge two lists::

  merge :: Ord a => [a] -> [a] -> [a]
  merge xs [] = xs
  merge [] xs = xs
  merge (x:xs) (y:ys) | x < y = (x : merge xs (y:ys))
                      | otherwise = (y : merge (x:xs) ys)


Exercise 5
==========
::

  msort :: Ord a => [a] -> [a]
  msort [] = []
  msort [x] = [x] -- This is necessary to end the recursion.
  msort xs = merge (msort (fst hh)) (msort (snd hh))
             where hh = halve xs

  halve :: [a] -> ([a], [a])
  halve xs = (take n xs, drop n xs)
      where n = (length xs) `div` 2

Some main program::

  main = (putStrLn . show) (halve [1..17])


Exercise 6
==========

(Too basic, I didn't bother.)

----------------------------------------------------------------------
From ryani.spam at gmail.com  Sat Jun 21 14:28:47 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Sat Jun 21 14:20:31 2008
Subject: [Haskell-cafe] another FFI question
In-Reply-To: <5ae4f2ba0806202052w143dc215x281a1faa4884ec@mail.gmail.com>
References: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
	<1662913902.20080621002016@gmail.com>
	<5ae4f2ba0806202052w143dc215x281a1faa4884ec@mail.gmail.com>
Message-ID: <2f9b2d30806211128u2646e8aen3a830b5b27ebd834@mail.gmail.com>

You just have the arguments to "poke" wrong:
   poke :: Storable a => Ptr a -> a -> IO ()

So you are missing the pointer argument
   poke p Signal = poke p signal_int_value

I didn't know about the (#const) syntax.  Interesting.

Also, alignment of signal should match the alignment of the underlying
type (although I think that isn't really used at the moment).

  -- ryan

2008/6/20 Galchin, Vasili <vigalchin@gmail.com>:
> I am still reading the web pages. Here is what I tried:
>
> data SigNotify = Signal | None | Thread | ThreadId
>
>
> instance Storable SigNotify where
>
>    sizeOf _ = (#const sizeof (int))
>
>    alignment _ = 1
>
>    poke Signal = (#const SIGEV_SIGNAL)
>
>    poke None = poke (#const SIGEV_NONE)
>
>    poke Thread = poke (#const SIGEV_THREAD)
>
>    poke ThreadId = poke (#const SIGEV_THREAD_ID)
>
>
> but I got ...
>
>     Couldn't match expected type `Ptr SigNotify'
>            against inferred type `SigNotify'
>     In the pattern: Signal
>     In the definition of `poke': poke Signal = poke (0)
>     In the definition for method `poke'
>
> Basically I want to marshall SigInfo constructors to CInt values. ??
>
> Regards, Vasili
>
>
> On Fri, Jun 20, 2008 at 3:20 PM, Bulat Ziganshin <bulat.ziganshin@gmail.com>
> wrote:
>>
>> Hello Vasili,
>>
>> Friday, June 20, 2008, 11:51:11 PM, you wrote:
>> > data Bonzo = A | B |C
>>
>> > How do I write the poke functions and call them?
>>
>> instance Storable Bonzo
>>  poke A = poke 0
>>  poke B = poke 1
>>  poke C = poke 4
>>
>> call as "poke x"
>>
>> probably, you don't understand differences between OOP classes and
>> type classes. look at http://haskell.org/haskellwiki/OOP_vs_type_classes
>> and papers mentioned there
>>
>>
>> --
>> Best regards,
>>  Bulat                            mailto:Bulat.Ziganshin@gmail.com
>>
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
From dons at galois.com  Sat Jun 21 15:12:55 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun 21 15:04:41 2008
Subject: [Haskell-cafe] ANNOUNCE: Pipe 1.0
In-Reply-To: <g3j92p$jh1$1@ger.gmane.org>
References: <g3j92p$jh1$1@ger.gmane.org>
Message-ID: <20080621191255.GA2361@scytale.galois.com>

matti.niemenmaa+news:
> Greetings,
> 
> I hereby announce the release of the Pipe library, a library for piping 
> data through a pipeline of processes.
> 
> A web page with (hopefully) all the necessary info and a simple example can 
> be found at http://iki.fi/matti.niemenmaa/pipe/
> 
> The package is at Hackage: 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Pipe
> 
> Feel free to comment on any part of it, either here or straight to my 
> e-mail address.
> 
> I've tested it on Windows XP and Linux (Gentoo) and GHC 6.8.2 and 6.8.3. 
> Since the code is rather low-level it'd be interesting to hear whether it 
> works on other systems, say the BSDs or OS X.

Interesting.
Does it depend on an unreleased version of the process library?

-- Don
From xj2106 at columbia.edu  Sat Jun 21 15:12:38 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sat Jun 21 15:04:49 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
Message-ID: <87tzfmtxeh.fsf@columbia.edu>

Hi,

I'm wondering how usually you parse command line arguments
list safely.  If the given argument is wrong, the program
can still print out some error information instead of giving
something like

Prelude.read: no parse

Let's make the discussion concrete.  Suppose we have the
following code.

-->8----------8<--
import System.Environment

data Conf = Conf { number :: Int }

parseArgs [] = error "need at least one argument"
parseArgs (x:_) = Conf { number = read x }

work (Conf { number = n }) = n * (n-1) `div` 2

main = print . work . parseArgs =<< getArgs
-->8----------8<--

If the "read x" fails in line 8, the program dies with

Prelude.read: no parse

What is the standard way to make the error message useful?

Xiao-Yong
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From ndmitchell at gmail.com  Sat Jun 21 15:19:31 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Sat Jun 21 15:11:13 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
In-Reply-To: <87tzfmtxeh.fsf@columbia.edu>
References: <87tzfmtxeh.fsf@columbia.edu>
Message-ID: <404396ef0806211219u2130911k619d0ce9dc5ac31@mail.gmail.com>

Hi

>  I'm wondering how usually you parse command line arguments
>  list safely.  If the given argument is wrong, the program
>  can still print out some error information instead of giving
>  something like

Either use reads instead, and deal with the case where there is no
parse. Or use the safe library, on hackage, and something like:

import Safe

readNote "please enter a number" x

Where if x is "test", you'll get:

Program error: Prelude.read: no parse, please enter a number, on "test"

Or use readDef:

readDef (error "Please enter a number") x

Which will just give you:

Program error: Please enter a number

Or, readMay, which will return a Nothing if you fail, which you can
deal with as you wish.

Thanks

Neil
From dons at galois.com  Sat Jun 21 15:19:32 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun 21 15:11:23 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
In-Reply-To: <87tzfmtxeh.fsf@columbia.edu>
References: <87tzfmtxeh.fsf@columbia.edu>
Message-ID: <20080621191932.GC2361@scytale.galois.com>

xj2106:
> Hi,
> 
> I'm wondering how usually you parse command line arguments
> list safely.  If the given argument is wrong, the program
> can still print out some error information instead of giving
> something like
> 
> Prelude.read: no parse
> 
> Let's make the discussion concrete.  Suppose we have the
> following code.
> 
> -->8----------8<--
> import System.Environment
> 
> data Conf = Conf { number :: Int }
> 
> parseArgs [] = error "need at least one argument"
> parseArgs (x:_) = Conf { number = read x }
> 
> work (Conf { number = n }) = n * (n-1) `div` 2
> 
> main = print . work . parseArgs =<< getArgs
> -->8----------8<--
> 
> If the "read x" fails in line 8, the program dies with
> 
> Prelude.read: no parse
> 
> What is the standard way to make the error message useful?
> 
> Xiao-Yong
> -- 

The main thing is to define a safe read. This will be in the base
library soon,

      maybeRead :: Read a => String -> Maybe a
      maybeRead s = case reads s of
          [(x, "")] -> Just x
          _         -> Nothing

Then you can pattern match on the failure case as Nothing.

Cheers,
  Don
From vigalchin at gmail.com  Sat Jun 21 15:27:59 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sat Jun 21 15:19:41 2008
Subject: [Haskell-cafe] another FFI question
In-Reply-To: <2f9b2d30806211128u2646e8aen3a830b5b27ebd834@mail.gmail.com>
References: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
	<1662913902.20080621002016@gmail.com>
	<5ae4f2ba0806202052w143dc215x281a1faa4884ec@mail.gmail.com>
	<2f9b2d30806211128u2646e8aen3a830b5b27ebd834@mail.gmail.com>
Message-ID: <5ae4f2ba0806211227v668a9941ycde85314793afab7@mail.gmail.com>

On Sat, Jun 21, 2008 at 1:28 PM, Ryan Ingram <ryani.spam@gmail.com> wrote:

> You just have the arguments to "poke" wrong:
>   poke :: Storable a => Ptr a -> a -> IO ()
>
> So you are missing the pointer argument
>   poke p Signal = poke p signal_int_value

                                              ^^ what is "signal_int_value"?


>
>
> I didn't know about the (#const) syntax.  Interesting.
>
> Also, alignment of signal should match the alignment of the underlying
> type (although I think that isn't really used at the moment).
>
>  -- ryan
>
> 2008/6/20 Galchin, Vasili <vigalchin@gmail.com>:
> > I am still reading the web pages. Here is what I tried:
> >
> > data SigNotify = Signal | None | Thread | ThreadId
> >
> >
> > instance Storable SigNotify where
> >
> >    sizeOf _ = (#const sizeof (int))
> >
> >    alignment _ = 1
> >
> >    poke Signal = (#const SIGEV_SIGNAL)
> >
> >    poke None = poke (#const SIGEV_NONE)
> >
> >    poke Thread = poke (#const SIGEV_THREAD)
> >
> >    poke ThreadId = poke (#const SIGEV_THREAD_ID)
> >
> >
> > but I got ...
> >
> >     Couldn't match expected type `Ptr SigNotify'
> >            against inferred type `SigNotify'
> >     In the pattern: Signal
> >     In the definition of `poke': poke Signal = poke (0)
> >     In the definition for method `poke'
> >
> > Basically I want to marshall SigInfo constructors to CInt values. ??
> >
> > Regards, Vasili
> >
> >
> > On Fri, Jun 20, 2008 at 3:20 PM, Bulat Ziganshin <
> bulat.ziganshin@gmail.com>
> > wrote:
> >>
> >> Hello Vasili,
> >>
> >> Friday, June 20, 2008, 11:51:11 PM, you wrote:
> >> > data Bonzo = A | B |C
> >>
> >> > How do I write the poke functions and call them?
> >>
> >> instance Storable Bonzo
> >>  poke A = poke 0
> >>  poke B = poke 1
> >>  poke C = poke 4
> >>
> >> call as "poke x"
> >>
> >> probably, you don't understand differences between OOP classes and
> >> type classes. look at
> http://haskell.org/haskellwiki/OOP_vs_type_classes
> >> and papers mentioned there
> >>
> >>
> >> --
> >> Best regards,
> >>  Bulat                            mailto:Bulat.Ziganshin@gmail.com
> >>
> >
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe@haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> >
>
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From matti.niemenmaa+news at iki.fi  Sat Jun 21 15:33:56 2008
From: matti.niemenmaa+news at iki.fi (Matti Niemenmaa)
Date: Sat Jun 21 15:25:49 2008
Subject: [Haskell-cafe] Re: ANNOUNCE: Pipe 1.0
In-Reply-To: <20080621191255.GA2361@scytale.galois.com>
References: <g3j92p$jh1$1@ger.gmane.org>
	<20080621191255.GA2361@scytale.galois.com>
Message-ID: <g3jl35$lqj$1@ger.gmane.org>

Don Stewart wrote:
> Interesting.
> Does it depend on an unreleased version of the process library?

Indeed it does. Actually most of the code was written using the current released 
version, I just jumped the gun a bit when I saw how nice the new interface was.

I'm hoping that the release of the new process library (GHC ticket #2233) isn't 
that far off, which is why I figured I'd shove Pipe out in this state. If that's 
not the case and it turns out that people want to use Pipe without the hassle, I 
might be persuaded to release a version that doesn't need it.

The only 'real' dependency that can't be worked around is the handlePipe 
function, which is only a non-exported optimization that gets applied via RULES.

From xj2106 at columbia.edu  Sat Jun 21 15:46:57 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sat Jun 21 15:39:01 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
In-Reply-To: <20080621191932.GC2361@scytale.galois.com> (Don Stewart's message
	of "Sat, 21 Jun 2008 12:19:32 -0700")
References: <87tzfmtxeh.fsf@columbia.edu>
	<20080621191932.GC2361@scytale.galois.com>
Message-ID: <87lk0ytvta.fsf@columbia.edu>

Don Stewart <dons@galois.com> writes:

> The main thing is to define a safe read. This will be in the base
> library soon,
>
>       maybeRead :: Read a => String -> Maybe a
>       maybeRead s = case reads s of
>           [(x, "")] -> Just x
>           _         -> Nothing
>
> Then you can pattern match on the failure case as Nothing.

When will it be in the base library?

X-Y
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From lanny at cisco.com  Sat Jun 21 17:06:31 2008
From: lanny at cisco.com (Lanny Ripple)
Date: Sat Jun 21 16:58:29 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <485C94C1.6030006@cisco.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>	<a66b8c070806201744v1e7d05d8jd0ab33efb395f553@mail.gmail.com>
	<485C94C1.6030006@cisco.com>
Message-ID: <485D6D57.10606@cisco.com>

Lanny Ripple wrote:
> I had luck with this the other day using Database.HDBC.ODBC.  For
> Ubuntu's Hardy I found that Oracle's 10.2.0.3 worked best.
> (10.2.0.4 and 11 seemed to have problems for me at least.)
> 
> http://www.oracle.com/technology/software/tech/oci/instantclient/htdocs/linuxsoft.html
> 
> Grab the basic (not basic-lite), odbc, and sqlplus (to test) zips.

Oops. And the sdk zip.

> The odbc_update_ini.sh should be run from inside the
> instantclient_10_2 directory as root
> 
>   sudo /bin/sh odbc_update_ini.sh /
> 
> (assuming a standard unixODBC install.)  You'll also need a
> tnsnames.ora file to describe your connection(s) to the DB(s).
> You'll also need to define some environment variables to run against
> all this.  I use a small script:
> 
>   #!/bin/sh
>   oracle_home=/opt/lib/oracle/instantclient_10_2
>   export TNS_ADMIN=$oracle_home
>   export LD_LIBRARY_PATH=$oracle_home
>   [ $# = 0 ] && exit 1
>   exec "$@"
> 
> Best of luck,
>   -ljr
> 
> 
> Steve Lihn wrote:
>> You may want to check this out.
>>
>> http://www.orafaq.com/wiki/ODBC_FAQ#Where_can_one_get_ODBC_drivers_for_Oracle_and_Rdb.3F
>>
>> As Oracle is a commercial company who is not interested in open source
>> historically, it is little chance that you will get robust software
>> for free -- from someone with many years of Oracle DBA experience :-)
>>
>>
>> On 6/19/08, Henning Thielemann <lemming@henning-thielemann.de> wrote:
>>> Is there a way of accessing a remote Oracle database by one of the common
>>> Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get
>>> unixODBC and Oracle's Instant Client running on a Linux machine, but I'm
>>> trapped in the notorious error:
>>>
>>> $ isql USER -v
>>> [IM004][unixODBC][Driver Manager]Driver's SQLAllocHandle on SQL_HANDLE_HENV
>>> failed
>>> [ISQL]ERROR: Could not SQLConnect
>>>
>>> This error message is discussed in various web forums, but there seems to be
>>> no systematic way to track down the problem. So I wonder whether there is
>>> another way to access the Oracle data base from Haskell.
>>> _______________________________________________
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe@haskell.org
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From dan.doel at gmail.com  Sat Jun 21 17:37:24 2008
From: dan.doel at gmail.com (Dan Doel)
Date: Sat Jun 21 17:29:09 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
In-Reply-To: <20080621191932.GC2361@scytale.galois.com>
References: <87tzfmtxeh.fsf@columbia.edu>
	<20080621191932.GC2361@scytale.galois.com>
Message-ID: <200806211737.24484.dan.doel@gmail.com>

On Saturday 21 June 2008, Don Stewart wrote:
>       maybeRead :: Read a => String -> Maybe a
>       maybeRead s = case reads s of
>           [(x, "")] -> Just x
>           _         -> Nothing

Note, if you want to match the behavior of read, you'll probably want 
something like:

    maybeRead :: Read a => String -> Maybe a
    maybeRead s = case reads s of
        [(x, str)] | all isSpace str -> Just x
        _                            -> Nothing

Otherwise, trailing spaces will yield a bad parse.

-- Dan
From byorgey at seas.upenn.edu  Sat Jun 21 21:11:10 2008
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Sat Jun 21 21:02:50 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <1214016756.26144.15.camel@derek-laptop>
References: <485C3A08.8070302@math.ku.edu>
	<20080621023117.GA2741@minus.seas.upenn.edu>
	<1214016756.26144.15.camel@derek-laptop>
Message-ID: <20080622011110.GA9877@minus.seas.upenn.edu>

On Fri, Jun 20, 2008 at 09:52:36PM -0500, Derek Elkins wrote:
> On Fri, 2008-06-20 at 22:31 -0400, Brent Yorgey wrote:
> > On Fri, Jun 20, 2008 at 06:15:20PM -0500, George Kangas wrote:
> > > 
> > > foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
> > > foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0
> > > 
> > 
> > Hi George,
> > 
> > This is very cool!  I have never thought of folds in quite this way
> > before.  It makes a lot of things (such as the identities you point
> > out) obvious and elegant.
> > 
> > >   We can also see the following identities:
> > > 
> > > foldright f as == foldright (.) (map f as) id
> > > foldleft f as == foldright (flip (.)) (map f as) id
> > > 
> > >   I like that second one, after trying to read another definition of 
> > > left fold in terms of right fold (in the web book "Real World Haskell").
> > > 
> > >   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
> > > (b -> b)), suggests generalization to another type constructor C: (a -> 
> > > (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
> > > sense?
> > 
> > As Brandon points out, you have rediscovered Data.Foldable. =) There's
> > nothing wrong with that, congratulations on discovering it for
> > yourself!  But again, I like this way of organizing the type
> > signature: I had never thought of a fold as a sort of 'lift' before.
> > If f :: a -> b -> b, then foldright 'lifts' f to foldright f :: [a] ->
> > b -> b (or C a -> b -> b, more generally).  
> > 
> > >   Okay, it goes without saying that this is useless dabbling, but have 
> > > I entertained anyone?  Or have I just wasted your time?  I eagerly await 
> > > comments on this, my first posting.
> > 
> > Not at all!  Welcome, and thanks for posting.
> 
> Look into the theory of monoids, monoid homomorphisms, M-sets and free
> monoids.

Thanks for the pointers!  Here's what I've come up with, after
re-reading some Barr-Wells lecture notes.

First, given finite sets A (representing an 'alphabet') and S
(representing 'states'), we can describe a finite state machine by a
function phi : A x S -> S, which gives 'transition rules' giving a new
state for each combination of alphabet character and state.  If we
squint and wave our hands and ignore the fact that types aren't
exactly sets, and most of the types we care about have infinitely many
values, this is very much like the Haskell type (a,s) -> s, or
(curried) a -> s -> s, i.e. a -> (s -> s).  So we can think of a
Haskell function phi :: a -> (s -> s) as a sort of 'state machine'.

Also, for a monoid M and set S, an action of M on S is given by a
function f : M x S -> S for which 

  (1)  f(1,s) = s, and 
  (2)  f(mn,s) = f(m,f(n,s)).  

Of course, in Haskell we would write f :: m -> (s -> s), and we would
write criteria (1) and (2) as

  (1)  f mempty = id
  (2)  f (m `mappend` n) = f m . f n

Now look at the type of foldright:

  foldright :: (a -> (s -> s)) -> ([a] -> (s -> s))

We can see that foldright exactly corresponds to the observation that
any state machine with alphabet a and states s induces a monoid action
on s by the free monoid [a].  It's not hard to check that the
function produced by foldright indeed satisfies the requirements to be
a monoid action.

First, recall that 

  foldright f = chain where
      chain (a:as) = (f a).(chain as)
      chain _ = id

Now, we can easily prove (1):

  (foldright f) []
= chain []
= id

The proof of (2) is by induction on the length of m. The base case is
obvious, given the proof of (1).

  (foldright f) (m ++ n)
=                          { defn. of foldright, assume m = x:xs }
  chain ((x:xs) ++ n)
=                          { defn. of (++) }
  chain (x:(xs ++ n))
=                          { defn. of chain }
  f x . chain (xs ++ n)
=                          { inductive hypothesis }
  f x . chain xs . chain n 
=                          { defn. of chain, associativity of (.) }
  chain (x:xs) . chain n
=                          { defn. of foldright, m }
  (foldright f) m . (foldright f) n


How'd I do?  I'm still trying to figure out how the generalization to
Traversable fits in here.  I'm guessing this is where the monoid
homomorphisms come in.

-Brent
From lrpalmer at gmail.com  Sat Jun 21 22:17:51 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Sat Jun 21 22:09:32 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <20080622011110.GA9877@minus.seas.upenn.edu>
References: <485C3A08.8070302@math.ku.edu>
	<20080621023117.GA2741@minus.seas.upenn.edu>
	<1214016756.26144.15.camel@derek-laptop>
	<20080622011110.GA9877@minus.seas.upenn.edu>
Message-ID: <7ca3f0160806211917h29cfd8edtd6fb6655823fd7bb@mail.gmail.com>

On Sat, Jun 21, 2008 at 7:11 PM, Brent Yorgey <byorgey@seas.upenn.edu> wrote:
> First, given finite sets A (representing an 'alphabet') and S
> (representing 'states'), we can describe a finite state machine by a
> function phi : A x S -> S, which gives 'transition rules' giving a new
> state for each combination of alphabet character and state.  If we
> squint and wave our hands and ignore the fact that types aren't
> exactly sets, and most of the types we care about have infinitely many
> values, this is very much like the Haskell type (a,s) -> s, or
> (curried) a -> s -> s, i.e. a -> (s -> s).  So we can think of a
> Haskell function phi :: a -> (s -> s) as a sort of 'state machine'.
>
> Also, for a monoid M and set S, an action of M on S is given by a
> function f : M x S -> S for which
>
>  (1)  f(1,s) = s, and
>  (2)  f(mn,s) = f(m,f(n,s)).
>
> Of course, in Haskell we would write f :: m -> (s -> s), and we would
> write criteria (1) and (2) as
>
>  (1)  f mempty = id
>  (2)  f (m `mappend` n) = f m . f n
>
> Now look at the type of foldright:
>
>  foldright :: (a -> (s -> s)) -> ([a] -> (s -> s))

Wow!  I commend you on this excellent, enlightening post!

Luke

> We can see that foldright exactly corresponds to the observation that
> any state machine with alphabet a and states s induces a monoid action
> on s by the free monoid [a].  It's not hard to check that the
> function produced by foldright indeed satisfies the requirements to be
> a monoid action.
>
> First, recall that
>
>  foldright f = chain where
>      chain (a:as) = (f a).(chain as)
>      chain _ = id
>
> Now, we can easily prove (1):
>
>  (foldright f) []
> = chain []
> = id
>
> The proof of (2) is by induction on the length of m. The base case is
> obvious, given the proof of (1).
>
>  (foldright f) (m ++ n)
> =                          { defn. of foldright, assume m = x:xs }
>  chain ((x:xs) ++ n)
> =                          { defn. of (++) }
>  chain (x:(xs ++ n))
> =                          { defn. of chain }
>  f x . chain (xs ++ n)
> =                          { inductive hypothesis }
>  f x . chain xs . chain n
> =                          { defn. of chain, associativity of (.) }
>  chain (x:xs) . chain n
> =                          { defn. of foldright, m }
>  (foldright f) m . (foldright f) n
>
>
> How'd I do?  I'm still trying to figure out how the generalization to
> Traversable fits in here.  I'm guessing this is where the monoid
> homomorphisms come in.
>
> -Brent
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From derek.a.elkins at gmail.com  Sat Jun 21 22:36:06 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Sat Jun 21 22:27:49 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <20080622011110.GA9877@minus.seas.upenn.edu>
References: <485C3A08.8070302@math.ku.edu>
	<20080621023117.GA2741@minus.seas.upenn.edu>
	<1214016756.26144.15.camel@derek-laptop>
	<20080622011110.GA9877@minus.seas.upenn.edu>
Message-ID: <1214102166.26144.19.camel@derek-laptop>

On Sat, 2008-06-21 at 21:11 -0400, Brent Yorgey wrote:
> On Fri, Jun 20, 2008 at 09:52:36PM -0500, Derek Elkins wrote:
> > On Fri, 2008-06-20 at 22:31 -0400, Brent Yorgey wrote:
> > > On Fri, Jun 20, 2008 at 06:15:20PM -0500, George Kangas wrote:
> > > > 
> > > > foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
> > > > foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0
> > > > 
> > > 
> > > Hi George,
> > > 
> > > This is very cool!  I have never thought of folds in quite this way
> > > before.  It makes a lot of things (such as the identities you point
> > > out) obvious and elegant.
> > > 
> > > >   We can also see the following identities:
> > > > 
> > > > foldright f as == foldright (.) (map f as) id
> > > > foldleft f as == foldright (flip (.)) (map f as) id
> > > > 
> > > >   I like that second one, after trying to read another definition of 
> > > > left fold in terms of right fold (in the web book "Real World Haskell").
> > > > 
> > > >   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
> > > > (b -> b)), suggests generalization to another type constructor C: (a -> 
> > > > (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
> > > > sense?
> > > 
> > > As Brandon points out, you have rediscovered Data.Foldable. =) There's
> > > nothing wrong with that, congratulations on discovering it for
> > > yourself!  But again, I like this way of organizing the type
> > > signature: I had never thought of a fold as a sort of 'lift' before.
> > > If f :: a -> b -> b, then foldright 'lifts' f to foldright f :: [a] ->
> > > b -> b (or C a -> b -> b, more generally).  
> > > 
> > > >   Okay, it goes without saying that this is useless dabbling, but have 
> > > > I entertained anyone?  Or have I just wasted your time?  I eagerly await 
> > > > comments on this, my first posting.
> > > 
> > > Not at all!  Welcome, and thanks for posting.
> > 
> > Look into the theory of monoids, monoid homomorphisms, M-sets and free
> > monoids.
> 
> Thanks for the pointers!  Here's what I've come up with, after
> re-reading some Barr-Wells lecture notes.
> 
> First, given finite sets A (representing an 'alphabet') and S
> (representing 'states'), we can describe a finite state machine by a
> function phi : A x S -> S, which gives 'transition rules' giving a new
> state for each combination of alphabet character and state.  If we
> squint and wave our hands and ignore the fact that types aren't
> exactly sets, and most of the types we care about have infinitely many
> values, this is very much like the Haskell type (a,s) -> s, or
> (curried) a -> s -> s, i.e. a -> (s -> s).  So we can think of a
> Haskell function phi :: a -> (s -> s) as a sort of 'state machine'.
> 
> Also, for a monoid M and set S, an action of M on S is given by a
> function f : M x S -> S for which 
> 
>   (1)  f(1,s) = s, and 
>   (2)  f(mn,s) = f(m,f(n,s)).  
> 
> Of course, in Haskell we would write f :: m -> (s -> s), 

This change is not completely trivial.

> and we would
> write criteria (1) and (2) as
> 
>   (1)  f mempty = id
>   (2)  f (m `mappend` n) = f m . f n

So what does this make f?  Hint: What is (s -> s)?

From byorgey at seas.upenn.edu  Sat Jun 21 22:48:59 2008
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Sat Jun 21 22:40:38 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <1214102166.26144.19.camel@derek-laptop>
References: <485C3A08.8070302@math.ku.edu>
	<20080621023117.GA2741@minus.seas.upenn.edu>
	<1214016756.26144.15.camel@derek-laptop>
	<20080622011110.GA9877@minus.seas.upenn.edu>
	<1214102166.26144.19.camel@derek-laptop>
Message-ID: <20080622024859.GA23472@minus.seas.upenn.edu>

On Sat, Jun 21, 2008 at 09:36:06PM -0500, Derek Elkins wrote:
> On Sat, 2008-06-21 at 21:11 -0400, Brent Yorgey wrote:
> > On Fri, Jun 20, 2008 at 09:52:36PM -0500, Derek Elkins wrote:
> > > On Fri, 2008-06-20 at 22:31 -0400, Brent Yorgey wrote:
> > > > On Fri, Jun 20, 2008 at 06:15:20PM -0500, George Kangas wrote:
> > > > > 
> > > > > foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
> > > > > foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0
> > > > > 
> > > > 
> > > > Hi George,
> > > > 
> > > > This is very cool!  I have never thought of folds in quite this way
> > > > before.  It makes a lot of things (such as the identities you point
> > > > out) obvious and elegant.
> > > > 
> > > > >   We can also see the following identities:
> > > > > 
> > > > > foldright f as == foldright (.) (map f as) id
> > > > > foldleft f as == foldright (flip (.)) (map f as) id
> > > > > 
> > > > >   I like that second one, after trying to read another definition of 
> > > > > left fold in terms of right fold (in the web book "Real World Haskell").
> > > > > 
> > > > >   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
> > > > > (b -> b)), suggests generalization to another type constructor C: (a -> 
> > > > > (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
> > > > > sense?
> > > > 
> > > > As Brandon points out, you have rediscovered Data.Foldable. =) There's
> > > > nothing wrong with that, congratulations on discovering it for
> > > > yourself!  But again, I like this way of organizing the type
> > > > signature: I had never thought of a fold as a sort of 'lift' before.
> > > > If f :: a -> b -> b, then foldright 'lifts' f to foldright f :: [a] ->
> > > > b -> b (or C a -> b -> b, more generally).  
> > > > 
> > > > >   Okay, it goes without saying that this is useless dabbling, but have 
> > > > > I entertained anyone?  Or have I just wasted your time?  I eagerly await 
> > > > > comments on this, my first posting.
> > > > 
> > > > Not at all!  Welcome, and thanks for posting.
> > > 
> > > Look into the theory of monoids, monoid homomorphisms, M-sets and free
> > > monoids.
> > 
> > Thanks for the pointers!  Here's what I've come up with, after
> > re-reading some Barr-Wells lecture notes.
> > 
> > First, given finite sets A (representing an 'alphabet') and S
> > (representing 'states'), we can describe a finite state machine by a
> > function phi : A x S -> S, which gives 'transition rules' giving a new
> > state for each combination of alphabet character and state.  If we
> > squint and wave our hands and ignore the fact that types aren't
> > exactly sets, and most of the types we care about have infinitely many
> > values, this is very much like the Haskell type (a,s) -> s, or
> > (curried) a -> s -> s, i.e. a -> (s -> s).  So we can think of a
> > Haskell function phi :: a -> (s -> s) as a sort of 'state machine'.
> > 
> > Also, for a monoid M and set S, an action of M on S is given by a
> > function f : M x S -> S for which 
> > 
> >   (1)  f(1,s) = s, and 
> >   (2)  f(mn,s) = f(m,f(n,s)).  
> > 
> > Of course, in Haskell we would write f :: m -> (s -> s), 
> 
> This change is not completely trivial.

Hmm... why is that?  Is it because of the types-aren't-really-sets
thing?  Or are there other reasons as well?

> 
> > and we would
> > write criteria (1) and (2) as
> > 
> >   (1)  f mempty = id
> >   (2)  f (m `mappend` n) = f m . f n
> 
> So what does this make f?  Hint: What is (s -> s)?

Aha!  f is a monoid homomorphism to the monoid of endomorphisms on s!
Right?

-Brent
From derek.a.elkins at gmail.com  Sat Jun 21 23:32:21 2008
From: derek.a.elkins at gmail.com (Derek Elkins)
Date: Sat Jun 21 23:24:03 2008
Subject: [Haskell-cafe] Pretty little definitions of left and right folds
In-Reply-To: <20080622024859.GA23472@minus.seas.upenn.edu>
References: <485C3A08.8070302@math.ku.edu>
	<20080621023117.GA2741@minus.seas.upenn.edu>
	<1214016756.26144.15.camel@derek-laptop>
	<20080622011110.GA9877@minus.seas.upenn.edu>
	<1214102166.26144.19.camel@derek-laptop>
	<20080622024859.GA23472@minus.seas.upenn.edu>
Message-ID: <1214105541.26144.27.camel@derek-laptop>

On Sat, 2008-06-21 at 22:48 -0400, Brent Yorgey wrote:
> On Sat, Jun 21, 2008 at 09:36:06PM -0500, Derek Elkins wrote:
> > On Sat, 2008-06-21 at 21:11 -0400, Brent Yorgey wrote:
> > > On Fri, Jun 20, 2008 at 09:52:36PM -0500, Derek Elkins wrote:
> > > > On Fri, 2008-06-20 at 22:31 -0400, Brent Yorgey wrote:
> > > > > On Fri, Jun 20, 2008 at 06:15:20PM -0500, George Kangas wrote:
> > > > > > 
> > > > > > foldright (+) [1, 2, 3] 0 == ( (1 +).(2 +).(3 +).id ) 0
> > > > > > foldleft (+) [1, 2, 3] 0 == ( id.(3 +).(2 +).(1 +) ) 0
> > > > > > 
> > > > > 
> > > > > Hi George,
> > > > > 
> > > > > This is very cool!  I have never thought of folds in quite this way
> > > > > before.  It makes a lot of things (such as the identities you point
> > > > > out) obvious and elegant.
> > > > > 
> > > > > >   We can also see the following identities:
> > > > > > 
> > > > > > foldright f as == foldright (.) (map f as) id
> > > > > > foldleft f as == foldright (flip (.)) (map f as) id
> > > > > > 
> > > > > >   I like that second one, after trying to read another definition of 
> > > > > > left fold in terms of right fold (in the web book "Real World Haskell").
> > > > > > 
> > > > > >   The type signature, which could be written (a -> (b -> b)) -> ([a] -> 
> > > > > > (b -> b)), suggests generalization to another type constructor C: (a -> 
> > > > > > (b -> b)) -> (C a -> (b -> b)).  Would a "foldable" typeclass make any 
> > > > > > sense?
> > > > > 
> > > > > As Brandon points out, you have rediscovered Data.Foldable. =) There's
> > > > > nothing wrong with that, congratulations on discovering it for
> > > > > yourself!  But again, I like this way of organizing the type
> > > > > signature: I had never thought of a fold as a sort of 'lift' before.
> > > > > If f :: a -> b -> b, then foldright 'lifts' f to foldright f :: [a] ->
> > > > > b -> b (or C a -> b -> b, more generally).  
> > > > > 
> > > > > >   Okay, it goes without saying that this is useless dabbling, but have 
> > > > > > I entertained anyone?  Or have I just wasted your time?  I eagerly await 
> > > > > > comments on this, my first posting.
> > > > > 
> > > > > Not at all!  Welcome, and thanks for posting.
> > > > 
> > > > Look into the theory of monoids, monoid homomorphisms, M-sets and free
> > > > monoids.
> > > 
> > > Thanks for the pointers!  Here's what I've come up with, after
> > > re-reading some Barr-Wells lecture notes.
> > > 
> > > First, given finite sets A (representing an 'alphabet') and S
> > > (representing 'states'), we can describe a finite state machine by a
> > > function phi : A x S -> S, which gives 'transition rules' giving a new
> > > state for each combination of alphabet character and state.  If we
> > > squint and wave our hands and ignore the fact that types aren't
> > > exactly sets, and most of the types we care about have infinitely many
> > > values, this is very much like the Haskell type (a,s) -> s, or
> > > (curried) a -> s -> s, i.e. a -> (s -> s).  So we can think of a
> > > Haskell function phi :: a -> (s -> s) as a sort of 'state machine'.
> > > 
> > > Also, for a monoid M and set S, an action of M on S is given by a
> > > function f : M x S -> S for which 
> > > 
> > >   (1)  f(1,s) = s, and 
> > >   (2)  f(mn,s) = f(m,f(n,s)).  
> > > 
> > > Of course, in Haskell we would write f :: m -> (s -> s), 
> > 
> > This change is not completely trivial.
> 
> Hmm... why is that?  Is it because of the types-aren't-really-sets
> thing?  Or are there other reasons as well?

No, it's just that though these types are isomorphic (in our squinted
vision), they are still not identical and each is different way of
viewing the same thing.

> 
> > 
> > > and we would
> > > write criteria (1) and (2) as
> > > 
> > >   (1)  f mempty = id
> > >   (2)  f (m `mappend` n) = f m . f n
> > 
> > So what does this make f?  Hint: What is (s -> s)?
> 
> Aha!  f is a monoid homomorphism to the monoid of endomorphisms on s!
> Right?

Yep.

So the monoid action, MxS -> S can be curried to give M -> (S->S), a
monoid homomorphism, or further we can swap the arguments and curry
giving S -> (M->S); one name for this last form, connected to a totally
different field, is a flow.  In this case, let M be the monoid of time
(the non-negative reals under addition) and S be points in space (R^3
say).  Usually, in this case, the "monoid action" will be the solution
of a differential equation.

From nfjinjing at gmail.com  Sun Jun 22 00:19:30 2008
From: nfjinjing at gmail.com (jinjing)
Date: Sun Jun 22 00:11:28 2008
Subject: [Haskell-cafe] message passing style like in Haskell?
In-Reply-To: <20080621171028.GA1077@matrix.chaos.earth.li>
References: <81ea7d400806182033h40885ac5l96b415849f2d9d11@mail.gmail.com>
	<878wx1khcj.fsf@malde.org> <20080619171812.GA25606@dell>
	<485AE4CB.4080708@vex.net> <874p7ops0p.fsf@malde.org>
	<20080621171028.GA1077@matrix.chaos.earth.li>
Message-ID: <81ea7d400806212119o657a1e94v4b60b7c638652026@mail.gmail.com>

After some fiddling with this style, here is what I came up with
for the 8 queens problem in the 99 problem set. It's quite entertaining ...
( note: it's brute force and requires a combination library )

queens2 n = n.permutations.filter all_satisfied where
  all_satisfied queens = queens.diff_col && queens.diff_diag
  diff_col queens = queens.unique.is queens
  diff_diag queens =
    n .combinations 2
      .map (map (subtract 1))
      .map (id &&& flip cherry_pick queens)
      .any same_dist.not where
        same_dist (row_pair, col_pair) =
          row_pair.foldl1 (-).abs == col_pair.foldl1 (-).abs

  -- generic helper
  cherry_pick ids xs = ids.map (xs !!)
  is a b = a == b
  unique xs = nub xs

Guess this can conclude this experiment :)

jinjing

On Sun, Jun 22, 2008 at 1:10 AM, Ian Lynagh <igloo@earth.li> wrote:
> On Fri, Jun 20, 2008 at 07:57:58AM +0200, Ketil Malde wrote:
>> "Albert Y. C. Lai" <trebla@vex.net> writes:
>>
>> >> While we are kind of on this topic, what makes the characters ? ?
>> >> prefix operator by default, while ? and most other odd ones infix?
>>
>> > alphanumeric vs non-alphanumeric
>>
>> Testing this, I find that isAlpha is True also for '?', but as the OP
>> claims, Haskell will use it as a(n infix) symbol.
>
> This is a bug in GHC. The characters <= '\255' were done specially, but
> incorrectly for many of those >= '\128'. I'll fix it, probably by just
> removing the specialisation for them.
>
>
> Thanks
> Ian
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From briqueabraque at yahoo.com  Sun Jun 22 01:52:33 2008
From: briqueabraque at yahoo.com (=?ISO-8859-1?Q?Maur=ED=ADcio?=)
Date: Sun Jun 22 01:44:22 2008
Subject: [Haskell-cafe] IMAP and NNTP libraries
Message-ID: <g3kpb2$22c$1@ger.gmane.org>

Hi,

Are there mature libraries for IMAP and NNTP
available to Haskell?

Thanks,
Maur?cio

From vigalchin at gmail.com  Sun Jun 22 02:47:35 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Sun Jun 22 02:39:15 2008
Subject: [Haskell-cafe] "C" buffer suggestions??
Message-ID: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>

Hello,

    I want to model an I/O read/write buffer in Haskell and marshall down
into ANSI C.

1) ByteString? Or Ptr Word8?

2) What are example values of the types in 1)?


Kind regards, Vasili
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From seanmcl at gmail.com  Sun Jun 22 11:37:03 2008
From: seanmcl at gmail.com (Sean McLaughlin)
Date: Sun Jun 22 11:28:43 2008
Subject: [Haskell-cafe] ieee 754
Message-ID: <6579f8680806220837i9fe85e2ya161609d63eb4568@mail.gmail.com>

Hello,

  I'm considering using Haskell for a numerical application.  However,
I need to rely
on IEEE 754 standards being implemented correctly.  What is the
current state of 754 in Haskell?
The definition has this paragraph, which makes me suspect Haskell is
not appropriate for this
application:

"The default floating point operations defined by the Haskell Prelude
do not conform to current language independent arithmetic (LIA)
standards. These standards require considerably more complexity in the
numeric structure and have thus been relegated to a library. Some, but
not all, aspects of the IEEE floating point standard have been
accounted for in Prelude class RealFloat."

Thank you,

Sean
From lennart at augustsson.net  Sun Jun 22 12:21:34 2008
From: lennart at augustsson.net (Lennart Augustsson)
Date: Sun Jun 22 12:13:13 2008
Subject: [Haskell-cafe] ieee 754
In-Reply-To: <6579f8680806220837i9fe85e2ya161609d63eb4568@mail.gmail.com>
References: <6579f8680806220837i9fe85e2ya161609d63eb4568@mail.gmail.com>
Message-ID: <f4876cd70806220921o691013b7ub0239a30cb18786@mail.gmail.com>

Haskell does not allow you to change rounding mode, NaN signallng mode, etc.
But otherwise Haskell on modern platforms conforms to IEEE 754.

  -- Lennart

On Sun, Jun 22, 2008 at 9:37 AM, Sean McLaughlin <seanmcl@gmail.com> wrote:
> Hello,
>
>  I'm considering using Haskell for a numerical application.  However,
> I need to rely
> on IEEE 754 standards being implemented correctly.  What is the
> current state of 754 in Haskell?
> The definition has this paragraph, which makes me suspect Haskell is
> not appropriate for this
> application:
>
> "The default floating point operations defined by the Haskell Prelude
> do not conform to current language independent arithmetic (LIA)
> standards. These standards require considerably more complexity in the
> numeric structure and have thus been relegated to a library. Some, but
> not all, aspects of the IEEE floating point standard have been
> accounted for in Prelude class RealFloat."
>
> Thank you,
>
> Sean
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From lemming at henning-thielemann.de  Sun Jun 22 15:56:05 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun Jun 22 15:47:46 2008
Subject: [Haskell-cafe] Scripting OpenOffice with Haskell
Message-ID: <Pine.LNX.4.64.0806222153450.14824@anubis.informatik.uni-halle.de>


Has someone already tried to communicate with OpenOffice via Haskell? An 
interface seems to exist:
   http://framework.openoffice.org/scripting/index.html

For instance, I like to mark some cells in oocalc, preprocess them and 
write them to a database.
From haskell.hall at live.com  Sun Jun 22 15:58:44 2008
From: haskell.hall at live.com (Haskell Hall)
Date: Sun Jun 22 15:50:24 2008
Subject: [Haskell-cafe] Testing
Message-ID: <BAY121-W51040450A09B044A54D863F0A70@phx.gbl>


Testing Testing
_________________________________________________________________
Need to know now? Get instant answers with Windows Live Messenger.
http://www.windowslive.com/messenger/connect_your_way.html?ocid=TXT_TAGLM_WL_Refresh_messenger_062008
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From haskell.hall at live.com  Sun Jun 22 16:08:26 2008
From: haskell.hall at live.com (Haskell Hall)
Date: Sun Jun 22 16:00:04 2008
Subject: [Haskell-cafe] INVITATION
Message-ID: <BAY121-W12C3ED4C6AAAAD0914E738F0A70@phx.gbl>


Haskell Hall is up and running. Haskell Hall is a mailing list, a forum, where you can discuss Haskell, functional programming and anything related, freely and openly with fellow enthusiasts. We welcome people of all abilities and know-how. So, if you fancy a change from what you get on Haskell Cafe send an email to haskell-request@freelists.org with the word subscribe in the subject field.The first 10 members will have access to the wine cellar. :-)
_________________________________________________________________
The i?m Talkathon starts 6/24/08.? For now, give amongst yourselves.
http://www.imtalkathon.com?source=TXT_EML_WLH_LearnMore_GiveAmongst
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From lemming at henning-thielemann.de  Sun Jun 22 16:32:21 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun Jun 22 16:23:58 2008
Subject: [Haskell-cafe] ieee 754
In-Reply-To: <f4876cd70806220921o691013b7ub0239a30cb18786@mail.gmail.com>
References: <6579f8680806220837i9fe85e2ya161609d63eb4568@mail.gmail.com>
	<f4876cd70806220921o691013b7ub0239a30cb18786@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806222227310.14824@anubis.informatik.uni-halle.de>


On Sun, 22 Jun 2008, Lennart Augustsson wrote:

> Haskell does not allow you to change rounding mode, NaN signallng mode, etc.
> But otherwise Haskell on modern platforms conforms to IEEE 754.

It just uses the machine floating point implementation, which is most 
oftenly IEEE. However the good news are - if someone manually writes 
functions for IEEE number representation, they could be used exactly the 
same way as Float and Double, and chances are good that with some 
optimizer RULES the operations can be replaced by efficient FPU operations 
on IEEE compliant FPUs.
From nielsadb at gmail.com  Sun Jun 22 16:39:57 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Sun Jun 22 16:31:36 2008
Subject: [Haskell-cafe] another FFI question
In-Reply-To: <1662913902.20080621002016@gmail.com>
References: <5ae4f2ba0806201251v3a11188cq9ab71d44d9d996da@mail.gmail.com>
	<1662913902.20080621002016@gmail.com>
Message-ID: <1214167197.12672.46.camel@porcupine>

On Sat, 2008-06-21 at 00:20 +0400, Bulat Ziganshin wrote:
> 
> probably, you don't understand differences between OOP classes and
> type classes. look at http://haskell.org/haskellwiki/OOP_vs_type_classes
> and papers mentioned there

I took the liberty to update some of the C++ code on that page so that
the code will compile and work as expected.

Reading the rest of the page I have a question regarding section 4.2,
Type classes correspond to parameterized abstract classes (Gabriel Dos
Reis). This is probably more related to C++ than Haskell, so not all
readers might find it of interest.



--- off topic ---

Looking at 4.2, it's interesting to see how type classes are translated
into C++. Admittedly C++ isn't the prettiest language to look at, but I
feel one must be fair, and the code presented at the Wiki is too
complex, using virtuals and templates where they're not needed. Normal
overloading suffices.

Operator definitions can already be placed outside of a class scope,
e.g. the many overloads of << to print something to a stream. By default
these definitions cannot access private members of their operands but
the code at the Wiki has the same problem.

Just a small example:

// --- somewhere in a file ---
struct Aap {
    int x;
    explicit Aap(int x) : x(x) {}
    Aap add(Aap const& other) const { return Aap(x + other.x); }
};

// --- somewhere in another file ---
Aap operator+(Aap const& lhs, Aap const& rhs) {
    return lhs.add(rhs);
}

Overloading functions is not different. I've omitted some other (more
complex) ways you can achieve the same (aside from normal overloads it's
also allowed to introduce new specializations later).

At the time of writing it's not possible in C++ to restrict a type to
allow a certain operation (concepts[1] will hopefully fill that gap some
day, but I think it'll be a long time before tool support is ready for
prime-time). Rather, it's common to just use the operation and let the
compiler generate a (sometimes very cryptic) error message if it cannot
find the right code.
[1]: http://www.generic-programming.org/software/ConceptGCC/

A very poor man's solution to see if an operation is defined would be:

template<typename T> struct has_add;
template<> struct has_add<Aap> {};
int main() {
    (void)sizeof(has_add<Aap>); // okay
?    (void)sizeof(has_add<int>); // fails to compile, put useful comment
here
}

It's not hard to add some primitive predicate logic (at compile time) to
resemble type classes in some sense, but I think this is off-topic
enough as it is.

Regards,
Niels


From lemming at henning-thielemann.de  Sun Jun 22 16:45:51 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun Jun 22 16:37:29 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
In-Reply-To: <87tzfmtxeh.fsf@columbia.edu>
References: <87tzfmtxeh.fsf@columbia.edu>
Message-ID: <Pine.LNX.4.64.0806222241090.14824@anubis.informatik.uni-halle.de>


On Sat, 21 Jun 2008, Xiao-Yong Jin wrote:

> Hi,
>
> I'm wondering how usually you parse command line arguments
> list safely.  If the given argument is wrong, the program
> can still print out some error information instead of giving
> something like
>
> Prelude.read: no parse

It's generally not a good idea to call 'read' on user data. 'read' expects 
well-formed input. Calling 'read' with other input is a programming 
_error_. If the user enters garbage, this is an _exception_ and this must 
be handled with 'reads' or 'maybeRead' as others suggested.
  http://www.haskell.org/haskellwiki/Error
  http://www.haskell.org/haskellwiki/Exception

From james at neurogami.com  Sun Jun 22 19:05:50 2008
From: james at neurogami.com (James Britt)
Date: Sun Jun 22 18:57:36 2008
Subject: [Haskell-cafe] INVITATION
In-Reply-To: <BAY121-W12C3ED4C6AAAAD0914E738F0A70@phx.gbl>
References: <BAY121-W12C3ED4C6AAAAD0914E738F0A70@phx.gbl>
Message-ID: <485EDACE.1080009@neurogami.com>

Haskell Hall wrote:
 > Haskell Hall is up and running. Haskell Hall is a mailing list, a 
forum, where you can discuss Haskell, functional programming and 
anything related, freely and openly with fellow enthusiasts. We welcome 
people of all abilities and know-how. So, if you fancy a change from 
what you get on Haskell Cafe send an email to 
haskell-request@freelists.org with the word subscribe in the subject 
field.The first 10 members will have access to the wine cellar. :-)


How does or will Haskell Hall differ?

I.e., why would I want to join another list?




James
From dons at galois.com  Sun Jun 22 19:16:22 2008
From: dons at galois.com (Don Stewart)
Date: Sun Jun 22 19:08:03 2008
Subject: [Haskell-cafe] INVITATION
In-Reply-To: <485EDACE.1080009@neurogami.com>
References: <BAY121-W12C3ED4C6AAAAD0914E738F0A70@phx.gbl>
	<485EDACE.1080009@neurogami.com>
Message-ID: <20080622231622.GD7178@scytale.galois.com>

james:
> Haskell Hall wrote:
> > Haskell Hall is up and running. Haskell Hall is a mailing list, a 
> forum, where you can discuss Haskell, functional programming and 
> anything related, freely and openly with fellow enthusiasts. We welcome 
> people of all abilities and know-how. So, if you fancy a change from 
> what you get on Haskell Cafe send an email to 
> haskell-request@freelists.org with the word subscribe in the subject 
> field.The first 10 members will have access to the wine cellar. :-)
> 
> 
> How does or will Haskell Hall differ?
> 
> I.e., why would I want to join another list?

This is a list set up by PR Stanley after he was moderated last week,
during a flame war in this channel.

    http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41413/focus=41444

Make of that what you will.

-- Don

From ok at cs.otago.ac.nz  Sun Jun 22 22:23:26 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Sun Jun 22 22:15:10 2008
Subject: [Haskell-cafe] Lambda and closures in PHP -- could someone	please
	comment?
In-Reply-To: <485B95A9.2090002@jellybean.co.uk>
References: <7e270cea0806170945l50f68d35p4761e6a0ee131104@mail.gmail.com>	<1213755981.3338.15.camel@jonathans-macbook>	<7e270cea0806172136m67f5eb22o6fda46db93b49053@mail.gmail.com>	<CAA2FB84-BCB6-4F4D-8572-9C2EFFA3FF5A@cs.otago.ac.nz>	<4859F46B.5060602@jellybean.co.uk>	<279D0571-7E22-41C1-8F46-8FF40E12506A@cs.otago.ac.nz>	<4859FBC1.2070102@jellybean.co.uk>
	<1213896576.5557.55.camel@derek-laptop>
	<485B95A9.2090002@jellybean.co.uk>
Message-ID: <0B58BD73-20F8-4845-BCFF-92C6C85D88AE@cs.otago.ac.nz>

This is increasingly less relevant to Haskell, except
of course to demonstrate what a nice language Haskell is.
On 20 Jun 2008, at 11:34 pm, Jules Bean wrote:
> I think where I differ on you is how to map the semantics of a C- 
> like language to explicit references.
>
> I would argue that the glyph "c" in a C-like language denotes the  
> value of C, not the reference to it. C-like languages have, for the  
> most part, value semantics, and call-by-value.
>
> The exception of course is what C-like languages called "lvalues",  
> but lvalues are only really on the left of the = sign and a few  
> other special positions. I think that's the exception and not the  
> rule.

No, this is back to front.  C basically follows the Algol 68 idea that
the lvalue is the normative thing, and that there is an IMPLICIT  
COERCION
from a variable to its value in certain contexts.  C is full of implicit
coercions: perhaps the most famous is the one that says that in almost  
all
contexts an array is quietly coerced to a pointer to its first element.

The key observation is that an implicit coercion from a variable to its
contents is possible, whereas an implicit coercion from a value to "the"
variable that holds it is not.   Only the "a variable really stands for
its address" view is coherent.

> In C, of course, if you want to capture the reference you do it  
> explicitly with "&c".

If we can use evidence from a relative to probe such questions,
the fact that you *don't* need an explicit "&" in C++ (when you find a  
'reference'
to a variable, you use "c", not "&c") strongly suggests that the  
"variable stands
for location" view is the more useful one.

Thankfully, Haskell saves us these perplexities.
(And replaces them with other perplexities...)

From xj2106 at columbia.edu  Sun Jun 22 23:26:58 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Sun Jun 22 23:19:16 2008
Subject: [Haskell-cafe] What is a rigid type variable?
Message-ID: <87r6aokf0d.fsf@columbia.edu>

Hi all,

I'm writing a short function as follows, but I'm not able to
find a suitable type signature for `go'.  It uses
Numeric.LinearAlgebra from hmatrix.


-- | Map each element in a vector to vectors and thus form a matrix
-- | row by row
mapVecToMat :: (Element a, Element b) =>
               (a -> Vector b) -> Vector a -> Matrix b
mapVecToMat f v = fromRows $ go (d - 1) []
    where
      d = dim v
      go :: Element b => Int -> [Vector b] -> [Vector b]
      go 0 vs = f (v @> 0) : vs
      go !j !vs = go (j - 1) (f (v @> j) : vs)


If I give the type signature to go as this, I got the
following error

    Couldn't match expected type `b1' against inferred type `b'
      `b1' is a rigid type variable bound by
           the type signature for `go' at test.hs:36:20
      `b' is a rigid type variable bound by
          the type signature for `mapVecToMat' at test.hs:31:35
      Expected type: Vector b1
      Inferred type: Vector b
    In the first argument of `(:)', namely `f (v @> 0)'
    In the expression: f (v @> 0) : vs

So what is this rigid type variable all about and what is
correct type of the function `go'?

Thanks in advance,
X-Y
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From jamiiecb at googlemail.com  Mon Jun 23 01:51:09 2008
From: jamiiecb at googlemail.com (Jamie Brandon)
Date: Mon Jun 23 01:42:47 2008
Subject: [Haskell-cafe] Planet haskell
Message-ID: <10ed1a750806222251s6a276fd4ha6a5f77195fd663c@mail.gmail.com>

I was hoping to have my summer of code blog added to planet haskell
but planet@community.haskell.org no longer seems to exist. Hopefully
the owner is subscribed to this list?

Jamie
From lrpalmer at gmail.com  Mon Jun 23 01:58:50 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Mon Jun 23 01:50:26 2008
Subject: [Haskell-cafe] What is a rigid type variable?
In-Reply-To: <87r6aokf0d.fsf@columbia.edu>
References: <87r6aokf0d.fsf@columbia.edu>
Message-ID: <7ca3f0160806222258t1e08397etb6a98d8566665c0e@mail.gmail.com>

On Mon, Jun 23, 2008 at 3:26 AM, Xiao-Yong Jin <xj2106@columbia.edu> wrote:
> Hi all,
>
> I'm writing a short function as follows, but I'm not able to
> find a suitable type signature for `go'.  It uses
> Numeric.LinearAlgebra from hmatrix.
>
>
> -- | Map each element in a vector to vectors and thus form a matrix
> -- | row by row
> mapVecToMat :: (Element a, Element b) =>
>               (a -> Vector b) -> Vector a -> Matrix b
> mapVecToMat f v = fromRows $ go (d - 1) []
>    where
>      d = dim v
>      go :: Element b => Int -> [Vector b] -> [Vector b]
>      go 0 vs = f (v @> 0) : vs
>      go !j !vs = go (j - 1) (f (v @> j) : vs)

If you want to give a type signature for 'go', you need a GHC
extension called ScopeTypeVariables (IIRC).  The problem is that the
'b' in the signature of mapVecToMat is not the same b as the one in
'go'.  With this extension, you can put those variables into scope for
the body of the definition using explicit 'forall' quantifiers:

mapVecToMat :: forall a b. (Element a, Element b) =>
               (a -> Vector b) -> Vector a -> Matrix b
-- rest as before

But the Element b constraint is redundant in the signature of 'go',
since that constraint is already in place by the above signature.

As far as I can tell, giving an explicit signature for 'go' is not
possible without this extension.

Luke
From lrpalmer at gmail.com  Mon Jun 23 02:02:13 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Mon Jun 23 01:53:51 2008
Subject: [Haskell-cafe] What is a rigid type variable?
In-Reply-To: <7ca3f0160806222258t1e08397etb6a98d8566665c0e@mail.gmail.com>
References: <87r6aokf0d.fsf@columbia.edu>
	<7ca3f0160806222258t1e08397etb6a98d8566665c0e@mail.gmail.com>
Message-ID: <7ca3f0160806222302i3bf31925ke5c23dc4cbe0f3b9@mail.gmail.com>

On Mon, Jun 23, 2008 at 5:58 AM, Luke Palmer <lrpalmer@gmail.com> wrote:
> On Mon, Jun 23, 2008 at 3:26 AM, Xiao-Yong Jin <xj2106@columbia.edu> wrote:
>> Hi all,
>>
>> I'm writing a short function as follows, but I'm not able to
>> find a suitable type signature for `go'.  It uses
>> Numeric.LinearAlgebra from hmatrix.
>>
>>
>> -- | Map each element in a vector to vectors and thus form a matrix
>> -- | row by row
>> mapVecToMat :: (Element a, Element b) =>
>>               (a -> Vector b) -> Vector a -> Matrix b
>> mapVecToMat f v = fromRows $ go (d - 1) []
>>    where
>>      d = dim v
>>      go :: Element b => Int -> [Vector b] -> [Vector b]
>>      go 0 vs = f (v @> 0) : vs
>>      go !j !vs = go (j - 1) (f (v @> j) : vs)
>
> If you want to give a type signature for 'go', you need a GHC
> extension called ScopeTypeVariables (IIRC).

I was indeed correct on the name of this extension, but it would be no
help to you to know this since I made a typo :-)

The extension is called ScopedTypeVaraibles.

You probably already know that this can be enabled with:

{-# LANGUAGE ScopedTypeVariables #-}

Luke
From leledumbo_cool at yahoo.co.id  Mon Jun 23 02:30:51 2008
From: leledumbo_cool at yahoo.co.id (leledumbo)
Date: Mon Jun 23 02:23:31 2008
Subject: [Haskell-cafe] Help with generalizing function
Message-ID: <18063291.post@talk.nabble.com>


I've successfully create a function to return lists of N-ple that satisfy the
following function:
x1 + x2 + x3 + ... + xN = C
But unfortunately, it's not generic. The N is supposed to be an input, too.
I don't know how to make a dynamic N-ple (is it possible anyway?).
Currently, here's the implementation:
[code]
findAllAns c = [ (x1,x2,x3,x4,x5) |
    x1 <- [0..c],
    x2 <- [0..c],
    x3 <- [0..c],
    x4 <- [0..c],
    x5 <- [0..c],
    x1 + x2 + x3 + x4 + x5 == c
  ]
[/code]
I tried using lists of lists, like this:
[code]
findAllAns c n = [ [x] | x <- [0..c], length [x] == n ]
[/code]
but [x] doesn't mean "a list of x", instead it's "a list that contains an x,
where x in [0..c]". Can anyone help me?
-- 
View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18063291.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From ryani.spam at gmail.com  Mon Jun 23 02:37:25 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun 23 02:29:02 2008
Subject: [Haskell-cafe] What is a rigid type variable?
In-Reply-To: <87r6aokf0d.fsf@columbia.edu>
References: <87r6aokf0d.fsf@columbia.edu>
Message-ID: <2f9b2d30806222337r7f462c9el89a3e8c58986ec8d@mail.gmail.com>

To answer the question in the subject:

>From "Simple unification-based type inference for GADTs",
Peyton-Jones, et al.  ICFP 2006.
http://research.microsoft.com/users/simonpj/papers/gadt/

"Instead of "user-specified type", we use the briefer term rigid
type to describe a type that is completely specified, in some
direct fashion, by a programmer-supplied type annotation."

So a rigid type is any type specified by a programmer type signature.
All other types are "wobbly".

Does anyone know what is going to change about the terminology with
the new "boxy types" paper?
http://research.microsoft.com/users/simonpj/papers/boxy/

  -- ryan

  -- ryan

On Sun, Jun 22, 2008 at 8:26 PM, Xiao-Yong Jin <xj2106@columbia.edu> wrote:
> Hi all,
>
> I'm writing a short function as follows, but I'm not able to
> find a suitable type signature for `go'.  It uses
> Numeric.LinearAlgebra from hmatrix.
>
>
> -- | Map each element in a vector to vectors and thus form a matrix
> -- | row by row
> mapVecToMat :: (Element a, Element b) =>
>               (a -> Vector b) -> Vector a -> Matrix b
> mapVecToMat f v = fromRows $ go (d - 1) []
>    where
>      d = dim v
>      go :: Element b => Int -> [Vector b] -> [Vector b]
>      go 0 vs = f (v @> 0) : vs
>      go !j !vs = go (j - 1) (f (v @> j) : vs)
>
>
> If I give the type signature to go as this, I got the
> following error
>
>    Couldn't match expected type `b1' against inferred type `b'
>      `b1' is a rigid type variable bound by
>           the type signature for `go' at test.hs:36:20
>      `b' is a rigid type variable bound by
>          the type signature for `mapVecToMat' at test.hs:31:35
>      Expected type: Vector b1
>      Inferred type: Vector b
>    In the first argument of `(:)', namely `f (v @> 0)'
>    In the expression: f (v @> 0) : vs
>
> So what is this rigid type variable all about and what is
> correct type of the function `go'?
>
> Thanks in advance,
> X-Y
> --
>    c/*    __o/*
>    <\     * (__
>    */\      <
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From ryani.spam at gmail.com  Mon Jun 23 02:42:43 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun 23 02:34:20 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <18063291.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
Message-ID: <2f9b2d30806222342i300d6a3s5006eb6eb485e6a3@mail.gmail.com>

Hint: use recursion.

Hint 2: You can use <- in a list comprehension or list "do"-block to
select a single list from a list of lists.

  -- ryan

On Sun, Jun 22, 2008 at 11:30 PM, leledumbo <leledumbo_cool@yahoo.co.id> wrote:
>
> I've successfully create a function to return lists of N-ple that satisfy the
> following function:
> x1 + x2 + x3 + ... + xN = C
> But unfortunately, it's not generic. The N is supposed to be an input, too.
> I don't know how to make a dynamic N-ple (is it possible anyway?).
> Currently, here's the implementation:
> [code]
> findAllAns c = [ (x1,x2,x3,x4,x5) |
>    x1 <- [0..c],
>    x2 <- [0..c],
>    x3 <- [0..c],
>    x4 <- [0..c],
>    x5 <- [0..c],
>    x1 + x2 + x3 + x4 + x5 == c
>  ]
> [/code]
> I tried using lists of lists, like this:
> [code]
> findAllAns c n = [ [x] | x <- [0..c], length [x] == n ]
> [/code]
> but [x] doesn't mean "a list of x", instead it's "a list that contains an x,
> where x in [0..c]". Can anyone help me?
> --
> View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18063291.html
> Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From bulat.ziganshin at gmail.com  Mon Jun 23 02:42:33 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Mon Jun 23 02:35:53 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <18063291.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
Message-ID: <1038886043.20080623104233@gmail.com>

Hello leledumbo,

Monday, June 23, 2008, 10:30:51 AM, you wrote:

> I've successfully create a function to return lists of N-ple that satisfy the

tuples may contain any combination of types, use lists instead

-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From harald.rotter at sagem.com  Mon Jun 23 02:50:33 2008
From: harald.rotter at sagem.com (Harald ROTTER)
Date: Mon Jun 23 02:42:44 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
Message-ID: <OF14B1FE9C.D4AC6BAA-ONC1257471.0024B113-C1257471.002596A0@sagem.com>

Hello,

sorry for the late answer, I was off for the weekend :-)

The paper "Number-parameterized types" by Oleg Kielyov is located at

      http://okmij.org/ftp/papers/number-parameterized-types.pdf

It impressively shows what one can do with Haskell's type system.
What I am after is the replacement of a "chain" of digits, like e.g.
      D1 $ D0 $ D0 $ Sz
by a list
      [D1,D0,D0]
so I can effectively use list operations on those "typed numbers". I also
wonder if there is some kind of
"generalized" foldr such that, e.g.
      D1 $ D0 $ D0 $ Sz = specialFoldr ($) Sz [D1,D0,D0]
I think that this foldr must be some "special" foldr that augments the data
type of the result in each foldr step.
Would this be possible or am I just chasing phantoms ?

Thanks

Harald.



" Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes  pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel  ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite." 

" This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."
From leledumbo_cool at yahoo.co.id  Mon Jun 23 04:04:58 2008
From: leledumbo_cool at yahoo.co.id (leledumbo)
Date: Mon Jun 23 03:56:35 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <2f9b2d30806222342i300d6a3s5006eb6eb485e6a3@mail.gmail.com>
References: <18063291.post@talk.nabble.com>
	<2f9b2d30806222342i300d6a3s5006eb6eb485e6a3@mail.gmail.com>
Message-ID: <18064396.post@talk.nabble.com>


>> tuples may contain any combination of types, use lists instead
I think so, too.

>> You can use <- in a list comprehension or list "do"-block to select a
>> single list from a list of lists.
Is it related with my question? I mean, instead of extracting, I need to
construct lists.
-- 
View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18064396.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From lrpalmer at gmail.com  Mon Jun 23 04:05:33 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Mon Jun 23 03:57:08 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
In-Reply-To: <OF14B1FE9C.D4AC6BAA-ONC1257471.0024B113-C1257471.002596A0@sagem.com>
References: <OF14B1FE9C.D4AC6BAA-ONC1257471.0024B113-C1257471.002596A0@sagem.com>
Message-ID: <7ca3f0160806230105h56fa14b7g1acc3201be6f06f8@mail.gmail.com>

On Mon, Jun 23, 2008 at 6:50 AM, Harald ROTTER <harald.rotter@sagem.com> wrote:
> Hello,
>
> sorry for the late answer, I was off for the weekend :-)
>
> The paper "Number-parameterized types" by Oleg Kielyov is located at
>
>      http://okmij.org/ftp/papers/number-parameterized-types.pdf
>
> It impressively shows what one can do with Haskell's type system.
> What I am after is the replacement of a "chain" of digits, like e.g.
>      D1 $ D0 $ D0 $ Sz
> by a list
>      [D1,D0,D0]
> so I can effectively use list operations on those "typed numbers". I also
> wonder if there is some kind of
> "generalized" foldr such that, e.g.
>      D1 $ D0 $ D0 $ Sz = specialFoldr ($) Sz [D1,D0,D0]
> I think that this foldr must be some "special" foldr that augments the data
> type of the result in each foldr step.
> Would this be possible or am I just chasing phantoms ?

Mostly I believe you are.  What you are describing is firmly in the
realm of dependent types, far beyond Haskell's type system. See
Epigram or Agda for languages which have attempted to tackle this
problem.

Luke
From antti-juhani at kaijanaho.fi  Mon Jun 23 04:08:50 2008
From: antti-juhani at kaijanaho.fi (Antti-Juhani Kaijanaho)
Date: Mon Jun 23 04:00:27 2008
Subject: [Haskell-cafe] Planet haskell
In-Reply-To: <10ed1a750806222251s6a276fd4ha6a5f77195fd663c@mail.gmail.com>
References: <10ed1a750806222251s6a276fd4ha6a5f77195fd663c@mail.gmail.com>
Message-ID: <20080623080849.GE4901@kukkaseppele.kaijanaho.fi>

On Mon, Jun 23, 2008 at 06:51:09AM +0100, Jamie Brandon wrote:
> I was hoping to have my summer of code blog added to planet haskell
> but planet@community.haskell.org no longer seems to exist. Hopefully
> the owner is subscribed to this list?

It exists but seems to be broken.  Thank you for letting me know.

In the mean time, just contact myself or Don Stewart.

--
Antti-Juhani Kaijanaho, Jyv?skyl?, Finland
http://antti-juhani.kaijanaho.fi/newblog/
http://www.flickr.com/photos/antti-juhani/
From lrpalmer at gmail.com  Mon Jun 23 04:11:46 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Mon Jun 23 04:03:22 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <18063291.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
Message-ID: <7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>

On Mon, Jun 23, 2008 at 6:30 AM, leledumbo <leledumbo_cool@yahoo.co.id> wrote:
> I've successfully create a function to return lists of N-ple that satisfy the
> following function:
> x1 + x2 + x3 + ... + xN = C
> But unfortunately, it's not generic. The N is supposed to be an input, too.
> I don't know how to make a dynamic N-ple (is it possible anyway?).
> Currently, here's the implementation:
> [code]
> findAllAns c = [ (x1,x2,x3,x4,x5) |
>    x1 <- [0..c],
>    x2 <- [0..c],
>    x3 <- [0..c],
>    x4 <- [0..c],
>    x5 <- [0..c],
>    x1 + x2 + x3 + x4 + x5 == c
>  ]
> [/code]

You will not be able to do this with a straight list comprehension
without using recursion.  It may help you to know that:

    [ e | x <- as, y <- bs ]   -- for any expression e

Is equivalent to

    concat [ [ e | y <- bs ] | x <- as ]

That is a way commas in list comprehensions can be factored out.

Luke
From alfonso.acosta at gmail.com  Mon Jun 23 04:26:30 2008
From: alfonso.acosta at gmail.com (Alfonso Acosta)
Date: Mon Jun 23 04:18:12 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
In-Reply-To: <OF9A1B2713.7561B55B-ONC125746E.004183E0-C125746E.004207DE@sagem.com>
References: <OF9A1B2713.7561B55B-ONC125746E.004183E0-C125746E.004207DE@sagem.com>
Message-ID: <6a7c66fc0806230126w6886a427j50265ad60389b0f3@mail.gmail.com>

Inspired in Oleg's ideas, I implemented the packages type-level and
parameterized-data (which includes number-parameterized vectors).


To get an idea about how they work you might want to read their
haddock documentation in hackage:

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parameterized-data

You can get their darcs repositories (including some minor updates) from:

darcs get http://code.haskell.org/type-level
darcs get http://code.haskell.org/parameterized-data

On Fri, Jun 20, 2008 at 8:01 AM, Harald ROTTER <harald.rotter@sagem.com> wrote:
>
> Dear Haskellers,
>
> after reading Oleg Kiselyov's paper on number-parameterized types I started
> to play around with
> the class Digits that encodes decimal numbers in types. The "typed number"
> 10 would e.g. be defined as
>
>      D1 $ D0 $ Sz
>
> I wondered if it would be possible replace the expression above by a
> heterogeneous list like
>
>      [D1,D0]
>
> so I tried to define
>
>      data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
>
> Loading this into ghci yields:
>
> :t Digit D0
>
> <interactive>:1:0:
>    Ambiguous type variable `a' in the constraint:
>      `Digits a' arising from a use of `Digit' at <interactive>:1:0-7
>    Probable fix: add a type signature that fixes these type variable(s)
>
> Removing the type constraints in the definition of "Digit":
>
>      data Digit = forall a b.Digit (a -> b a)
>
> makes it work like this:
>
>      :t Digit D0
>      Digit D0 :: Digit
>
>      :t [Digit D0, Digit D1]
>      [Digit D0, Digit D1] :: [Digit]
>
> "Digit", however, is far too general (it also includes e.g. \x -> [x]), but
> I would like it to be restricted to the Digit class.
>
> Any help is appreciated.
>
> Thanks
>
> Harald.
>
>
> CODE:
>
> module Test where
>
> data D0 a = D0 a
> data D1 a = D1 a
> data D2 a = D2 a
> data D3 a = D3 a
> data D4 a = D4 a
> data D5 a = D5 a
> data D6 a = D6 a
> data D7 a = D7 a
> data D8 a = D8 a
> data D9 a = D9 a
>
> class Digits ds where
>    d2num :: Num a => ds -> a -> a
>
> data Sz = Sz    -- zero size
> instance Digits Sz where
>    d2num _ acc = acc
>
> instance Digits ds => Digits (D0 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc)
> instance Digits ds => Digits (D1 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+1)
> instance Digits ds => Digits (D2 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+2)
> instance Digits ds => Digits (D3 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+3)
> instance Digits ds => Digits (D4 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+4)
> instance Digits ds => Digits (D5 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+5)
> instance Digits ds => Digits (D6 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+6)
> instance Digits ds => Digits (D7 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+7)
> instance Digits ds => Digits (D8 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+8)
> instance Digits ds => Digits (D9 ds) where
>    d2num dds acc = d2num (t22 dds) (10*acc+9)
>
> t22 :: f x -> x
> t22 = undefined
>
> --data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
> data Digit = forall a b.Digit (a -> b a)
>
> -------------------------------------------------------------------------------------------------
>
>
>
> " Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes  pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel  ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite."
>
> " This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From leledumbo_cool at yahoo.co.id  Mon Jun 23 05:00:51 2008
From: leledumbo_cool at yahoo.co.id (leledumbo)
Date: Mon Jun 23 04:52:28 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
Message-ID: <18065206.post@talk.nabble.com>


I give up %-|, I'll go back to Pascal instead. Thanks for your answers.
-- 
View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18065206.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From Malcolm.Wallace at cs.york.ac.uk  Mon Jun 23 05:04:14 2008
From: Malcolm.Wallace at cs.york.ac.uk (Malcolm Wallace)
Date: Mon Jun 23 05:00:22 2008
Subject: [Haskell-cafe] Safe way to parse arguments?
In-Reply-To: <Pine.LNX.4.64.0806222241090.14824@anubis.informatik.uni-halle.de>
References: <87tzfmtxeh.fsf@columbia.edu>
	<Pine.LNX.4.64.0806222241090.14824@anubis.informatik.uni-halle.de>
Message-ID: <20080623100414.2b530b10.Malcolm.Wallace@cs.york.ac.uk>

> > I'm wondering how usually you parse command line arguments
> > list safely.
> >
> > Prelude.read: no parse
> 
> It's generally not a good idea to call 'read' on user data.

There is (at least one) proper parsing library intended as a direct
replacement for Read:

    http://www.cs.york.ac.uk/fp/polyparse/haddock/Text-Parse.html

The basic idea is that the function 'parse' replaces 'read', and to use
it at any specific type T:

    (runParser parse) :: String -> (Either String T, String)

You get back either an error message or the value, along with the
remaining unparsed text.  Instances of the Parse class are defined for
all Prelude types, and you can easily derive instances for any of your
own types, using the DrIFT tool.  Parse is assumed to be an inverse of
Show, that is, the derived instances of Parse will read back a
canonically derived Show value.

Another benefit of using a real parser library is that you can plumb
together several parsers quickly if you need to.  e.g.
    runParser (exactly 3 parse) :: String -> (Either String [T], String)

Regards,
    Malcolm
From vigalchin at gmail.com  Mon Jun 23 05:10:33 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun 23 05:02:10 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
Message-ID: <5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>

Basically I want to model POSIX async io "aiocb"(
http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in
particular the aiocb field "aio_buf"!

Kind regards, Vasili

On Sun, Jun 22, 2008 at 1:47 AM, Galchin, Vasili <vigalchin@gmail.com>
wrote:

> Hello,
>
>     I want to model an I/O read/write buffer in Haskell and marshall down
> into ANSI C.
>
> 1) ByteString? Or Ptr Word8?
>
> 2) What are example values of the types in 1)?
>
>
> Kind regards, Vasili
>
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From chaddai.fouche at gmail.com  Mon Jun 23 05:42:25 2008
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Mon Jun 23 05:34:01 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <18065206.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
Message-ID: <e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>

2008/6/23 leledumbo <leledumbo_cool@yahoo.co.id>:
>
> I give up %-|, I'll go back to Pascal instead. Thanks for your answers.

Don't give up so fast !! (Note that you can't do what you asked for in
Pascal either, in fact Pascal don't support n-uplet)

A recursive way to do it is :

findAllAns 0 0 = [[]]
findAllAns 0 s = []
findAllAns n s = [ x:xs | x <- [0..s], xs <- findAllAns (n - 1) (s - x) ]


For all those little questions that bug you, you'll get your answers
faster by asking on the #haskell channel on irc.freenode.org .

-- 
Jeda?
From bulat.ziganshin at gmail.com  Mon Jun 23 05:45:30 2008
From: bulat.ziganshin at gmail.com (Bulat Ziganshin)
Date: Mon Jun 23 05:38:48 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
	<e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
Message-ID: <1316971110.20080623134530@gmail.com>

Hello Chaddai,

Monday, June 23, 2008, 1:42:25 PM, you wrote:

>> I give up %-|, I'll go back to Pascal instead. Thanks for your answers.

> findAllAns 0 0 = [[]]
> findAllAns 0 s = []
> findAllAns n s = [ x:xs | x <- [0..s], xs <- findAllAns (n - 1) (s - x) ]

seems that leledumbo found a new way to force us give the answers to
those homeworks LOL




-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

From isaacdupree at charter.net  Mon Jun 23 06:56:12 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Mon Jun 23 06:47:51 2008
Subject: [Haskell-cafe] ANNOUNCE: Pipe 1.0
In-Reply-To: <20080621191255.GA2361@scytale.galois.com>
References: <g3j92p$jh1$1@ger.gmane.org>
	<20080621191255.GA2361@scytale.galois.com>
Message-ID: <485F814C.7090105@charter.net>

Don Stewart wrote:
> Interesting.
> Does it depend on an unreleased version of the process library?

by the way, is there a policy for when new versions of packages 
maintained by libraries@h.o are *released*?  Or do patches just collect 
in the darcs repository until they're picked up by some major release 
like GHC's?  I would tend to think that for any change nontrivial enough 
to be discussed on libraries@, why not quickly release the newer version 
with an appropriately incremented version number?

-Isaac
From leledumbo_cool at yahoo.co.id  Mon Jun 23 07:03:18 2008
From: leledumbo_cool at yahoo.co.id (leledumbo)
Date: Mon Jun 23 06:54:55 2008
Subject: Re[Haskell-cafe] [2]: Help with generalizing function
In-Reply-To: <1316971110.20080623134530@gmail.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
	<e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
	<1316971110.20080623134530@gmail.com>
Message-ID: <18066860.post@talk.nabble.com>


>> Don't give up so fast !! (Note that you can't do what you asked for in
>> Pascal either, in fact Pascal don't support n-uplet) 
I'm not going to use n-uplet, dynamic array of array of Byte is enough.
Though not very optimizing, I can use 2 step process:
1. Generate all lists (array of Byte) of length N which each element ranges
from 0 to C.
2. Filter which has sum=C.

>> seems that leledumbo found a new way to force us give the answers to
>> those homeworks LOL
Don't worry, I'm not gonna use it because it has to be done in procedural
way (I haven't taken Functional Programming class yet). The reason why I ask
is I'm HOPING that if I can understand how it works, implementing the
procedural form would be easy. I've read somewhere that functional language
can be implemented in procedural one. In fact, GHC outputs C code.

Thanks for the answer. I'll use it to learn, it's quite difficult to switch
from procedural to functional. I mean, in procedural it's easy to find the
fastest solution using brute force. This can't be done in functional.
-- 
View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18066860.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From leledumbo_cool at yahoo.co.id  Mon Jun 23 07:04:18 2008
From: leledumbo_cool at yahoo.co.id (leledumbo)
Date: Mon Jun 23 06:55:54 2008
Subject: Re[Haskell-cafe] [2]: Help with generalizing function
In-Reply-To: <1316971110.20080623134530@gmail.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
	<e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
	<1316971110.20080623134530@gmail.com>
Message-ID: <18066861.post@talk.nabble.com>


>> Don't give up so fast !! (Note that you can't do what you asked for in
>> Pascal either, in fact Pascal don't support n-uplet) 
I'm not going to use n-uplet, dynamic array of array of Byte is enough.
Though not very optimizing, I can use 2 step process:
1. Generate all lists (array of Byte) of length N which each element ranges
from 0 to C.
2. Filter which has sum=C.

>> seems that leledumbo found a new way to force us give the answers to
>> those homeworks LOL
Don't worry, I'm not gonna use it because it has to be done in procedural
way (I haven't taken Functional Programming class yet). The reason why I ask
is I'm HOPING that if I can understand how it works, implementing the
procedural form would be easy. I've read somewhere that functional language
can be implemented in procedural one. In fact, GHC outputs C code.

Thanks for the answer. I'll use it to learn, it's quite difficult to switch
from procedural to functional. I mean, in procedural it's easy to find the
fastest solution using brute force. This can't be done in functional.
-- 
View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18066861.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From abhay.parvate at gmail.com  Mon Jun 23 07:20:30 2008
From: abhay.parvate at gmail.com (Abhay Parvate)
Date: Mon Jun 23 07:12:06 2008
Subject: [Haskell-cafe] Literal programming in Haskell with rst-literals
In-Reply-To: <20080621181854.184193C8002@banane.furius.ca>
References: <20080621181854.184193C8002@banane.furius.ca>
Message-ID: <3c4d5adf0806230420w56198d39n4027f00341f90b17@mail.gmail.com>

Hello,

You might already know this, but in case you don't: there is another
literate style:

... non-code ...
\begin{code}
... code ...
\end{code}
... non-code ...

in which you do not put prefixes to each line. (In fact the standard says
somewhere it is not recommended to mix the two styles if I remember right.)

I hope I am not being redundant!
Abhay


On Sat, Jun 21, 2008 at 11:48 PM, Martin Blais <blais@furius.ca> wrote:

>
> Hello Haskell community!
>
> I just did a marginally cool thing and I wanted to share it
> with you.
>
> "rst-literals" is a small program I wrote a while ago in
> order to write documents in reStructuredText format that
> would embed SQL code for data models in them, a form of
> literal programming for SQL if you will; I would describe my
> needs for the schema in prose, and reST literal-blocks were
> used to embed SQL code, blocks that look like this::
>
>  CLASS Employee (
>     firstname VARCHAR,
>     lastname VARCHAR
>  )
>
> I wrote the script to be entirely generic: it parses the
> reST documents using the docutils code and outputs only the
> literal-blocks, with indentation removed; you can then run
> your favourite interpreter/compiler on the result (in that
> case, psql to initialize a database).
>
> Recently, while experimenting with Haskell, I started using
> both the literal (.lhs) and non-literal (.hs) styles of
> Haskell input, and I found the literal style a bit
> unpleasant to use, in particular, I don't like to have to
> prefix every line of code I write, despite the help that
> Emacs' haskell-mode provides.
>
> So I tried pulling a similar trick and embedding Haskell
> code in literal-blocks within reST documents, extracting
> that code using rst-literals, and it turns out that it works
> like a charm. Here is an example makefile for doing this::
>
>  .SUFFIXES: .rst .hs
>
>  all: chap6
>
>  .rst.hs:
>          rst-literals $< > $@
>
>  chap6: chap6.hs
>          ghc --make chap6.hs
>
> An example reST document with some embedded Haskell code
> follows this email. Note that since rst-literals is using
> the docutils parser, you can make use of all of the
> recursive reST syntax, sections, bulleted items and much
> more. Only the literal-blocks are extracted, anywhere they
> appear. You can also easily process the reST source into
> HTML pages or LaTeX documents using the tools that come with
> docutils.
>
> You can find rst-literals here:
> http://furius.ca/pubcode/
>
> Enjoy,
>
>
>
>
> --
> Martin
>
> P.S. If there is a way to output cpp-like directives for
> GHC, like "#line <filename> <lineno>", it would be easy to
> modify rst-literals to generate those, so that compilation
> errors could refer to the source reST document instead of
> the extracted source.
>
>
>
> chap6.hs:
> ----------------------------------------------------------------------
>
> ===========================================
>   Exercises from Hutton book, Chapter 6
> ===========================================
>
> .. contents::
> ..
>    1  Introduction
>    2  Exercise 1
>    3  Exercise 2
>    4  Exercise 3
>    5  Exercise 4
>    6  Exercise 5
>    7  Exercise 6
>
>
> Introduction
> ============
>
> Bla bla bla blablablablablabla bla bla blabla. Bla bla bla
> blablablablablabla bla bla blabla. Bla bla bla blablablablablabla bla
> bla blabla. Bla bla bla blablablablablabla bla bla blabla. Bla bla bla
> blablablablablabla bla bla blabla. Bla bla bla blablablablablabla bla
> bla blabla.
>
>
> Exercise 1
> ==========
> ::
>
>  myexp :: Int -> Int -> Int
>  myexp b 0 = 1
>  myexp b (n+1) = b * (myexp b n)
>
>
> Exercise 2
> ==========
>
> (Exercise 2 consisted in derivations, so we mark the literal
> blocks as another type of block with "#!example", so that
> they don't get included in the output when only the
> "default" literal blocks get extracted. See rst-literals
> docstring for details.)
>
> Length::
>
>    #!example
>    1 + (length [2, 3])
>    1 + 1 + (length [3])
>    1 + 1 + (1)
>    3
>
> Drop::
>
>  #!example
>  drop 3 [1, 2, 3, 4, 5]
>  [] ++ drop 3 [2, 3, 4, 5]
>  [] ++ [] ++ drop 3 [3, 4, 5]
>  [] ++ [] ++ [] ++ [4, 5]
>  [4, 5]
>
> Init::
>
>  #!example
>  init [1, 2, 3]
>  [1] ++ init [2, 3]
>  [1] ++ [2] ++ init [3]
>  [1] ++ [2] ++ []
>  [1, 2]
>
>
> Exercise 3
> ==========
>
> These are alternate versions of the example functions defined in the
> text::
>
>  and' :: [Bool] -> Bool
>  and' [x] = x
>  and' (x:xs) = x && and' xs
>
>  concat' :: [[a]] -> [a]
>  concat' [] = []
>  concat' (x:xs) = x ++ concat' xs
>
>  replicate' :: Int -> a -> [a]
>  replicate' 0 x = []
>  replicate' (n+1) x = (x : replicate' n x)
>
>  select' :: [a] -> Int -> a
>  select' (x:xs) 0 = x
>  select' (x:xs) (n+1) = select' xs n
>
>  elem' :: Eq a => a -> [a] -> Bool
>  elem' _ [] = False
>  elem' y (x:xs) | x == y = True
>                 | otherwise = elem' y xs
>
> Exercise 4
> ==========
>
> The exercise asked to implement a function to merge two lists::
>
>  merge :: Ord a => [a] -> [a] -> [a]
>  merge xs [] = xs
>  merge [] xs = xs
>  merge (x:xs) (y:ys) | x < y = (x : merge xs (y:ys))
>                      | otherwise = (y : merge (x:xs) ys)
>
>
> Exercise 5
> ==========
> ::
>
>  msort :: Ord a => [a] -> [a]
>  msort [] = []
>  msort [x] = [x] -- This is necessary to end the recursion.
>  msort xs = merge (msort (fst hh)) (msort (snd hh))
>             where hh = halve xs
>
>  halve :: [a] -> ([a], [a])
>  halve xs = (take n xs, drop n xs)
>      where n = (length xs) `div` 2
>
> Some main program::
>
>  main = (putStrLn . show) (halve [1..17])
>
>
> Exercise 6
> ==========
>
> (Too basic, I didn't bother.)
>
> ----------------------------------------------------------------------
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
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From marlowsd at gmail.com  Mon Jun 23 09:14:14 2008
From: marlowsd at gmail.com (Simon Marlow)
Date: Mon Jun 23 09:05:56 2008
Subject: [Haskell-cafe] Re: ANNOUNCE: Pipe 1.0
In-Reply-To: <485F814C.7090105@charter.net>
References: <g3j92p$jh1$1@ger.gmane.org>	<20080621191255.GA2361@scytale.galois.com>
	<485F814C.7090105@charter.net>
Message-ID: <485FA1A6.9040208@gmail.com>

Isaac Dupree wrote:
> Don Stewart wrote:
>> Interesting.
>> Does it depend on an unreleased version of the process library?
> 
> by the way, is there a policy for when new versions of packages 
> maintained by libraries@h.o are *released*?  Or do patches just collect 
> in the darcs repository until they're picked up by some major release 
> like GHC's?  I would tend to think that for any change nontrivial enough 
> to be discussed on libraries@, why not quickly release the newer version 
> with an appropriately incremented version number?

There are some further changes we've been discussing, see Duncan's message 
here:

http://www.haskell.org/pipermail/libraries/2008-May/009695.html

and I'd like to batch all these together in one release.

Cheers,
	Simon
From xj2106 at columbia.edu  Mon Jun 23 09:31:59 2008
From: xj2106 at columbia.edu (Xiao-Yong Jin)
Date: Mon Jun 23 09:24:18 2008
Subject: [Haskell-cafe] What is a rigid type variable?
In-Reply-To: <7ca3f0160806222302i3bf31925ke5c23dc4cbe0f3b9@mail.gmail.com>
	(Luke Palmer's message of "Mon, 23 Jun 2008 06:02:13 +0000")
References: <87r6aokf0d.fsf@columbia.edu>
	<7ca3f0160806222258t1e08397etb6a98d8566665c0e@mail.gmail.com>
	<7ca3f0160806222302i3bf31925ke5c23dc4cbe0f3b9@mail.gmail.com>
Message-ID: <87ej6ojn00.fsf@columbia.edu>

"Luke Palmer" <lrpalmer@gmail.com> writes:

> On Mon, Jun 23, 2008 at 5:58 AM, Luke Palmer <lrpalmer@gmail.com> wrote:
>> On Mon, Jun 23, 2008 at 3:26 AM, Xiao-Yong Jin <xj2106@columbia.edu> wrote:
>>> Hi all,
>>>
>>> I'm writing a short function as follows, but I'm not able to
>>> find a suitable type signature for `go'.  It uses
>>> Numeric.LinearAlgebra from hmatrix.
>>>
>>>
>>> -- | Map each element in a vector to vectors and thus form a matrix
>>> -- | row by row
>>> mapVecToMat :: (Element a, Element b) =>
>>>               (a -> Vector b) -> Vector a -> Matrix b
>>> mapVecToMat f v = fromRows $ go (d - 1) []
>>>    where
>>>      d = dim v
>>>      go :: Element b => Int -> [Vector b] -> [Vector b]
>>>      go 0 vs = f (v @> 0) : vs
>>>      go !j !vs = go (j - 1) (f (v @> j) : vs)
>>
>> If you want to give a type signature for 'go', you need a GHC
>> extension called ScopeTypeVariables (IIRC).
>
> I was indeed correct on the name of this extension, but it would be no
> help to you to know this since I made a typo :-)
>
> The extension is called ScopedTypeVaraibles.
>
> You probably already know that this can be enabled with:
>
> {-# LANGUAGE ScopedTypeVariables #-}
>
> Luke

Thanks for the explanation.  I guess it's just easier for me
not to give any type signature to `go', since ghc should do
the type inference quite nicely and reliably.

X-Y
-- 
    c/*    __o/*
    <\     * (__
    */\      <
From claus.reinke at talk21.com  Mon Jun 23 09:40:27 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Mon Jun 23 09:32:10 2008
Subject: GSoC project blogs? (Re: [Haskell-cafe] Planet haskell)
References: <10ed1a750806222251s6a276fd4ha6a5f77195fd663c@mail.gmail.com>
	<20080623080849.GE4901@kukkaseppele.kaijanaho.fi>
Message-ID: <00c901c8d536$b5fac540$ea038351@cr3lt>

It would be nice to have blogs for all Haskell GSoC projects
on Planet Haskell.

Infrequent updates (such as Neil's weekly summaries) would
be quite okay - details can always be followed up in email,
provided that interested parties are aware of them in the
first place;-)

Otherwise, we end up with little community involvement,
and questions like "wasn't there a GSoC project on X last
year? What ever happened to that?"

Claus

> On Mon, Jun 23, 2008 at 06:51:09AM +0100, Jamie Brandon wrote:
>> I was hoping to have my summer of code blog added to planet haskell
>> but planet@community.haskell.org no longer seems to exist. Hopefully
>> the owner is subscribed to this list?
>
> It exists but seems to be broken.  Thank you for letting me know.
>
> In the mean time, just contact myself or Don Stewart.
>
> --
> Antti-Juhani Kaijanaho, Jyv?skyl?, Finland
> http://antti-juhani.kaijanaho.fi/newblog/
> http://www.flickr.com/photos/antti-juhani/
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe 

From antti-juhani at kaijanaho.fi  Mon Jun 23 09:57:58 2008
From: antti-juhani at kaijanaho.fi (Antti-Juhani Kaijanaho)
Date: Mon Jun 23 09:49:34 2008
Subject: GSoC project blogs? (Re: [Haskell-cafe] Planet haskell)
In-Reply-To: <00c901c8d536$b5fac540$ea038351@cr3lt>
References: <10ed1a750806222251s6a276fd4ha6a5f77195fd663c@mail.gmail.com>
	<20080623080849.GE4901@kukkaseppele.kaijanaho.fi>
	<00c901c8d536$b5fac540$ea038351@cr3lt>
Message-ID: <20080623135757.GF4901@kukkaseppele.kaijanaho.fi>

(I'd rather people did not send me copies of list posts.)

On Mon, Jun 23, 2008 at 02:40:27PM +0100, Claus Reinke wrote:
> It would be nice to have blogs for all Haskell GSoC projects
> on Planet Haskell.

Any such blogs would certainly qualify.  Authors should read
http://planet.haskell.org/policy.html - and while our alias address is
out of commission, send addition requests to me or Don Stewart.

-- 
Antti-Juhani Kaijanaho, Jyv?skyl?, Finland
http://antti-juhani.kaijanaho.fi/newblog/
http://www.flickr.com/photos/antti-juhani/
From jonathanccast at fastmail.fm  Mon Jun 23 10:06:29 2008
From: jonathanccast at fastmail.fm (Jonathan Cast)
Date: Mon Jun 23 09:58:05 2008
Subject: Re[Haskell-cafe] [2]: Help with generalizing function
In-Reply-To: <18066860.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
	<e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
	<1316971110.20080623134530@gmail.com> <18066860.post@talk.nabble.com>
Message-ID: <1214229989.6302.7.camel@jonathans-macbook>

On Mon, 2008-06-23 at 04:03 -0700, leledumbo wrote:
> >> Don't give up so fast !! (Note that you can't do what you asked for in
> >> Pascal either, in fact Pascal don't support n-uplet) 
> I'm not going to use n-uplet, dynamic array of array of Byte is enough.
> Though not very optimizing, I can use 2 step process:

> 1. Generate all lists (array of Byte) of length N which each element ranges
> from 0 to C.

Come now, you really think this is harder in Haskell than in Pascal?
Understanding Haskell takes a little work, granted, but then I always
thought the same was true of Pascal...

> 2. Filter which has sum=C.

Come now.  Try your browser's search engine on the standard prelude,
word by word.  You can't really expect this to be just given to you, but
you must realise that sometimes it is...

> 
> >> seems that leledumbo found a new way to force us give the answers to
> >> those homeworks LOL
> Don't worry, I'm not gonna use it because it has to be done in procedural
> way (I haven't taken Functional Programming class yet). The reason why I ask
> is I'm HOPING that if I can understand how it works, implementing the
> procedural form would be easy. I've read somewhere that functional language
> can be implemented in procedural one. In fact, GHC outputs C code.
> 
> Thanks for the answer. I'll use it to learn, it's quite difficult to switch
> from procedural to functional. I mean, in procedural it's easy to find the
> fastest solution using brute force.

Huh?  The brute force solution is usually the /slowest/ solution, even
in imperative languages.  Consider bubble sort (bogo sort if you want to
push it) vs. quick sort.

>  This can't be done in functional.

If you mean `find a brute-force solution quickly', getting to the brute
force solution is indeed usually /faster/ in a functional language (it's
usually shorter, too), because of the higher level of abstraction.  (The
same is true for other modern languages, such as Perl, Ruby, to a
certain extent Python, and soon enough (hopefully) PHP, but then it's
questionable in what way the languages (as opposed to their programming
cultures) fail to be functional in the first place).

jcc



From Malcolm.Wallace at cs.york.ac.uk  Mon Jun 23 11:10:16 2008
From: Malcolm.Wallace at cs.york.ac.uk (Malcolm Wallace)
Date: Mon Jun 23 11:06:36 2008
Subject: GSoC project blogs? (Re: [Haskell-cafe] Planet haskell)
In-Reply-To: <00c901c8d536$b5fac540$ea038351@cr3lt>
References: <10ed1a750806222251s6a276fd4ha6a5f77195fd663c@mail.gmail.com>
	<20080623080849.GE4901@kukkaseppele.kaijanaho.fi>
	<00c901c8d536$b5fac540$ea038351@cr3lt>
Message-ID: <20080623161016.5dec64a8.Malcolm.Wallace@cs.york.ac.uk>

> It would be nice to have blogs for all Haskell GSoC projects
> on Planet Haskell.

See also
    http://hackage.haskell.org/trac/summer-of-code/wiki/progress2008

Regards,
    Malcolm
From stephen at enterity.com  Mon Jun 23 11:16:10 2008
From: stephen at enterity.com (Stephen Howard)
Date: Mon Jun 23 11:07:01 2008
Subject: [Haskell-cafe] expected vs inferred type confusion
Message-ID: <485FBE3A.70806@enterity.com>

I am having issues with type signatures for the resourceHandler action 
below.  I haven't figured out what I'm doing wrong to cause the wrong 
type to be returned.  It looks like Haskell is inferring that I'm 
returning a function from this action, when from the type signature I've 
specified, that is not what I'm wanting.  The gist of the code is based 
on the request_method of the passed in HttpRequest, choose an action to 
run and pass it the needed parameters.

the error:

renao.hs:6:4:
    Couldn't match `HttpResponse' against `IO HttpResponse'
      Expected type: IO HttpResponse
      Inferred type: IO (IO HttpResponse)
    In the expression: return $ (handler session request)
    In the result of a 'do' expression: return $ (handler session request)

the code:

import HttpMessage
import HttpSession

resourceHandler :: HttpSession -> HttpRequest -> IO HttpResponse
resourceHandler session request = do
    return $ handler session request
    where
        handler = which_handler request
        which_handler r = case request_method r of
            Get    -> get_resources
            Head   -> last_modified
            Post   -> update_resources
            Put    -> create_resources
            Delete -> delete_resources


get_resources :: HttpSession -> HttpRequest -> IO HttpResponse
get_resources session request = undefined

-- ... the same stubbed definition for the other handlers 
(last_modified, etc)
From Alistair.Bayley at invesco.com  Mon Jun 23 11:19:04 2008
From: Alistair.Bayley at invesco.com (Bayley, Alistair)
Date: Mon Jun 23 11:10:43 2008
Subject: [Haskell-cafe] expected vs inferred type confusion
In-Reply-To: <485FBE3A.70806@enterity.com>
References: <485FBE3A.70806@enterity.com>
Message-ID: <125EACD0CAE4D24ABDB4D148C4593DA9049E9432@GBLONXMB02.corp.amvescap.net>

> From: haskell-cafe-bounces@haskell.org 
> [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Stephen Howard
> 
> the error:
> 
> renao.hs:6:4:
>     Couldn't match `HttpResponse' against `IO HttpResponse'
>       Expected type: IO HttpResponse
>       Inferred type: IO (IO HttpResponse)
>     In the expression: return $ (handler session request)
>     In the result of a 'do' expression: return $ (handler 
> session request)
> 
> the code:
> 
> import HttpMessage
> import HttpSession
> 
> resourceHandler :: HttpSession -> HttpRequest -> IO HttpResponse
> resourceHandler session request = do
>     return $ handler session request
>     where
>         handler = which_handler request
>         which_handler r = case request_method r of
>             Get    -> get_resources
>             Head   -> last_modified
>             Post   -> update_resources
>             Put    -> create_resources
>             Delete -> delete_resources
> 
> 
> get_resources :: HttpSession -> HttpRequest -> IO HttpResponse
> get_resources session request = undefined
> 
> -- ... the same stubbed definition for the other handlers 
> (last_modified, etc)


Try removing the do ... return $  e.g.

> resourceHandler session request =
>     handler session request
>     where

Alistair
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From lemming at henning-thielemann.de  Mon Jun 23 11:22:10 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Mon Jun 23 11:13:47 2008
Subject: [Haskell-cafe] What is a rigid type variable?
In-Reply-To: <87ej6ojn00.fsf@columbia.edu>
References: <87r6aokf0d.fsf@columbia.edu>
	<7ca3f0160806222258t1e08397etb6a98d8566665c0e@mail.gmail.com>
	<7ca3f0160806222302i3bf31925ke5c23dc4cbe0f3b9@mail.gmail.com>
	<87ej6ojn00.fsf@columbia.edu>
Message-ID: <Pine.LNX.4.64.0806231721160.6173@anubis.informatik.uni-halle.de>


On Mon, 23 Jun 2008, Xiao-Yong Jin wrote:

> Thanks for the explanation.  I guess it's just easier for me
> not to give any type signature to `go', since ghc should do
> the type inference quite nicely and reliably.

If you want to stay Haskell98 'asTypeOf' can help you in similar cases.
From darrinth at gmail.com  Mon Jun 23 12:16:43 2008
From: darrinth at gmail.com (Darrin Thompson)
Date: Mon Jun 23 12:08:18 2008
Subject: [Haskell-cafe] Literal programming in Haskell with rst-literals
In-Reply-To: <3c4d5adf0806230420w56198d39n4027f00341f90b17@mail.gmail.com>
References: <20080621181854.184193C8002@banane.furius.ca>
	<3c4d5adf0806230420w56198d39n4027f00341f90b17@mail.gmail.com>
Message-ID: <a2e649c70806230916s2d227383if8c0fc790e4a306@mail.gmail.com>

2008/6/23 Abhay Parvate <abhay.parvate@gmail.com>:
> Hello,
>
> You might already know this, but in case you don't: there is another
> literate style:
>

I had trouble finding the docs on this, as I expected them to be in
the ghc user guide. For the record, the relevant docs are in the h98
report:

http://www.haskell.org/onlinereport/literate.html

And the wiki:

http://www.haskell.org/haskellwiki/Literate_programming

--
Darrin
From anton.tayanovskyy at gmail.com  Mon Jun 23 12:17:01 2008
From: anton.tayanovskyy at gmail.com (Anton Tayanovskyy)
Date: Mon Jun 23 12:08:37 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
In-Reply-To: <6a7c66fc0806230126w6886a427j50265ad60389b0f3@mail.gmail.com>
References: <OF9A1B2713.7561B55B-ONC125746E.004183E0-C125746E.004207DE@sagem.com>
	<6a7c66fc0806230126w6886a427j50265ad60389b0f3@mail.gmail.com>
Message-ID: <ab7bd6010806230917g26b0609ar284c8303504c1aea@mail.gmail.com>

Alfonso,

Thanks! For didactic purposes I will defer looking into your code. It
does not always help to know the correct solution :)


Bests,

--A

On Mon, Jun 23, 2008 at 11:26 AM, Alfonso Acosta
<alfonso.acosta@gmail.com> wrote:
> Inspired in Oleg's ideas, I implemented the packages type-level and
> parameterized-data (which includes number-parameterized vectors).
>
>
> To get an idea about how they work you might want to read their
> haddock documentation in hackage:
>
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parameterized-data
>
> You can get their darcs repositories (including some minor updates) from:
>
> darcs get http://code.haskell.org/type-level
> darcs get http://code.haskell.org/parameterized-data
>
> On Fri, Jun 20, 2008 at 8:01 AM, Harald ROTTER <harald.rotter@sagem.com> wrote:
>>
>> Dear Haskellers,
>>
>> after reading Oleg Kiselyov's paper on number-parameterized types I started
>> to play around with
>> the class Digits that encodes decimal numbers in types. The "typed number"
>> 10 would e.g. be defined as
>>
>>      D1 $ D0 $ Sz
>>
>> I wondered if it would be possible replace the expression above by a
>> heterogeneous list like
>>
>>      [D1,D0]
>>
>> so I tried to define
>>
>>      data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
>>
>> Loading this into ghci yields:
>>
>> :t Digit D0
>>
>> <interactive>:1:0:
>>    Ambiguous type variable `a' in the constraint:
>>      `Digits a' arising from a use of `Digit' at <interactive>:1:0-7
>>    Probable fix: add a type signature that fixes these type variable(s)
>>
>> Removing the type constraints in the definition of "Digit":
>>
>>      data Digit = forall a b.Digit (a -> b a)
>>
>> makes it work like this:
>>
>>      :t Digit D0
>>      Digit D0 :: Digit
>>
>>      :t [Digit D0, Digit D1]
>>      [Digit D0, Digit D1] :: [Digit]
>>
>> "Digit", however, is far too general (it also includes e.g. \x -> [x]), but
>> I would like it to be restricted to the Digit class.
>>
>> Any help is appreciated.
>>
>> Thanks
>>
>> Harald.
>>
>>
>> CODE:
>>
>> module Test where
>>
>> data D0 a = D0 a
>> data D1 a = D1 a
>> data D2 a = D2 a
>> data D3 a = D3 a
>> data D4 a = D4 a
>> data D5 a = D5 a
>> data D6 a = D6 a
>> data D7 a = D7 a
>> data D8 a = D8 a
>> data D9 a = D9 a
>>
>> class Digits ds where
>>    d2num :: Num a => ds -> a -> a
>>
>> data Sz = Sz    -- zero size
>> instance Digits Sz where
>>    d2num _ acc = acc
>>
>> instance Digits ds => Digits (D0 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc)
>> instance Digits ds => Digits (D1 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+1)
>> instance Digits ds => Digits (D2 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+2)
>> instance Digits ds => Digits (D3 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+3)
>> instance Digits ds => Digits (D4 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+4)
>> instance Digits ds => Digits (D5 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+5)
>> instance Digits ds => Digits (D6 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+6)
>> instance Digits ds => Digits (D7 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+7)
>> instance Digits ds => Digits (D8 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+8)
>> instance Digits ds => Digits (D9 ds) where
>>    d2num dds acc = d2num (t22 dds) (10*acc+9)
>>
>> t22 :: f x -> x
>> t22 = undefined
>>
>> --data Digit = forall a b.(Digits a, Digits (b a)) => Digit (a -> b a)
>> data Digit = forall a b.Digit (a -> b a)
>>
>> -------------------------------------------------------------------------------------------------
>>
>>
>>
>> " Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes  pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel  ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite."
>>
>> " This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."
>> _______________________________________________
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>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From agl at imperialviolet.org  Mon Jun 23 13:07:25 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Mon Jun 23 12:59:01 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
Message-ID: <396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>

2008/6/23 Galchin, Vasili <vigalchin@gmail.com>:
> Basically I want to model POSIX async io "aiocb"(
> http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in
> particular the aiocb field "aio_buf"!

That's a mutable buffer, so this has to be pretty low level in your
wrapping of the AIO interface. I would keep it as a Ptr Word8 at that
point. ByteStrings are probably the correct type for the user visible
interface, but I would guess not here.

Plus, ByteString data lives in the Haskell heap so could get moved
about by the collector. Since an AIO interface is probably going to
return while the IO is still in progress, you don't want to stop the
collector, but nor do you want the data moving because the kernel's
pointer isn't going to move with it.

AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From agl at imperialviolet.org  Mon Jun 23 13:09:50 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Mon Jun 23 13:01:50 2008
Subject: [Haskell-cafe] IMAP and NNTP libraries
In-Reply-To: <g3kpb2$22c$1@ger.gmane.org>
References: <g3kpb2$22c$1@ger.gmane.org>
Message-ID: <396556a20806231009k3d3352d4yebe4883168357d60@mail.gmail.com>

On Sat, Jun 21, 2008 at 10:52 PM, Maur??cio <briqueabraque@yahoo.com> wrote:
> Are there mature libraries for IMAP and NNTP
> available to Haskell?

Pretty much, if a Haskell library exist it will be listed at [1].
Since I don't see anything for IMAP, nor NNTP I can be pretty sure
that the answer is "no" I'm afraid. Perhaps you would care to write
such libraries if you have a need?


[1] http://hackage.haskell.org/packages/archive/pkg-list.html

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From vigalchin at gmail.com  Mon Jun 23 16:15:42 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun 23 16:07:17 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
Message-ID: <5ae4f2ba0806231315h6406e004tcccc092a5088d059@mail.gmail.com>

On Mon, Jun 23, 2008 at 12:07 PM, Adam Langley <agl@imperialviolet.org>
wrote:

> 2008/6/23 Galchin, Vasili <vigalchin@gmail.com>:
> > Basically I want to model POSIX async io "aiocb"(
> > http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in
> > particular the aiocb field "aio_buf"!
>
> That's a mutable buffer, so this has to be pretty low level in your
> wrapping of the AIO interface. I would keep it as a Ptr Word8 at that
> point. ByteStrings are probably the correct type for the user visible
> interface, but I would guess not here.

     I tried to write a test value of Word8 without success. Can you give an
example?

>
>
> Plus, ByteString data lives in the Haskell heap so could get moved
> about by the collector. Since an AIO interface is probably going to
> return while the IO is still in progress, you don't want to stop the
> collector, but nor do you want the data moving because the kernel's
> pointer isn't going to move with it.

       ^^ Interesting about moving around in the heap. I cannot use it for
AIO.

>
>
> AGL
>
> --
> Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
>
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From sjanssen at cse.unl.edu  Mon Jun 23 16:26:12 2008
From: sjanssen at cse.unl.edu (Spencer Janssen)
Date: Mon Jun 23 16:17:55 2008
Subject: [Haskell-cafe] IMAP and NNTP libraries
In-Reply-To: <g3kpb2$22c$1@ger.gmane.org>
References: <g3kpb2$22c$1@ger.gmane.org>
Message-ID: <20080623202612.GA29551@celeborn>

On Sun, Jun 22, 2008 at 02:52:33AM -0300, Maur??cio wrote:
> Hi,
>
> Are there mature libraries for IMAP and NNTP
> available to Haskell?
>
> Thanks,
> Maur?cio

There is the haskellnet project:

    http://darcs.haskell.org/SoC/haskellnet/

I'm not sure whether it is mature or maintained.


Cheers,
Spencer Janssen
From agl at imperialviolet.org  Mon Jun 23 17:00:34 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Mon Jun 23 16:52:09 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <5ae4f2ba0806231315h6406e004tcccc092a5088d059@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
	<5ae4f2ba0806231315h6406e004tcccc092a5088d059@mail.gmail.com>
Message-ID: <396556a20806231400q6a2cd3b6t4935ebd17c9b447b@mail.gmail.com>

On Mon, Jun 23, 2008 at 1:15 PM, Galchin, Vasili <vigalchin@gmail.com> wrote:
>      I tried to write a test value of Word8 without success. Can you give an example?

I'm not quite sure what you would want in such an example. See [1] for
the malloc function. Then you take the result and wrap it with [2]:
 fp <- mallocBytes nbytes >>= newForeignPtr finalizerFree

When you want to use it, use [3] to unwrap fp and get a raw Ptr Word8.
You can pass these to foreign functions any place they expect a
uint8_t *, char * etc.


[1] http://www.haskell.org/hoogle/hoodoc.cgi?module=Foreign.Marshal.Alloc&name=mallocBytes&mode=func
[2] http://www.haskell.org/hoogle/hoodoc.cgi?module=Foreign.ForeignPtr&name=newForeignPtr&mode=func
[3] http://www.haskell.org/hoogle/hoodoc.cgi?module=Foreign.ForeignPtr&name=withForeignPtr&mode=func

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From chris at eidhof.nl  Mon Jun 23 17:02:20 2008
From: chris at eidhof.nl (Chris Eidhof)
Date: Mon Jun 23 16:53:56 2008
Subject: [Haskell-cafe] IMAP and NNTP libraries
In-Reply-To: <20080623202612.GA29551@celeborn>
References: <g3kpb2$22c$1@ger.gmane.org> <20080623202612.GA29551@celeborn>
Message-ID: <950583A7-37B3-411E-BCF8-2330F67C3339@eidhof.nl>

On 23 jun 2008, at 22:26, Spencer Janssen wrote:

> On Sun, Jun 22, 2008 at 02:52:33AM -0300, Maur? cio wrote:
>> Hi,
>>
>> Are there mature libraries for IMAP and NNTP
>> available to Haskell?
>>
>> Thanks,
>> Maur?cio
>
> There is the haskellnet project:
>
>    http://darcs.haskell.org/SoC/haskellnet/
>
> I'm not sure whether it is mature or maintained.
I don't think it's maintained or mature: last time I checked, I  
couldn't get it to work (probably due to library changes), and there  
is not a lot of documentation nor comments.

I was actually thinking of writing a binding myself, to libEtPan!,  
which seems to have a well-documented and clean interface. I'm not  
sure how hard this is though. I've also looked a bit at the UW c- 
client, but I haven't seen any good examples of how to use it.

-chris
From dons at galois.com  Mon Jun 23 17:27:03 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun 23 17:18:43 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
Message-ID: <20080623212703.GE10144@scytale.galois.com>

agl:
> 2008/6/23 Galchin, Vasili <vigalchin@gmail.com>:
> > Basically I want to model POSIX async io "aiocb"(
> > http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in
> > particular the aiocb field "aio_buf"!
> 
> That's a mutable buffer, so this has to be pretty low level in your
> wrapping of the AIO interface. I would keep it as a Ptr Word8 at that
> point. ByteStrings are probably the correct type for the user visible
> interface, but I would guess not here.
> 
> Plus, ByteString data lives in the Haskell heap so could get moved
> about by the collector. Since an AIO interface is probably going to

ByteStrings are allocated into pinned memory, so they're easy to pass to
C and back. It uses the fast 'mallocPlainForeignPtr' api,

    -- GHC notes: 'mallocPlainForeignPtr' has a heavily optimised
    -- implementation in GHC.  It uses pinned memory in the garbage
    -- collected heap, as for mallocForeignPtr. 

So heap allocated and collected, but not moved.

> return while the IO is still in progress, you don't want to stop the
> collector, but nor do you want the data moving because the kernel's
> pointer isn't going to move with it.

-- Don
From dons at galois.com  Mon Jun 23 17:35:13 2008
From: dons at galois.com (Don Stewart)
Date: Mon Jun 23 17:26:48 2008
Subject: [Haskell-cafe] IMAP and NNTP libraries
In-Reply-To: <396556a20806231009k3d3352d4yebe4883168357d60@mail.gmail.com>
References: <g3kpb2$22c$1@ger.gmane.org>
	<396556a20806231009k3d3352d4yebe4883168357d60@mail.gmail.com>
Message-ID: <20080623213513.GF10144@scytale.galois.com>

agl:
> On Sat, Jun 21, 2008 at 10:52 PM, Maur??cio <briqueabraque@yahoo.com> wrote:
> > Are there mature libraries for IMAP and NNTP
> > available to Haskell?
> 
> Pretty much, if a Haskell library exist it will be listed at [1].
> Since I don't see anything for IMAP, nor NNTP I can be pretty sure
> that the answer is "no" I'm afraid. Perhaps you would care to write
> such libraries if you have a need?
> 
> 
> [1] http://hackage.haskell.org/packages/archive/pkg-list.html

Or FFI bind to some existing library. cabal-install will take care of
the rest.
From jgoerzen at complete.org  Mon Jun 23 17:43:31 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Mon Jun 23 17:35:09 2008
Subject: [Haskell-cafe] IMAP and NNTP libraries
In-Reply-To: <396556a20806231009k3d3352d4yebe4883168357d60@mail.gmail.com>
References: <g3kpb2$22c$1@ger.gmane.org>
	<396556a20806231009k3d3352d4yebe4883168357d60@mail.gmail.com>
Message-ID: <48601903.6020600@complete.org>

Adam Langley wrote:
> On Sat, Jun 21, 2008 at 10:52 PM, Maur??cio <briqueabraque@yahoo.com> wrote:
>> Are there mature libraries for IMAP and NNTP
>> available to Haskell?
> 
> Pretty much, if a Haskell library exist it will be listed at [1].
> Since I don't see anything for IMAP, nor NNTP I can be pretty sure
> that the answer is "no" I'm afraid. Perhaps you would care to write
> such libraries if you have a need?

I'm aware of neither.  NNTP is a pretty trivial protocol, and should be
trivial to implement.

IMAP is more complex.  I may write such a library someday, if I ever
port OfflineIMAP to Haskell, but it will not be real soon now by any means.

From ryani.spam at gmail.com  Mon Jun 23 18:21:28 2008
From: ryani.spam at gmail.com (Ryan Ingram)
Date: Mon Jun 23 18:13:04 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
In-Reply-To: <7ca3f0160806230105h56fa14b7g1acc3201be6f06f8@mail.gmail.com>
References: <OF14B1FE9C.D4AC6BAA-ONC1257471.0024B113-C1257471.002596A0@sagem.com>
	<7ca3f0160806230105h56fa14b7g1acc3201be6f06f8@mail.gmail.com>
Message-ID: <2f9b2d30806231521m7eb2f92fp25dd8b7ce18098b4@mail.gmail.com>

Literate haskell response:
> {-# LANGUAGE GADTs, RankNTypes #-}
> module Digits where
> {-

On 6/23/08, Luke Palmer <lrpalmer@gmail.com> wrote:

> > I also wonder if there is some kind of "generalized" foldr such that, e.g.
> >      D1 $ D0 $ D0 $ Sz = specialFoldr ($) Sz [D1,D0,D0]
> > I think that this foldr must be some "special" foldr that augments the data
> > type of the result in each foldr step.
> > Would this be possible or am I just chasing phantoms ?

> Mostly I believe you are.  What you are describing is firmly in the
> realm of dependent types, far beyond Haskell's type system. See
> Epigram or Agda for languages which have attempted to tackle this
> problem.

> -}

I'm not so sure, as long as you are willing to live with the result
being existentially quantified.  Here's an example:
ghci> mkNat [x1, x0, x3, x2]
(reifyInt 1032)
ghci> :t mkNat [x1, x0, x3, x2]
mkNat [x1, x0, x3, x2] :: AnyNat

I slightly specialize the constructors to wrap them in existential types:
d0 = AnyNat . D0  -- and so on for d1..d9
x0 = NatFn d0 -- and so on for x1..x9


Full code:

> data Sz = Sz
> data D0 a = D0 a
> data D1 a = D1 a
> data D2 a = D2 a
> data D3 a = D3 a
> data D4 a = D4 a
> data D5 a = D5 a
> data D6 a = D6 a
> data D7 a = D7 a
> data D8 a = D8 a
> data D9 a = D9 a

> class Nat n where
>    toIntAccum :: n -> Integer -> Integer

> toInt :: Nat n => n -> Integer
> toInt n = toIntAccum n 0

> instance Nat Sz where toIntAccum _ acc = acc

> instance Nat a => Nat (D0 a) where
>     toIntAccum (D0 n) acc = toIntAccum n (10 * acc + 0)
> instance Nat a => Nat (D1 a) where
>     toIntAccum (D1 n) acc = toIntAccum n (10 * acc + 1)
> instance Nat a => Nat (D2 a) where
>     toIntAccum (D2 n) acc = toIntAccum n (10 * acc + 2)
> instance Nat a => Nat (D3 a) where
>     toIntAccum (D3 n) acc = toIntAccum n (10 * acc + 3)
> instance Nat a => Nat (D4 a) where
>     toIntAccum (D4 n) acc = toIntAccum n (10 * acc + 4)
> instance Nat a => Nat (D5 a) where
>     toIntAccum (D5 n) acc = toIntAccum n (10 * acc + 5)
> instance Nat a => Nat (D6 a) where
>     toIntAccum (D6 n) acc = toIntAccum n (10 * acc + 6)
> instance Nat a => Nat (D7 a) where
>     toIntAccum (D7 n) acc = toIntAccum n (10 * acc + 7)
> instance Nat a => Nat (D8 a) where
>     toIntAccum (D8 n) acc = toIntAccum n (10 * acc + 8)
> instance Nat a => Nat (D9 a) where
>     toIntAccum (D9 n) acc = toIntAccum n (10 * acc + 9)

> data AnyNat where AnyNat :: Nat n => n -> AnyNat

> d0, d1, d2, d3, d4, d5, d6, d7, d8, d9 :: Nat n => n -> AnyNat
> d0 = AnyNat . D0
> d1 = AnyNat . D1
> d2 = AnyNat . D2
> d3 = AnyNat . D3
> d4 = AnyNat . D4
> d5 = AnyNat . D5
> d6 = AnyNat . D6
> d7 = AnyNat . D7
> d8 = AnyNat . D8
> d9 = AnyNat . D9

> reifyDigit :: Integer -> (forall n. Nat n => n -> AnyNat)
> reifyDigit 0 = d0
> reifyDigit 1 = d1
> reifyDigit 2 = d2
> reifyDigit 3 = d3
> reifyDigit 4 = d4
> reifyDigit 5 = d5
> reifyDigit 6 = d6
> reifyDigit 7 = d7
> reifyDigit 8 = d8
> reifyDigit 9 = d9
> reifyDigit _ = error "not a digit"

> reifyIntAccum :: Integer -> AnyNat -> AnyNat
> reifyIntAccum 0 acc          = acc
> reifyIntAccum n (AnyNat rhs) = let (l, r) = divMod n 10 in
>                                reifyIntAccum l (reifyDigit r rhs)

> reifyInt :: Integer -> AnyNat
> reifyInt n | n < 0  = error "negative"
> reifyInt n          = reifyIntAccum n (AnyNat Sz)

> instance Show AnyNat where
>     show (AnyNat n) = "(reifyInt " ++ show (toInt n) ++ ")"

> data NatFn where NatFn :: (forall n. Nat n => n -> AnyNat) -> NatFn

> x0, x1, x2, x3, x4, x5, x6, x7, x8, x9 :: NatFn
> x0 = NatFn d0
> x1 = NatFn d1
> x2 = NatFn d2
> x3 = NatFn d3
> x4 = NatFn d4
> x5 = NatFn d5
> x6 = NatFn d6
> x7 = NatFn d7
> x8 = NatFn d8
> x9 = NatFn d9

> foldNat :: [NatFn] -> AnyNat -> AnyNat
> foldNat []           z = z
> foldNat (NatFn f:xs) z = case foldNat xs z of AnyNat n -> f n

> mkNat :: [NatFn] -> AnyNat
> mkNat xs = foldNat xs (AnyNat Sz)

  -- ryan
From agl at imperialviolet.org  Mon Jun 23 19:13:15 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Mon Jun 23 19:04:49 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <20080623212703.GE10144@scytale.galois.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
	<20080623212703.GE10144@scytale.galois.com>
Message-ID: <396556a20806231613x483aa2e1ree26d5690b558854@mail.gmail.com>

On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart <dons@galois.com> wrote:
> So heap allocated and collected, but not moved.

My bad. In that case, you might want to work with ByteStrings all the
way since it might make building the visible interface (which probably
should use ByteStrings) easier.


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From ok at cs.otago.ac.nz  Mon Jun 23 19:46:25 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Mon Jun 23 19:38:02 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <18063291.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
Message-ID: <7DE61A0C-B403-42C5-A1CC-2A0D53F1CFA3@cs.otago.ac.nz>


On 23 Jun 2008, at 6:30 pm, leledumbo wrote:
> I've successfully create a function to return lists of N-ple that  
> satisfy the
> following function:
> x1 + x2 + x3 + ... + xN = C
> But unfortunately, it's not generic.

Why do you want it to be a tuple?  All the elements are the same type,  
so it
might as well be a list.

	part 0 c | c == 0 = [[]]
         part (n+1) c | c >= 0 = [(x:xs) | x <- [0..c],
                                           xs <- part n (c-x)]

(WARNING: UNTESTED CODE!)
Knuth TAOCP Volume 4 has some stuff on enumerating partitions.

From vigalchin at gmail.com  Mon Jun 23 21:13:39 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun 23 21:05:12 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <396556a20806231613x483aa2e1ree26d5690b558854@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
	<20080623212703.GE10144@scytale.galois.com>
	<396556a20806231613x483aa2e1ree26d5690b558854@mail.gmail.com>
Message-ID: <5ae4f2ba0806231813w227992bdub3a0cc5af11e5b50@mail.gmail.com>

ok .....

1) how do I marshall from ByteString to char * (poke)??

2) how do I write

         let x =??? :: Word8

3) how do I write

         let y = ??? ::ByteString

Kind regards, Vasili


On Mon, Jun 23, 2008 at 6:13 PM, Adam Langley <agl@imperialviolet.org>
wrote:

> On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart <dons@galois.com> wrote:
> > So heap allocated and collected, but not moved.
>
> My bad. In that case, you might want to work with ByteStrings all the
> way since it might make building the visible interface (which probably
> should use ByteStrings) easier.
>
>
> AGL
>
> --
> Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
>
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From vigalchin at gmail.com  Mon Jun 23 21:18:23 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Mon Jun 23 21:09:58 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <5ae4f2ba0806231813w227992bdub3a0cc5af11e5b50@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
	<20080623212703.GE10144@scytale.galois.com>
	<396556a20806231613x483aa2e1ree26d5690b558854@mail.gmail.com>
	<5ae4f2ba0806231813w227992bdub3a0cc5af11e5b50@mail.gmail.com>
Message-ID: <5ae4f2ba0806231818p4ef26615q3c6724c20d7a4011@mail.gmail.com>

e.g. on Word8 .....

         let aiocb = AIOCB{
                       aioFd=fd,
                       aioLioOpcode=0,
                       aioReqPrio=0,
                       aioOffset=0,
                       aioBuf=??,        <<<<<<<<<<<<<<<<<<<<<   Ptr Word8
                       aioBytes=128,
                       aioSigevent=event}

???

Kind regards, Vasili

On Mon, Jun 23, 2008 at 8:13 PM, Galchin, Vasili <vigalchin@gmail.com>
wrote:

> ok .....
>
> 1) how do I marshall from ByteString to char * (poke)??
>
> 2) how do I write
>
>          let x =??? :: Word8
>
> 3) how do I write
>
>          let y = ??? ::ByteString
>
> Kind regards, Vasili
>
>
>
> On Mon, Jun 23, 2008 at 6:13 PM, Adam Langley <agl@imperialviolet.org>
> wrote:
>
>> On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart <dons@galois.com> wrote:
>> > So heap allocated and collected, but not moved.
>>
>> My bad. In that case, you might want to work with ByteStrings all the
>> way since it might make building the visible interface (which probably
>> should use ByteStrings) easier.
>>
>>
>> AGL
>>
>> --
>> Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
>>
>
>
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From droundy at darcs.net  Mon Jun 23 21:32:57 2008
From: droundy at darcs.net (David Roundy)
Date: Mon Jun 23 21:24:31 2008
Subject: [Haskell-cafe] Re: "C" buffer suggestions??
In-Reply-To: <5ae4f2ba0806231818p4ef26615q3c6724c20d7a4011@mail.gmail.com>
References: <5ae4f2ba0806212347r56df45fdu962fccc1bd532ac9@mail.gmail.com>
	<5ae4f2ba0806230210m6453be5aqfbeaecf342291291@mail.gmail.com>
	<396556a20806231007j3c1446dev1f1c83c887c32e08@mail.gmail.com>
	<20080623212703.GE10144@scytale.galois.com>
	<396556a20806231613x483aa2e1ree26d5690b558854@mail.gmail.com>
	<5ae4f2ba0806231813w227992bdub3a0cc5af11e5b50@mail.gmail.com>
	<5ae4f2ba0806231818p4ef26615q3c6724c20d7a4011@mail.gmail.com>
Message-ID: <20080624013256.GG32397@darcs.net>

See the Data.ByteString.Internal docs:

http://www.haskell.org/ghc/docs/latest/html/libraries/bytestring/Data-ByteString-Internal.html#v%3AtoForeignPtr

Of course, you'd better not write to the contents of that pointer, or
bad things could happen...

David

On Mon, Jun 23, 2008 at 08:18:23PM -0500, Galchin, Vasili wrote:
> e.g. on Word8 .....
> 
>          let aiocb = AIOCB{
>                        aioFd=fd,
>                        aioLioOpcode=0,
>                        aioReqPrio=0,
>                        aioOffset=0,
>                        aioBuf=??,        <<<<<<<<<<<<<<<<<<<<<   Ptr Word8
>                        aioBytes=128,
>                        aioSigevent=event}
> 
> ???
> 
> Kind regards, Vasili
> 
> On Mon, Jun 23, 2008 at 8:13 PM, Galchin, Vasili <vigalchin@gmail.com>
> wrote:
> 
> > ok .....
> >
> > 1) how do I marshall from ByteString to char * (poke)??
> >
> > 2) how do I write
> >
> >          let x =??? :: Word8
> >
> > 3) how do I write
> >
> >          let y = ??? ::ByteString
> >
> > Kind regards, Vasili
> >
> >
> >
> > On Mon, Jun 23, 2008 at 6:13 PM, Adam Langley <agl@imperialviolet.org>
> > wrote:
> >
> >> On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart <dons@galois.com> wrote:
> >> > So heap allocated and collected, but not moved.
> >>
> >> My bad. In that case, you might want to work with ByteStrings all the
> >> way since it might make building the visible interface (which probably
> >> should use ByteStrings) easier.
> >>
> >>
> >> AGL
From oleg at okmij.org  Tue Jun 24 01:03:43 2008
From: oleg at okmij.org (oleg@okmij.org)
Date: Tue Jun 24 00:57:39 2008
Subject: [Haskell-cafe] Re: number-parameterized types and heterogeneous
	lists
In-Reply-To: <OF14B1FE9C.D4AC6BAA-ONC1257471.0024B113-C1257471.002596A0%40sagem.com>
Message-ID: <20080624050343.A8D6CAA92@Adric.metnet.fnmoc.navy.mil>


Luke Palmer wrote in response to Harald ROTTER
> > I also wonder if there is some kind of "generalized" foldr such that, e.g.
> >      D1 $ D0 $ D0 $ Sz = specialFoldr ($) Sz [D1,D0,D0]
> > I think that this foldr must be some "special" foldr that augments the data
> > type of the result in each foldr step.
> > Would this be possible or am I just chasing phantoms ?

> Mostly I believe you are.  What you are describing is firmly in the
> realm of dependent types, far beyond Haskell's type system. See
> Epigram or Agda for languages which have attempted to tackle this
> problem.

First of all, Haskell (as implemented by released versions of GHC for
at least two years) already permits dependent types, in the
strict sense of a type of an expression being determined by the value
of one argument of that expression:

	http://okmij.org/ftp/Computation/tagless-typed.html#tc-GADT-tc

Second, (values of) types like D0 and D1 can be collected in a
heterogenous list (HList), which does have the corresponding fold
operator, called HFoldr in

	http://darcs.haskell.org/HList/Data/HList/HListPrelude.hs

From vigalchin at gmail.com  Tue Jun 24 01:36:51 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun 24 01:28:24 2008
Subject: [Haskell-cafe] safe vs unsafe
Message-ID: <5ae4f2ba0806232236q2e9b95d5kd1d1eafbf0e12b61@mail.gmail.com>

Hello,

    At runtime, I am getting ....

aio: schedule: re-entered unsafely.
   Perhaps a 'foreign import unsafe' should be 'safe'?

I want to understand from an implementation viewpoint .. deeper. This is a
GC issue yes?

Kind regards, Vasili
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From lemming at henning-thielemann.de  Tue Jun 24 10:17:12 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue Jun 24 10:08:47 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>


On Fri, 20 Jun 2008, Alistair Bayley wrote:

> Another problem is that the Oracle installation process assumes that,
> for all platforms, the library is called oci i.e. the linker option
> -loci is used. For Unix clients, the OCI library seems to be
> libclnstsh.so, so I guess it should pass -lclnstsh. This highlights
> the lack of testing on non-Windows platforms. If you'd like to help
> get this working better, perhaps we can discuss off-list.

(I remain on the list in order to fill the archive with information, 
others may need, too.)

I have now installed the OCI SDK
   http://download.oracle.com/otn/linux/instantclient/10204/oracle-instantclient-devel-10.2.0.4-1.i386.rpm
  and Cabal-1.4 in order to get Takusen from Darcs repository running. I 
configure the package with -f oracle and the package gets compiled (and 
emits several warnings from Haddock-2.0). (Btw. Takusen should be split 
into several packages for all database backends because Cabal flags must 
not influence the package interface.) But on installation Cabal complains 
about missing /usr/oci directory. I assume that this must be the include 
dir of OCI include files. For me this is
   /usr/include/oracle/10.2.0.4/client/
  I can add this path with
     runhaskell Setup.hs configure --extra-include-dirs=/usr/include/oracle/10.2.0.4/client
  but I cannot replace /usr/oci. If I remove /usr/oci manually from 
dist/installed-pkg-config then the path /usr/oci is again added by
     runhaskell Setup.hs install .
  I'm lost. Am I on the right track?

Once I will get Takusen running with OCI - how would I use it? Is there a 
minimal example which connects to an Oracle database, performing a very 
simple query?
From alistair at abayley.org  Tue Jun 24 10:55:09 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Tue Jun 24 10:46:41 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
Message-ID: <79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>

2008/6/24 Henning Thielemann <lemming@henning-thielemann.de>:
>
> (I remain on the list in order to fill the archive with information, others
> may need, too.)

As you wish.


> (Btw. Takusen should be split into
> several packages for all database backends because Cabal flags must not
> influence the package interface.)

I don't understand this (cabal flags must not influence package
interface). I thought that was the point of cabal flags? I wanted to
have a single package installation, and this seems like the best way.


> But on installation Cabal complains about missing /usr/oci directory.

When you run configure, you should get output that says:
Using Oracle: <path>

What is <path>?

The Setup.hs assumes the entire Oracle installation is under a single
root folder ($ORACLE_HOME); is this not true on Linux? If not, then we
will have to find some other way of locating the bin and include
folders. Perhaps we can do something like the Postgres installation,
where there is a program you can run which will print the include and
lib folders. That may mean a little hacking on Setup.hs, but there's
already a good example there for Postgres.


> Once I will get Takusen running with OCI - how would I use it? Is there a
> minimal example which connects to an Oracle database, performing a very
> simple query?

There's an example in the README.txt, which I've tweaked here for Oracle:

{-# OPTIONS -fglasgow-exts #-}
{-# OPTIONS -fallow-overlapping-instances #-}
module Main where
import Database.Oracle.Enumerator
import Control.Monad.Trans (liftIO)
main = flip catchDB reportRethrow $
  withSession (connect "user" "pswd" "dbname") (do
    let iter (s::String) (_::String) = result s
    result <- doQuery (sql "select 'Hello world.' from dual") iter ""
    liftIO (putStrLn result)
    )

Alistair
From agl at imperialviolet.org  Tue Jun 24 13:03:04 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Tue Jun 24 12:54:36 2008
Subject: [Haskell-cafe] safe vs unsafe
In-Reply-To: <5ae4f2ba0806232236q2e9b95d5kd1d1eafbf0e12b61@mail.gmail.com>
References: <5ae4f2ba0806232236q2e9b95d5kd1d1eafbf0e12b61@mail.gmail.com>
Message-ID: <396556a20806241003t5f32194aqd629d2933ba03538@mail.gmail.com>

2008/6/23 Galchin, Vasili <vigalchin@gmail.com>:
> aio: schedule: re-entered unsafely.
>    Perhaps a 'foreign import unsafe' should be 'safe'?
>
> I want to understand from an implementation viewpoint .. deeper. This is a
> GC issue yes?

Are you reentering Haskell on a path which involves an unsafe FFI
call? e.g. you enter C land via an unsafe FFI call and, on the same
call path, reenter Haskell with a callback?

http://www.cse.unsw.edu.au/~chak/haskell/ffi/ffi/ffise3.html#x6-130003.3 says:

"Optionally, an import declaration can specify, after the calling
convention, the safety level that should be used when invoking an
external entity. A safe call is less efficient, but guarantees to
leave the Haskell system in a state that allows callbacks from the
external code. In contrast, an unsafe call, while carrying less
overhead, must not trigger a callback into the Haskell system. If it
does, the system behaviour is undefined. The default for an invocation
is to be safe. Note that a callback into the Haskell system implies
that a garbage collection might be triggered after an external entity
was called, but before this call returns. Consequently, objects other
than stable pointers (cf. Section 5.6) may be moved or garbage
collected by the storage manager."

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From lgreg.meredith at biosimilarity.com  Tue Jun 24 13:18:17 2008
From: lgreg.meredith at biosimilarity.com (Greg Meredith)
Date: Tue Jun 24 13:09:50 2008
Subject: [Haskell-cafe] NW Functional Programming Interest Group
In-Reply-To: <5de3f5ca0802011155l771cc649wa0e671bbe3abe364@mail.gmail.com>
References: <5de3f5ca0802011155l771cc649wa0e671bbe3abe364@mail.gmail.com>
Message-ID: <5de3f5ca0806241018o5b582ebfufcfd4c1b371cdc12@mail.gmail.com>

All,

Apologies for multiple listings.

A small cadre of us, collectively known as the Northwest Functional
Programming
Interest Group, have been meeting monthly to discuss all things functional.
Our next meeting is at

The Seattle Public Library
5009 Roosevelt Way N.E. *
Seattle*, WA 98105
206-684-4063

from 18:30 - 19:50 on June 25th.

We'd hoped to have Andrew Birkett talk on a Haskell implementation of an
emacs-like editor, but sadly could not secure a meeting venue before
Andrew's flight back to the UK. Maybe we can set up a skype session for a
presentation by Andrew in future. Since it's so late in the game i will step
in and offer a presentation on a compositional representation of graphs i've
been tinkering wit<http://biosimilarity.blogspot.com/2008/06/algebra-of-graphs-individually-and.html>h
-- unless someone has something they'd like to talk about at a moment's
notice.

Hope to see you there.

Monadically yours,

--greg

-- 
L.G. Meredith
Managing Partner
Biosimilarity LLC
806 55th St NE
Seattle, WA 98105

+1 206.650.3740

http://biosimilarity.blogspot.com
<http://biosimilarity.blogspot.com>
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From jeremy at n-heptane.com  Tue Jun 24 14:27:03 2008
From: jeremy at n-heptane.com (Jeremy Shaw)
Date: Tue Jun 24 14:16:22 2008
Subject: Haskell on ARM (was Re: [Haskell-cafe] ANN: Topkata)
In-Reply-To: <20080617201233.GD19304@scytale.galois.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
	<87ej6ww9dy.fsf_-_@columbia.edu>
	<20080617201233.GD19304@scytale.galois.com>
Message-ID: <871w2mit8o.wl%jeremy@n-heptane.com>

Hello,

I have, on two occasions made an *unregisterised* of GHC for the ARM
(specifically the Maemo on Nokia 770). Mostly I just followed the
unregisterised porting directions in the GHC user manual.

I documented one attempt here:

http://hackage.haskell.org/trac/ghc/wiki/ArmLinuxGhc

Note: This procedure is for building a version of GHC that runs on ARM
and generates ARM code. So, it is not build a cross-compiler, just a
native ARM compiler.

The unregisterised build is not that useful because:

 1. no FFI
 2. uses trampolining for tail calls
 3. no threads I think
 4. some other stuff I have forgotten

So, the next step is to registerise the build. This is online a few
lines a code. Basically stuff like:

 1. add ARM support to the evil mangler (basically, a few regexps to
 strip prolog and epilogue stuff from the ASM)

 2. #define which registers exist and what they should be used for

 3. implement the tail call ASM

 4. define some aspects of the C calling convention

 5. (Optional), implement native assembly generation

This is not a lot of code. However, it is very low-level code.

I think that doing a registerised build is pretty easy, the *second*
time you do it. The big problem is that there is pretty much no
documentation on how to do it. (The porting guide does tell you, very
generally, what needs to be done).

Also, running GHC on an emulated ARM processor is slow. I think it
took GHC 6.4 8+ hours to build. 

Now that many of the extra libs have been split out into the extra
libs package, that should help significantly with the build time.

If any does attempt to build for the ARM, please, please, please,
document what you do in the wiki. And, if you do, edit the wiki as you
go, you definitely won't be able to remember what you did after the
fact. (Or, at the very least, use some program to capture everything
you do so that you can refer to it later).

And, finally, I heard vague rumors a while ago that made me think that
GHC 6.10 might have a pure ANSI-C backend? Is there any truth to this?
That would make porting much easier if it meant you did not have to do
steps 1-4.

j.  

ps. I would be happy to try to answer any questions if someone tries a
port. I would still like to run GHC on my 770, and I hope to own an
iPhone if they fix a few ommisions (bluetooth keyboard support, and
similar stuff).

At Tue, 17 Jun 2008 13:12:33 -0700,
Don Stewart wrote:
> 
> xj2106:
> > "Ariel J. Birnbaum" <valgarv@gmx.net> writes:
> > 
> > >> In the mean time -- who knows enough to make ghc target
> > >> ARM, and get this to link against the iPhone libraries?
> > >> This would be quite a coup if it could be made to run
> > >> there!
> > > For that matter, there's another ARM-based target in which
> > > I'm interested: Nintendo DS. Has anyone got any Haskell
> > > code to run on one of these?  PS: Maybe this discussion
> > > should be moved to a new "Haskell on ARM" thread?
> > 
> > I would be interested to see ghc running on Nokia n8xx or
> > iRex iliad.  Both of them are quite open linux based
> > systems.
> 
> Jeremy Shaw had ghc targeting the nokia last year, iirc.
> Perhaps he'll have more info.
> 
> -- Don
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
From vigalchin at gmail.com  Tue Jun 24 15:08:00 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Tue Jun 24 14:59:32 2008
Subject: [Haskell-cafe] safe vs unsafe
In-Reply-To: <396556a20806241003t5f32194aqd629d2933ba03538@mail.gmail.com>
References: <5ae4f2ba0806232236q2e9b95d5kd1d1eafbf0e12b61@mail.gmail.com>
	<396556a20806241003t5f32194aqd629d2933ba03538@mail.gmail.com>
Message-ID: <5ae4f2ba0806241208i2a0570c0i91f41bbfac8d91a5@mail.gmail.com>

yes I am invoking a callback function written in Haskell.



On Tue, Jun 24, 2008 at 12:03 PM, Adam Langley <agl@imperialviolet.org>
wrote:

> 2008/6/23 Galchin, Vasili <vigalchin@gmail.com>:
> > aio: schedule: re-entered unsafely.
> >    Perhaps a 'foreign import unsafe' should be 'safe'?
> >
> > I want to understand from an implementation viewpoint .. deeper. This is
> a
> > GC issue yes?
>
> Are you reentering Haskell on a path which involves an unsafe FFI
> call? e.g. you enter C land via an unsafe FFI call and, on the same
> call path, reenter Haskell with a callback?
>
> http://www.cse.unsw.edu.au/~chak/haskell/ffi/ffi/ffise3.html#x6-130003.3<http://www.cse.unsw.edu.au/%7Echak/haskell/ffi/ffi/ffise3.html#x6-130003.3>says:
>
> "Optionally, an import declaration can specify, after the calling
> convention, the safety level that should be used when invoking an
> external entity. A safe call is less efficient, but guarantees to
> leave the Haskell system in a state that allows callbacks from the
> external code. In contrast, an unsafe call, while carrying less
> overhead, must not trigger a callback into the Haskell system. If it
> does, the system behaviour is undefined. The default for an invocation
> is to be safe. Note that a callback into the Haskell system implies
> that a garbage collection might be triggered after an external entity
> was called, but before this call returns. Consequently, objects other
> than stable pointers (cf. Section 5.6) may be moved or garbage
> collected by the storage manager."
>
> --
> Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
>
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From agl at imperialviolet.org  Tue Jun 24 15:10:37 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Tue Jun 24 15:02:09 2008
Subject: [Haskell-cafe] safe vs unsafe
In-Reply-To: <5ae4f2ba0806241208i2a0570c0i91f41bbfac8d91a5@mail.gmail.com>
References: <5ae4f2ba0806232236q2e9b95d5kd1d1eafbf0e12b61@mail.gmail.com>
	<396556a20806241003t5f32194aqd629d2933ba03538@mail.gmail.com>
	<5ae4f2ba0806241208i2a0570c0i91f41bbfac8d91a5@mail.gmail.com>
Message-ID: <396556a20806241210o1f513f11pb162c75e0ab51ee7@mail.gmail.com>

On Tue, Jun 24, 2008 at 12:08 PM, Galchin, Vasili <vigalchin@gmail.com> wrote:
> yes I am invoking a callback function written in Haskell.

Then you should just need to remove the "unsafe" from the foreign
import decl which leads to the callback getting called.


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From robgreayer at yahoo.com  Tue Jun 24 15:43:22 2008
From: robgreayer at yahoo.com (Robert Greayer)
Date: Tue Jun 24 15:34:53 2008
Subject: [Haskell-cafe] Template Haskell ListT wrinkle
Message-ID: <890508.88590.qm@web65709.mail.ac4.yahoo.com>


In messing around with TH, I noticed (what I consider
to be an) odd wrinkle in the handling of list types
within TH's syntax meta-data.  For example, given the
program at the end of this email, which prints out the
TH representation of the types 'Ints' and '[Int]',
where 'Ints' is just a type-alias for '[Int]', the
following results are generated:

Ints is: AppT (ConT GHC.Base.[]) (ConT GHC.Base.Int)
[Int] is: AppT ListT (ConT GHC.Base.Int)

type0, 'Ints' resolves to the application of the named
type constructor "GHC.Base.[]" to the named type
constructor "GHC.Base.Int" (which makes perfect
sense).  type1, '[Int]' resolves to the application of
the 'built-in' ListT type constructor to the named
type constructor "GHC.Base.Int" (which also makes
perfect sense).  What's odd (to me) is that in one
situation, the 'named' constructor 'GHC.Base.[]'
appears, and in the other, the 'built-in' constructor
appears.

Does anyone have insight into why this might be? 
(These results were obtained with GHC 6.8.2, btw).

> {-# OPTIONS_GHC -XTemplateHaskell #-}
> module Main where
> import Language.Haskell.TH
>
> type Ints = [Int]
>
> type0 = $( reify ''Ints >>= (\ (TyConI (TySynD _ _
t)) -> return $ show t) >>= \s -> [| s |])
> type1 = $( [t| [Int] |] >>= return . show >>= \s ->
[| s |])
>
> main = do
>    putStrLn ("Ints is: " ++ type0)
>    putStrLn ("[Int] is: " ++ type1)

Thanks
rcg


      
From ndmitchell at gmail.com  Tue Jun 24 15:50:32 2008
From: ndmitchell at gmail.com (Neil Mitchell)
Date: Tue Jun 24 15:42:05 2008
Subject: [Haskell-cafe] Template Haskell ListT wrinkle
In-Reply-To: <890508.88590.qm@web65709.mail.ac4.yahoo.com>
References: <890508.88590.qm@web65709.mail.ac4.yahoo.com>
Message-ID: <404396ef0806241250k7c39c96eg1984a2823d78c9f6@mail.gmail.com>

Hi Robert,

The derive program [http://www.cs.york.ac.uk/~ndm/derive] works
extensively with Template Haskell, and has come across loads of
instances where you get either AppT or ListT, and similarly where you
get either ListE or AppE - and I seem to remember ListP as well. I
think the same also holds for TupT/TupE/TupP My advice is to treat
them all the same, and if it matters to you, normalise them before you
start work. I think the pretty printer may print them differently, but
otherwise they are equivalent. For example derive has:

peep (AppE (AppE cons x) nil)
    | cons ~= ":" && nil ~= "[]" = ListE [x]

i.e. if you have a list using cons, change it to a list using the list notation.

Thanks

Neil


On 6/24/08, Robert Greayer <robgreayer@yahoo.com> wrote:
>
>  In messing around with TH, I noticed (what I consider
>  to be an) odd wrinkle in the handling of list types
>  within TH's syntax meta-data.  For example, given the
>  program at the end of this email, which prints out the
>  TH representation of the types 'Ints' and '[Int]',
>  where 'Ints' is just a type-alias for '[Int]', the
>  following results are generated:
>
>  Ints is: AppT (ConT GHC.Base.[]) (ConT GHC.Base.Int)
>  [Int] is: AppT ListT (ConT GHC.Base.Int)
>
>  type0, 'Ints' resolves to the application of the named
>  type constructor "GHC.Base.[]" to the named type
>  constructor "GHC.Base.Int" (which makes perfect
>  sense).  type1, '[Int]' resolves to the application of
>  the 'built-in' ListT type constructor to the named
>  type constructor "GHC.Base.Int" (which also makes
>  perfect sense).  What's odd (to me) is that in one
>  situation, the 'named' constructor 'GHC.Base.[]'
>  appears, and in the other, the 'built-in' constructor
>  appears.
>
>  Does anyone have insight into why this might be?
>  (These results were obtained with GHC 6.8.2, btw).
>
>  > {-# OPTIONS_GHC -XTemplateHaskell #-}
>  > module Main where
>  > import Language.Haskell.TH
>  >
>  > type Ints = [Int]
>  >
>  > type0 = $( reify ''Ints >>= (\ (TyConI (TySynD _ _
>  t)) -> return $ show t) >>= \s -> [| s |])
>  > type1 = $( [t| [Int] |] >>= return . show >>= \s ->
>  [| s |])
>  >
>  > main = do
>  >    putStrLn ("Ints is: " ++ type0)
>  >    putStrLn ("[Int] is: " ++ type1)
>
>  Thanks
>  rcg
>
>
>
>  _______________________________________________
>  Haskell-Cafe mailing list
>  Haskell-Cafe@haskell.org
>  http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From wojtowicz.norbert at gmail.com  Tue Jun 24 15:57:46 2008
From: wojtowicz.norbert at gmail.com (Norbert Wojtowicz)
Date: Tue Jun 24 15:49:18 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
Message-ID: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>

Hello,

I am trying to use the SDL-mixer bindings to play wav files. I've hit
a wierd error and I can't figure out how to solve it:

Prelude> import Graphics.UI.SDL.Mixer.Music
Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"
Loading package SDL-0.5.4 ... linking ... done.
Loading package SDL-mixer-0.5.2 ... linking ... <interactive>:
/home/norbert/bin/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o:
unknown symbol `Mix_LoadWAV'
ghc-6.8.2: unable to load package `SDL-mixer-0.5.2'

I've looked up the source code; Mix_LoadWAV seems to be #defined, so I
suspect it's some kind of library path issue but I don't grok the
whole system well enough to figure it out; maybe someone could point
me in the right direction?

Have the issue now on Ubuntu 8.04 and previously had the same issue
when I tested it on a FreeBSD box. I did install all of the
"libsdl-*-dev" in the Ubuntu repo.

- Norbert
From lemming at henning-thielemann.de  Tue Jun 24 16:04:41 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue Jun 24 15:56:13 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806242201160.8335@anubis.informatik.uni-halle.de>


On Tue, 24 Jun 2008, Norbert Wojtowicz wrote:

> Hello,
>
> I am trying to use the SDL-mixer bindings to play wav files. I've hit
> a wierd error and I can't figure out how to solve it:
>
> Prelude> import Graphics.UI.SDL.Mixer.Music
> Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"

Is the package installed? Otherwise you may have to give an -lSDL_mixer 
option when starting ghci.

From dons at galois.com  Tue Jun 24 16:05:29 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 24 15:57:10 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
Message-ID: <20080624200529.GG17394@scytale.galois.com>

wojtowicz.norbert:
> Hello,
> 
> I am trying to use the SDL-mixer bindings to play wav files. I've hit
> a wierd error and I can't figure out how to solve it:
> 
> Prelude> import Graphics.UI.SDL.Mixer.Music
> Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"
> Loading package SDL-0.5.4 ... linking ... done.
> Loading package SDL-mixer-0.5.2 ... linking ... <interactive>:
> /home/norbert/bin/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o:
> unknown symbol `Mix_LoadWAV'
> ghc-6.8.2: unable to load package `SDL-mixer-0.5.2'
> 
> I've looked up the source code; Mix_LoadWAV seems to be #defined, so I
> suspect it's some kind of library path issue but I don't grok the
> whole system well enough to figure it out; maybe someone could point
> me in the right direction?
> 
> Have the issue now on Ubuntu 8.04 and previously had the same issue
> when I tested it on a FreeBSD box. I did install all of the
> "libsdl-*-dev" in the Ubuntu repo.

Ah, well spotted. I get the same issue on Arch, in ghci:

    Prelude> import Graphics.UI.SDL.Mixer.Music
    Prelude Graphics.UI.SDL.Mixer.Music> loadMUS
    "/usr/share/hback-0.0.3/sounds/t.wav"
    <interactive>: /usr/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o:
    unknown symbol `Mix_LoadWAV'
    ghc-6.8.2: unable to load package `SDL-mixer-0.5.2'

Looking in the source we see:

    foreign import ccall unsafe "Mix_LoadWAV"
        mixLoadWAV :: CString -> IO (Ptr ChunkStruct)
         
Lemmih, any ideas? -lSDL and -lSDL_mixer seem to be there.

-- Don
From dons at galois.com  Tue Jun 24 16:07:02 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 24 15:58:36 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <Pine.LNX.4.64.0806242201160.8335@anubis.informatik.uni-halle.de>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<Pine.LNX.4.64.0806242201160.8335@anubis.informatik.uni-halle.de>
Message-ID: <20080624200702.GH17394@scytale.galois.com>

lemming:
> 
> On Tue, 24 Jun 2008, Norbert Wojtowicz wrote:
> 
> >Hello,
> >
> >I am trying to use the SDL-mixer bindings to play wav files. I've hit
> >a wierd error and I can't figure out how to solve it:
> >
> >Prelude> import Graphics.UI.SDL.Mixer.Music
> >Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"
> 
> Is the package installed? Otherwise you may have to give an -lSDL_mixer 
> option when starting ghci.

That's not enough, for some reason:

    $ ghci -lSDL_mixer
    Prelude>  import Graphics.UI.SDL.Mixer.Music
    Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"
    <interactive>:
    /home/dons/.cabal/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o:
    unknown symbol `Mix_LoadWAV'
    ghc-6.8.2: unable to load package `SDL-mixer-0.5.2'

Despite it being defined in 

    $ grep Mix_LoadWAV /usr/lib/*      
    Binary file /usr/lib/libSDL_mixer-1.2.so.0 matches
    Binary file /usr/lib/libSDL_mixer-1.2.so.0.2.6 matches
    Binary file /usr/lib/libSDL_mixer.a matches
    Binary file /usr/lib/libSDL_mixer.so matches

Hmm.
From marcot at riseup.net  Tue Jun 24 16:13:47 2008
From: marcot at riseup.net (Marco =?ISO-8859-1?Q?T=FAlio?= Gontijo e Silva)
Date: Tue Jun 24 16:04:58 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
Message-ID: <1214338427.2850.16.camel@quindinho.domain.invalid>

Em Ter, 2008-06-24 ?s 14:57 -0500, Norbert Wojtowicz escreveu:
> Prelude> import Graphics.UI.SDL.Mixer.Music
> Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"
> Loading package SDL-0.5.4 ... linking ... done.
> Loading package SDL-mixer-0.5.2 ... linking ... <interactive>:
> /home/norbert/bin/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o:
> unknown symbol `Mix_LoadWAV'
> ghc-6.8.2: unable to load package `SDL-mixer-0.5.2'

Hello.

SDL-mixer does not support the most recent SDL version.  The problem is
that in SDL now Mix_LoadWAV is a macro.

-- 
Marco T?lio Gontijo e Silva
P?gina: http://marcotmarcot.googlepages.com/
Blog: http://marcotmarcot.wordpress.com/
Correio: marcot@riseup.net
XMPP: marcot@jabber.org
IRC: marcot@irc.freenode.net
Telefone: 25151920
Celular: 98116720
Endere?o:
 Rua Turfa, 639/701
 Prado 30410-370
 Belo Horizonte/MG Brasil


From dons at galois.com  Tue Jun 24 16:14:53 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 24 16:06:26 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <1214338427.2850.16.camel@quindinho.domain.invalid>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<1214338427.2850.16.camel@quindinho.domain.invalid>
Message-ID: <20080624201453.GI17394@scytale.galois.com>

marcot:
> Em Ter, 2008-06-24 ?s 14:57 -0500, Norbert Wojtowicz escreveu:
> > Prelude> import Graphics.UI.SDL.Mixer.Music
> > Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav"
> > Loading package SDL-0.5.4 ... linking ... done.
> > Loading package SDL-mixer-0.5.2 ... linking ... <interactive>:
> > /home/norbert/bin/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o:
> > unknown symbol `Mix_LoadWAV'
> > ghc-6.8.2: unable to load package `SDL-mixer-0.5.2'
> 
> Hello.
> 
> SDL-mixer does not support the most recent SDL version.  The problem is
> that in SDL now Mix_LoadWAV is a macro.

Ah ha, so it needs a cbits wrapper over the macro.
From lemming at henning-thielemann.de  Tue Jun 24 16:38:34 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue Jun 24 16:30:05 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>


On Tue, 24 Jun 2008, Alistair Bayley wrote:

> 2008/6/24 Henning Thielemann <lemming@henning-thielemann.de>:
>>
>> (Btw. Takusen should be split into
>> several packages for all database backends because Cabal flags must not
>> influence the package interface.)
>
> I don't understand this (cabal flags must not influence package
> interface). I thought that was the point of cabal flags? I wanted to
> have a single package installation, and this seems like the best way.

No, if a package imports Takusen - how can it be assert that it can import 
the Oracle back-end? It can't because it can reference the Takusen package 
only by its name and a version. Flags are there to make a package appear 
consistent under different circumstances (e.g. Windows and Unix, or 
GHC-6.4 and GHC-6.8). If the back-end modules would not be exported, then 
the API would remain the same for different back-ends and that would be 
ok.

>> But on installation Cabal complains about missing /usr/oci directory.
>
> When you run configure, you should get output that says:
> Using Oracle: <path>
>
> What is <path>?

I don't get these questions.

> The Setup.hs assumes the entire Oracle installation is under a single
> root folder ($ORACLE_HOME); is this not true on Linux?

Ah, I must have set ORACLE_HOME for the Takusen installation ... should be 
documented. However in my case, this doesn't change the path used by 
Takusen's Setup/install.


$ echo $ORACLE_HOME
/usr/lib/oracle/10.2.0.4/client
$ ls $ORACLE_HOME
bin  lib
$ ll $ORACLE_HOME/lib
-rw-r--r-- 1 root root     1525 17. Feb 09:58 glogin.sql
lrwxrwxrwx 1 root root       17 24. Jun 15:36 libclntsh.so -> libclntsh.so.10.1
-rw-r--r-- 1 root root 19076649 17. Feb 09:57 libclntsh.so.10.1
-rw-r--r-- 1 root root  5656445 17. Feb 09:57 libnnz10.so
lrwxrwxrwx 1 root root       15 24. Jun 15:36 libocci.so -> libocci.so.10.1
-rw-r--r-- 1 root root  1398244 17. Feb 09:57 libocci.so.10.1
-rw-r--r-- 1 root root 72698427 17. Feb 09:57 libociei.so
-rw-r--r-- 1 root root   120443 17. Feb 09:57 libocijdbc10.so
-rw-r--r-- 1 root root  1434263 17. Feb 09:58 libsqlplusic.so
-rw-r--r-- 1 root root  1069221 17. Feb 09:58 libsqlplus.so
-rw-r--r-- 1 root root   781311 17. Feb 09:58 libsqora.so.10.1
-rw-r--r-- 1 root root  1555682 17. Feb 09:57 ojdbc14.jar

I assume that libociei.so is the library I need.


$ runhaskell Setup.hs configure --user -f oracle
Configuring Takusen-0.8.2...
$ runhaskell Setup.hs build && runhaskell Setup.hs haddock
Preprocessing library Takusen-0.8.2...
Building Takusen-0.8.2...
/usr/bin/ar: creating dist/build/libHSTakusen-0.8.2.a
Preprocessing library Takusen-0.8.2...
Running Haddock for Takusen-0.8.2...
Preprocessing library Takusen-0.8.2...
...
Documentation created: dist/doc/html/Takusen/index.html
$ runhaskell Setup.hs install
Installing:
[...]/lib/Takusen-0.8.2/ghc-6.8.2
Registering Takusen-0.8.2...
Reading package info from "dist/installed-pkg-config" ... done.
ghc-pkg: /usr/oci doesn't exist or isn't a directory (use --force to override)



>> Once I will get Takusen running with OCI - how would I use it? Is there a
>> minimal example which connects to an Oracle database, performing a very
>> simple query?
>
> There's an example in the README.txt, which I've tweaked here for Oracle:
>
> {-# OPTIONS -fglasgow-exts #-}
> {-# OPTIONS -fallow-overlapping-instances #-}
> module Main where
> import Database.Oracle.Enumerator
> import Control.Monad.Trans (liftIO)
> main = flip catchDB reportRethrow $
>  withSession (connect "user" "pswd" "dbname") (do
>    let iter (s::String) (_::String) = result s
>    result <- doQuery (sql "select 'Hello world.' from dual") iter ""
>    liftIO (putStrLn result)
>    )

Thanks for the adapted example!
From lemming at henning-thielemann.de  Tue Jun 24 16:54:38 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue Jun 24 16:46:09 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <485C94C1.6030006@cisco.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<a66b8c070806201744v1e7d05d8jd0ab33efb395f553@mail.gmail.com>
	<485C94C1.6030006@cisco.com>
Message-ID: <Pine.LNX.4.64.0806242248530.8335@anubis.informatik.uni-halle.de>


On Sat, 21 Jun 2008, Lanny Ripple wrote:

> I had luck with this the other day using Database.HDBC.ODBC.  For
> Ubuntu's Hardy I found that Oracle's 10.2.0.3 worked best.
> (10.2.0.4 and 11 seemed to have problems for me at least.)
>
> http://www.oracle.com/technology/software/tech/oci/instantclient/htdocs/linuxsoft.html
>
> Grab the basic (not basic-lite), odbc, and sqlplus (to test) zips.
> The odbc_update_ini.sh should be run from inside the
> instantclient_10_2 directory as root
>
>  sudo /bin/sh odbc_update_ini.sh /
>
> (assuming a standard unixODBC install.)  You'll also need a
> tnsnames.ora file to describe your connection(s) to the DB(s).
> You'll also need to define some environment variables to run against
> all this.  I use a small script:
>
>  #!/bin/sh
>  oracle_home=/opt/lib/oracle/instantclient_10_2
>  export TNS_ADMIN=$oracle_home
>  export LD_LIBRARY_PATH=$oracle_home
>  [ $# = 0 ] && exit 1
>  exec "$@"

Thank you for the detailed hints! However, I tried a lot of this and that, 
but without a possibility to track down what went wrong, the ways to fix 
the probable problems are unbounded. Finally I get 'Driver's 
SQLAllocHandle on SQL_HANDLE_HENV failed' when I start 'isql' and that's 
where systematic error analysis stops and wild guessing starts. Since OCI 
and sqlplus work on my machine, I'll try to follow this way.
From nielsadb at gmail.com  Tue Jun 24 17:04:42 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Tue Jun 24 16:56:15 2008
Subject: [Haskell-cafe] Two questions regarding Alex/Parsec
Message-ID: <1214341482.13477.26.camel@porcupine>

Hello Haskellers,

As an experiment I'm writing a parser for MediaWiki language. I'm using
the Alex lexer and Parsec. I have novice two questions.

(I've tried using Happy but I was unable to get a grammar file to
compile, which must be because I have no real experience using Yacc and
the like. I've also attempted to write an ad-hoc recursive descent
parser, but that become too complex to be fun very quickly.)

== SourcePos and AlexPosn ==

My first question is about Parsec's SourcePos. I have a definition like:

  type LexToken = (AlexPosn, Token)

  type MWP a = GenParser LexToken () a

  toSourcePos :: AlexPosn -> SourcePos
  toSourcePos (AlexPn _ line col) = undefined

  mwtok :: (Token -> Maybe a) -> MWP a
  mwtok test = token showToken posToken posTest
             where
               showToken = show . snd
               posToken = toSourcePos . fst
               posTest = test . snd

The definition of ?toSourcePos isn't 100% satisfactory. The constructor
SourcePos is hidden, so I cannot simply use (SourcePos line col). Is
there a way to convert an AlexPosn value to a SourcePos?

== Data Constructors as Parameters and Tags ==

Secondly, I frequently encounter the pattern where I try to match a
token, return Just some result if it matches, and Nothing otherwise. So
I tried to fix this pattern in a nice reusable function.

  onTok0 :: Token -> a -> MWP a
  onTok0 t x = mwtok (\tok -> if tok `isTok` t then Just x else Nothing)

This seems to work, but I'd also like a definition for data constructors
taking one parameter:

  onTok1 :: (a -> Token) -> (a -> b) -> MWP b
  onTok1 t f = mwtok (\tok -> case tok of
                                   (t n) = Just $ f n
                                   _ = Nothing)

This doesn't work, the pattern match (t n) fails, which is
understandable: n is used as a parameter to t and a matched result,
which looks like a paradox. t is a function (constructor) but also a
tag. Is it possible to pass a tag as an argument? Or is there another
way to extract this pattern?

Regards,
Niels


From dons at galois.com  Tue Jun 24 17:08:29 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 24 17:00:05 2008
Subject: [Haskell-cafe] Two questions regarding Alex/Parsec
In-Reply-To: <1214341482.13477.26.camel@porcupine>
References: <1214341482.13477.26.camel@porcupine>
Message-ID: <20080624210829.GL17394@scytale.galois.com>

nielsadb:
> Hello Haskellers,
> 
> As an experiment I'm writing a parser for MediaWiki language. I'm using
> the Alex lexer and Parsec. I have novice two questions.

Just a quick question, did you try using the pandoc markdown parser?

    http://hackage.haskell.org/packages/archive/pandoc/0.46/doc/html/Text-Pandoc-Readers-Markdown.html

It'd be useful to know if that was enough for printing and generation
of wiki content. Though being GPLd, it'd also be nice to have a BSD-ish
licensed wiki parser/pretty printer.

-- Don
From alistair at abayley.org  Tue Jun 24 17:35:56 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Tue Jun 24 17:27:26 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
Message-ID: <79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>

>> 2008/6/24 Henning Thielemann <lemming@henning-thielemann.de>:
>>>
>> When you run configure, you should get output that says:
>> Using Oracle: <path>
>>
>> What is <path>?
>
> I don't get these questions.

Sorry. I was really asking (not very clearly): what is the output from
"runhaskell Setup.hs configure -foracle" ? You've answered that below.


> Ah, I must have set ORACLE_HOME for the Takusen installation ... should be
> documented. However in my case, this doesn't change the path used by
> Takusen's Setup/install.

Well, you don't actually need it set for the Takusen install (it
doesn''t use it). But $ORACLE_HOME/bin should be in your path. And it
needs to contain the executable sqlplus. Can you run sqlplus? It looks
as though you don't have it.

If sqlplus is not in my path then I get this error in the configure
step, because I have specified sqlplus as a buildtool in
Takusen.cabal:

  > setup configure -foracle
  Configuring Takusen-0.8.2...
  setup: sqlplus is required but it could not be found.

Note: sqlplus isn't really needed to build; this is just a validation
step, to check you have $ORACLE_HOME/bin in your path.


> $ echo $ORACLE_HOME
> /usr/lib/oracle/10.2.0.4/client
> $ ls $ORACLE_HOME
> bin  lib
> $ ll $ORACLE_HOME/lib
> ...
> I assume that libociei.so is the library I need.

Actually it's libclntsh.so. You need to change the oracle section in
Takusen.cabal to this:

  If flag(oracle)
    Exposed-modules:
        Database.Oracle.Enumerator
      , Database.Oracle.OCIConstants
      , Database.Oracle.OCIFunctions
    Build-Tools: sqlplus
    If os(windows)
      Extra-Libraries: oci
    Else
      Extra-Libraries: clntsh

Your $ORACLE_HOME installation looks fairly normal, if somewhat
minimal. I would normally expect to see sqlplus, and maybe some other
executables, like tnsping. And a folder $ORACLE_HOME/oci/include,
which contains the OCI header files. Perhaps you could also install
the sqplus and SDK packages, as Lanny Ripple suggested, although I
suspect they may not be strictly necessary, as you can apparently
successfully compile, as evidenced below.

> $ runhaskell Setup.hs configure --user -f oracle
> Configuring Takusen-0.8.2...

Here, I would expect to see "Using Oracle: /usr/lib/oracle/10.2.0.4/client"

After setup configure you can say:
  $ runhaskell Setup.hs register --gen-pkg-config

and then take a look at the generated Takusen-0.8.2.conf. Check the
library-dirs and include-dirs fields.

Alistair
From oddron at gmail.com  Tue Jun 24 17:46:56 2008
From: oddron at gmail.com (Ronald Guida)
Date: Tue Jun 24 17:38:27 2008
Subject: [Haskell-cafe] Bug in Emacs Haskell Mode
Message-ID: <62728db30806241446m68799c4q95851f8b2bbb2b@mail.gmail.com>

Emacs Haskell Mode has the following useful feature: when "Haskell ->
Load File" is used to load a file into GHCi from Emacs, Haskell Mode
automatically looks for a "*.cabal" file in an attempt to find the
project directory.

When Haskell Mode finds the *.cabal file, it fails to check whether it
has found a file or a folder.  As a result, if I want to load a
Haskell file that has no corresponding .cabal file, then Haskell Mode
locates my "~/.cabal" *folder* and assumes that it's my project
directory.

I have a "~/.cabal" folder because Cabal-Install puts it there.
Cabal-Install is part of Haskell's new package management system.

Now I don't know very much Emacs Lisp, but I figured out a fix for the
problem.  In Haskell-Mode-2.4, in the file haskell-cabal.el, I changed
the function "haskell-cabal-find-file" so that it explicitly checks to
make sure that any *.cabal file is in fact a file and not a folder.

I don't know if comparing the first letter of the file mode string to
'd' is the right way to diferentiate a folder from a file, but so far
it appears to work for me, so I thought I'd share it.

(defun haskell-cabal-find-file ()
  "Return a buffer visiting the cabal file of the current directory, or nil."
  (catch 'found
    (let ((user (nth 2 (file-attributes default-directory)))
          ;; Abbreviate, so as to stop when we cross ~/.
          (root (abbreviate-file-name default-directory))
          files)
      (while (and root (equal user (nth 2 (file-attributes root))))
	(let ((files (directory-files root 'full "\\.cabal\\'")))
	  (if (and files
		   (not (equal 100 (aref (nth 8
			   (file-attributes (car files))) 0))))
	      (throw 'found (find-file-noselect (car files)))
	    (if (equal root
		       (setq root (file-name-directory
				   (directory-file-name root))))
		(setq root nil))))
	nil))))
From daniil.elovkov at googlemail.com  Tue Jun 24 17:51:10 2008
From: daniil.elovkov at googlemail.com (Daniil Elovkov)
Date: Tue Jun 24 17:42:57 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806242248530.8335@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>	<a66b8c070806201744v1e7d05d8jd0ab33efb395f553@mail.gmail.com>	<485C94C1.6030006@cisco.com>
	<Pine.LNX.4.64.0806242248530.8335@anubis.informatik.uni-halle.de>
Message-ID: <48616C4E.4000101@gmail.com>

Henning Thielemann wrote:
> 
> On Sat, 21 Jun 2008, Lanny Ripple wrote:
> 
>> I had luck with this the other day using Database.HDBC.ODBC.  For
>> Ubuntu's Hardy I found that Oracle's 10.2.0.3 worked best.
>> (10.2.0.4 and 11 seemed to have problems for me at least.)
>>
>> http://www.oracle.com/technology/software/tech/oci/instantclient/htdocs/linuxsoft.html 
>>
>>
>> Grab the basic (not basic-lite), odbc, and sqlplus (to test) zips.
>> The odbc_update_ini.sh should be run from inside the
>> instantclient_10_2 directory as root
>>
>>  sudo /bin/sh odbc_update_ini.sh /
>>
>> (assuming a standard unixODBC install.)  You'll also need a
>> tnsnames.ora file to describe your connection(s) to the DB(s).
>> You'll also need to define some environment variables to run against
>> all this.  I use a small script:
>>
>>  #!/bin/sh
>>  oracle_home=/opt/lib/oracle/instantclient_10_2
>>  export TNS_ADMIN=$oracle_home
>>  export LD_LIBRARY_PATH=$oracle_home
>>  [ $# = 0 ] && exit 1
>>  exec "$@"
> 
> Thank you for the detailed hints! However, I tried a lot of this and 
> that, but without a possibility to track down what went wrong, the ways 
> to fix the probable problems are unbounded. Finally I get 'Driver's 
> SQLAllocHandle on SQL_HANDLE_HENV failed' when I start 'isql' and that's 
> where systematic error analysis stops and wild guessing starts. Since 
> OCI and sqlplus work on my machine, I'll try to follow this way.

There are also

Database.HSQL
Database.HSQL.Oracle

It works through OCI as well.

It's not clear (to me at least) if it is/will be supported.
It has back-ends for multiple DBs (is Takusen only for Oracle?)
It doesn't take the typeful approach, that Takusen takes (may be a plus 
in some situations)


From wojtowicz.norbert at gmail.com  Tue Jun 24 19:19:24 2008
From: wojtowicz.norbert at gmail.com (Norbert Wojtowicz)
Date: Tue Jun 24 19:10:54 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <20080624201453.GI17394@scytale.galois.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<1214338427.2850.16.camel@quindinho.domain.invalid>
	<20080624201453.GI17394@scytale.galois.com>
Message-ID: <cf83716f0806241619g2703cdc8s63f11f387aa59d32@mail.gmail.com>

>> SDL-mixer does not support the most recent SDL version.  The problem is
>> that in SDL now Mix_LoadWAV is a macro.

I've tried it with SDL-0.5.2 from hackage as well with the same
problem. (Unless you mean an earlier version of the actual SDL
library?)

> Ah ha, so it needs a cbits wrapper over the macro.

This is above my head. If we know what the problem is, will this by
any chance hit someone's todo list soon or is this a big hurdle?

Are there any other cross-platform (windows + linux at the minimum)
ways of playing sounds that anyone can recommend?

- Norbert
From dons at galois.com  Tue Jun 24 19:31:41 2008
From: dons at galois.com (Don Stewart)
Date: Tue Jun 24 19:23:17 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <cf83716f0806241619g2703cdc8s63f11f387aa59d32@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<1214338427.2850.16.camel@quindinho.domain.invalid>
	<20080624201453.GI17394@scytale.galois.com>
	<cf83716f0806241619g2703cdc8s63f11f387aa59d32@mail.gmail.com>
Message-ID: <20080624233141.GU17394@scytale.galois.com>

wojtowicz.norbert:
> >> SDL-mixer does not support the most recent SDL version.  The problem is
> >> that in SDL now Mix_LoadWAV is a macro.
> 
> I've tried it with SDL-0.5.2 from hackage as well with the same
> problem. (Unless you mean an earlier version of the actual SDL
> library?)
> 
> > Ah ha, so it needs a cbits wrapper over the macro.
> 
> This is above my head. If we know what the problem is, will this by
> any chance hit someone's todo list soon or is this a big hurdle?
> 
> Are there any other cross-platform (windows + linux at the minimum)
> ways of playing sounds that anyone can recommend?

Attached is a patched version of SDL_mixer 0.5.2 with a C wrapper
for this macro. I'm now able to run loadWAV in ghci.

We need to have the maintainer upload the amended version to Hackage,
or to give me leave to do so.

-- Don
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From wojtowicz.norbert at gmail.com  Tue Jun 24 20:34:08 2008
From: wojtowicz.norbert at gmail.com (Norbert Wojtowicz)
Date: Tue Jun 24 20:25:39 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <cf83716f0806241730hca36091uf20fdbde6b0dc496@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<1214338427.2850.16.camel@quindinho.domain.invalid>
	<20080624201453.GI17394@scytale.galois.com>
	<cf83716f0806241619g2703cdc8s63f11f387aa59d32@mail.gmail.com>
	<20080624233141.GU17394@scytale.galois.com>
	<cf83716f0806241730hca36091uf20fdbde6b0dc496@mail.gmail.com>
Message-ID: <cf83716f0806241734t7ebd06b6kcd4c19a6e7d04615@mail.gmail.com>

> Attached is a patched version of SDL_mixer 0.5.2 with a C wrapper
> for this macro. I'm now able to run loadWAV in ghci.

Works for me, thanks!

Now I just need to learn how to make my WAVs sound not like
computer-generated children voices. For example, using the hback wav
files and this:

import Control.Concurrent (threadDelay)
import Graphics.UI.SDL.Mixer.General
import Graphics.UI.SDL.Mixer.Music

main = do
 openAudio 22050 AudioS16Sys 2 4096
 w <- loadMUS "c.wav"
 playMusic w 1
 threadDelay 2000000
 freeMusic w
 closeAudio

It plays (which is an immense improvement), but I can't get it to
sound the way it does from eg. mplayer. I have almost no knowledge of
the inner workings of computer sound drivers, so if there is something
obvious I'm missing please do speak up.

- Norbert
From Braden.Shepherdson at gmail.com  Tue Jun 24 20:43:45 2008
From: Braden.Shepherdson at gmail.com (Braden Shepherdson)
Date: Tue Jun 24 20:37:26 2008
Subject: [Haskell-cafe] Re: Haskell on ARM (was Re: ANN: Topkata)
In-Reply-To: <871w2mit8o.wl%jeremy@n-heptane.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>	<200806170851.22718.valgarv@gmx.net>	<87ej6ww9dy.fsf_-_@columbia.edu>	<20080617201233.GD19304@scytale.galois.com>
	<871w2mit8o.wl%jeremy@n-heptane.com>
Message-ID: <g3s4fr$9h2$1@ger.gmane.org>

Jeremy Shaw wrote:
> If any does attempt to build for the ARM, please, please, please,
> document what you do in the wiki. And, if you do, edit the wiki as you
> go, you definitely won't be able to remember what you did after the
> fact. (Or, at the very least, use some program to capture everything
> you do so that you can refer to it later).
> 
> And, finally, I heard vague rumors a while ago that made me think that
> GHC 6.10 might have a pure ANSI-C backend? Is there any truth to this?
> That would make porting much easier if it meant you did not have to do
> steps 1-4.
> 
> j.  
> 
> ps. I would be happy to try to answer any questions if someone tries a
> port. I would still like to run GHC on my 770, and I hope to own an
> iPhone if they fix a few ommisions (bluetooth keyboard support, and
> similar stuff).
> 


I recently acquired the ARM-based Nokia N810 (and <3 it), powered by 
Maemo. Running a uname -a on it:

Linux Nokia-N810-42-19 2.6.21-omap1 #2 Fri Nov 16 16:24:58 EET 2007 
armv6l unknown

I would love a working GHC implementation on it, if for nothing else 
than how awesome it would be. Whether that means using a C back-end or 
native compilation doesn't matter to me so much.

I might be one to attempt this, as I know C and ARM-ish asm decently 
well and have a powerful desktop to compile on. I have no familiarity
with GHC internals, though. Lastly, I won't have anything like the time 
to attempt this seriously until mid-September or so.


Braden Shepherdson
shepheb

From monnier at iro.umontreal.ca  Tue Jun 24 21:39:00 2008
From: monnier at iro.umontreal.ca (Stefan Monnier)
Date: Tue Jun 24 21:30:41 2008
Subject: [Haskell-cafe] Re: Bug in Emacs Haskell Mode
In-Reply-To: <62728db30806241446m68799c4q95851f8b2bbb2b@mail.gmail.com>
	(Ronald Guida's message of "Tue, 24 Jun 2008 17:46:56 -0400")
References: <62728db30806241446m68799c4q95851f8b2bbb2b@mail.gmail.com>
Message-ID: <jwv4p7imgzp.fsf-monnier+emacs@gnu.org>

> Emacs Haskell Mode has the following useful feature: when "Haskell ->
> Load File" is used to load a file into GHCi from Emacs, Haskell Mode
> automatically looks for a "*.cabal" file in an attempt to find the
> project directory.

I'm truly sorry about the fact that I only release new versions
rather rarely.  I recommend you use the CVS version, where this bug was
fixed a few months ago.


        Stefan
From thomas.dubuisson at gmail.com  Tue Jun 24 21:52:48 2008
From: thomas.dubuisson at gmail.com (Thomas M. DuBuisson)
Date: Tue Jun 24 21:44:21 2008
Subject: [Haskell-cafe] Why the exception?
Message-ID: <1214358768.20040.9.camel@tom-laptop>

Cafe
I'm a bit lost on this exception and curious about what's going on.  Is
there a valid reason for this exception that I am missing?  Note the
hard-coded [0..100] could be any Word8 list you want (generated via
arbitrary, [], or other) and it gives the same result.

Load the module and perform:
      :break prop_LPS
      quickCheck prop_LPS
      :step
      :force ps
     *** Exception: Prelude.head: empty list

> import qualified Data.ByteString as L
> import Test.QuickCheck
>
> instance Arbitrary L.ByteString where
>     arbitrary = do
>         return $ L.pack [0..100]
>
> prop_LPS :: L.ByteString -> Bool
> prop_LPS ps = ps `seq` True

P.S. Same result with GHCi 6.8.2 and 6.8.3.

From tphyahoo at gmail.com  Tue Jun 24 22:32:56 2008
From: tphyahoo at gmail.com (tphyahoo)
Date: Tue Jun 24 22:24:26 2008
Subject: [Haskell-cafe] Fwd: Cabalized, Self-Demoing,
	HStringTemplate-using HAppS Tutorial
In-Reply-To: <0fb0a9bd-89fa-4001-b0a7-3dbaec828b87@z32g2000prh.googlegroups.com>
References: <0fb0a9bd-89fa-4001-b0a7-3dbaec828b87@z32g2000prh.googlegroups.com>
Message-ID: <f0f4b47d-3f85-49ee-b57a-f2b3fe626477@l28g2000prd.googlegroups.com>

---------- Forwarded message ----------
From: tphyahoo <thomashartm...@googlemail.com>
Date: Jun 24, 7:26?pm
Subject: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial
To: HAppS


Hello HAppSers!

I have created a self-demoing, HStringTemplate-using intro to HAppS.

There is a live demo at

http://rippledeals.com:5001

It is cabalized at

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tuto...

and should install fine with sudo cabal install happs-tutorial.

There is a darcs repo at

http://code.haskell.org/happs-examples

And a google project at

http://code.google.com/p/happs-tutorial/

which currently isn't used, but who knows, maybe for the wiki or issue
tracking. (I started at google hosting before migrating to darcs.)

I have all kinds of additional lessons planned, but under the release
early/release often motto I'm letting it out in its embryonic state.

Enjoy!

Thomas.
From tphyahoo at gmail.com  Tue Jun 24 23:08:46 2008
From: tphyahoo at gmail.com (tphyahoo)
Date: Tue Jun 24 23:00:16 2008
Subject: [Haskell-cafe] Fwd: Cabalized, Self-Demoing,
	HStringTemplate-using HAppS Tutorial
In-Reply-To: <00c66891-143a-4d1c-92ac-c2c3c22d7e16@w4g2000prd.googlegroups.com>
References: <0fb0a9bd-89fa-4001-b0a7-3dbaec828b87@z32g2000prh.googlegroups.com>
	<00c66891-143a-4d1c-92ac-c2c3c22d7e16@w4g2000prd.googlegroups.com>
Message-ID: <8398182c-f80e-4620-9f7b-be9d167823ca@y22g2000prd.googlegroups.com>




---------- Forwarded message ----------
From: tphyahoo <thomashartm...@googlemail.com>
Date: Jun 24, 7:46?pm
Subject: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial
To: HAppS


There are some issues with the cabalized project -- templates are
missing. Doh.

Use darcs for now.

Thomas.

On Jun 24, 7:26?pm, tphyahoo <thomashartm...@googlemail.com> wrote:

> Hello HAppSers!

> I have created a self-demoing, HStringTemplate-using intro to HAppS.

> There is a live demo at

>http://rippledeals.com:5001

> It is cabalized at

>http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tuto...

> and should install fine with sudo cabal install happs-tutorial.

> There is a darcs repo at

>http://code.haskell.org/happs-examples

> And a google project at

>http://code.google.com/p/happs-tutorial/

> which currently isn't used, but who knows, maybe for the wiki or issue
> tracking. (I started at google hosting before migrating to darcs.)

> I have all kinds of additional lessons planned, but under the release
> early/release often motto I'm letting it out in its embryonic state.

> Enjoy!

> Thomas.
From tphyahoo at gmail.com  Tue Jun 24 23:40:21 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Tue Jun 24 23:31:55 2008
Subject: [Haskell-cafe] Fwd: Cabalized, Self-Demoing,
	HStringTemplate-using HAppS Tutorial
In-Reply-To: <8398182c-f80e-4620-9f7b-be9d167823ca@y22g2000prd.googlegroups.com>
References: <0fb0a9bd-89fa-4001-b0a7-3dbaec828b87@z32g2000prh.googlegroups.com>
	<00c66891-143a-4d1c-92ac-c2c3c22d7e16@w4g2000prd.googlegroups.com>
	<8398182c-f80e-4620-9f7b-be9d167823ca@y22g2000prd.googlegroups.com>
Message-ID: <910ddf450806242040r5bcbaacweec95cb2c7abc13c@mail.gmail.com>

Uy.

I think I got the cabal install version as well, but I had to specify
a mess of files manually.

So I'll probably be using darcs tag for future release if there are any ;)

thomas.

2008/6/24 tphyahoo <tphyahoo@gmail.com>:
>
>
>
> ---------- Forwarded message ----------
> From: tphyahoo <thomashartm...@googlemail.com>
> Date: Jun 24, 7:46 pm
> Subject: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial
> To: HAppS
>
>
> There are some issues with the cabalized project -- templates are
> missing. Doh.
>
> Use darcs for now.
>
> Thomas.
>
> On Jun 24, 7:26 pm, tphyahoo <thomashartm...@googlemail.com> wrote:
>
>> Hello HAppSers!
>
>> I have created a self-demoing, HStringTemplate-using intro to HAppS.
>
>> There is a live demo at
>
>>http://rippledeals.com:5001
>
>> It is cabalized at
>
>>http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tuto...
>
>> and should install fine with sudo cabal install happs-tutorial.
>
>> There is a darcs repo at
>
>>http://code.haskell.org/happs-examples
>
>> And a google project at
>
>>http://code.google.com/p/happs-tutorial/
>
>> which currently isn't used, but who knows, maybe for the wiki or issue
>> tracking. (I started at google hosting before migrating to darcs.)
>
>> I have all kinds of additional lessons planned, but under the release
>> early/release often motto I'm letting it out in its embryonic state.
>
>> Enjoy!
>
>> Thomas.
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From tphyahoo at gmail.com  Tue Jun 24 23:41:37 2008
From: tphyahoo at gmail.com (Thomas Hartman)
Date: Tue Jun 24 23:33:08 2008
Subject: [Haskell-cafe] Fwd: Cabalized, Self-Demoing,
	HStringTemplate-using HAppS Tutorial
In-Reply-To: <910ddf450806242040r5bcbaacweec95cb2c7abc13c@mail.gmail.com>
References: <0fb0a9bd-89fa-4001-b0a7-3dbaec828b87@z32g2000prh.googlegroups.com>
	<00c66891-143a-4d1c-92ac-c2c3c22d7e16@w4g2000prd.googlegroups.com>
	<8398182c-f80e-4620-9f7b-be9d167823ca@y22g2000prd.googlegroups.com>
	<910ddf450806242040r5bcbaacweec95cb2c7abc13c@mail.gmail.com>
Message-ID: <910ddf450806242041n25aa02b7s3fdd2fcc46ca9fa7@mail.gmail.com>

... cabal install version _working_ as well...

(v0.2)

2008/6/24 Thomas Hartman <tphyahoo@gmail.com>:
> Uy.
>
> I think I got the cabal install version as well, but I had to specify
> a mess of files manually.
>
> So I'll probably be using darcs tag for future release if there are any ;)
>
> thomas.
>
> 2008/6/24 tphyahoo <tphyahoo@gmail.com>:
>>
>>
>>
>> ---------- Forwarded message ----------
>> From: tphyahoo <thomashartm...@googlemail.com>
>> Date: Jun 24, 7:46 pm
>> Subject: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial
>> To: HAppS
>>
>>
>> There are some issues with the cabalized project -- templates are
>> missing. Doh.
>>
>> Use darcs for now.
>>
>> Thomas.
>>
>> On Jun 24, 7:26 pm, tphyahoo <thomashartm...@googlemail.com> wrote:
>>
>>> Hello HAppSers!
>>
>>> I have created a self-demoing, HStringTemplate-using intro to HAppS.
>>
>>> There is a live demo at
>>
>>>http://rippledeals.com:5001
>>
>>> It is cabalized at
>>
>>>http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tuto...
>>
>>> and should install fine with sudo cabal install happs-tutorial.
>>
>>> There is a darcs repo at
>>
>>>http://code.haskell.org/happs-examples
>>
>>> And a google project at
>>
>>>http://code.google.com/p/happs-tutorial/
>>
>>> which currently isn't used, but who knows, maybe for the wiki or issue
>>> tracking. (I started at google hosting before migrating to darcs.)
>>
>>> I have all kinds of additional lessons planned, but under the release
>>> early/release often motto I'm letting it out in its embryonic state.
>>
>>> Enjoy!
>>
>>> Thomas.
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
From skynare at gmail.com  Tue Jun 24 23:58:01 2008
From: skynare at gmail.com (skynare@gmail.com)
Date: Tue Jun 24 23:49:35 2008
Subject: [Haskell-cafe] Why the exception?
In-Reply-To: <1214358768.20040.9.camel@tom-laptop>
References: <1214358768.20040.9.camel@tom-laptop>
Message-ID: <4e7aa0f80806242058j156b27e1w66accd7ebdaa718d@mail.gmail.com>

Probably you need to implement coarbitrary, too.
My ghci session for your code:

$ ghci
GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> :l t.hs
[1 of 1] Compiling Main             ( t.hs, interpreted )

t.hs:4:0:
    Warning: No explicit method nor default method for `coarbitrary'
    In the instance declaration for `Arbitrary L.ByteString'
Ok, modules loaded: Main.
*Main> quickCheck prop_LPS
Loading package array-0.1.0.0 ... linking ... done.
Loading package bytestring-0.9.0.1 ... linking ... done.
Loading package old-locale-1.0.0.0 ... linking ... done.
Loading package old-time-1.0.0.0 ... linking ... done.
Loading package random-1.0.0.0 ... linking ... done.
Loading package QuickCheck-1.1.0.0 ... linking ... done.
OK, passed 100 tests.




On 6/24/08, Thomas M. DuBuisson <thomas.dubuisson@gmail.com> wrote:
> Cafe
> I'm a bit lost on this exception and curious about what's going on.  Is
> there a valid reason for this exception that I am missing?  Note the
> hard-coded [0..100] could be any Word8 list you want (generated via
> arbitrary, [], or other) and it gives the same result.
>
> Load the module and perform:
>       :break prop_LPS
>       quickCheck prop_LPS
>       :step
>       :force ps
>      *** Exception: Prelude.head: empty list
>
>> import qualified Data.ByteString as L
>> import Test.QuickCheck
>>
>> instance Arbitrary L.ByteString where
>>     arbitrary = do
>>         return $ L.pack [0..100]
>>
>> prop_LPS :: L.ByteString -> Bool
>> prop_LPS ps = ps `seq` True
>
> P.S. Same result with GHCi 6.8.2 and 6.8.3.
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From lrpalmer at gmail.com  Wed Jun 25 01:16:16 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun 25 01:07:45 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <cf83716f0806241734t7ebd06b6kcd4c19a6e7d04615@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<1214338427.2850.16.camel@quindinho.domain.invalid>
	<20080624201453.GI17394@scytale.galois.com>
	<cf83716f0806241619g2703cdc8s63f11f387aa59d32@mail.gmail.com>
	<20080624233141.GU17394@scytale.galois.com>
	<cf83716f0806241730hca36091uf20fdbde6b0dc496@mail.gmail.com>
	<cf83716f0806241734t7ebd06b6kcd4c19a6e7d04615@mail.gmail.com>
Message-ID: <7ca3f0160806242216y76b99d80x6e52a2b575829ce@mail.gmail.com>

On Tue, Jun 24, 2008 at 6:34 PM, Norbert Wojtowicz
<wojtowicz.norbert@gmail.com> wrote:
>> Attached is a patched version of SDL_mixer 0.5.2 with a C wrapper
>> for this macro. I'm now able to run loadWAV in ghci.
>
> Works for me, thanks!
>
> Now I just need to learn how to make my WAVs sound not like
> computer-generated children voices. For example, using the hback wav
> files and this:
>
> import Control.Concurrent (threadDelay)
> import Graphics.UI.SDL.Mixer.General
> import Graphics.UI.SDL.Mixer.Music
>
> main = do
>  openAudio 22050 AudioS16Sys 2 4096

This is probably the issue.  Most wavs are sampled at 44100, not
22050, and I think you have to ask mplayer specifically to downsample.
 Changing this to

  openAudio 44100 AudioS16Sys 2 4096

should do the trick.

Luke

>  w <- loadMUS "c.wav"
>  playMusic w 1
>  threadDelay 2000000
>  freeMusic w
>  closeAudio
>
> It plays (which is an immense improvement), but I can't get it to
> sound the way it does from eg. mplayer. I have almost no knowledge of
> the inner workings of computer sound drivers, so if there is something
> obvious I'm missing please do speak up.
>
> - Norbert
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
From lrpalmer at gmail.com  Wed Jun 25 01:17:17 2008
From: lrpalmer at gmail.com (Luke Palmer)
Date: Wed Jun 25 01:08:50 2008
Subject: [Haskell-cafe] sdl-mixer loading issue
In-Reply-To: <7ca3f0160806242216y76b99d80x6e52a2b575829ce@mail.gmail.com>
References: <cf83716f0806241257v12b2a0bmf6621219d569272@mail.gmail.com>
	<1214338427.2850.16.camel@quindinho.domain.invalid>
	<20080624201453.GI17394@scytale.galois.com>
	<cf83716f0806241619g2703cdc8s63f11f387aa59d32@mail.gmail.com>
	<20080624233141.GU17394@scytale.galois.com>
	<cf83716f0806241730hca36091uf20fdbde6b0dc496@mail.gmail.com>
	<cf83716f0806241734t7ebd06b6kcd4c19a6e7d04615@mail.gmail.com>
	<7ca3f0160806242216y76b99d80x6e52a2b575829ce@mail.gmail.com>
Message-ID: <7ca3f0160806242217v7a0fb25fpaa6aea42201547eb@mail.gmail.com>

On Tue, Jun 24, 2008 at 11:16 PM, Luke Palmer <lrpalmer@gmail.com> wrote:
> On Tue, Jun 24, 2008 at 6:34 PM, Norbert Wojtowicz
> <wojtowicz.norbert@gmail.com> wrote:
>>> Attached is a patched version of SDL_mixer 0.5.2 with a C wrapper
>>> for this macro. I'm now able to run loadWAV in ghci.
>>
>> Works for me, thanks!
>>
>> Now I just need to learn how to make my WAVs sound not like
>> computer-generated children voices. For example, using the hback wav
>> files and this:
>>
>> import Control.Concurrent (threadDelay)
>> import Graphics.UI.SDL.Mixer.General
>> import Graphics.UI.SDL.Mixer.Music
>>
>> main = do
>>  openAudio 22050 AudioS16Sys 2 4096
>
> This is probably the issue.  Most wavs are sampled at 44100, not
> 22050, and I think you have to ask mplayer specifically to downsample.

Er, ask sdl-mixer specifically... you knew what I meant.

>  Changing this to
>
>  openAudio 44100 AudioS16Sys 2 4096
>
> should do the trick.
>
> Luke
>
>>  w <- loadMUS "c.wav"
>>  playMusic w 1
>>  threadDelay 2000000
>>  freeMusic w
>>  closeAudio
>>
>> It plays (which is an immense improvement), but I can't get it to
>> sound the way it does from eg. mplayer. I have almost no knowledge of
>> the inner workings of computer sound drivers, so if there is something
>> obvious I'm missing please do speak up.
>>
>> - Norbert
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
From harald.rotter at sagem.com  Wed Jun 25 02:33:34 2008
From: harald.rotter at sagem.com (Harald ROTTER)
Date: Wed Jun 25 02:26:52 2008
Subject: [Haskell-cafe] number-parameterized types and heterogeneous lists
Message-ID: <OF7EEDD69A.D363E9FE-ONC1257473.0022EF09-C1257473.00240845@sagem.com>


Hello Anton,

thanks for your enlightening piece of code. "foldD" does exactly what I was
hoping for.
Now it becomes very obvious to me that the positions of the forall's in the
Digit definition are crucial.

Thanks a lot to Alfonso, Luke and Ryan as well. Haskell Cafe is a really
good place to learn new things :-)

Harald.



" Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes  pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel  ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite." 

" This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."
From leledumbo_cool at yahoo.co.id  Wed Jun 25 04:05:12 2008
From: leledumbo_cool at yahoo.co.id (leledumbo)
Date: Wed Jun 25 03:56:42 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
	<e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
Message-ID: <18106999.post@talk.nabble.com>


Hi, I'm back. I have some troubles understanding your code:

Chadda? Fouch?-2 wrote:
> 
> findAllAns 0 0 = [[]]
> findAllAns 0 s = []
> findAllAns n s = [ x:xs | x <- [0..s], xs <- findAllAns (n - 1) (s - x) ]
> 

Let's try a test case (CMIIW) for findAllAns 2 1:
findAllAns 2 1 = [ 0:(findAllAns 1 1) ]
                   = [ 0:0:(findAllAns 0 1) ]
                   = [ 0:0:[] ] // Not a solution
                   
                   = [ 0:(findAllAns 1 1) ]
                   = [ 0:1:(findAllAns 0 0) ]
                   = [ 0:1:[[]] ] // A solution

                   = [ 1:(findAllAns 1 0) ]
                   = [ 1:0:(findAllAns 0 0) ]
                   = [ 1:0:[[]] ] // A solution

                      ( 1:1:? is never reached. )

I don't understand why if the last element is [[]] then it's included in the
result and not if it's [].
-- 
View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18106999.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

From alistair at abayley.org  Wed Jun 25 04:10:56 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Wed Jun 25 04:02:26 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
Message-ID: <79d7c4980806250110m38c8da33h790c2b3da22f9d2c@mail.gmail.com>

>> $ ll $ORACLE_HOME/lib
>> ...
>> I assume that libociei.so is the library I need.
>
> Actually it's libclntsh.so. You need to change the oracle section in
> Takusen.cabal to this:

<hand-slaps-forehead/>

Another difference between Windows and Linux Oracle installations is
that the client libs are in $ORACLE_HOME/lib on Linux, but in
$ORACLE_HOME/bin on Windows. The Setup.hs script has the Windows case
baked in. You should change the configOracle function like so:

configOracle verbose buildtools =
  createConfigByFindingExe verbose buildtools "Oracle" sqlplusProgram
parentFolder oracleLibDir "oci/include"
    -- location of OCI client library differs between Windows and Unix
    where oracleLibDir = if isWindows then "bin" else "lib"


Alistair
From sasko.mateski at gmail.com  Wed Jun 25 04:15:03 2008
From: sasko.mateski at gmail.com (Sasko Mateski)
Date: Wed Jun 25 04:06:33 2008
Subject: [Haskell-cafe] Problem installing Cabal-1.4.0.1 with ghc-6.8.3
Message-ID: <110ac8380806250115i7f628013xd45982f5c7112ca5@mail.gmail.com>

Hi,



After reading the latest article on the Haskell Hacking blog (Daily Haskell:
Download and analyse logs, then generate
sparklines<http://cgi.cse.unsw.edu.au/%7Edons/blog/2008/06/24#daily-haskell-one>)
I wanted to install cabal-install to check it out. Soon I found out that it
has a dependency on
Cabal (>=1.4&&<1.5), so next thing to do was getting and installing
Cabal-1.4.0.1 (since the version coming with
ghc-6.8.3 is 1.2.4.0). But during the configuration part of the installation
I got the following error:

During interactive linking, GHCi couldn't find the following symbol:
  SHGetFolderPathA@20
This may be due to you not asking GHCi to load extra object files,
archives or DLLs needed by your current session.  Restart GHCi, specifying
the missing library using the -L/path/to/object/dir and -lmissinglibname
flags, or simply by naming the relevant files on the GHCi command line.
Alternatively, this link failure might indicate a bug in GHCi.
If you suspect the latter, please send a bug report to:
  glasgow-haskell-bugs@haskell.org

<glasgow-haskell-bugs@haskell.org>



After some googling, I couldn't find anything on the web related to the
problem, so posting to a Haskell mailing list seemed like an obvious next
step.  Since I'm a novice Haskell any help would be very much appreciated,
indeed.

I'm using *ghc-6.8.3* on a *Windows XP Professional SP3*.



Regards

*Sasko*
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From lemming at henning-thielemann.de  Wed Jun 25 04:59:38 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun 25 04:51:08 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>


On Tue, 24 Jun 2008, Alistair Bayley wrote:

>>> 2008/6/24 Henning Thielemann <lemming@henning-thielemann.de>:
>>>>
>>> When you run configure, you should get output that says:
>>> Using Oracle: <path>
>>>
>>> What is <path>?
>>
>> I don't get these questions.
>
> Sorry. I was really asking (not very clearly): what is the output from
> "runhaskell Setup.hs configure -foracle" ?

It doesn't output the Oracle path. :-(

>> Ah, I must have set ORACLE_HOME for the Takusen installation ... should be
>> documented. However in my case, this doesn't change the path used by
>> Takusen's Setup/install.
>
> Well, you don't actually need it set for the Takusen install (it
> doesn''t use it). But $ORACLE_HOME/bin should be in your path. And it
> needs to contain the executable sqlplus. Can you run sqlplus?

Yes, I have successfully connected to a database with sqlplus, already.

> If sqlplus is not in my path then I get this error in the configure
> step, because I have specified sqlplus as a buildtool in
> Takusen.cabal:
>
>  > setup configure -foracle
>  Configuring Takusen-0.8.2...
>  setup: sqlplus is required but it could not be found.
>
> Note: sqlplus isn't really needed to build; this is just a validation
> step, to check you have $ORACLE_HOME/bin in your path.

I don't get an error. sqlplus is in $ORACLE_HOME/bin, but the RPM package 
also sets a link from /usr/bin/sqlplus to $ORACLE_HOME/bin, thus 'sqlplus' 
is in the $PATH also without $ORACLE_HOME. (But sqlplus cannot be started 
until the LD_LIBRARY_PATH is extended to Oracles libraries.)


>> $ echo $ORACLE_HOME
>> /usr/lib/oracle/10.2.0.4/client
>> $ ls $ORACLE_HOME
>> bin  lib
>> $ ll $ORACLE_HOME/lib
>> ...
>> I assume that libociei.so is the library I need.
>
> Actually it's libclntsh.so. You need to change the oracle section in
> Takusen.cabal to this:
>
>  If flag(oracle)
>    Exposed-modules:
>        Database.Oracle.Enumerator
>      , Database.Oracle.OCIConstants
>      , Database.Oracle.OCIFunctions
>    Build-Tools: sqlplus
>    If os(windows)
>      Extra-Libraries: oci
>    Else
>      Extra-Libraries: clntsh
>
> Your $ORACLE_HOME installation looks fairly normal, if somewhat
> minimal. I would normally expect to see sqlplus, and maybe some other
> executables, like tnsping. And a folder $ORACLE_HOME/oci/include,
> which contains the OCI header files.

They got installed to:
   /usr/include/oracle/10.2.0.4/client/
  That is, they are not in $ORACLE_HOME. :-(

>> $ runhaskell Setup.hs configure --user -f oracle
>> Configuring Takusen-0.8.2...
>
> Here, I would expect to see "Using Oracle: /usr/lib/oracle/10.2.0.4/client"

It does not tell me. :-(

> After setup configure you can say:
>  $ runhaskell Setup.hs register --gen-pkg-config
>
> and then take a look at the generated Takusen-0.8.2.conf. Check the
> library-dirs and include-dirs fields.

Takusen-0.8.2.conf and dist/installed-pkg-config contain the same.
They contain

include-dirs: /usr/oci

independent from my setting of ORACLE_HOME. As I said, I cannot manually 
fix dist/installed-pkg-config, because it gets overwritten by 'Setup 
install'.
From Alistair.Bayley at invesco.com  Wed Jun 25 05:24:14 2008
From: Alistair.Bayley at invesco.com (Bayley, Alistair)
Date: Wed Jun 25 05:16:44 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de><79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com><79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com><Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de><79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com><Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de><79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
Message-ID: <125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>

> From: haskell-cafe-bounces@haskell.org 
> [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of 
> Henning Thielemann
> 
> I don't get an error. sqlplus is in $ORACLE_HOME/bin, but the 
> RPM package 
> also sets a link from /usr/bin/sqlplus to $ORACLE_HOME/bin, 
> thus 'sqlplus' 
> is in the $PATH also without $ORACLE_HOME. (But sqlplus 
> cannot be started 
> until the LD_LIBRARY_PATH is extended to Oracles libraries.)

Ahhh... so Setup.hs thinks sqlplus is in /usr/bin, rather than
$ORACLE_HOME/bin. That explains:
  include-dirs: /usr/oci

I'll have to change the way that Setup.hs tries to find $ORACLE_HOME.
Using getEnv would be a much better idea. I don't recall why I didn't
use it before; perhaps it's not always set on Windows installations.


> > Your $ORACLE_HOME installation looks fairly normal, if somewhat
> > minimal. I would normally expect to see sqlplus, and maybe 
> some other
> > executables, like tnsping. And a folder $ORACLE_HOME/oci/include,
> > which contains the OCI header files.
> 
> They got installed to:
>    /usr/include/oracle/10.2.0.4/client/
>   That is, they are not in $ORACLE_HOME. :-(

I'm not sure how Setup.hs would find out where these are installed. Any
ideas? It may not matter, as I think you can compile without them. I'd
expect problems if you compile -fvia-C, though.


> >> $ runhaskell Setup.hs configure --user -f oracle
> >> Configuring Takusen-0.8.2...
> >
> > Here, I would expect to see "Using Oracle: 
> /usr/lib/oracle/10.2.0.4/client"
> 
> It does not tell me. :-(

That is odd.

Alistair
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From duncan.coutts at worc.ox.ac.uk  Wed Jun 25 05:33:46 2008
From: duncan.coutts at worc.ox.ac.uk (Duncan Coutts)
Date: Wed Jun 25 05:20:05 2008
Subject: [Haskell-cafe] Problem installing Cabal-1.4.0.1 with ghc-6.8.3
In-Reply-To: <110ac8380806250115i7f628013xd45982f5c7112ca5@mail.gmail.com>
References: <110ac8380806250115i7f628013xd45982f5c7112ca5@mail.gmail.com>
Message-ID: <1214386426.15010.1135.camel@localhost>


On Wed, 2008-06-25 at 10:15 +0200, Sasko Mateski wrote:
> I wanted to install cabal-install to check it out. Soon I found out
> that it has a dependency on Cabal (>=1.4&&<1.5), so next thing to do
> was getting and installing Cabal-1.4.0.1 (since the version coming
> with  ghc-6.8.3 is 1.2.4.0). But during the configuration part of the
> installation I got the following error:
>  
> During interactive linking, GHCi couldn't find the following symbol:
>   SHGetFolderPathA@20
> This may be due to you not asking GHCi to load extra object files,

Instead of using runghc Setup.hs configure, use:

ghc --make Setup.hs
Setup.exe configure
Setup.exe build
Setup.exe install

(This is documented in the README in the Cabal package tarball)

That way you are compiling Setup.hs using ghc rather than running it
using ghci. The problem is that on Windows Cabal needs to use some Win32
FFI calls and ghci doesn't know about the libs we are linking to.

You only have to use this workaround when installing Cabal itself (and
only on Windows). Once it's installed the runghc method works for all
other packages.

Even better, once you've got cabal-install working there'll be no need
for this kind of fiddling at all as cabal-install will compile Setup.hs
automatically (if that's necessary, often it can do it directly without
compiling Setup.hs at all).

Duncan

From chaddai.fouche at gmail.com  Wed Jun 25 05:55:13 2008
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Wed Jun 25 05:46:43 2008
Subject: [Haskell-cafe] Help with generalizing function
In-Reply-To: <18106999.post@talk.nabble.com>
References: <18063291.post@talk.nabble.com>
	<7ca3f0160806230111o36adb13cl96ebd67773718924@mail.gmail.com>
	<18065206.post@talk.nabble.com>
	<e9350eaf0806230242x69ac6e19y4408b1601653a45b@mail.gmail.com>
	<18106999.post@talk.nabble.com>
Message-ID: <e9350eaf0806250255m3b4634b1n5af52b67aedc339e@mail.gmail.com>

2008/6/25 leledumbo <leledumbo_cool@yahoo.co.id>:
>
> Hi, I'm back. I have some troubles understanding your code:
>
>                      ( 1:1:? is never reached. )

Why would 1:1 be reached when we search for lists with a sum of 1 ??

Your derivation is incorrect, when you're reading a list comprehension
you must see it as imbricated loops, let's see a correct derivation :

findAllAns 2 1 ==> [ x:xs | x <- [0..1], xs <- findAllAns 1 (1 - x) ]
  ==> concat [ [ 0 : xs | xs <- findAllAns 1 1 ], [ 1 : xs | xs <-
findAllAns 1 0 ] ]

findAllAns 1 1 ==> [ concat [ [ [ 0 : xs | xs <- findAllAns 0 1 ], [ 1
: xs | xs <- findAllAns 0 0 ] ]
 ==> concat [ [], [[1]] ] ==> [ [ 1 ] ]

In reality, all list comprehensions are translated to ordinary
functions under the hood, the translation is the following :

[ x:xs | x <- [0..s], xs <- findAllAns (n - 1) (s - x) ] == concatMap
(x -> concatMap (\xs -> x : xs) (findAllAns (n - 1) (s - x)) [0..s]

which is then easier to derive.

> I don't understand why if the last element is [[]] then it's included in the
> result and not if it's [].

I think with the concatMap above you'll understand better what's going on :

"concatMap (\xs -> 0 : xs) (findAllAns 0 1)" returns the empty list
because "findAllAns 0 1" is an empty list while "concatMap (\xs -> 1 :
xs) (findAllAns 0 0)" returns [[1]] because "findAllAns 0 0" is a list
that contains the empty list.

But you don't have to think so hard to find the good response, just
think of the edge cases logically : faire une somme de 0 avec 0
?l?ments c'est possible (parce que 0 est l'?l?ment neutre de
l'addition), tandis que faire une somme diff?rente de 0 avec 0
?l?ments est impossible.
(The sum of 0 elements is always 0, and the product of 0 elements is always 1)

-- 
Jeda?
From alistair at abayley.org  Wed Jun 25 06:07:49 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Wed Jun 25 05:59:21 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
Message-ID: <79d7c4980806250307h64bfba7dh95b518967c171384@mail.gmail.com>

> I'll have to change the way that Setup.hs tries to find $ORACLE_HOME.
> Using getEnv would be a much better idea. I don't recall why I didn't
> use it before; perhaps it's not always set on Windows installations.

Try this version of configOracle in Setup.hs:

configOracle verbose buildtools = do
  if not (sqlplusProgram `isElem` buildtools)
    then return Nothing
    else do
      path <- getEnv "ORACLE_HOME"
      info verbose ("Using Oracle: " ++ path)
      makeConfig path libDir "oci/include"
    where libDir = if isWindows then "bin" else "lib"


You'll also need to add this import:

import System.Environment (getEnv)

I always used to get the "Using..." messages, but now it seems I need to say:
  $ setup configure -v -foracle

Alistair
From jgoerzen at complete.org  Wed Jun 25 09:25:34 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Wed Jun 25 09:17:11 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
Message-ID: <4862474E.8070801@complete.org>

Henning Thielemann wrote:
> On Tue, 24 Jun 2008, Alistair Bayley wrote:
> 
>> 2008/6/24 Henning Thielemann <lemming@henning-thielemann.de>:
>>> (Btw. Takusen should be split into
>>> several packages for all database backends because Cabal flags must not
>>> influence the package interface.)
>> I don't understand this (cabal flags must not influence package
>> interface). I thought that was the point of cabal flags? I wanted to
>> have a single package installation, and this seems like the best way.
> 
> No, if a package imports Takusen - how can it be assert that it can import 

I haven't read this entire thread, but I might also just interject here
that HDBC supports ODBC (on Windows, and on Linux/Posix platforms via
unixODBC, iODBC, or similar), which may be another avenue for you to
try.  I'm sure there are ODBC Oracle drivers out there, and so if you
have your ODBC layer working, you get Haskell support easily.

-- John
From lemming at henning-thielemann.de  Wed Jun 25 09:31:27 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun 25 09:23:02 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <4862474E.8070801@complete.org>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<4862474E.8070801@complete.org>
Message-ID: <Pine.LNX.4.64.0806251529030.11636@anubis.informatik.uni-halle.de>


On Wed, 25 Jun 2008, John Goerzen wrote:

> I haven't read this entire thread, but I might also just interject here
> that HDBC supports ODBC (on Windows, and on Linux/Posix platforms via
> unixODBC, iODBC, or similar), which may be another avenue for you to
> try.  I'm sure there are ODBC Oracle drivers out there, and so if you
> have your ODBC layer working, you get Haskell support easily.

This was actually how the thread started: I don't get ODBC for Oracle 
working on Linux. :-(
  Maybe this is an unixODBC issue - is iODBC an API-compatible replacement?
From icfp.publicity at googlemail.com  Wed Jun 25 10:01:03 2008
From: icfp.publicity at googlemail.com (Matthew Fluet (ICFP Publicity Chair))
Date: Wed Jun 25 09:52:37 2008
Subject: [Haskell-cafe] ICFP08 Final Call for posters
Message-ID: <53ff55480806250701u79d6fba1lcd089c69de68691d@mail.gmail.com>

ICFP 2008 poster session
September 21, 2008
Call for presentation proposals

ICFP 2008 will feature a poster session for researchers and
practitioners, including students.  The session will provide friendly
feedback for work that is in gestation or ongoing, as well as
opportunities to meet each other and exchange ideas.  We welcome poster
submissions on all ICFP topics, especially presentations of

  - applications of and to functional programming;
  - recent work presented at more distant venues; and
  - ongoing work, whether or not submitted to ICFP.

There will be no formal proceedings, but presenters will be invited to
submit working notes, demo code, and other materials to supplement their
abstract and poster.  These materials will be released informally on a
Web page dedicated to the poster session.  An accepted submission is not
intended to replace conference or journal publication.

Persons interested in presenting a poster are invited to submit a
one-page abstract in SIGPLAN conference style
    http://www.acm.org/sigs/sigplan/authorInformation.htm
to the Web site
    https://www.softconf.com/s08/icfp08-posters/submit.html
by June 30, 2008.  The program committee will review the submissions
for relevance and interest, and notify the authors by July 14, 2008.
Accepted posters must be presented by the authors in person on Sunday,
September 21, 2008.

Important dates:
Submission: Monday, June 30, 2008
Notification: Monday, July 14, 2008
Presentation: Sunday, September 21, 2008

Program committee:
Benjamin Pierce (University of Pennsylvania)
Colin Runciman (University of York)
Chung-chieh Shan (Rutgers University)
From conal at conal.net  Wed Jun 25 10:50:59 2008
From: conal at conal.net (Conal Elliott)
Date: Wed Jun 25 10:42:29 2008
Subject: [Haskell-cafe] history of tuples vs pairs
Message-ID: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>

I have a foggy memory that early ML had only binary pairing, nesting for
n-tuples.  Can anyone confirm this memory.  If so, does anyone remember the
rationale for going to n-tuples?  Performance, perhaps?

Similarly, did the Haskell designers consider pairs as an alternative to
n-ary tuples?

The reason I ask is that while ghc and libraries suppors n-tuples for some
values of n, the support is generally incomplete and inconsistent.  And some
abstractions are very heavily biased toward pairing, particularly Arrow and
the pair instances of Monad and Applicative.  And of course, inclusion of
fst and snd in the prelude but lack of similar standard functions for
n-tuples with n>2.

  - Conal
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From dcespin at fastmail.fm  Wed Jun 25 11:37:30 2008
From: dcespin at fastmail.fm (Dominic Espinosa)
Date: Wed Jun 25 11:28:59 2008
Subject: [Haskell-cafe] Simple question about processing XML with HaXml
Message-ID: <20080625153729.GD2960@argivia.columbus.rr.com>

Hello,

I'm trying to learn how to use HaXml, but I'm having trouble getting off
the ground. I can see from the documentation how to process XML using
the combinators and processXmlWith, but processXmlWith seems to "hide"
the actual process of reading and parsing the XML. Suppose that
processXmlWith isn't suitable for a program. How then do you load the
XML and apply filters to it?

I guess what I'm asking is, given the following code:

load filename = do
  handle <- IO.openFile filename IO.ReadMode
  contents <- IO.getContents handle
  IO.hclose handle
  return $ xmlParse filename contents

myTest fname = do
  -- read file
  d <- load fname
  --- ?? now what?

I'm sure the answer to this is quite simple, but I'm coming from a
background of OO and SAX, and the HaXml docs are a bit cryptic as yet.

Additionally, if anyone knows of any tutorials pertaining to HaXml,
other than the papers on the HaXml website and the blog entries on
cleaning legacy HTML, I'd appreciate some pointers.

Thanks.

From Christian.Maeder at dfki.de  Wed Jun 25 11:49:20 2008
From: Christian.Maeder at dfki.de (Christian Maeder)
Date: Wed Jun 25 11:40:50 2008
Subject: [Haskell-cafe] Re: history of tuples vs pairs
In-Reply-To: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
Message-ID: <48626900.5090809@dfki.de>

Conal Elliott wrote:
> I have a foggy memory that early ML had only binary pairing, nesting for 
> n-tuples.  Can anyone confirm this memory.  If so, does anyone remember 
> the rationale for going to n-tuples?  Performance, perhaps?

In Isabelle HOL "*" is a right-associative (pair) type constructor.
So "T1 * T2 * T3" is the same as "T1 * (T2 * T3)".
Although the concept is minimal it is sort of asymmetric (wrt.
associativity).

Cheers Christian


From dave at zednenem.com  Wed Jun 25 13:29:53 2008
From: dave at zednenem.com (David Menendez)
Date: Wed Jun 25 13:21:26 2008
Subject: [Haskell-cafe] history of tuples vs pairs
In-Reply-To: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
Message-ID: <49a77b7a0806251029s7fc1ad3bj8535a8d9d9217474@mail.gmail.com>

2008/6/25 Conal Elliott <conal@conal.net>:
> I have a foggy memory that early ML had only binary pairing, nesting for
> n-tuples.  Can anyone confirm this memory.  If so, does anyone remember the
> rationale for going to n-tuples?  Performance, perhaps?
>
> Similarly, did the Haskell designers consider pairs as an alternative to
> n-ary tuples?

I think performance was part of it: accessing the nth element of a
tuple is O(1), but the nth element of a nested pair is O(n).

On the other hand, you can't internally represent nested pairs as
n-tuples because of laziness. (a,(b,c)) has elements of the form
(x,_|_) that don't correspond to any triple.

-- 
Dave Menendez <dave@zednenem.com>
<http://www.eyrie.org/~zednenem/>
From nielsadb at gmail.com  Wed Jun 25 13:42:16 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Wed Jun 25 13:33:47 2008
Subject: [Haskell-cafe] Two questions regarding Alex/Parsec
In-Reply-To: <20080624210829.GL17394@scytale.galois.com>
References: <1214341482.13477.26.camel@porcupine>
	<20080624210829.GL17394@scytale.galois.com>
Message-ID: <1214415736.8450.16.camel@porcupine>

On Tue, 2008-06-24 at 14:08 -0700, Don Stewart wrote:

> Just a quick question, did you try using the pandoc markdown parser?
> 
>     http://hackage.haskell.org/packages/archive/pandoc/0.46/doc/html/Text-Pandoc-Readers-Markdown.html
> 
> It'd be useful to know if that was enough for printing and generation
> of wiki content. Though being GPLd, it'd also be nice to have a BSD-ish
> licensed wiki parser/pretty printer.

No, I did not. In fact I didn't know about this project, but it looks
very interesting. I'll definitely go and look at the code.

One of the reasons I started worked on a MediaWikiParser was because I
wanted to use the Haskell language and some of its tools rather than just
read about them. I'm not really interested in making a clone of something
that already exists just for the sake of ideology (although personally
I'm much more fond of BSD-style licenses than of GPL).

On a side note: are there any lexer/parser generators out there I should
be aware of? As mentioned in my original post I've tried using Happy, but
I was unable to understand its very concise error message 'parE'.
It would be really nice to have a tool that generates an AST automatically
(e.g. something like ANTLR).

Regards,
Niels


From dons at galois.com  Wed Jun 25 13:46:30 2008
From: dons at galois.com (Don Stewart)
Date: Wed Jun 25 13:38:04 2008
Subject: [Haskell-cafe] Two questions regarding Alex/Parsec
In-Reply-To: <1214415736.8450.16.camel@porcupine>
References: <1214341482.13477.26.camel@porcupine>
	<20080624210829.GL17394@scytale.galois.com>
	<1214415736.8450.16.camel@porcupine>
Message-ID: <20080625174630.GA21487@scytale.galois.com>

nielsadb:
> On Tue, 2008-06-24 at 14:08 -0700, Don Stewart wrote:
> 
> > Just a quick question, did you try using the pandoc markdown parser?
> > 
> >     http://hackage.haskell.org/packages/archive/pandoc/0.46/doc/html/Text-Pandoc-Readers-Markdown.html
> > 
> > It'd be useful to know if that was enough for printing and generation
> > of wiki content. Though being GPLd, it'd also be nice to have a BSD-ish
> > licensed wiki parser/pretty printer.
> 
> No, I did not. In fact I didn't know about this project, but it looks
> very interesting. I'll definitely go and look at the code.
  
> One of the reasons I started worked on a MediaWikiParser was because I
> wanted to use the Haskell language and some of its tools rather than just
> read about them. I'm not really interested in making a clone of something
> that already exists just for the sake of ideology (although personally
> I'm much more fond of BSD-style licenses than of GPL).

Personally, I'd find a MediaWiki parser/pretty printer quite useful!
  
> On a side note: are there any lexer/parser generators out there I should
> be aware of? As mentioned in my original post I've tried using Happy, but
> I was unable to understand its very concise error message 'parE'.
> It would be really nice to have a tool that generates an AST automatically
> (e.g. something like ANTLR).

There's lots, but probably Alex (lexer) and Happy (parser) or Parsec are
the most widely used.

-- Don
From nielsadb at gmail.com  Wed Jun 25 13:50:08 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Wed Jun 25 13:41:37 2008
Subject: [Haskell-cafe] history of tuples vs pairs
In-Reply-To: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
Message-ID: <1214416208.8450.22.camel@porcupine>

On Wed, 2008-06-25 at 16:50 +0200, Conal Elliott wrote:
> I have a foggy memory that early ML had only binary pairing, nesting
> for n-tuples.  Can anyone confirm this memory.  If so, does anyone
> remember the rationale for going to n-tuples?  Performance, perhaps?

?What is the difference between a list build up of Cons and a "tuple"
made out of pairs? I think the latter wouldn't really add anything new.

A question of my own: is there much difference between e.g.
  data MyData = MyData Int Bool Char
and
  type MyData = (Int, Bool, Char)
other than the syntax of course?

Regards,
Niels

From jgoerzen at complete.org  Wed Jun 25 14:09:35 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Wed Jun 25 14:01:09 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806251529030.11636@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<4862474E.8070801@complete.org>
	<Pine.LNX.4.64.0806251529030.11636@anubis.informatik.uni-halle.de>
Message-ID: <486289DF.70107@complete.org>

Henning Thielemann wrote:
> On Wed, 25 Jun 2008, John Goerzen wrote:
> 
>> I haven't read this entire thread, but I might also just interject here
>> that HDBC supports ODBC (on Windows, and on Linux/Posix platforms via
>> unixODBC, iODBC, or similar), which may be another avenue for you to
>> try.  I'm sure there are ODBC Oracle drivers out there, and so if you
>> have your ODBC layer working, you get Haskell support easily.
> 
> This was actually how the thread started: I don't get ODBC for Oracle 
> working on Linux. :-(
>   Maybe this is an unixODBC issue - is iODBC an API-compatible replacement?
> 

Yes, iODBC is.  There are also proprietary ODBC implementations.  At
work, we have to deal with Progress databases.  Their ODBC library,
presumably due to being a rather ancient shared library, doesn't work
with unixODBC -- but they ship their entire own ODBC framework, Merant
ODBC.  HDBC compiles against it (though must be modified to not support
wide characters, which Merant ODBC doesn't support).

-- John
From nielsadb at gmail.com  Wed Jun 25 14:17:09 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Wed Jun 25 14:08:38 2008
Subject: [Haskell-cafe] Two questions regarding Alex/Parsec
In-Reply-To: <20080625174630.GA21487@scytale.galois.com>
References: <1214341482.13477.26.camel@porcupine>
	<20080624210829.GL17394@scytale.galois.com>
	<1214415736.8450.16.camel@porcupine>
	<20080625174630.GA21487@scytale.galois.com>
Message-ID: <1214417829.8450.44.camel@porcupine>

On Wed, 2008-06-25 at 10:46 -0700, Don Stewart wrote:

> > One of the reasons I started worked on a MediaWikiParser was because I
> > wanted to use the Haskell language and some of its tools rather than just
> > read about them. I'm not really interested in making a clone of something
> > that already exists just for the sake of ideology (although personally
> > I'm much more fond of BSD-style licenses than of GPL).
> 
> Personally, I'd find a MediaWiki parser/pretty printer quite useful!

Oh yes, don't yet me wrong, this isn't just a study project for me; I
really want to have a working parser. I'm just saying that if there was
such a parser for Haskell already under the GPL I wouldn't be bothered
rewriting it just so I could license it under MIT/BSD.

> > On a side note: are there any lexer/parser generators out there I should
> > be aware of? As mentioned in my original post I've tried using Happy, but
> > I was unable to understand its very concise error message 'parE'.
> > It would be really nice to have a tool that generates an AST automatically
> > (e.g. something like ANTLR).
> 
> There's lots, but probably Alex (lexer) and Happy (parser) or Parsec are
> the most widely used.

Okay, in that case I'll stick to Alex + Parsec, it's quite comfortable
so far.

By the way, does anyone know the answer to my original question?
Especially the first one (Alex' AlexPosn vs. Parsec's SourcePos) is
worrying me somewhat.

Regards,
Niels


From byorgey at seas.upenn.edu  Wed Jun 25 14:24:57 2008
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Wed Jun 25 14:16:25 2008
Subject: [Haskell-cafe] history of tuples vs pairs
In-Reply-To: <1214416208.8450.22.camel@porcupine>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
	<1214416208.8450.22.camel@porcupine>
Message-ID: <20080625182456.GA12376@minus.seas.upenn.edu>

On Wed, Jun 25, 2008 at 07:50:08PM +0200, Niels Aan de Brugh wrote:
> On Wed, 2008-06-25 at 16:50 +0200, Conal Elliott wrote:
> > I have a foggy memory that early ML had only binary pairing, nesting
> > for n-tuples.  Can anyone confirm this memory.  If so, does anyone
> > remember the rationale for going to n-tuples?  Performance, perhaps?
> 
> ???What is the difference between a list build up of Cons and a "tuple"
> made out of pairs? I think the latter wouldn't really add anything new.

The difference is that all the elements of a list must be the same
type, whereas nested tuples could have elements of any type.  For
example,

  (True, (6, 'c')) :: (Bool, (Int, Char))

and there is no corresponding three-element list.  However, you're
right in noting the similarity between lists and nested tuples -- in
fact, this is exactly how lists are implemented in lisp (which is
where we get the tern 'cons').

> 
> A question of my own: is there much difference between e.g.
>   data MyData = MyData Int Bool Char
> and
>   type MyData = (Int, Bool, Char)
> other than the syntax of course?

Conceptually, there is not much difference; these types are clearly
isomorphic.  Practically speaking, there are differences other than
just the syntax.  For example, in Haskell 98 you are not allowed to
make class instances for type synonyms.  Another big difference is
that this:

  type MyData = (Int, Bool, MyData)

is illegal, whereas this:

  data MyData = MyData Int Bool MyData

is perfectly fine.

-Brent
From nielsadb at gmail.com  Wed Jun 25 14:58:18 2008
From: nielsadb at gmail.com (Niels Aan de Brugh)
Date: Wed Jun 25 14:49:46 2008
Subject: [Haskell-cafe] Two questions regarding Alex/Parsec
In-Reply-To: <1214417829.8450.44.camel@porcupine>
References: <1214341482.13477.26.camel@porcupine>
	<20080624210829.GL17394@scytale.galois.com>
	<1214415736.8450.16.camel@porcupine>
	<20080625174630.GA21487@scytale.galois.com>
	<1214417829.8450.44.camel@porcupine>
Message-ID: <1214420298.8450.48.camel@porcupine>

On Wed, 2008-06-25 at 20:17 +0200, Niels Aan de Brugh wrote:

> By the way, does anyone know the answer to my original question?
> Especially the first one (Alex' AlexPosn vs. Parsec's SourcePos) is
> worrying me somewhat.

To answer my own question: as it turns out I was using an old version of
Parsec (2.1.0, the one that comes with Ubuntu Linux). A newer version of
Parsec (3.0.0) adds a newPos function in ?Text.Parsec.Pos that trivially
constructs a new SourcePos.

Regards,
Niels

From wagner.andrew at gmail.com  Wed Jun 25 16:14:21 2008
From: wagner.andrew at gmail.com (Andrew Wagner)
Date: Wed Jun 25 16:05:50 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
Message-ID: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>

This post borders on being off-topic, but it seems like people on this
list would be interested.

First, some of you know that I had the distinct privilege of flying
out to Microsoft this week to interview for a Software Development
Engineer position on their Live Search team. So I want to first tell
you about their reaction to my Haskell experience, and then give you
some interesting coding problems that they asked me to solve, which
could be good practice to tackle in Haskell.

So the first task I was given to do, long before my in-person
interview, was to complete a technical assessment. This consisted of
two fairly simple algorithms to write. I chose to do so in Haskell. On
the basis of this assessment, they decided I was worth a phone
interview. When I got on that interview, one of the first things the
interviewer said was "So, one thing that jumped out immediately was
that you did the assessment in Haskell. Tell me a little bit about
that." It led to a good discussion about why I like Haskell and
functional programming. When I actually flew out there, several people
made comments about me being "that guy who writes Haskell". The
recruiter even said something along the lines of "anyone who knows
haskell is certainly worth our time to talk to." Moral of the story:
Haskell rocks, and even Microsoft knows it!

That said, here are some interesting problems to work through in
Haskell, if you'd like:

1.) A "rotated array" is an array of integers in ascending order,
after which for every element i, it has been moved to element (i + n)
mod sizeOfList. Write a function that takes a rotated array and, in
less-than-linear time, returns n (the amount of rotation).

2.) You are given a list of Ball objects. Each Ball is either Red or
Blue. Write a function that partitions these balls so that all of the
balls of each color are contiguous. Return the index of the first ball
of the second color (your result can be Red balls, then Blue balls, or
the other way around). In haskell, you'll probably want to return a
([Ball],Int).

3.) Live Search is a search engine. Suppose it was to be tied into an
online store. Now you're given two lists. One is a [(SessionId,
NormalizedQuery)]. That is, when a particular user performs a query,
it is turned into some consistent format, based on their apparent
intent, and stored in this logfile. The second list is a [(SessionId,
ProductId)]. This indicates the product bought by a particular user.
Now, you want to take these two (potentially very long) lists, and
return some structure that will make it easy to take a query and
return a list of the most popular resulting purchases. That is, of
people who have run this query in the past, what are the most common
products they've wound up buying? The interviewer said that this is an
instance of a well-known problem, but I didn't catch the name of it.

4.) You're given an array which contains the numbers from 1 to n, in
random order, except there is one missing. Write a function to return
the missing number.

5.) Write a function to reconstruct a binary tree from its preorder
traversal and inorder traversal. Take into account that the traversals
could be invalid.

6.) You have a [(WeatherStationId, Latitude, Longitude)]. Similar to
#3, write a function which will, off-line, turn this into a data
structure from which you can easily determine the nearest Weather
Station, given an arbitrary Latitude and Longitude.

7.) Write a function for scoring a mastermind guess. That is, in a
game of mastermind
(http://en.wikipedia.org/wiki/Mastermind_(board_game)), given a guess,
and the actual answer, determine the number correct, the number wrong,
and the number out of place.

8.) Implement a trie (http://en.wikipedia.org/wiki/Trie) data
structure. Write a function add, which takes a word, and a trie, and
adds the word to the trie. Write another function lookup, which takes
a prefix and a trie, and returns all the words in the trie that start
with that prefix.

9.) Write an algorithm to shuffle a deck of cards. Now write a
function to perform some kind of evaluation of "how shuffled" a deck
of cards is.

Hope you enjoy!
From droundy at darcs.net  Wed Jun 25 16:35:34 2008
From: droundy at darcs.net (David Roundy)
Date: Wed Jun 25 16:27:03 2008
Subject: [Haskell-cafe] history of tuples vs pairs
In-Reply-To: <20080625182456.GA12376@minus.seas.upenn.edu>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
	<1214416208.8450.22.camel@porcupine>
	<20080625182456.GA12376@minus.seas.upenn.edu>
Message-ID: <20080625203533.GA19738@darcs.net>

On Wed, Jun 25, 2008 at 02:24:57PM -0400, Brent Yorgey wrote:
> On Wed, Jun 25, 2008 at 07:50:08PM +0200, Niels Aan de Brugh wrote:
> > On Wed, 2008-06-25 at 16:50 +0200, Conal Elliott wrote:
> > > I have a foggy memory that early ML had only binary pairing, nesting
> > > for n-tuples.  Can anyone confirm this memory.  If so, does anyone
> > > remember the rationale for going to n-tuples?  Performance, perhaps?
> > 
> > ???What is the difference between a list build up of Cons and a "tuple"
> > made out of pairs? I think the latter wouldn't really add anything new.
> 
> The difference is that all the elements of a list must be the same
> type, whereas nested tuples could have elements of any type.  For
> example,
> 
>   (True, (6, 'c')) :: (Bool, (Int, Char))
> 
> and there is no corresponding three-element list.  However, you're
> right in noting the similarity between lists and nested tuples -- in
> fact, this is exactly how lists are implemented in lisp (which is
> where we get the tern 'cons').

The other difference is that nested tuples have the number of elements
specified in the type, while lists do not.
-- 
David Roundy
Department of Physics
Oregon State University
From lemming at henning-thielemann.de  Wed Jun 25 16:49:43 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed Jun 25 16:41:12 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806252246560.31708@anubis.informatik.uni-halle.de>


On Wed, 25 Jun 2008, Andrew Wagner wrote:

> The recruiter even said something along the lines of "anyone who knows 
> haskell is certainly worth our time to talk to." Moral of the story: 
> Haskell rocks, and even Microsoft knows it!

Interesting. That is they are aware what they support in Cambridge for years?

From wagner.andrew at gmail.com  Wed Jun 25 16:54:45 2008
From: wagner.andrew at gmail.com (Andrew Wagner)
Date: Wed Jun 25 16:46:14 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <Pine.LNX.4.64.0806252246560.31708@anubis.informatik.uni-halle.de>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<Pine.LNX.4.64.0806252246560.31708@anubis.informatik.uni-halle.de>
Message-ID: <b8a8636e0806251354s2e83399aibb1d54e42503eb24@mail.gmail.com>

I would guess that there are a lot of things their research department
does that doesn't get used or thought about on a daily basis by the
implementation teams. Either way, the sarcasm is not necessary.

On Wed, Jun 25, 2008 at 4:49 PM, Henning Thielemann
<lemming@henning-thielemann.de> wrote:
>
> On Wed, 25 Jun 2008, Andrew Wagner wrote:
>
>> The recruiter even said something along the lines of "anyone who knows
>> haskell is certainly worth our time to talk to." Moral of the story: Haskell
>> rocks, and even Microsoft knows it!
>
> Interesting. That is they are aware what they support in Cambridge for
> years?
>
>
From byorgey at seas.upenn.edu  Wed Jun 25 17:10:31 2008
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Wed Jun 25 17:01:59 2008
Subject: [Haskell-cafe] Haskell Weekly News: Issue 74 - June 25, 2008
Message-ID: <20080625211031.GA31043@minus.seas.upenn.edu>

---------------------------------------------------------------------------
Haskell Weekly News
http://sequence.complete.org/hwn/20080625
Issue 74 - June 25, 2008
---------------------------------------------------------------------------

   Welcome to issue 74 of HWN, a newsletter covering developments in the
   [1]Haskell community.

   This week, you'll notice a bit more detail in the 'Blogs' section. I've
   added summaries to some of the posts, to help you decide which you
   might be interested to read (only a few this week, since I added them
   at the last minute). I've also >>> highlighted blogs not syndicated on
   Planet Haskell---mostly people who have just begun learning Haskell and
   decided to blog about it. Go show them some comment love, and invite
   them into the community!

Community News

   Andrew Wagner (chessguy) recently flew out to Microsoft for an
   interview with their Live Search team. In [2]an email to the cafe, he
   shares some stories from his experience and some interesting coding
   challenges.

Announcements

   HAppS self-demoing tutorial. Thomas Hartman [3]announced a
   self-demoing, HStringTemplate-using intro to HAppS. Check out the
   [4]live demo or obtain it [5]from Hackage.

   NWFP Interest Group. Greg Meredith [6]announced the next monthly
   meeting of the NW Functional Programmers Interest group, 6:30 on June
   25 at the Seattle Public Library. Greg will talk about a very cool
   [7]compositional representation of graphs he's been tinkering with
   recently.

   ICFP final call for posters. Matthew Fluet [8]announced the final call
   for proposals for the ICFP 2008 poster session, which should be
   [9]submitted by June 30. Let people know what you're working on!

   type-level and parameterized-data packages. Alfonso Acosta
   [10]announced the release of the [11]type-level and parameterized-data
   packages, which provide type-level computation and parameterized types
   a la a dependently-typed system.

   Lambda in the sun. James Iry [12]announced the creation of [13]Southern
   California Functional Programmers (SoCalFP), a group for people in LA,
   Orange County, and San Diego to meet to discuss, debate, present, and
   learn about functional programming concepts and techniques in various
   languages.

   Real World Haskell. Bryan O'Sullivan [14]announced the availability of
   ten new draft chapters of [15]Real World Haskell, the upcoming O'Reilly
   book being written by Bryan, John Goerzen, and Don Stewart. In case you
   were worried, yes, you'll be able to have one in your Christmas
   stocking!

   Pugs on hackage!. Audrey Tang has uploaded to Hackage [16]version
   6.2.13.2 of [17]Pugs, an implementation of Perl 6 in Haskell.

   Literal programming with rst-literals. Martin Blais [18]described a
   neat use of his utility [19]rst-literals to extract Haskell code from
   ReST documents, enabling a different style of literate programming.

   Pipe 1.0. Matti Niemenmaa [20]announced the release of [21]Pipe, a
   library for piping data through a pipeline of processes.

   HUnit. Richard Giraud [22]announced that he has improved the HUnit
   documentation and published the changes in a [23]darcs repository.

   hback. Norbert Wojtowicz [24]announced a new release of [25]hback, a
   Haskell implementation of the [26]dual n-back memory game using
   [27]gtk2hs.

Google Summer of Code

   Progress updates from participants in the 2008 [28]Google Summer of
   Code.

   Hoogle 4. Neil Mitchell (ndm) is working on Hoogle 4, and recently
   [29]added two new features, multi-word search and intelligent
   suggestions.

   DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a physics
   engine using [30]Data Parallel Haskell. [31]This week he intended to
   implement simple ad-hoc cubic collision geometry to test collisions
   with rotation, but the code became too cumbersome and non-extensible.
   He took a break to read some papers, and found [32]a better solution.

   GHC plugins. Max Bolingbroke is working on dynamically loaded plugins
   for GHC. [33]This week he worked on adding arbitrary user-specified
   phases to GHC, implementing a control system, pipeline generation, and
   [34]Template Haskell integration. Next he plans to work on a plugin
   annotation system.

   Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a
   make-like dependency analysis framework for Cabal. He has posted [35]a
   detailed explanation of his project, some of the issues involved, and
   his progress so far.

   Language.C. Benedikt Huber (visq) is working on Language.C, a
   standalone parser/pretty printer library for C99. This week he worked
   on AST documentation and improvements, prepared to port the AST
   analysis from c2hs, and worked on the pretty printer's internals.

   Generic tries. Jamie Brandon is working on a library for efficient maps
   using generalized tries. Recently he has worked on implementing some
   [36]bitpacking tools to save memory.

   GHC API. Thomas Schilling (nominolo) is supposedly working on
   [37]improvements to the GHC API. However, officials at HWN headquarters
   have begun privately speculating that Thomas does not, in fact, exist.

Discussion

   history of tuples vs pairs. Conal Elliott [38]asked about the history
   of support for n-tuples in Haskell and ML.

   hackageDB maintainer policy. Ross Paterson began a lengthy
   [39]discussion towards agreeing on a policy for uploading packages to
   Hackage, specifying whether the package is maintained and who is
   maintaining it, and other related issues.

   What is a rigid type variable?. Xiao-Yong Jin [40]asked what the 'rigid
   type variables' are that are sometimes referred to in GHC error
   messages. Read the thread for a concise discussion and the solution to
   the original problem.

   Map interface. Jamie Brandon started a [41]thread asking for feedback
   on his proposed API for generic tries, and the discussion is still
   ongoing.

   Left and right folds. George Kangas [42]exhibited a pair of very
   elegant alternate definitions for left and right fold, and showed how
   this alternate viewpoint makes obvious several algebraic identities as
   well as the generalization to [43]Data.Foldable. A must-read for the
   aspiring functional programmer.

   ribbonsPerLine. Alfonso Acosta asked an interesting [44]question about
   "ribbonsPerLine" in the Text.PrettyPrint.HughesPJ library. Do you know
   what it does? The answer can be found in the [45]original paper
   describing the library.

Jobs

   PhD position at University of Strathclyde, Glasgow. Simon Marlow
   [46]announced, on behalf of Patricia Johann, an open PhD position in
   operational and categorical approaches to parametricity. The funded
   position is in the newly-formed Mathematically Structured Programming
   group at the University of Strathclyde, comprising Neil Ghani, Patricia
   Johann, and Conor McBride.

   Quantitative Trading Developer Position at Hutchin Hill Capital. Neil
   Mehra [47]announced an open position for a Quantitative Trading
   Developer at Hutchin Hill Capital, a newly formed multi-strategy hedge
   fund located in midtown Manhattan.

Blog noise

   [48]Haskell news from the [49]blogosphere.
     * >>> Blockcipher: [50]Converting Geospatial Coordinates. Blockcipher
       has had enough of reading Haskell tutorials, and is itching to
       actually create something useful!
     * Roman Cheplyaka: [51]V-Clip algorithm (status update). An update on
       Roman's Google Summer of Code project.
     * Andy Gill: [52]Memo class using type families.
     * >>> blueapple: [53]Project Euler. blueapple is hooked on
       [54]Project Euler and has been using it as an opportunity to learn
       Haskell.
     * >>> Dinesh Pillay: [55]Haskell & Type Inference. Dinesh has been
       learning Haskell for just a few days now and is really enjoying it.
       In this post he shares a problem he was having with types and its
       solution.
     * Don Stewart (dons): [56]Daily Haskell: Download and analyse logs,
       then generate sparklines. A new series on gluing Hackage libraries
       together to get things done.
     * Max Bolingbroke: [57]Compiler Plugins For GHC: Week Two. An update
       on Max's Google Summer of Code project.
     * Edward Kmett: [58]Paramorphism.
     * Edward Kmett: [59]Catamorphism.
     * Edward Kmett: [60]Recursion Schemes: A Field Guide. Edward is
       writing up a 'field guide' to all those 'foomorphism' recursion
       schemes.
     * Neil Mitchell: [61]GSoC Hoogle: Week 4.
     * Real World Haskell: [62]Ten new draft chapters.
     * Jamie Brandon: [63]Bitpacking. Updates on Jamie's Google Summer of
       Code project.
     * Jamie Brandon: [64]Finally!.
     * Brent Yorgey: [65]ZipEdit. Brent describes a new library for
       creating simple interactive list editors.
     * Real-World Haskell: [66]Video of my concurrent/multicore Haskell
       talk is up.
     * Roman Cheplyaka: [67]Status report: week 4. An update on Roman's
       Google Summer of Code project.
     * Osfameron: [68]More Countdown: laziness, Scheme, and German frogs.
     * Andrea Vezzosi (Saizan): [69]a dependency analysis framework for
       Cabal.
     * Osfameron: [70]Schwartzian transform in Haskell.
     * Neil Mitchell: [71]Hoogle 4 New Features.
     * Thomas M. DuBuisson: [72]Past and Future libraries.
     * >>> codeflow: [73]Haskell + a grain of Python. codeflow talks about
       his experience learning Haskell and functional programming.
     * >>> Peter Christensen: [74]Hey Language Snobs: Don't Pinch Pennies.
     * >>> Micah Elliott: [75]1983-96: The Golden Age of Programming
       Languages.

Quotes of the Week

     * povman: when does ghc6.10 plan to release itself?
     * Baughn: So I just rewrote a fairly complex text extraction/indexing
       system to pipeline its work across several processors - painlessly,
       in less than five minutes. Bravo, haskell!
     * monochrom: We need to cabalise Cale.
     * Botje: h0t (monoid `mappend` monoid) action?
     * quicksilver: the only tool we have in haskell98 for performing an
       action is the magic sigil 'main ='
     * solrize: haskell has a very steep unlearning curve :)
     * Botje: drug users pass around needles, haskell users pass around
       Oleg papers
     * qwe1234: i know haskell, ocaml, scheme and prolog better than you
       ever will.

About the Haskell Weekly News

   New editions are posted to [76]the Haskell mailing list as well as to
   [77]the Haskell Sequence and [78]Planet Haskell. [79]RSS is also
   available, and headlines appear on [80]haskell.org. Headlines are
   available as [81]PDF.

   To help create new editions of this newsletter, please see the
   information on [82]how to contribute. Send stories to byorgey at seas
   dot upenn dot edu. The darcs repository is available at darcs get
   [83]http://code.haskell.org/~byorgey/code/hwn/ .

References

   1. http://haskell.org/
   2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41760
   3. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044696.html
   4. http://rippledeals.com:5001/
   5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tutorial
   6. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044671.html
   7. http://biosimilarity.blogspot.com/2008/06/algebra-of-graphs-individually-and.html
   8. http://article.gmane.org/gmane.comp.lang.haskell.general/16263
   9. https://www.softconf.com/s08/icfp08-posters/submit.html
  10. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044630.html
  11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level
  12. http://article.gmane.org/gmane.comp.lang.haskell.general/16260
  13. http://socalfp.blogspot.com/
  14. http://www.realworldhaskell.org/blog/2008/06/22/ten-new-draft-chapters/
  15. http://www.realworldhaskell.org/blog/
  16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Pugs-6.2.13.2
  17. http://pugscode.org/
  18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41621
  19. http://furius.ca/pubcode/pub/conf/common/bin/rst-literals.html
  20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41619
  21. http://iki.fi/matti.niemenmaa/pipe/
  22. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14661
  23. http://richardg.name/
  24. http://article.gmane.org/gmane.comp.lang.haskell.general/16252
  25. http://code.google.com/p/hback/
  26. http://www.pnas.org/cgi/content/abstract/0801268105v1
  27. http://www.haskell.org/gtk2hs/
  28. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008
  29. http://neilmitchell.blogspot.com/2008/06/hoogle-4-new-features.html
  30. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell
  31. http://physics-dph.blogspot.com/2008/06/status-report-week-4.html
  32. http://physics-dph.blogspot.com/2008/06/v-clip-algorithm-status-update.html
  33. http://blog.omega-prime.co.uk/2008/06/23/compiler-plugins-for-ghc-week-two/
  34. http://www.haskell.org/haskellwiki/Template_Haskell
  35. http://vezzosi.blogspot.com/2008/06/my-summer-of-code-project-dependency.html
  36. http://jamiiecb.blogspot.com/2008/06/gsoc-week-1.html
  37. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus
  38. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41749
  39. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9334
  40. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41651
  41. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9259
  42. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41607
  43. http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Foldable.html
  44. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41506
  45. http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps
  46. http://article.gmane.org/gmane.comp.lang.haskell.general/16253
  47. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41584
  48. http://planet.haskell.org/
  49. http://haskell.org/haskellwiki/Blog_articles
  50. http://idea-guy.blogspot.com/2008/06/converting-geosptial-coordinates.html
  51. http://physics-dph.blogspot.com/2008/06/v-clip-algorithm-status-update.html
  52. http://blog.unsafeperformio.com/?p=30
  53. http://blueappledev.wordpress.com/2008/06/24/project-euler/
  54. http://projecteuler.net/
  55. http://dpillay.blogspot.com/2008/06/haskell-type-inference.html
  56. http://www.cse.unsw.edu.au/~dons/blog/2008/06/24#daily-haskell-one
  57. http://blog.omega-prime.co.uk/2008/06/23/compiler-plugins-for-ghc-week-two/
  58. http://comonad.com/reader/2008/paramorphism/
  59. http://comonad.com/reader/2008/catamorphism/
  60. http://comonad.com/reader/2008/recursion-schemes/
  61. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-4.html
  62. http://www.realworldhaskell.org/blog/2008/06/22/ten-new-draft-chapters/
  63. http://jamiiecb.blogspot.com/2008/06/bitpacking.html
  64. http://jamiiecb.blogspot.com/2008/06/finally.html
  65. http://byorgey.wordpress.com/2008/06/21/zipedit/
  66. http://www.realworldhaskell.org/blog/2008/06/20/video-of-my-concurrentmulticore-haskell-talk-is-up/
  67. http://physics-dph.blogspot.com/2008/06/status-report-week-4.html
  68. http://osfameron.vox.com/library/post/more-countdown-laziness-scheme-and-german-frogs.html?_c=feed-atom
  69. http://vezzosi.blogspot.com/2008/06/my-summer-of-code-project-dependency.html
  70. http://osfameron.vox.com/library/post/schwartzian-transform-in-haskell.html?_c=feed-atom
  71. http://neilmitchell.blogspot.com/2008/06/hoogle-4-new-features.html
  72. http://tommd.wordpress.com/2008/06/18/past-and-future-libraries/
  73. http://codeflow.wordpress.com/2008/06/18/haskell-a-grain-of-python/
  74. http://www.pchristensen.com/blog/articles/hey-language-snobs-dont-pinch-pennies/
  75. http://micahelliott.blogspot.com/2008/06/1983-96-golden-age-of-programming.html
  76. http://www.haskell.org/mailman/listinfo/haskell
  77. http://sequence.complete.org/
  78. http://planet.haskell.org/
  79. http://sequence.complete.org/node/feed
  80. http://haskell.org/
  81. http://code.haskell.org/~byorgey/code/hwn/archives/20080625.pdf
  82. http://haskell.org/haskellwiki/HWN
  83. http://code.haskell.org/~byorgey/code/hwn/
From allbery at ece.cmu.edu  Wed Jun 25 17:47:10 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Wed Jun 25 17:38:41 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <Pine.LNX.4.64.0806252246560.31708@anubis.informatik.uni-halle.de>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<Pine.LNX.4.64.0806252246560.31708@anubis.informatik.uni-halle.de>
Message-ID: <8E854EDE-43AC-4D3D-959C-6F6EF509DF2C@ece.cmu.edu>


On 2008 Jun 25, at 16:49, Henning Thielemann wrote:

>
> On Wed, 25 Jun 2008, Andrew Wagner wrote:
>
>> The recruiter even said something along the lines of "anyone who  
>> knows haskell is certainly worth our time to talk to." Moral of the  
>> story: Haskell rocks, and even Microsoft knows it!
>
> Interesting. That is they are aware what they support in Cambridge  
> for years?


The sales office doesn't always pay attention to MSR.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From lennart at augustsson.net  Wed Jun 25 20:50:23 2008
From: lennart at augustsson.net (Lennart Augustsson)
Date: Wed Jun 25 20:41:50 2008
Subject: [Haskell-cafe] history of tuples vs pairs
In-Reply-To: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
Message-ID: <f4876cd70806251750ob93f9e6n215dcef4831b70a2@mail.gmail.com>

Yes, early ML had nested pairs.  We introduced n-tuples in Lazy ML
because in a lazy language n-tuples are not isomorphic to nested pairs
(whereas they are in a strict language).  So n-tuples are nasty
because they are not inductive, but they are in many ways much more
reasonable than lazy nested pairs.
BTW, early ML also had binary sums.  Again, they are not isomorphic to
n-ary sums.

  -- Lennart

2008/6/25 Conal Elliott <conal@conal.net>:
> I have a foggy memory that early ML had only binary pairing, nesting for
> n-tuples.  Can anyone confirm this memory.  If so, does anyone remember the
> rationale for going to n-tuples?  Performance, perhaps?
>
> Similarly, did the Haskell designers consider pairs as an alternative to
> n-ary tuples?
>
> The reason I ask is that while ghc and libraries suppors n-tuples for some
> values of n, the support is generally incomplete and inconsistent.  And some
> abstractions are very heavily biased toward pairing, particularly Arrow and
> the pair instances of Monad and Applicative.  And of course, inclusion of
> fst and snd in the prelude but lack of similar standard functions for
> n-tuples with n>2.
>
>   - Conal
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
From ok at cs.otago.ac.nz  Thu Jun 26 00:23:27 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Thu Jun 26 00:15:02 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
Message-ID: <A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>


On 26 Jun 2008, at 8:14 am, Andrew Wagner wrote:
> 6.) You have a [(WeatherStationId, Latitude, Longitude)]. Similar to
> #3, write a function which will, off-line, turn this into a data
> structure from which you can easily determine the nearest Weather
> Station, given an arbitrary Latitude and Longitude.

I actually set something not entirely unlike this as a problem in
a 4th year OO class.  Despite telling them over and over and over
again that the Earth is not flat, and despite telling them how to
convert (Latitude, Longitude) to 3-dimensional coordinates on the
unit sphere, and despite telling them that greatest circle distance
between two points on the surface of the Earth is a monotone
function of Euclidean distance between points on the unit sphere,
so that all they had to do was to glue these pieces together,

EVERY SINGLE ONE used Euclidean distance between (Latitude,
Longitude) pairs as if they were co-ordinates on a flat 2-d plane.
And we even live near the International Date Line, which is where
this mistake goes horribly wrong.

Did they score you on coding or on geometry?

For what it's worth, a 3-dimensional kd tree really flew on this  
problem.




From vigalchin at gmail.com  Thu Jun 26 02:00:23 2008
From: vigalchin at gmail.com (Galchin, Vasili)
Date: Thu Jun 26 01:51:51 2008
Subject: [Haskell-cafe] looking for advice on "lifting" and FFI
Message-ID: <5ae4f2ba0806252300l5d22b275tb1293e3b553cddb6@mail.gmail.com>

Hello,

     I am thinking about "glue"/"binding" code for POSIX listio and
aio_suspend. E.g. http://docs.hp.com/en/B9106-90009/lio_listio.2.html

1) It seems to me that this is a "lifting" problem where we lift to a
Haskell list of "aiocb's" to a C array of pointers?? An example of the "C
array of pointers" is described by
http://docs.hp.com/en/B9106-90009/lio_listio.2.html


2) Is it reasonable for the domain of the 1) mapping to be a Haskell list of
"aiocb's"??

Kind regards, Vasili
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From rwbarton at math.harvard.edu  Thu Jun 26 03:00:27 2008
From: rwbarton at math.harvard.edu (Reid Barton)
Date: Thu Jun 26 02:50:40 2008
Subject: [Haskell-cafe] ghc-HEAD: build succeeds,
	but install fails with linker errors?
Message-ID: <20080626070027.GD8867@rwbarton.mit.edu>

I'm trying to install GHC from the darcs repository for the first
time, so I'm hoping someone here can tell me if I'm doing something
wrong before I bother cvs-ghc.

I'm currently running ghc 6.8.2 on Debian x86 Linux.  Following the
instructions on the wiki, I put the following in a file and ran it:

#!/bin/bash
darcs get --partial http://darcs.haskell.org/ghc
cd ghc
chmod +x darcs-all
./darcs-all get
sh boot
./configure --prefix=$HOME/ghc-HEAD
make
make install

but during the "make install" step I get the error

../../compiler/stage1/ghc-inplace -no-user-package-conf -o ghc-pkg.bin -H32m -O  -cpp -Wall -fno-warn-name-shadowing -fno-warn-unused-matches -package Cabal -Rghc-timing  -package unix -package containers       Main.o Version.o CRT_noglob.o  
Main.o: In function `s7AP_info':
(.text+0x1d): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_con_info'
{- hundreds of similar errors (not all from the pretty package, some from base and others as well) -}
collect2: ld returned 1 exit status
<<ghc: 50428432 bytes, 6 GCs, 131072/131072 avg/max bytes residency (1 samples), 31M in use, 0.00 INIT (0.00 elapsed), 0.07 MUT (0.55 elapsed), 0.02 GC (0.02 elapsed) :ghc>>
make[2]: *** [ghc-pkg.bin] Error 1
Failed making install in ghc-pkg: 1
make[1]: *** [install] Error 1
make: *** [install] Error 1

Have I got some of the steps wrong?

Regards,
Reid Barton
From eeoam at ukfsn.org  Thu Jun 26 06:40:41 2008
From: eeoam at ukfsn.org (Eric)
Date: Thu Jun 26 06:32:13 2008
Subject: [Haskell-cafe] Parsing problem
Message-ID: <48637229.7000904@ukfsn.org>

Hi all,

I'm using the Parsec library to parse the following grammar

expr = atom+
atom = integer | var | (expr)

The input to the parser is a list of (Token, SourcePos). I have the 
following code for atom:

atom
  =  try variable <|> try integerr <|>
     do{sat(== Reserved "("); (e,pos) <- expression;  sat(==Reserved 
")"); return (e,pos)}
    
sat p = do  (t,pos) <- item
            if p t then return(t,pos) else pzero
    
When I run the code on the input "(_ineg_ 0)" the parser fails, but 
removing

sat(==Reserved ")")

and it succeeds. Can any one see why?

E.

From isaacdupree at charter.net  Thu Jun 26 06:54:05 2008
From: isaacdupree at charter.net (Isaac Dupree)
Date: Thu Jun 26 06:45:46 2008
Subject: [Haskell-cafe] history of tuples vs pairs
In-Reply-To: <f4876cd70806251750ob93f9e6n215dcef4831b70a2@mail.gmail.com>
References: <ea8ae9fb0806250750h1c25da30x1fcdaf4143d3e2de@mail.gmail.com>
	<f4876cd70806251750ob93f9e6n215dcef4831b70a2@mail.gmail.com>
Message-ID: <4863754D.8000903@charter.net>

Lennart Augustsson wrote:
> Yes, early ML had nested pairs.  We introduced n-tuples in Lazy ML
> because in a lazy language n-tuples are not isomorphic to nested pairs
> (whereas they are in a strict language).  So n-tuples are nasty
> because they are not inductive, but they are in many ways much more
> reasonable than lazy nested pairs.

although it is possible in a slightly different (and less left-right 
symmetric) way in Haskell:
data P a b = P a !b
pair: P Int (P Bool ())
triple: P Char (P Int (P Bool ())
single: P Bool ()
unit: ()

> BTW, early ML also had binary sums.  Again, they are not isomorphic to
> n-ary sums.

data E a b = L a | R !b
data Z --since Haskell Prelude provides us with the unit type () but not 
the uninhabited "zero" type, I'll use GHC's EmptyDataDecls syntax for this.
either: E Int (E Bool Z)
3: E Char (E Int (E Bool Z)
1: E Bool Z
0: Z

Still, these don't have isomorphic *representations*: the efficiency is 
lacking.  I wonder if it would be possible to allow {-#UNPACK#-} for 
those polymorphic arguments in such a way that either/both of the above 
were actually equivalent to n-tuple/sums.

-Isaac
From quarantedeux42 at yahoo.fr  Thu Jun 26 08:01:49 2008
From: quarantedeux42 at yahoo.fr (Fernand)
Date: Thu Jun 26 07:53:18 2008
Subject: [Haskell-cafe] Stupid question about Cabal file
Message-ID: <4863852D.60104@yahoo.fr>

Hi,

Excuse me in advance if this is a trivial question, but I have been 
unable to find (understand?) the answer in Cabal's documentation.
My issue is simple : I build a Cabal package named, let's say, "foo". 
That package is a library (libHSfoo.a, something like that), which 
exposes its Foo.Bar and Foobar modules. I wrote the cabal file, register 
it, everything seems fine.
The issue comes when I try to use that package when compiling a main 
program, like this :

ghc -package foo MyMain.hs [other options]

I get an error about the compiler not finding the interface files 
Foobar.hi and Bar.hi, as I have "import Bar" and "import Foo.Bar" in my 
"MyMain.hs" file. Of course, I could add "-l" flags to point to the 
".hi" files that I used to compile my package, but I get the well-known 
issue about the fact that the package's names of the interface files 
(which were compiled with the "-package-name foo" option) are not the 
correct ones ("Bad interface file: ../foo/Foobar.hi, Something is amiss; 
requested module  main:Foobar differs from name found in the interface 
file foo:Foobar") ; and that solution is ugly anyway.

So far, I found some Cabal documentation talking about the import-dirs 
property, but I did not manage to "make it work", I mean, my package 
does not seems to "include" the interface files. I am sure, on the other 
hand, that it is possible :)

Sincerely yours,

Fernand
From gwern0 at gmail.com  Thu Jun 26 08:20:43 2008
From: gwern0 at gmail.com (Gwern Branwen)
Date: Thu Jun 26 08:12:54 2008
Subject: [Haskell-cafe] ghc-HEAD: build succeeds, but install fails
	with linker errors?
In-Reply-To: <20080626070027.GD8867@rwbarton.mit.edu>
References: <20080626070027.GD8867@rwbarton.mit.edu>
Message-ID: <20080626122043.GA3598@craft>

On 2008.06.26 03:00:27 -0400, Reid Barton <rwbarton@math.harvard.edu> scribbled 1.4K characters:
> I'm trying to install GHC from the darcs repository for the first
> time, so I'm hoping someone here can tell me if I'm doing something
> wrong before I bother cvs-ghc.
>
> I'm currently running ghc 6.8.2 on Debian x86 Linux.  Following the
> instructions on the wiki, I put the following in a file and ran it:
>
> #!/bin/bash
> darcs get --partial http://darcs.haskell.org/ghc
> cd ghc
> chmod +x darcs-all
> ./darcs-all get
> sh boot
> ./configure --prefix=$HOME/ghc-HEAD
> make
> make install
>
> but during the "make install" step I get the error
>
> ../../compiler/stage1/ghc-inplace -no-user-package-conf -o ghc-pkg.bin -H32m -O  -cpp -Wall -fno-warn-name-shadowing -fno-warn-unused-matches -package Cabal -Rghc-timing  -package unix -package containers       Main.o Version.o CRT_noglob.o
> Main.o: In function `s7AP_info':
> (.text+0x1d): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_con_info'
> {- hundreds of similar errors (not all from the pretty package, some from base and others as well) -}
> collect2: ld returned 1 exit status
> <<ghc: 50428432 bytes, 6 GCs, 131072/131072 avg/max bytes residency (1 samples), 31M in use, 0.00 INIT (0.00 elapsed), 0.07 MUT (0.55 elapsed), 0.02 GC (0.02 elapsed) :ghc>>
> make[2]: *** [ghc-pkg.bin] Error 1
> Failed making install in ghc-pkg: 1
> make[1]: *** [install] Error 1
> make: *** [install] Error 1
>
> Have I got some of the steps wrong?
>
> Regards,
> Reid Barton

For what it's worth, I've gotten the same exact problem building darcs GHC - innumerable link errors during make install. I haven't figured out what the problem was yet (hadn't gotten around to reporting it yet either). This was on a Hardy Heron Ubuntu/GHC 6.8.2 etc.

--
gwern
football Pine UXO SASCOM Comirex shelter ARDA/DTO industrial NSES Mace
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From daniel.is.fischer at web.de  Thu Jun 26 08:41:36 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Thu Jun 26 08:31:03 2008
Subject: [Haskell-cafe] Stupid question about Cabal file
In-Reply-To: <4863852D.60104@yahoo.fr>
References: <4863852D.60104@yahoo.fr>
Message-ID: <200806261441.36077.daniel.is.fischer@web.de>

Am Donnerstag, 26. Juni 2008 14:01 schrieb Fernand:
> Hi,
>
> Excuse me in advance if this is a trivial question, but I have been
> unable to find (understand?) the answer in Cabal's documentation.
> My issue is simple : I build a Cabal package named, let's say, "foo".
> That package is a library (libHSfoo.a, something like that), which
> exposes its Foo.Bar and Foobar modules. I wrote the cabal file, register
> it, everything seems fine.
> The issue comes when I try to use that package when compiling a main
> program, like this :
>
> ghc -package foo MyMain.hs [other options]
>
> I get an error about the compiler not finding the interface files
> Foobar.hi and Bar.hi, as I have "import Bar" and "import Foo.Bar" in my
> "MyMain.hs" file. Of course, I could add "-l" flags to point to the
> ".hi" files that I used to compile my package, but I get the well-known
> issue about the fact that the package's names of the interface files
> (which were compiled with the "-package-name foo" option) are not the
> correct ones ("Bad interface file: ../foo/Foobar.hi, Something is amiss;
> requested module  main:Foobar differs from name found in the interface
> file foo:Foobar") ; and that solution is ugly anyway.
>
> So far, I found some Cabal documentation talking about the import-dirs
> property, but I did not manage to "make it work", I mean, my package
> does not seems to "include" the interface files. I am sure, on the other
> hand, that it is possible :)
>
> Sincerely yours,
>
> Fernand

Did you create your package using Cabal, i.e. have a module Setup.(l)hs in the 
same directory as the .cabal file and then

runhaskell Setup.hs configure --prefix=WhereYouWantIt
runhaskell Setup.hs build
runhaskell Setup.hs haddock (optionally)
runhaskell Setup.hs install
?

Then you shouldn't even need the -package option to use it, ghc-pkg would know 
where to find the interface files.

Cheers,
Daniel
From lemming at henning-thielemann.de  Thu Jun 26 08:40:18 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 26 08:31:49 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806260142m41baeab4m2a13dde21b83cefc@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
	<79d7c4980806250307h64bfba7dh95b518967c171384@mail.gmail.com>
	<79d7c4980806260142m41baeab4m2a13dde21b83cefc@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806261420580.27282@anubis.informatik.uni-halle.de>


On Thu, 26 Jun 2008, Alistair Bayley wrote:

>> Try this version of configOracle in Setup.hs:
>>
>> configOracle verbose buildtools = do
>>  if not (sqlplusProgram `isElem` buildtools)
>>    then return Nothing
>>    else do
>>      path <- getEnv "ORACLE_HOME"
>>      info verbose ("Using Oracle: " ++ path)
>>      makeConfig path libDir "oci/include"
>>    where libDir = if isWindows then "bin" else "lib"
>>
>>
>> You'll also need to add this import:
>>
>> import System.Environment (getEnv)
>
> Did you get a chance to try this? I'm quite keen to fix the
> non-Windows parts of the installation process, if I can.

I have replaced configOracle by

configOracle verbose buildtools = do
  if not (sqlplusProgram `isElem` buildtools)
    then return Nothing
    else do
      path <- getEnv "ORACLE_HOME"
      info verbose ("Using Oracle: " ++ path)
      let (libDir, includeDir) =
              if isWindows
                then ("bin", "oci/include")
                else ("lib", "/usr/include/oracle/10.2.0.4/client")
      makeConfig path libDir includeDir

This is obviously a hack. We should get the Oracle include path from the 
user, maybe via another environment variable or a custom Cabal option.

Now I can start GHCi with the example program you gave me. However I have 
to start with -lclntsh, otherwise symbol OCIEnvCreate cannot by found.
I thought I do not need this option, because the installed Takusen package 
contains the library name:

$ grep clntsh dist/installed-pkg-config
extra-libraries: clntsh clntsh

I wonder why it appears twice, because in dist/setup-config it exists
only once:
   extraLibs = ["clntsh"]


Nevertheless I can start GHCi with the example program and I can see 
'hello world'! Great - many thanks for the hints that led me to that 
state!


Next step is to fetch real data from the database. But now I encounter new 
problems. If I write a real 'select' statement I get at best:

Unexpected null in row 1, column 1.
*** Exception: (unknown)

and at worst:

50001752
*** glibc detected *** /usr/lib/ghc-6.8.2/ghc-6.8.2: free(): invalid 
pointer: 0x08d10065 ***
======= Backtrace: =========
/lib/libc.so.6[0xb7dba4b6]
/lib/libc.so.6(cfree+0x89)[0xb7dbc179]
/usr/lib/oracle/10.2.0.4/client/lib/libclntsh.so(lfvclose+0x1c)[0xb5df9c1e]
/usr/lib/oracle/10.2.0.4/client/lib/libclntsh.so(SlfMunmap+0x3f)[0xb5e70c3b]
/usr/lib/oracle/10.2.0.4/client/lib/libclntsh.so(ldiutzd+0x37)[0xb5e49e7b]
/usr/lib/oracle/10.2.0.4/client/lib/libclntsh.so(kputerm+0x51)[0xb54c96b9]
/usr/lib/oracle/10.2.0.4/client/lib/libclntsh.so(OCITerminate+0x1c)[0xb5596888]
[0xb6a33801]
/usr/lib/ghc-6.8.2/ghc-6.8.2[0x8a600de]
======= Memory map: ========
...

then GHCi quits.


> BTW, the location of your header files is still a puzzle. Oracle's docs:
> http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14250/ociabdem.htm#i459676
>
> state that the header files shoulld be in $ORACLE_HOME/rdbms/public.
> But perhaps things are different for the Instant Client.

I don't know. I have just installed the RPMs and I expect that others will 
do so as well.
From alistair at abayley.org  Thu Jun 26 08:54:06 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Thu Jun 26 08:45:34 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806261420580.27282@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
	<79d7c4980806250307h64bfba7dh95b518967c171384@mail.gmail.com>
	<79d7c4980806260142m41baeab4m2a13dde21b83cefc@mail.gmail.com>
	<Pine.LNX.4.64.0806261420580.27282@anubis.informatik.uni-halle.de>
Message-ID: <79d7c4980806260554w3698f3d3p624dde7f16b6b06d@mail.gmail.com>

> Now I can start GHCi with the example program you gave me. However I have to
> start with -lclntsh, otherwise symbol OCIEnvCreate cannot by found.
> I thought I do not need this option, because the installed Takusen package
> contains the library name:
>
> $ grep clntsh dist/installed-pkg-config
> extra-libraries: clntsh clntsh
>
> I wonder why it appears twice, because in dist/setup-config it exists
> only once:
>  extraLibs = ["clntsh"]

Yes, puzzling. I don't know why you need to say -lclntsh, because
that's the point of all of this Setup shenanigans: to get things set
up so that ghci works nicely.

That's why we have flags that expose/hide modules in the API: ghci has
a custom linker, and this tries to link everything in the library, and
of course this fails if you don't have the .ddl/.so installed for a
particular backend. ghc uses gnu ld to link, and this does not try to
link unused modules, so this works fine with the entire library API
compiled.

Do you need to say -lclntsh when you use ghc to compile?


> Next step is to fetch real data from the database. But now I encounter new
> problems. If I write a real 'select' statement I get at best:
>
> Unexpected null in row 1, column 1.
> *** Exception: (unknown)

This looks like you are fetching a null value back with an iteratee
that does not expect nulls. We use Maybe to specify that a column in
the result-set can be null e.g.

  iter :: Int -> Maybe Int -> Maybe String -> IterAct [(Int, Maybe
Int, Maybe String)]

The first column must never contain null. If it does then you get the
"Unexpected null" exception.


> and at worst:
>
> 50001752
> *** glibc detected *** /usr/lib/ghc-6.8.2/ghc-6.8.2: free(): invalid
> pointer: 0x08d10065 ***
> ======= Backtrace: =========

If this continues, can you provide a test case for me?

Alistair
From quarantedeux42 at yahoo.fr  Thu Jun 26 08:56:41 2008
From: quarantedeux42 at yahoo.fr (Fernand)
Date: Thu Jun 26 08:48:11 2008
Subject: [Haskell-cafe] Stupid question about Cabal file
In-Reply-To: <200806261441.36077.daniel.is.fischer@web.de>
References: <4863852D.60104@yahoo.fr>
	<200806261441.36077.daniel.is.fischer@web.de>
Message-ID: <48639209.9040300@yahoo.fr>

Daniel Fischer ?????:
> Did you create your package using Cabal, i.e. have a module Setup.(l)hs in the 
> same directory as the .cabal file and then
>
> runhaskell Setup.hs configure --prefix=WhereYouWantIt
> runhaskell Setup.hs build
> runhaskell Setup.hs haddock (optionally)
> runhaskell Setup.hs install
> ?
>
> Then you shouldn't even need the -package option to use it, ghc-pkg would know 
> where to find the interface files.
>
> Cheers,
> Daniel
>   
No, I did not, because I actually inherited a large Makefile with huge 
dependencies and twisted built options.
If using Setup is the right (and only) way to create the package, I will 
then try it.

thank you,

Fernand

From daniel.is.fischer at web.de  Thu Jun 26 09:12:06 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Thu Jun 26 09:02:05 2008
Subject: [Haskell-cafe] Stupid question about Cabal file
In-Reply-To: <48639209.9040300@yahoo.fr>
References: <4863852D.60104@yahoo.fr>
	<200806261441.36077.daniel.is.fischer@web.de>
	<48639209.9040300@yahoo.fr>
Message-ID: <200806261512.06175.daniel.is.fischer@web.de>

Am Donnerstag, 26. Juni 2008 14:56 schrieb Fernand:
> Daniel Fischer ?????:
> > Did you create your package using Cabal, i.e. have a module Setup.(l)hs
> > in the same directory as the .cabal file and then
> >
> > runhaskell Setup.hs configure --prefix=WhereYouWantIt
> > runhaskell Setup.hs build
> > runhaskell Setup.hs haddock (optionally)
> > runhaskell Setup.hs install
> > ?
> >
> > Then you shouldn't even need the -package option to use it, ghc-pkg would
> > know where to find the interface files.
> >
> > Cheers,
> > Daniel
>
> No, I did not, because I actually inherited a large Makefile with huge
> dependencies and twisted built options.
> If using Setup is the right (and only) way to create the package, I will
> then try it.
>
> thank you,
>
> Fernand

If it's a complicated build, you should certainly take a close look at the 
Cabal user guide, because then you will probably need more than 
main = defaultMain
in your Setup.hs. On the other hand, the GHC user's guide should also contain 
some sections on building and registering packages.

The Cabal / Setup way is intended to be the simplest and standard way to build 
packages, but it's not the only one and won't be for a long time.

Cheers,
Daniel

From quarantedeux42 at yahoo.fr  Thu Jun 26 09:50:35 2008
From: quarantedeux42 at yahoo.fr (Fernand)
Date: Thu Jun 26 09:42:03 2008
Subject: [Haskell-cafe] Stupid question about Cabal file
In-Reply-To: <200806261512.06175.daniel.is.fischer@web.de>
References: <4863852D.60104@yahoo.fr>
	<200806261441.36077.daniel.is.fischer@web.de>
	<48639209.9040300@yahoo.fr>
	<200806261512.06175.daniel.is.fischer@web.de>
Message-ID: <48639EAB.7020401@yahoo.fr>

I had a look at the Distribution.Make import, which may be the answer.
Thank you for pointing the GHC documentation : I found a way to have the 
build process work, but after having patched my local package.conf file 
by hand, and installed manually the interfaces files accordingly. I now 
just need to understand how to obtain the same result using make, I think.

Haskelly yours,

Fernand

Daniel Fischer ?????:
>
>
> If it's a complicated build, you should certainly take a close look at the 
> Cabal user guide, because then you will probably need more than 
> main = defaultMain
> in your Setup.hs. On the other hand, the GHC user's guide should also contain 
> some sections on building and registering packages.
>
> The Cabal / Setup way is intended to be the simplest and standard way to build 
> packages, but it's not the only one and won't be for a long time.
>
> Cheers,
> Daniel
>
>
>   

From daniel.is.fischer at web.de  Thu Jun 26 09:54:50 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Thu Jun 26 09:44:17 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <48637229.7000904@ukfsn.org>
References: <48637229.7000904@ukfsn.org>
Message-ID: <200806261554.50830.daniel.is.fischer@web.de>

Am Donnerstag, 26. Juni 2008 12:40 schrieb Eric:
> Hi all,
>
> I'm using the Parsec library to parse the following grammar
>
> expr = atom+
> atom = integer | var | (expr)
>
> The input to the parser is a list of (Token, SourcePos). I have the
> following code for atom:
>
> atom
>   =  try variable <|> try integerr <|>
>      do{sat(== Reserved "("); (e,pos) <- expression;  sat(==Reserved
> ")"); return (e,pos)}
>
> sat p = do  (t,pos) <- item
>             if p t then return(t,pos) else pzero
>
> When I run the code on the input "(_ineg_ 0)" the parser fails, but
> removing
>
> sat(==Reserved ")")
>
> and it succeeds. Can any one see why?
>
> E.
>
What does the tokeniser return?
I would have to see more of the code to diagnose it.

Cheers,
Daniel
From lemming at henning-thielemann.de  Thu Jun 26 09:59:23 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 26 09:50:50 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806260554w3698f3d3p624dde7f16b6b06d@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
	<79d7c4980806250307h64bfba7dh95b518967c171384@mail.gmail.com>
	<79d7c4980806260142m41baeab4m2a13dde21b83cefc@mail.gmail.com>
	<Pine.LNX.4.64.0806261420580.27282@anubis.informatik.uni-halle.de>
	<79d7c4980806260554w3698f3d3p624dde7f16b6b06d@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806261551520.17991@anubis.informatik.uni-halle.de>


On Thu, 26 Jun 2008, Alistair Bayley wrote:

> Yes, puzzling. I don't know why you need to say -lclntsh, because
> that's the point of all of this Setup shenanigans: to get things set
> up so that ghci works nicely.
>
> That's why we have flags that expose/hide modules in the API: ghci has
> a custom linker, and this tries to link everything in the library, and
> of course this fails if you don't have the .ddl/.so installed for a
> particular backend. ghc uses gnu ld to link, and this does not try to
> link unused modules, so this works fine with the entire library API
> compiled.
>
> Do you need to say -lclntsh when you use ghc to compile?

Ah, I see, I must run both GHCi and GHC with -package Takusen and 
everything is fine.

>> Next step is to fetch real data from the database. But now I encounter new
>> problems. If I write a real 'select' statement I get at best:
>>
>> Unexpected null in row 1, column 1.
>> *** Exception: (unknown)
>
> This looks like you are fetching a null value back with an iteratee
> that does not expect nulls. We use Maybe to specify that a column in
> the result-set can be null e.g.
>
>  iter :: Int -> Maybe Int -> Maybe String -> IterAct [(Int, Maybe Int, Maybe String)]

Indeed, using Maybe as type solves that problem.

>> and at worst:
>>
>> 50001752
>> *** glibc detected *** /usr/lib/ghc-6.8.2/ghc-6.8.2: free(): invalid
>> pointer: 0x08d10065 ***
>> ======= Backtrace: =========
>
> If this continues, can you provide a test case for me?

I cannot reliably reproduce this. Sometimes it seems that the first run of 
'main' succeeds, and the second one crashes in GHCi.


So, many thanks for the help!
From mailing_list at istitutocolli.org  Thu Jun 26 10:11:58 2008
From: mailing_list at istitutocolli.org (Andrea Rossato)
Date: Thu Jun 26 10:03:32 2008
Subject: [Haskell-cafe] hxt and pickler combinations
Message-ID: <20080626141157.GM27924@laptop.nowhere.net>

Hello,

I'm using HXT for writing a Citation Style Language
(http://xbiblio.sourceforge.net) implementation in Haskell and I'm
trying to use the hxt pickler library to parse XML data contained in
elements that can be interleaved, that is to say, elements that can
appear in any order within other elements.

For instance:
<data>
  <string>ciao</string>
  <int>2</int>
</data>
or
<data>
  <int>2</int>
  <string>ciao</string>
</data>

are both permitted.

I'm not able to write picklers able to parse such kind of data. I
indeed noticed that this is not possible with interleaved elements,
but it is possible with attributes.

To make myself hopefully clearer I included some code below. Suppose
we have a data structure like:

data Term = T Int String deriving ( Show )

If encoded in XML without respecting the ordering (first the Int and
then the String), picklers seem to fail. But if I use attributes to
store the values, this doesn't happen.

In other word, the xp1 pickler (taken from the example below) will
fail with such an xml doc:

<data>
  <string>ciao</string>
  <int>2</int>
</data>

since it requires the 'int' element to appear before the 'string'
element.

To test this behaviour, run the code below and see that:

- test doc1 xp1 will fail
- test doc2 xp1 will succeed

while:

- test doc3 xp2 will succeed
- test doc4 xp2 will succeed

What am I getting wrong? It's just a matter of wrong combinator I'm
choosing or I'm getting wrong something more fundamental?

TIA.

Andrea

The code:

import Text.XML.HXT.Arrow

test :: String -> PU Term -> IO ()
test t xp = do
      p <- runX ( constA t
                  >>>
                  xread
                  >>>
                  xunpickleVal xp
	   )
      putStrLn (show p)

data Term = T Int String deriving ( Show )

xp1, xp2 :: PU Term
xp1 = xpElem "data" $
      xpWrap (uncurry T, \(T i s) -> (i, s)) $
      xpPair (xpElem "int"    xpickle)
             (xpElem "string" xpText )
xp2 = xpElem "data" $
      xpWrap (uncurry T, \(T i s) -> (i, s)) $
      xpPair (xpAttr "int"    xpickle)
             (xpAttr "string" xpText )

doc1, doc2, doc3, doc4 :: String
doc1 = "<data><string>ciao</string><int>2</int></data>"
doc2 = "<data><int>2</int><string>ciao</string></data>"
doc3 = "<data int=\"2\" string=\"ciao\" />"
doc4 = "<data string=\"ciao\" int=\"4\" />"
From igloo at earth.li  Thu Jun 26 10:26:19 2008
From: igloo at earth.li (Ian Lynagh)
Date: Thu Jun 26 10:17:47 2008
Subject: Haskell on ARM (was Re: [Haskell-cafe] ANN: Topkata)
In-Reply-To: <871w2mit8o.wl%jeremy@n-heptane.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
	<87ej6ww9dy.fsf_-_@columbia.edu>
	<20080617201233.GD19304@scytale.galois.com>
	<871w2mit8o.wl%jeremy@n-heptane.com>
Message-ID: <20080626142619.GA4743@matrix.chaos.earth.li>

On Tue, Jun 24, 2008 at 11:27:03AM -0700, Jeremy Shaw wrote:
> 
> The unregisterised build is not that useful because:
> 
>  1. no FFI

If libffi supports it then this should now work.

>  1. add ARM support to the evil mangler (basically, a few regexps to
>  strip prolog and epilogue stuff from the ASM)

Note that the mangler is on the way out for 6.10:
http://www.haskell.org/pipermail/cvs-ghc/2008-June/042979.html

>  5. (Optional), implement native assembly generation

You'll need to do this instead.


Thanks
Ian

From lemming at henning-thielemann.de  Thu Jun 26 11:04:41 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Thu Jun 26 10:56:17 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <486289DF.70107@complete.org>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<4862474E.8070801@complete.org>
	<Pine.LNX.4.64.0806251529030.11636@anubis.informatik.uni-halle.de>
	<486289DF.70107@complete.org>
Message-ID: <Pine.LNX.4.64.0806261658110.17991@anubis.informatik.uni-halle.de>


On Wed, 25 Jun 2008, John Goerzen wrote:

> Henning Thielemann wrote:
>> On Wed, 25 Jun 2008, John Goerzen wrote:
>>
>>> I haven't read this entire thread, but I might also just interject here
>>> that HDBC supports ODBC (on Windows, and on Linux/Posix platforms via
>>> unixODBC, iODBC, or similar), which may be another avenue for you to
>>> try.  I'm sure there are ODBC Oracle drivers out there, and so if you
>>> have your ODBC layer working, you get Haskell support easily.
>>
>> This was actually how the thread started: I don't get ODBC for Oracle
>> working on Linux. :-(
>>   Maybe this is an unixODBC issue - is iODBC an API-compatible replacement?
>
> Yes, iODBC is.

Ok, I gave also iODBC a try and installed
   libiodbc-3.52.6-1.i386.rpm
   libiodbc-admin-3.52.6-1.i386.rpm
   libiodbc-devel-3.52.6-1.i386.rpm


After a bit of configuration I called:

$ iodbctest NMR2
iODBC Demonstration program
This program shows an interactive SQL processor
Driver Manager: 03.52.0607.1008
1: SQLDriverConnect = [iODBC][Driver Manager]/usr/lib/oracle/10.2.0.4/client/lib/libsqora.so.10.1: undefined 
symbol: _tcsnccmp (0) SQLSTATE=00000
2: SQLDriverConnect = [iODBC][Driver Manager]Specified driver could not be loaded (0) SQLSTATE=IM003


What is _tcsnccmp and where can I get it from? I hope it is nothing 
Windows specific.

Google suggests that its prototype is:
   int _tcsnccmp(const _TXCHAR* string1, const _TXCHAR* string2, size_t count);
From wagner.andrew at gmail.com  Thu Jun 26 11:11:21 2008
From: wagner.andrew at gmail.com (Andrew Wagner)
Date: Thu Jun 26 11:02:47 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>
Message-ID: <b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>

> Did they score you on coding or on geometry?
>

It was definitely more on coding and my ability to think about the problem.

> For what it's worth, a 3-dimensional kd tree really flew on this problem.
>

I did some reading up on this, and it seems interesting. It would be
need to implement something like this in Haskell, but I can't seem to
find any detailed specs on the data-structure. Got any
recommendations?
From cmb21 at kent.ac.uk  Thu Jun 26 11:17:07 2008
From: cmb21 at kent.ac.uk (C.M.Brown)
Date: Thu Jun 26 11:08:34 2008
Subject: [Haskell-cafe] Call Graph Tool?
Message-ID: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>

Hi,

I have approx. 100+ source files and I was wondering if anyone has a tool
that would let me see a visual call graph for the source files; i.e. a
visual hierarchy of which module is imported by what, and so forth.

Kind regards,
Chris.
From jgoerzen at complete.org  Thu Jun 26 11:30:08 2008
From: jgoerzen at complete.org (John Goerzen)
Date: Thu Jun 26 11:21:35 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806261658110.17991@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<79d7c4980806192210j11796038sc5008d669df926b5@mail.gmail.com>
	<79d7c4980806200251o6e74e409mbd993a09c835014@mail.gmail.com>
	<Pine.LNX.4.64.0806241605400.26528@anubis.informatik.uni-halle.de>
	<79d7c4980806240755p724777e3i9240067c3c050ccb@mail.gmail.com>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<4862474E.8070801@complete.org>
	<Pine.LNX.4.64.0806251529030.11636@anubis.informatik.uni-halle.de>
	<486289DF.70107@complete.org>
	<Pine.LNX.4.64.0806261658110.17991@anubis.informatik.uni-halle.de>
Message-ID: <4863B600.6040705@complete.org>

Henning Thielemann wrote:
> On Wed, 25 Jun 2008, John Goerzen wrote:
> 
> $ iodbctest NMR2
> iODBC Demonstration program
> This program shows an interactive SQL processor
> Driver Manager: 03.52.0607.1008
> 1: SQLDriverConnect = [iODBC][Driver Manager]/usr/lib/oracle/10.2.0.4/client/lib/libsqora.so.10.1: undefined 
> symbol: _tcsnccmp (0) SQLSTATE=00000
> 2: SQLDriverConnect = [iODBC][Driver Manager]Specified driver could not be loaded (0) SQLSTATE=IM003
> 
> 
> What is _tcsnccmp and where can I get it from? I hope it is nothing 
> Windows specific.

I don't know, but it could be that you are missing some Oracle
libraries, or that your Oracle library location isn't on your
LD_LIBRARY_PATH or /etc/ld.so.conf path.   Since this isn't a
Haskell-specific problem, I'd suggest you check it out on the Oracle,
unixODBC, or iODBC groups.

-- John
From igloo at earth.li  Thu Jun 26 11:43:01 2008
From: igloo at earth.li (Ian Lynagh)
Date: Thu Jun 26 11:34:27 2008
Subject: [Haskell-cafe] ghc-HEAD: build succeeds,
	but install fails with linker errors?
In-Reply-To: <20080626070027.GD8867@rwbarton.mit.edu>
References: <20080626070027.GD8867@rwbarton.mit.edu>
Message-ID: <20080626154301.GA4762@matrix.chaos.earth.li>

On Thu, Jun 26, 2008 at 03:00:27AM -0400, Reid Barton wrote:
> 
> but during the "make install" step I get the error

"make install" is probably broken at the moment. You should be able to
use it in-place, though (run compiler/stage2/ghc-inplace).


Thanks
Ian

From claus.reinke at talk21.com  Thu Jun 26 12:02:02 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Thu Jun 26 11:53:36 2008
Subject: [Haskell-cafe] Call Graph Tool?
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
Message-ID: <00d401c8d7a5$fb7ce0a0$351b8351@cr3lt>

> I have approx. 100+ source files and I was wondering if anyone has a tool
> that would let me see a visual call graph for the source files; i.e. a
> visual hierarchy of which module is imported by what, and so forth.

Hi Chris,

Programatica used to have such a thing for the module graph
(tools/base/Pfe0Cmds.hs; "graph"), via dot. But for that many
modules, the graph is highly likely to be neither pretty nor 
useful, I'm afraid..

Claus

http://en.wikipedia.org/wiki/DOT_language


From eeoam at ukfsn.org  Thu Jun 26 12:13:50 2008
From: eeoam at ukfsn.org (Eric)
Date: Thu Jun 26 12:05:38 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <200806261554.50830.daniel.is.fischer@web.de>
References: <48637229.7000904@ukfsn.org>
	<200806261554.50830.daniel.is.fischer@web.de>
Message-ID: <4863C03E.4050109@ukfsn.org>

Daniel Fischer wrote:
> Am Donnerstag, 26. Juni 2008 12:40 schrieb Eric:
>   
> What does the tokeniser return?
> I would have to see more of the code to diagnose it.
>   
Here is the code for the tokenizer:

type Scanner a = GenParser Char () a

data Token
  =  INum Integer | FNum Double
     | Varid String | Reserved String
  deriving (Show,Eq)

scan :: Scanner a -> Scanner(a, SourcePos)
scan p = do  pos <- getPosition
                    x <- p
                   return(x,pos)

scan_integer, scan_varid, hreserved, htoken :: Scanner 
(Token,SourcePos)            

scan_integer = do  (i,pos) <- scan(integer (makeTokenParser haskellDef))
                             return (INum i, pos)
                  
scan_varid = do  (c,pos) <- scan(hlower)
                          cs <- identifier(makeTokenParser haskellDef)
                         return (Varid (c:cs), pos)

hlower :: Scanner Char             
hlower = lower <|> char '_'

hreserved = do  (cs, pos) <- scan(string "(" <|> string ")")
                         return (Reserved cs,pos)
             
htoken = scan_integer <|> scan_varid <|> hreserved
                  
scanall :: String -> [(Token,SourcePos)]
scanall cs = let result = parse (many htoken) "" cs
                  in case result of
                         Right tkns -> tkns
                         Left err -> error (show err)

E.




From eeoam at ukfsn.org  Thu Jun 26 12:18:42 2008
From: eeoam at ukfsn.org (Eric)
Date: Thu Jun 26 12:10:50 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <4863C03E.4050109@ukfsn.org>
References: <48637229.7000904@ukfsn.org>
	<200806261554.50830.daniel.is.fischer@web.de>
	<4863C03E.4050109@ukfsn.org>
Message-ID: <4863C162.6030404@ukfsn.org>

Eric wrote:
> Daniel Fischer wrote:
>> Am Donnerstag, 26. Juni 2008 12:40 schrieb Eric:
>>   What does the tokeniser return?
>> I would have to see more of the code to diagnose it.   
Thunderbird mangled my code. I've attached it as a pdf file.

E.

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From mmitar at gmail.com  Thu Jun 26 12:34:08 2008
From: mmitar at gmail.com (Mitar)
Date: Thu Jun 26 12:25:33 2008
Subject: [Haskell-cafe] Internet Communications Engine and Haskell
Message-ID: <f63c4b2d0806260934j44a11ecey4fb16d5c08dc4c14@mail.gmail.com>

Hi!

Has been any work on implementing Internet Communications Engine in
Haskell already done? Any other suggestions how could I use ICE in
Haskell? Through FFI calls to its C++ version?

http://www.zeroc.com/ice.html


Mitar
From martindemello at gmail.com  Thu Jun 26 13:00:53 2008
From: martindemello at gmail.com (Martin DeMello)
Date: Thu Jun 26 12:52:20 2008
Subject: [Haskell-cafe] haskell and dockapps
Message-ID: <f93a6bcc0806261000j55057bcbu6e5bce258227bf33@mail.gmail.com>

Anyone written a windowmaker dockapp in Haskell? I thought it'd be a
fun project, but I don't quite know where to start.

martin
From mailing_list at istitutocolli.org  Thu Jun 26 13:03:23 2008
From: mailing_list at istitutocolli.org (Andrea Rossato)
Date: Thu Jun 26 12:55:03 2008
Subject: [Haskell-cafe] hxt and pickler combinations
In-Reply-To: <20080626141157.GM27924@laptop.nowhere.net>
References: <20080626141157.GM27924@laptop.nowhere.net>
Message-ID: <20080626170323.GA10224@laptop.nowhere.net>

On Thu, Jun 26, 2008 at 04:11:58PM +0200, Andrea Rossato wrote:
> Hello,
> 
> I'm using HXT for writing a Citation Style Language
> (http://xbiblio.sourceforge.net) implementation in Haskell and I'm
> trying to use the hxt pickler library to parse XML data contained in
> elements that can be interleaved, that is to say, elements that can
> appear in any order within other elements.
> 
> For instance:
> <data>
>   <string>ciao</string>
>   <int>2</int>
> </data>
> or
> <data>
>   <int>2</int>
>   <string>ciao</string>
> </data>
> 
> are both permitted.
> 
> I'm not able to write picklers able to parse such kind of data. I
> indeed noticed that this is not possible with interleaved elements,
> but it is possible with attributes.

Thanks to a suggestion from Uwe (I contacted the HXT authors too,
since I thought it could be a non intended behaviour: instead it is,
in order to conform to the standard DTD validation), I came up with
this solution. I'm leaving it here too, for the archives.

This is a pickler that search the element in the contents and match it
without regard to the elements' order:

xpElem'  :: String -> PU a -> PU a
xpElem' name pa
    = PU { appPickle   = ( \ (a, st) ->
                           let
                           st' = appPickle pa (a, emptySt)
                           in
                           addCont (XN.mkElement (mkName name) (attributes st') (contents st')) st
                                                    )
         , appUnPickle = \ st -> fromMaybe (Nothing, st) (unpickleElement st)
         , theSchema   = scElem name (theSchema pa)
         }
      where
      unpickleElement st
          = do
            let t = contents st
            n <- mapM XN.getElemName t
            case elemIndex name (map qualifiedName n) of
              Nothing -> fail "element name does not match"
              Just i  -> do
                let cs = XN.getChildren (t !! i)
                al <- XN.getAttrl (t !! i)
                res <- fst . appUnPickle pa $ St {attributes = al, contents = cs}
                return (Just res, st {contents = take i t ++ drop (i + 1) t})


Andrea
From dons at galois.com  Thu Jun 26 13:31:09 2008
From: dons at galois.com (Don Stewart)
Date: Thu Jun 26 13:22:37 2008
Subject: [Haskell-cafe] haskell and dockapps
In-Reply-To: <f93a6bcc0806261000j55057bcbu6e5bce258227bf33@mail.gmail.com>
References: <f93a6bcc0806261000j55057bcbu6e5bce258227bf33@mail.gmail.com>
Message-ID: <20080626173109.GA24704@scytale.galois.com>

martindemello:
> Anyone written a windowmaker dockapp in Haskell? I thought it'd be a
> fun project, but I don't quite know where to start.
> 

Might be fun to take hsclock, the gtk/cairo based clock,

    http://haskell.org/gtk2hs/archives/2006/01/26/cairo-eye-candy/

and turn it into a beautiful dock app.

-- Don
From dons at galois.com  Thu Jun 26 13:31:41 2008
From: dons at galois.com (Don Stewart)
Date: Thu Jun 26 13:23:09 2008
Subject: [Haskell-cafe] Internet Communications Engine and Haskell
In-Reply-To: <f63c4b2d0806260934j44a11ecey4fb16d5c08dc4c14@mail.gmail.com>
References: <f63c4b2d0806260934j44a11ecey4fb16d5c08dc4c14@mail.gmail.com>
Message-ID: <20080626173141.GB24704@scytale.galois.com>

mmitar:
> Hi!
> 
> Has been any work on implementing Internet Communications Engine in
> Haskell already done? Any other suggestions how could I use ICE in
> Haskell? Through FFI calls to its C++ version?
> 
> http://www.zeroc.com/ice.html

I think FFI would be the cheapest solution. There's likely a C api
somewhere on the internets.
From martindemello at gmail.com  Thu Jun 26 13:37:26 2008
From: martindemello at gmail.com (Martin DeMello)
Date: Thu Jun 26 13:28:52 2008
Subject: [Haskell-cafe] haskell and dockapps
In-Reply-To: <20080626173109.GA24704@scytale.galois.com>
References: <f93a6bcc0806261000j55057bcbu6e5bce258227bf33@mail.gmail.com>
	<20080626173109.GA24704@scytale.galois.com>
Message-ID: <f93a6bcc0806261037n33e02d5cpba9106237bf4a559@mail.gmail.com>

On Thu, Jun 26, 2008 at 10:31 AM, Don Stewart <dons@galois.com> wrote:
> martindemello:
>> Anyone written a windowmaker dockapp in Haskell? I thought it'd be a
>> fun project, but I don't quite know where to start.
>>
>
> Might be fun to take hsclock, the gtk/cairo based clock,
>
>    http://haskell.org/gtk2hs/archives/2006/01/26/cairo-eye-candy/
>
> and turn it into a beautiful dock app.

Thanks - the code looks very clean and easy to grasp. Would be nicely
appropriate too, given my last foray into dockapp writing :)

http://www.cs.rice.edu/~ssiyer/code/pclock-bezier/

martin
From sebastian.sylvan at gmail.com  Thu Jun 26 13:39:07 2008
From: sebastian.sylvan at gmail.com (Sebastian Sylvan)
Date: Thu Jun 26 13:30:32 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>
	<b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
Message-ID: <3d96ac180806261039y3a1b2bc0jf7d411fe4f380f11@mail.gmail.com>

On 6/26/08, Andrew Wagner <wagner.andrew@gmail.com> wrote:
>
> > Did they score you on coding or on geometry?
> >
>
>
> It was definitely more on coding and my ability to think about the problem.
>
>
> > For what it's worth, a 3-dimensional kd tree really flew on this problem.
> >
>
>
> I did some reading up on this, and it seems interesting. It would be
> need to implement something like this in Haskell, but I can't seem to
> find any detailed specs on the data-structure. Got any
> recommendations?

http://en.wikipedia.org/wiki/Kd_tree

-- 
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862
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From jeremy at n-heptane.com  Thu Jun 26 15:39:44 2008
From: jeremy at n-heptane.com (Jeremy Shaw)
Date: Thu Jun 26 15:28:53 2008
Subject: [Haskell-cafe] Re: Haskell on ARM (was Re: ANN: Topkata)
In-Reply-To: <g3s4fr$9h2$1@ger.gmane.org>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
	<87ej6ww9dy.fsf_-_@columbia.edu>
	<20080617201233.GD19304@scytale.galois.com>
	<871w2mit8o.wl%jeremy@n-heptane.com> <g3s4fr$9h2$1@ger.gmane.org>
Message-ID: <87vdzwgf3z.wl%jeremy@n-heptane.com>

At Tue, 24 Jun 2008 20:43:45 -0400,
Braden Shepherdson wrote:

> I recently acquired the ARM-based Nokia N810 (and <3 it), powered by 
> Maemo. Running a uname -a on it:

> I might be one to attempt this, as I know C and ARM-ish asm decently 
> well and have a powerful desktop to compile on. I have no familiarity
> with GHC internals, though. 

I think that is a fine set of qualifications. The porting process
requires low-level knowledge of C, asm, and the ARM more than GHC
internals. It's mostly stuff like #defining what the names of the ARM
registers are, and which ones are preserved across C function calls.

Also, if you are not starting until at least Sept, waiting for 6.10
might be a good choice, since it sounds like the backend will be
changing quite a bit. No point in doing it twice if there is no rush.

j.

ps. Perhaps we should have some sort of GHC on the ARM hackathon when
6.10 comes out. I think there are quite a few people who have tried or
who are interested in trying a port. Having more heads look at it
would probably make things go faster. 
From daniel.is.fischer at web.de  Thu Jun 26 16:55:16 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Thu Jun 26 16:44:41 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <48637229.7000904@ukfsn.org>
References: <48637229.7000904@ukfsn.org>
Message-ID: <200806262255.16404.daniel.is.fischer@web.de>

Am Donnerstag, 26. Juni 2008 12:40 schrieb Eric:
> Hi all,
>
> I'm using the Parsec library to parse the following grammar
>
> expr = atom+
> atom = integer | var | (expr)
>
> The input to the parser is a list of (Token, SourcePos). I have the
> following code for atom:
>
> atom
>   =  try variable <|> try integerr <|>
>      do{sat(== Reserved "("); (e,pos) <- expression;  sat(==Reserved
> ")"); return (e,pos)}
>
> sat p = do  (t,pos) <- item
>             if p t then return(t,pos) else pzero
>
> When I run the code on the input "(_ineg_ 0)" the parser fails, but
> removing
>
> sat(==Reserved ")")
>
> and it succeeds. Can any one see why?
>
> E.
>

I can't be absolutely sure without seeing your code for item and expression, 
possibly also variable and integerr, but I'm rather sure it's a case of a 
missing 'try'. 
I'd expect 'expression' using something like
many1 atom
, then when parsing the tokens of "(_ineg_ 0)", which, ignoring the SourcePos 
are [Reserved "(", Varid "_ineg_", INum 0, Reserved ")"], as it should be, 
variable and integerr fail, so the third branch is entered, 
sat (== Reserved "(") succeeds, the Varid and INum are parsed and finally only 
[Reserved ")"] is left over, on which atom is tried again. variable and 
integerr again fail gracefully, so sat (== Reserved "(") is tried on it, 
which fails, but unfortunately not gracefully, because item returns 
(Consumed _) and thus the overall failure consumes. Because of that, many1 
atom fails and the overall parse fails.

Can't be exactly that, though because then removing sat (== Reserved ")") 
shouldn't help. 
Anyway, I need at least the failure message, better the complete code, to 
diagnose.

Cheers,
Daniel

From eeoam at ukfsn.org  Thu Jun 26 17:22:13 2008
From: eeoam at ukfsn.org (Eric)
Date: Thu Jun 26 17:14:27 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <200806262255.16404.daniel.is.fischer@web.de>
References: <48637229.7000904@ukfsn.org>
	<200806262255.16404.daniel.is.fischer@web.de>
Message-ID: <48640885.7060408@ukfsn.org>

Daniel Fischer wrote:
>
> Can't be exactly that, though because then removing sat (== Reserved ")") 
> shouldn't help. 
> Anyway, I need at least the failure message, better the complete code, to 
> diagnose.
>   
I've attached the complete code.

E.
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From daniel.is.fischer at web.de  Thu Jun 26 18:16:23 2008
From: daniel.is.fischer at web.de (Daniel Fischer)
Date: Thu Jun 26 18:05:47 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <48640885.7060408@ukfsn.org>
References: <48637229.7000904@ukfsn.org>
	<200806262255.16404.daniel.is.fischer@web.de>
	<48640885.7060408@ukfsn.org>
Message-ID: <200806270016.23429.daniel.is.fischer@web.de>

Am Donnerstag, 26. Juni 2008 23:22 schrieb Eric:
> Daniel Fischer wrote:
> > Can't be exactly that, though because then removing sat (== Reserved ")")
> > shouldn't help.
> > Anyway, I need at least the failure message, better the complete code, to
> > diagnose.
>
> I've attached the complete code.
>
> E.
Thanks, though a plaintext file would've been better.
It's pretty much what I came up with myself, the odd thing is that I can't 
reproduce your behaviour, whether sat (== Reserved ")") is present or not 
doesn't make a difference. Which version of GHC and parsec are you using? (I 
tried with 6.8.3 & parsec-2.1.0.1, 6.8.2 & parsec-2.1.0.0 and 6.6.1 & 
parsec-2.0, all give the same results, 
*Eric2> parseall . scanall $ "(_ineg_ 0)"
*** Exception: (line 1, column 1):unknown parse error
with or without the second sat).

However, the problem is indeed that upon failure (sat p) returns a Consumed 
value (and removes the token from the input), make it

sat p = try $ do
    (t,pos) <- item
    if p t then return (t,pos) else pzero

and you're all set (you don't need the try's in atom, then).

Cheers,
Daniel
From ok at cs.otago.ac.nz  Thu Jun 26 18:34:03 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Thu Jun 26 18:25:32 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>
	<b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
Message-ID: <4E37FB1A-7721-45D2-B5F8-692777F76263@cs.otago.ac.nz>


On 27 Jun 2008, at 3:11 am, Andrew Wagner wrote:
For what it's worth, a 3-dimensional kd tree really flew on this  
problem.
>>
> I did some reading up on this, and it seems interesting. It would be
> need to implement something like this in Haskell, but I can't seem to
> find any detailed specs on the data-structure. Got any
> recommendations?

http://en.wikipedia.org/wiki/K-d_tree
is perhaps the obvious place to start.
There's a link there to Jon L. Bentley's original (1975) paper,
which is really very clear.  The key to getting an efficient
version in C was to specialise the code to the particular k that
I wanted (k=3).

Of course there are much newer data structures that can do all sorts
of things, but for simply finding the closest point in 1, 2, 3, or
4-dimensional space k-d trees are darned good.  There isn't much that
works well for high dimensions.  Last year I marked a 4th year project
that studied/evaluated a comparatively recent data structure that was
said to be good for high dimensions.  I had difficulty understanding
it, because I couldn't see where the recursive step was.  The answer
was that there wasn't one:  the algorithm worked better for high
dimensions than other trees because it turned into a simple linear
search after one partitioning step.  In effect, it was too dumb to
keep tripping over its own feet.  So _really_ don't expect k-d trees
to work well for large k.


>




From agl at imperialviolet.org  Thu Jun 26 19:36:53 2008
From: agl at imperialviolet.org (Adam Langley)
Date: Thu Jun 26 19:28:23 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>
	<b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
Message-ID: <396556a20806261636o1bda9d39g9c6e767a3287159c@mail.gmail.com>

On Thu, Jun 26, 2008 at 8:11 AM, Andrew Wagner <wagner.andrew@gmail.com> wrote:
> I did some reading up on this, and it seems interesting. It would be
> need to implement something like this in Haskell, but I can't seem to
> find any detailed specs on the data-structure. Got any
> recommendations?

Specialised for 2d only, but:

http://www.imperialviolet.org/binary/NearestNeighbour2D.hs

AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
From nornagon at gmail.com  Thu Jun 26 19:57:29 2008
From: nornagon at gmail.com (Jeremy Apthorp)
Date: Thu Jun 26 19:48:54 2008
Subject: [Haskell-cafe] Re: Haskell on ARM (was Re: ANN: Topkata)
In-Reply-To: <14d615330806241903s30734fe4q5c7af4569e9b421@mail.gmail.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net> <87ej6ww9dy.fsf_-_@columbia.edu>
	<20080617201233.GD19304@scytale.galois.com>
	<871w2mit8o.wl%jeremy@n-heptane.com> <g3s4fr$9h2$1@ger.gmane.org>
	<14d615330806241903s30734fe4q5c7af4569e9b421@mail.gmail.com>
Message-ID: <14d615330806261657h3ce55bebx74f8e89205a9854@mail.gmail.com>

2008/6/25 Braden Shepherdson <Braden.Shepherdson@gmail.com>:
> Jeremy Shaw wrote:
>>
>> If any does attempt to build for the ARM, please, please, please,
>> document what you do in the wiki. And, if you do, edit the wiki as you
>> go, you definitely won't be able to remember what you did after the
>> fact. (Or, at the very least, use some program to capture everything
>> you do so that you can refer to it later).
>>
>> And, finally, I heard vague rumors a while ago that made me think that
>> GHC 6.10 might have a pure ANSI-C backend? Is there any truth to this?
>> That would make porting much easier if it meant you did not have to do
>> steps 1-4.
>>
>> j.
>> ps. I would be happy to try to answer any questions if someone tries a
>> port. I would still like to run GHC on my 770, and I hope to own an
>> iPhone if they fix a few ommisions (bluetooth keyboard support, and
>> similar stuff).
>>
>
>
> I recently acquired the ARM-based Nokia N810 (and <3 it), powered by Maemo.
> Running a uname -a on it:
>
> Linux Nokia-N810-42-19 2.6.21-omap1 #2 Fri Nov 16 16:24:58 EET 2007 armv6l
> unknown
>
> I would love a working GHC implementation on it, if for nothing else than
> how awesome it would be. Whether that means using a C back-end or native
> compilation doesn't matter to me so much.
>
> I might be one to attempt this, as I know C and ARM-ish asm decently well
> and have a powerful desktop to compile on. I have no familiarity
> with GHC internals, though. Lastly, I won't have anything like the time to
> attempt this seriously until mid-September or so.

Oops, forgot to Cc the list.

Next year I'll be working on a project for my undergraduate computing
course at UNSW that will involve getting GHC to target the Nintendo
DS. It'll require cross-compilation, because the DS isn't powerful
enough to actually run GHC (4M main ram and a 66MHz processor). It'll
also require that I significantly strip down the runtime system, as
the current RTS won't fit in 4M and leave any left over for the main
application.

I'll be documenting the whole process, but I won't be starting until
next year...

Jeremy
From Ivan.Miljenovic at gmail.com  Thu Jun 26 23:13:18 2008
From: Ivan.Miljenovic at gmail.com (Ivan Miljenovic)
Date: Thu Jun 26 23:11:28 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
Message-ID: <loom.20080627T031111-823@post.gmane.org>

C.M.Brown <cmb21 <at> kent.ac.uk> writes:
> I have approx. 100+ source files and I was wondering if anyone has a tool
> that would let me see a visual call graph for the source files; i.e. a
> visual hierarchy of which module is imported by what, and so forth.

For my maths honours thesis, I'll be writing a tool to help people understand
the relationships in their Haskell code.  I'm hoping to have a visualisation
component in there, but that's a relatively low priority.

Assuming I get it included, is there any features in particular you'd want to
see in there?  Note that if I do have it produce visualisations, they'll be
static images as part of an analysis report rather than being interactive.




From ok at cs.otago.ac.nz  Fri Jun 27 00:33:35 2008
From: ok at cs.otago.ac.nz (Richard A. O'Keefe)
Date: Fri Jun 27 00:25:07 2008
Subject: [Haskell-cafe] Haskell, Microsoft, and interview questions
In-Reply-To: <396556a20806261636o1bda9d39g9c6e767a3287159c@mail.gmail.com>
References: <b8a8636e0806251314y435ab144u11be1509296f3bc5@mail.gmail.com>
	<A6A91D7B-0D5A-4F8B-B112-87DDE343AD73@cs.otago.ac.nz>
	<b8a8636e0806260811j3cdaf510mb149b32f87c8faa6@mail.gmail.com>
	<396556a20806261636o1bda9d39g9c6e767a3287159c@mail.gmail.com>
Message-ID: <C7EDE0B0-2EF1-411A-93DE-CE099F42417A@cs.otago.ac.nz>


On 27 Jun 2008, at 11:36 am, Adam Langley wrote:
> Specialised for 2d only, but:
>
> http://www.imperialviolet.org/binary/NearestNeighbour2D.hs

In my C code for this, specialised to 3D,
  - dimension numbers were never stored
  - no arrays were used
  - the "search in x" function called
    the "search in y" function, which called
    the "search in z" function, which called
    the "search in x" function

Here's the relevant part of my kd3.h:

typedef struct KD3_Node *kd3ptr;
struct KD3_Node {
     double x, y, z;
     kd3ptr left, right;
     bool   present;
  << payload data goes here >>
};


From nornagon at gmail.com  Fri Jun 27 01:18:45 2008
From: nornagon at gmail.com (Jeremy Apthorp)
Date: Fri Jun 27 01:10:09 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <loom.20080627T031111-823@post.gmane.org>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
Message-ID: <14d615330806262218o501df15k61845b6c705d5114@mail.gmail.com>

2008/6/27 Ivan Miljenovic <Ivan.Miljenovic@gmail.com>:
> C.M.Brown <cmb21 <at> kent.ac.uk> writes:
>> I have approx. 100+ source files and I was wondering if anyone has a tool
>> that would let me see a visual call graph for the source files; i.e. a
>> visual hierarchy of which module is imported by what, and so forth.
>
> For my maths honours thesis, I'll be writing a tool to help people understand
> the relationships in their Haskell code.  I'm hoping to have a visualisation
> component in there, but that's a relatively low priority.
>
> Assuming I get it included, is there any features in particular you'd want to
> see in there?  Note that if I do have it produce visualisations, they'll be
> static images as part of an analysis report rather than being interactive.

Just today I wished for something similar for this MATLAB code I'm
maintaining... would be good to have a pluggable syntax definition so
that it could be easily adapted for use with other languages.

Jeremy
From ivan.miljenovic at gmail.com  Fri Jun 27 01:57:46 2008
From: ivan.miljenovic at gmail.com (Ivan Lazar Miljenovic)
Date: Fri Jun 27 01:49:17 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <14d615330806262218o501df15k61845b6c705d5114@mail.gmail.com>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
	<14d615330806262218o501df15k61845b6c705d5114@mail.gmail.com>
Message-ID: <20080627155746.4065a8c8@gmail.com>

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Fri, 27 Jun 2008 15:18:45 +1000
"Jeremy Apthorp" <nornagon@gmail.com> wrote:

> 2008/6/27 Ivan Miljenovic <Ivan.Miljenovic@gmail.com>:
> > C.M.Brown <cmb21 <at> kent.ac.uk> writes:
> >> I have approx. 100+ source files and I was wondering if anyone has a tool
> >> that would let me see a visual call graph for the source files; i.e. a
> >> visual hierarchy of which module is imported by what, and so forth.
> >
> > For my maths honours thesis, I'll be writing a tool to help people
> > understand the relationships in their Haskell code.  I'm hoping to have a
> > visualisation component in there, but that's a relatively low priority.
> >
> > Assuming I get it included, is there any features in particular you'd want
> > to see in there?  Note that if I do have it produce visualisations, they'll
> > be static images as part of an analysis report rather than being
> > interactive.
> 
> Just today I wished for something similar for this MATLAB code I'm
> maintaining... would be good to have a pluggable syntax definition so
> that it could be easily adapted for use with other languages.

Technically, what I'm doing is a graph-theoretic analysis framework, with a
sample application in which Haskell code is parsed and analysed.  Once I get it
done, it should be pretty simple to port over to other languages but you'd need
to write a parser first (I plan on using Haskell-src and Haskell-src-exts).


> 
> Jeremy


- -- 
Ivan Lazar Miljenovic
Ivan.Miljenovic@gmail.com
IvanMiljenovic.wordpress.com
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From qdunkan at gmail.com  Fri Jun 27 03:18:18 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Fri Jun 27 03:09:45 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <loom.20080627T031111-823@post.gmane.org>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
Message-ID: <2518b95d0806270018u3aecb381h6f44a196720376e7@mail.gmail.com>

> Assuming I get it included, is there any features in particular you'd want to
> see in there?  Note that if I do have it produce visualisations, they'll be
> static images as part of an analysis report rather than being interactive.

I was just recently wondering about something like this.

I'd like the ability to show individual module dependencies, and then
to collapse modules in one package to just the package, so I could
"zoom out" and see how the packages relate to each other.  By
"package" here I mean the "A" in "A.B, A.C, etc."

It seems like it would be fairly simple to use Language.Haskell.Parse
to turn a set of modules into a graph, and then something to massage
that and give it to dot.

It actually brings up a question about module discipline in general:

At one point I wanted to have each package re-export its public
modules and then sibling packages can only export the "package" module
as some libraries do, but it got to be too much re-exporting
bookkeeppiing and I didn't so much like symbols having multiple
"homes", and most of all it was increasingly awkward to split packages
into strictly higher level and strictly lower level relationships
since this discipline means coarser granularity which means more
trouble avoiding circular imports.  So now I just import modules
directly from their packages.  I still have a general structure of
higher, lower, and sibling packages though, so some kind of
visualization would be handy to keep deps under control, look for
packages and modules that could be split up for a clearer hierarchy,
find good places to cut circular imports, etc.  I've also thought I
could move private modules in A to A.Private, so you can see that if
you're importing X.Private.Y from a module that doesn't start with X.
then something fishy is going on.

How do other people approach this issue?
From silva.samuel at gmail.com  Fri Jun 27 04:55:38 2008
From: silva.samuel at gmail.com (Samuel Silva)
Date: Fri Jun 27 04:47:01 2008
Subject: [Haskell-cafe] Fwd: Stack Overflow with HaXml
In-Reply-To: <382ead9b0806270153p3870e9dej83acd89f006e8dde@mail.gmail.com>
References: <382ead9b0806270153p3870e9dej83acd89f006e8dde@mail.gmail.com>
Message-ID: <382ead9b0806270155pf83c847qb3cad481252e841d@mail.gmail.com>

Hello

I presents a small case studie, when I was using HaXml with DtdToHaskell.

I write small DTD:
> <!ELEMENT top (#PCDATA|child)* >
> <!ELEMENT child (#PCDATA) >

I run DtdToHaskell small.DTD > Extsubext.hs
and test it with small XML
> <top><child></child></top>

Result it is presented below:
>$ ghci Extsubset.hs
>GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
>Loading package base ... linking ... done.
>[1 of 1] Compiling Extsubset        ( Extsubset.hs, interpreted )
>Ok, modules loaded: Extsubset.
>*Extsubset> fReadXml "sample.xml" :: IO Top
>Loading package array-0.1.0.0 ... linking ... done.
>Loading package bytestring-0.9.0.1 ... linking ... done.
>Loading package pretty-1.0.0.0 ... linking ... done.
>Loading package old-locale-1.0.0.0 ... linking ... done.
>Loading package old-time-1.0.0.0 ... linking ... done.
>Loading package filepath-1.1.0.0 ... linking ... done.
>Loading package directory-1.0.0.0 ... linking ... done.
>Loading package random-1.0.0.0 ... linking ... done.
>Loading package process-1.0.0.0 ... linking ... done.
>Loading package haskell98 ... linking ... done.
>Loading package polyparse-1.1 ... linking ... done.
>Loading package containers-0.1.0.1 ... linking ... done.
>Loading package HaXml-1.19.4 ... linking ... done.
>*** Exception: stack overflow
>*Extsubset>

HaXml is able handle XML mixed elements?

--
Don't hug that, Hugs ME!
Samuel Silva
From d.kahlenberg at googlemail.com  Fri Jun 27 06:34:16 2008
From: d.kahlenberg at googlemail.com (Daniel Kahlenberg)
Date: Fri Jun 27 06:25:39 2008
Subject: [Haskell-cafe] System.Console.Readline stifleHistory Question
In-Reply-To: <5d4de89e0806260531j5286947au8b1f839603897444@mail.gmail.com>
References: <5d4de89e0806260531j5286947au8b1f839603897444@mail.gmail.com>
Message-ID: <5d4de89e0806270334m6cbbcc5u13e55dda6fd693f2@mail.gmail.com>

Hello all,

I'm learning Haskell and so very likely will have advantages from the
history persistence feature added to the ghci haskell interpreter. It
drives very well in my setup (the history file is growing and used),
but I wanted to increase the number of saved history entries and now
my question concerning ghci: In the ticket
(http://hackage.haskell.org/trac/ghc/ticket/2050) associated with the
feature, there's written that one can call stifleHistory in its
dotghci file. Have done it like:
 :m +System.Console.Readline
 stifleHistory 300
 :m -System.Console.Readline

but now my ghci.exe says:

Could not find module `System.Console.Readline':
 Use -v to see a list of the files searched for.

<interactive>:1:0: Not in scope: `stifleHistory'

`uname -r`:
MINGW32_NT-5.1 CLE10 1.0.11(0.46/3/2) 2007-01-12 12:05 i686 Msys

Do you have an idea, where I'm wrong?

I'm starting my ghci session from zsh shell, provided by cygwin,
wrapped in a tty emulator:
$Drive\puttycyg\putty.exe -cygterm $Drive\zsh\bin\zsh.exe -p -c
'PATH=/cygdrive/h/zsh/bin:$PATH HOME=/cygdrive/h/.homedir rlwrap
$(which ghcii.sh) -package-conf
$Drive/.homedir/ghc/i386-mingw32-6.8.3/package.conf -read-dot-ghci'

So I did not expect Readline not to work, but maybe the ghc system
only sees the result from `uname -r` above??

Bye, Daniel.
From claus.reinke at talk21.com  Fri Jun 27 06:39:45 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Fri Jun 27 06:31:29 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk><loom.20080627T031111-823@post.gmane.org>
	<2518b95d0806270018u3aecb381h6f44a196720376e7@mail.gmail.com>
Message-ID: <006e01c8d842$271b97a0$4d268351@cr3lt>

>> Assuming I get it included, is there any features in particular you'd want to
>> see in there?  Note that if I do have it produce visualisations, they'll be
>> static images as part of an analysis report rather than being interactive.
> 
> I'd like the ability to show individual module dependencies, and then
> to collapse modules in one package to just the package, so I could
> "zoom out" and see how the packages relate to each other.  By
> "package" here I mean the "A" in "A.B, A.C, etc."
> 
> It seems like it would be fairly simple to use Language.Haskell.Parse
> to turn a set of modules into a graph, and then something to massage
> that and give it to dot.

If you wanted to go down that route, try using 'ghc --make -v2'
and translate that dependency graph to dot.

It isn't difficult to produce visualizations (though gathering the
data might be - proper dependency analysis in Haskell projects 
has rated a GSoC project this year, for Cabal). It is difficult 
to produce *useful* visualizations that *scale* to realistic 
projects. To begin with, it helps to see the visualization
as *input* for software development decisions, not as
pretty output for some data traversal.

However, the problem is far from new, and it is perhaps 
not unreasonable to assume that most papers in the area
are going to reference this one (so you could start with a 
reverse reference search, then try to separate the gimmicks
from the potentially useful approaches..):

    Thomas A. Ball and Stephen G. Eick. 
    Software visualization in the large. 
    IEEE Computer, 29(4):33--43, April 1996.
    http://citeseer.ist.psu.edu/78256.html

As far as I can tell, a variety of visualizations is needed in
practice, integrated in a single tool suite, with good 
interactivity/navigation/view switching, so that one can 
choose the most suitable view and focus/slice for each 
question one might have about a software project (and
change track as new questions arise interactively).

It would be great to have such a visualization suite
for Haskell projects..

There was Chris Ryder's Medina project (unreleased,
web site seems to have disappeared?), which focussed 
on a metrics library, with some example metrics and 
visualizations:

http://web.archive.org/web/20041229065821/www.cs.kent.ac.uk/people/rpg/cr24/medina/examples.shtml
http://www.cs.kent.ac.uk/pubs/2004/2236/index.html
http://www.haskell.org/communities/11-2002/html/report.html#sect4.5.1

Hth,
Claus


From d.kahlenberg at googlemail.com  Fri Jun 27 06:53:21 2008
From: d.kahlenberg at googlemail.com (Daniel Kahlenberg)
Date: Fri Jun 27 06:44:46 2008
Subject: [Haskell-cafe] Re: System.Console.Readline stifleHistory Question
In-Reply-To: <5d4de89e0806270334m6cbbcc5u13e55dda6fd693f2@mail.gmail.com>
References: <5d4de89e0806260531j5286947au8b1f839603897444@mail.gmail.com>
	<5d4de89e0806270334m6cbbcc5u13e55dda6fd693f2@mail.gmail.com>
Message-ID: <5d4de89e0806270353p8aa663fj4c2a806207609c18@mail.gmail.com>

OK,

I detected it was my own fail: I was misleaded by the creation of the
persistence file, which doesn't result from Readline.hs but simply
from the rlwrap utility I earlier piped in before the ghci call. For
those interested, the answer to the original question as usual from
the man page: option --histsize N for rlwrap does the job.

Maybe for a later discussion of using readline or some compatibility
library instead of the rlwrap tool on ms windows systems I will post
an extra message with a link.

Bye.


---------- Forwarded message ----------
From: Daniel Kahlenberg <d.kahlenberg@googlemail.com>
Date: 2008/6/27
Subject: System.Console.Readline stifleHistory Question
To: haskell-cafe@haskell.org


Hello all,

I'm learning Haskell and so very likely will have advantages from the
history persistence feature added to the ghci haskell interpreter. It
drives very well in my setup (the history file is growing and used),
but I wanted to increase the number of saved history entries and now
my question concerning ghci: In the ticket
(http://hackage.haskell.org/trac/ghc/ticket/2050) associated with the
feature, there's written that one can call stifleHistory in its
dotghci file. Have done it like:
 :m +System.Console.Readline
 stifleHistory 300
 :m -System.Console.Readline

but now my ghci.exe says:

Could not find module `System.Console.Readline':
 Use -v to see a list of the files searched for.

<interactive>:1:0: Not in scope: `stifleHistory'

`uname -r`:
MINGW32_NT-5.1 CLE10 1.0.11(0.46/3/2) 2007-01-12 12:05 i686 Msys

Do you have an idea, where I'm wrong?

I'm starting my ghci session from zsh shell, provided by cygwin,
wrapped in a tty emulator:
$Drive\puttycyg\putty.exe -cygterm $Drive\zsh\bin\zsh.exe -p -c
'PATH=/cygdrive/h/zsh/bin:$PATH HOME=/cygdrive/h/.homedir rlwrap
$(which ghcii.sh) -package-conf
$Drive/.homedir/ghc/i386-mingw32-6.8.3/package.conf -read-dot-ghci'

So I did not expect Readline not to work, but maybe the ghc system
only sees the result from `uname -r` above??

Bye, Daniel.
From jno at di.uminho.pt  Fri Jun 27 07:04:52 2008
From: jno at di.uminho.pt (J.N. Oliveira)
Date: Fri Jun 27 06:56:20 2008
Subject: [Haskell-cafe] Call Graph Tool?
In-Reply-To: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
Message-ID: <AA3F72F2-7653-47CB-BE98-3817F5C4F0BA@di.uminho.pt>

On Jun 26, 2008, at 4:17 PM, C.M.Brown wrote:

> Hi,
>
> I have approx. 100+ source files and I was wondering if anyone has  
> a tool
> that would let me see a visual call graph for the source files; i.e. a
> visual hierarchy of which module is imported by what, and so forth.
>
> Kind regards,
> Chris.

I suggest that you have a look at HaSlicer, a (visual) Haskell  
slicing tool available online from http://labdotnet.di.uminho.pt/ 
HaSlicer/HaSlicer.aspx , developed by Nuno Rodrigues (nfr@di.uminho.pt).

Best regards

jno

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From dougal at dougalstanton.net  Fri Jun 27 07:49:35 2008
From: dougal at dougalstanton.net (Dougal Stanton)
Date: Fri Jun 27 07:41:00 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <006e01c8d842$271b97a0$4d268351@cr3lt>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
	<2518b95d0806270018u3aecb381h6f44a196720376e7@mail.gmail.com>
	<006e01c8d842$271b97a0$4d268351@cr3lt>
Message-ID: <2d3641330806270449y7c6de172r27ae70e2b74980fc@mail.gmail.com>

On Fri, Jun 27, 2008 at 11:39 AM, Claus Reinke <claus.reinke@talk21.com> wrote:
> If you wanted to go down that route, try using 'ghc --make -v2'
> and translate that dependency graph to dot.

Also, if you want to get a quick 'n dirty list of which of your own
files depend on which others, "ghc -M $main.hs" works quite well. I've
had some success in the past shoving this stuff almost directly into
the graph libraries and out to graphviz. Be warned that it fiddles
with any file called Makefile in your working directory...

Cheers,

D

-- 
Dougal Stanton
dougal@dougalstanton.net // http://www.dougalstanton.net
From Malcolm.Wallace at cs.york.ac.uk  Fri Jun 27 08:32:49 2008
From: Malcolm.Wallace at cs.york.ac.uk (Malcolm Wallace)
Date: Fri Jun 27 08:26:53 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <2d3641330806270449y7c6de172r27ae70e2b74980fc@mail.gmail.com>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
	<2518b95d0806270018u3aecb381h6f44a196720376e7@mail.gmail.com>
	<006e01c8d842$271b97a0$4d268351@cr3lt>
	<2d3641330806270449y7c6de172r27ae70e2b74980fc@mail.gmail.com>
Message-ID: <20080627133249.764a62c3.Malcolm.Wallace@cs.york.ac.uk>

> > try using 'ghc --make -v2' and translate that dependency graph to dot.
> 
> "ghc -M $main.hs" works quite well

   hmake -M Main.hs

gives much the same output as ghc -M, but without side-effecting your
Makefile.  Even better,

   hmake -g Main.hs

gives the pure module graph dependencies without the .hs/.o clutter.

Caveat: You may need some extra commandline flags like -package base,
since hmake does not add those automatically.

Regards,
    Malcolm
From josef.svenningsson at gmail.com  Fri Jun 27 08:37:08 2008
From: josef.svenningsson at gmail.com (Josef Svenningsson)
Date: Fri Jun 27 08:28:31 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <006e01c8d842$271b97a0$4d268351@cr3lt>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
	<2518b95d0806270018u3aecb381h6f44a196720376e7@mail.gmail.com>
	<006e01c8d842$271b97a0$4d268351@cr3lt>
Message-ID: <8dde104f0806270537q19188e96p49975d24b7075410@mail.gmail.com>

On Fri, Jun 27, 2008 at 12:39 PM, Claus Reinke <claus.reinke@talk21.com> wrote:
>>> Assuming I get it included, is there any features in particular you'd
>>> want to
>>> see in there?  Note that if I do have it produce visualisations, they'll
>>> be
>>> static images as part of an analysis report rather than being
>>> interactive.
>>
>> I'd like the ability to show individual module dependencies, and then
>> to collapse modules in one package to just the package, so I could
>> "zoom out" and see how the packages relate to each other.  By
>> "package" here I mean the "A" in "A.B, A.C, etc."
>>
>> It seems like it would be fairly simple to use Language.Haskell.Parse
>> to turn a set of modules into a graph, and then something to massage
>> that and give it to dot.
>
> If you wanted to go down that route, try using 'ghc --make -v2'
> and translate that dependency graph to dot.
>
Yep, this is a pretty easy route and there is already a tool for doing
the translation: ocamldot. Don't be fooled by the name, it works on
Makefile's dependency information and in particular works well with
the output from ghc. Back in the days (like six years ago) I used it
on ghc itself. I also extended it so that different directories were
grouped together inside a box to get a better feel for the intended
structure of the program. ocamldot can be found here:
http://www.research.att.com/~trevor/ocamldot/

I should add that I didn't find the information the least bit helpful
so my general recommendation is to try to find some other method to
help understanding code.

All the best,

Josef
From claus.reinke at talk21.com  Fri Jun 27 08:53:44 2008
From: claus.reinke at talk21.com (Claus Reinke)
Date: Fri Jun 27 08:45:22 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk><loom.20080627T031111-823@post.gmane.org><2518b95d0806270018u3aecb381h6f44a196720376e7@mail.gmail.com><006e01c8d842$271b97a0$4d268351@cr3lt>
	<2d3641330806270449y7c6de172r27ae70e2b74980fc@mail.gmail.com>
Message-ID: <00be01c8d854$db36bff0$4d268351@cr3lt>

>> If you wanted to go down that route, try using 'ghc --make -v2'
>> and translate that dependency graph to dot.
>
> Also, if you want to get a quick 'n dirty list of which of your own
> files depend on which others, "ghc -M $main.hs" works quite well. I've
> had some success in the past shoving this stuff almost directly into
> the graph libraries and out to graphviz. Be warned that it fiddles
> with any file called Makefile in your working directory...

You can redirect the output of -M, but since it appears that
you cannot combine --make with -fno-code, the incantation
you want is probably something like:

    ghc -M -v2 -optdep-f -optdep depend Main.hs

which gives you dependency output in two forms, a module-based
one to stdout (-v2), a file-based one to file depend (-M -f depend):

$ ghc -M -v2 -optdep-f -optdep depend TestGMap.lhs
Glasgow Haskell Compiler, Version 6.9.20080514, for Haskell 98, stage 2 booted by GHC version 6.6.1
Using package config file: C:\ghc\ghc-6.9.20080514\package.conf
wired-in package ghc-prim mapped to ghc-prim-0.1
wired-in package integer mapped to integer-0.1
wired-in package base mapped to base-3.0
wired-in package rts mapped to rts-1.0
wired-in package haskell98 mapped to haskell98-1.0.1
wired-in package template-haskell mapped to template-haskell-2.2
wired-in package ndp not found.
Created temporary directory: C:\DOCUME~1\cr3\LOCALS~1\Temp\/ghc1564_0
*** Chasing dependencies:
Chasing modules from: TestGMap.lhs
*** Literate pre-processor:
Module dependencies
[NONREC
    ModSummary {
       ms_hs_date = Tue Jun 24 19:25:08 GMT Daylight Time 2008
       ms_mod = main:BinTreeDatatype,
       ms_imps = [Data.Generics]
       ms_srcimps = []
    },
 NONREC
    ModSummary {
       ms_hs_date = Tue Jun 24 19:35:32 GMT Daylight Time 2008
       ms_mod = main:GMap,
       ms_imps = [Unsafe.Coerce, Data.Generics, BinTreeDatatype]
       ms_srcimps = []
    },
 NONREC
    ModSummary {
       ms_hs_date = Tue Jun 24 19:24:46 GMT Daylight Time 2008
       ms_mod = main:Main,
       ms_imps = [GMap, BinTreeDatatype]
       ms_srcimps = []
    }]
*** Installing new makefile:
*** Deleting temp files:
*** Deleting temp dirs:

$ cat depend
# DO NOT DELETE: Beginning of Haskell dependencies
BinTreeDatatype.o : BinTreeDatatype.hs
GMap.o : GMap.hs
GMap.o : BinTreeDatatype.hi
TestGMap.o : TestGMap.lhs
TestGMap.o : GMap.hi
TestGMap.o : BinTreeDatatype.hi
# DO NOT DELETE: End of Haskell dependencies

Claus

http://www.haskell.org/ghc/docs/latest/html/users_guide/separate-compilation.html#makefile-dependencies


From alistair at abayley.org  Fri Jun 27 09:58:24 2008
From: alistair at abayley.org (Alistair Bayley)
Date: Fri Jun 27 09:49:48 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <Pine.LNX.4.64.0806261551520.17991@anubis.informatik.uni-halle.de>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
	<79d7c4980806250307h64bfba7dh95b518967c171384@mail.gmail.com>
	<79d7c4980806260142m41baeab4m2a13dde21b83cefc@mail.gmail.com>
	<Pine.LNX.4.64.0806261420580.27282@anubis.informatik.uni-halle.de>
	<79d7c4980806260554w3698f3d3p624dde7f16b6b06d@mail.gmail.com>
	<Pine.LNX.4.64.0806261551520.17991@anubis.informatik.uni-halle.de>
Message-ID: <79d7c4980806270658u78530f51qc2d32f372976f1a0@mail.gmail.com>

2008/6/26 Henning Thielemann <lemming@henning-thielemann.de>:
>
>> Do you need to say -lclntsh when you use ghc to compile?
>
> Ah, I see, I must run both GHCi and GHC with -package Takusen and everything
> is fine.

This still doesn't seem right. Both ghci and ghc --make should
automatically link the package. The only time you should need to use
-package is in ghc "batch" mode i.e. ghc sans --make.


> configOracle verbose buildtools = do
>  if not (sqlplusProgram `isElem` buildtools)
>   then return Nothing
>   else do
>     path <- getEnv "ORACLE_HOME"
>     info verbose ("Using Oracle: " ++ path)
>     let (libDir, includeDir) =
>             if isWindows
>               then ("bin", "oci/include")
>               else ("lib", "/usr/include/oracle/10.2.0.4/client")
>     makeConfig path libDir includeDir
>
> This is obviously a hack. We should get the Oracle include path from the
> user, maybe via another environment variable or a custom Cabal option.

Yes... I've had a quick look at the instant client packages. The SDK
zip just puts the headers under instantclient_10_2/sdk/include (which
is still not $ORACLE_HOME/rdbms/public, but c'est la vie). So it looks
like the .rpm puts them somewhere completely different:
/usr/include/oracle/10.2.0.4/client. Do you also have
$ORACLE_HOME/sdk/include, with headers in?

Alistair
From jefferson.r.heard at gmail.com  Fri Jun 27 10:15:23 2008
From: jefferson.r.heard at gmail.com (Jefferson Heard)
Date: Fri Jun 27 10:06:46 2008
Subject: [Haskell-cafe] Error in configure script for GHC
Message-ID: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>

I've tried all the 6.6 and 6.8 versions, trying to compile them on a
RHEL-based supercomputer, and I always see this error when I run
./configure:

-bash-3.00$ ./configure
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking target system type... x86_64-unknown-linux-gnu
Which we'll further canonicalise into: x86_64-unknown-linux
checking for path to top of build tree... pwd: timer_create: Invalid
argument
configure: error: cannot determine current directory

Is this a known bug with GHC, or is it my supercomputer?  We have several
supercomputers here running in production, so I can't really ask them to
change the configuration just for me, but nonetheless I'd like to run on
them.
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From eeoam at ukfsn.org  Fri Jun 27 12:02:27 2008
From: eeoam at ukfsn.org (Eric)
Date: Fri Jun 27 11:54:00 2008
Subject: [Haskell-cafe] Parsing problem
In-Reply-To: <200806270016.23429.daniel.is.fischer@web.de>
References: <48637229.7000904@ukfsn.org>
	<200806262255.16404.daniel.is.fischer@web.de>
	<48640885.7060408@ukfsn.org>
	<200806270016.23429.daniel.is.fischer@web.de>
Message-ID: <48650F13.3000007@ukfsn.org>

Daniel Fischer wrote:
> sat p = try $ do
>     (t,pos) <- item
>     if p t then return (t,pos) else pzero
>
> and you're all set (you don't need the try's in atom, then).
>   
Thanks, that works!

E.

From martindemello at gmail.com  Fri Jun 27 12:23:39 2008
From: martindemello at gmail.com (Martin DeMello)
Date: Fri Jun 27 12:15:08 2008
Subject: [Haskell-cafe] what's up with hackage.haskell.org?
Message-ID: <f93a6bcc0806270923q24444a36s90270a4d9c3f7918@mail.gmail.com>

haven't been able to get to it in a couple of days (at least)

martin
From simonpj at microsoft.com  Fri Jun 27 12:25:20 2008
From: simonpj at microsoft.com (Simon Peyton-Jones)
Date: Fri Jun 27 12:16:44 2008
Subject: [Haskell-cafe] what's up with hackage.haskell.org?
In-Reply-To: <f93a6bcc0806270923q24444a36s90270a4d9c3f7918@mail.gmail.com>
References: <f93a6bcc0806270923q24444a36s90270a4d9c3f7918@mail.gmail.com>
Message-ID: <638ABD0A29C8884A91BC5FB5C349B1C32AE71E1A94@EA-EXMSG-C334.europe.corp.microsoft.com>

| Subject: [Haskell-cafe] what's up with hackage.haskell.org?
|
| haven't been able to get to it in a couple of days (at least)

It's offline for 24 hrs while Galois move office.

Simon
From martindemello at gmail.com  Fri Jun 27 12:33:20 2008
From: martindemello at gmail.com (Martin DeMello)
Date: Fri Jun 27 12:24:42 2008
Subject: [Haskell-cafe] what's up with hackage.haskell.org?
In-Reply-To: <638ABD0A29C8884A91BC5FB5C349B1C32AE71E1A94@EA-EXMSG-C334.europe.corp.microsoft.com>
References: <f93a6bcc0806270923q24444a36s90270a4d9c3f7918@mail.gmail.com>
	<638ABD0A29C8884A91BC5FB5C349B1C32AE71E1A94@EA-EXMSG-C334.europe.corp.microsoft.com>
Message-ID: <f93a6bcc0806270933g7c3db341vb9ba88f8a25704d0@mail.gmail.com>

On Fri, Jun 27, 2008 at 9:25 AM, Simon Peyton-Jones
<simonpj@microsoft.com> wrote:
> | Subject: [Haskell-cafe] what's up with hackage.haskell.org?
> |
> | haven't been able to get to it in a couple of days (at least)
>
> It's offline for 24 hrs while Galois move office.

Ah, okay :) Just noticed it when I tried to click on a google result
that pointed there.

martin
From cmb21 at kent.ac.uk  Fri Jun 27 13:08:19 2008
From: cmb21 at kent.ac.uk (C.M.Brown)
Date: Fri Jun 27 12:59:41 2008
Subject: [Haskell-cafe] Re: Call Graph Tool?
In-Reply-To: <loom.20080627T031111-823@post.gmane.org>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<loom.20080627T031111-823@post.gmane.org>
Message-ID: <Pine.GSO.4.58.0806271806270.21294@myrtle.ukc.ac.uk>

Hi Ivan,

> Assuming I get it included, is there any features in particular you'd want to
> see in there?  Note that if I do have it produce visualisations, they'll be
> static images as part of an analysis report rather than being interactive.

I'd basically like to see a graph of the overall struture of a Haskell
project: what modules import what, and so forth. This would be useful to
show which modules are forming the core of a system say, and which modules
are acting on the top layer.

Hope that gives some insight...
Chris.

From cmb21 at kent.ac.uk  Fri Jun 27 13:10:13 2008
From: cmb21 at kent.ac.uk (C.M.Brown)
Date: Fri Jun 27 13:01:36 2008
Subject: [Haskell-cafe] Call Graph Tool?
In-Reply-To: <AA3F72F2-7653-47CB-BE98-3817F5C4F0BA@di.uminho.pt>
References: <Pine.GSO.4.58.0806261615210.21685@myrtle.ukc.ac.uk>
	<AA3F72F2-7653-47CB-BE98-3817F5C4F0BA@di.uminho.pt>
Message-ID: <Pine.GSO.4.58.0806271809220.21294@myrtle.ukc.ac.uk>

Hi Jno,

> I suggest that you have a look at HaSlicer, a (visual) Haskell
> slicing tool available online from http://labdotnet.di.uminho.pt/
> HaSlicer/HaSlicer.aspx , developed by Nuno Rodrigues (nfr@di.uminho.pt).

Oh excellent, yes I'd forgotten about this, thanks.

Chris.

From allbery at ece.cmu.edu  Fri Jun 27 14:00:08 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Fri Jun 27 13:51:31 2008
Subject: [Haskell-cafe] Error in configure script for GHC
In-Reply-To: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>
References: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>
Message-ID: <A79B2455-CFAA-44C9-A0B0-80419AA3B5D8@ece.cmu.edu>


On Jun 27, 2008, at 10:15 , Jefferson Heard wrote:

> checking for path to top of build tree... pwd: timer_create:  
> Invalid argument

Translated into plain English, this means "your glibc is too old for  
this binary distribution".
You will probably have to build from source with an older gcc as the  
bootstrap compiler.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From lemming at henning-thielemann.de  Fri Jun 27 14:35:57 2008
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Fri Jun 27 14:27:34 2008
Subject: [Haskell-cafe] Access to Oracle database from Haskell
In-Reply-To: <79d7c4980806270658u78530f51qc2d32f372976f1a0@mail.gmail.com>
References: <Pine.LNX.4.64.0806191706450.22555@anubis.informatik.uni-halle.de>
	<Pine.LNX.4.64.0806242208150.8335@anubis.informatik.uni-halle.de>
	<79d7c4980806241435y2d0f2054n714b1c8701c2eea@mail.gmail.com>
	<Pine.LNX.4.64.0806250800390.19369@anubis.informatik.uni-halle.de>
	<125EACD0CAE4D24ABDB4D148C4593DA9049E943F@GBLONXMB02.corp.amvescap.net>
	<79d7c4980806250307h64bfba7dh95b518967c171384@mail.gmail.com>
	<79d7c4980806260142m41baeab4m2a13dde21b83cefc@mail.gmail.com>
	<Pine.LNX.4.64.0806261420580.27282@anubis.informatik.uni-halle.de>
	<79d7c4980806260554w3698f3d3p624dde7f16b6b06d@mail.gmail.com>
	<Pine.LNX.4.64.0806261551520.17991@anubis.informatik.uni-halle.de>
	<79d7c4980806270658u78530f51qc2d32f372976f1a0@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0806272034121.32425@anubis.informatik.uni-halle.de>


On Fri, 27 Jun 2008, Alistair Bayley wrote:

> 2008/6/26 Henning Thielemann <lemming@henning-thielemann.de>:
>>
>>> Do you need to say -lclntsh when you use ghc to compile?
>>
>> Ah, I see, I must run both GHCi and GHC with -package Takusen and everything
>> is fine.
>
> This still doesn't seem right. Both ghci and ghc --make should
> automatically link the package. The only time you should need to use
> -package is in ghc "batch" mode i.e. ghc sans --make.

I actually called GHC without --make because the example program consists 
of only one (the main) module.

> Yes... I've had a quick look at the instant client packages. The SDK
> zip just puts the headers under instantclient_10_2/sdk/include (which
> is still not $ORACLE_HOME/rdbms/public, but c'est la vie). So it looks
> like the .rpm puts them somewhere completely different:
> /usr/include/oracle/10.2.0.4/client. Do you also have
> $ORACLE_HOME/sdk/include, with headers in?

No, in ORACLE_HOME there is only 'bin' and 'lib'.

From jeremy at n-heptane.com  Fri Jun 27 14:58:53 2008
From: jeremy at n-heptane.com (Jeremy Shaw)
Date: Fri Jun 27 14:48:00 2008
Subject: [Haskell-cafe] Re: Haskell on ARM (was Re: ANN: Topkata)
In-Reply-To: <14d615330806261657h3ce55bebx74f8e89205a9854@mail.gmail.com>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
	<87ej6ww9dy.fsf_-_@columbia.edu>
	<20080617201233.GD19304@scytale.galois.com>
	<871w2mit8o.wl%jeremy@n-heptane.com> <g3s4fr$9h2$1@ger.gmane.org>
	<14d615330806241903s30734fe4q5c7af4569e9b421@mail.gmail.com>
	<14d615330806261657h3ce55bebx74f8e89205a9854@mail.gmail.com>
Message-ID: <87tzfehfgy.wl%jeremy@n-heptane.com>

At Fri, 27 Jun 2008 09:57:29 +1000,
Jeremy Apthorp wrote:

> Next year I'll be working on a project for my undergraduate computing
> course at UNSW that will involve getting GHC to target the Nintendo
> DS. It'll require cross-compilation, because the DS isn't powerful
> enough to actually run GHC (4M main ram and a 66MHz processor).

Cool!

By cross-compilation, I assume you mean, a version of GHC which runs
on x86, but generates ARM assembly? Another option might be to use a
nintendo DS emulator which has been configured to support more RAM and
CPU power ?

A true cross-compiler would be nice though, because it will run much
faster. GHC does have some support for cross-compilation, but in the
current implementation, it is mostly (entirely?) there for
bootstrapping. I have no idea how the ghc backend rewrite for 6.10
will affect this.

Hope this helps,
j.
From rwbarton at math.harvard.edu  Fri Jun 27 14:59:20 2008
From: rwbarton at math.harvard.edu (Reid Barton)
Date: Fri Jun 27 14:49:22 2008
Subject: [Haskell-cafe] Error in configure script for GHC
In-Reply-To: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>
References: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>
Message-ID: <20080627185920.GH8867@rwbarton.mit.edu>

On Fri, Jun 27, 2008 at 10:15:23AM -0400, Jefferson Heard wrote:
> I've tried all the 6.6 and 6.8 versions, trying to compile them on a
> RHEL-based supercomputer, and I always see this error when I run
> ./configure:
> 
> -bash-3.00$ ./configure
> checking build system type... x86_64-unknown-linux-gnu
> checking host system type... x86_64-unknown-linux-gnu
> checking target system type... x86_64-unknown-linux-gnu
> Which we'll further canonicalise into: x86_64-unknown-linux
> checking for path to top of build tree... pwd: timer_create: Invalid
> argument
> configure: error: cannot determine current directory

I don't know whether this is related, but I've noticed that the most
recent source distribution of the HEAD branch (ghc-6.9.20080615)
includes a binary executable utils/pwd/pwd compiled for x86-64.  This
causes ./configure to break with a similar message, since I have a
32-bit system.  If I delete utils/pwd/pwd, the configure script
automatically rebuilds it and then completes successfully.

Regards,
Reid Barton
From adam.smyczek at gmail.com  Fri Jun 27 15:04:22 2008
From: adam.smyczek at gmail.com (Adam Smyczek)
Date: Fri Jun 27 14:55:50 2008
Subject: [Haskell-cafe] ghci vi mode?
Message-ID: <00D43556-2F67-4BF4-8524-2F8BF2E9A159@gmail.com>

If I remember correctly, ghci uses readline framework on Linux/OS X.
Is it possible to change ghci editing mode to vi?

Thanks,
Adam


From jefferson.r.heard at gmail.com  Fri Jun 27 15:04:51 2008
From: jefferson.r.heard at gmail.com (Jefferson Heard)
Date: Fri Jun 27 14:56:13 2008
Subject: [Haskell-cafe] Error in configure script for GHC
In-Reply-To: <A79B2455-CFAA-44C9-A0B0-80419AA3B5D8@ece.cmu.edu>
References: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>
	<A79B2455-CFAA-44C9-A0B0-80419AA3B5D8@ece.cmu.edu>
Message-ID: <4165d3a70806271204x74e2f680o61b420b3af746d79@mail.gmail.com>

Linux version 2.6.9-34.0.2.ELsmp (buildcentos@x8664-build.centos.org) (gcc
version 3.4.5 20051201 (Red Hat 3.4.5-2)) #1 SMP Fri Jul 7 18:22:55 CDT 2006

This is my version string if that helps...  I'd do the bootstrap build right
now, but hackage is down (I understand it's moving), and I can't get to the
instructions for bootstrapping.

On Fri, Jun 27, 2008 at 2:00 PM, Brandon S. Allbery KF8NH <
allbery@ece.cmu.edu> wrote:

>
> On Jun 27, 2008, at 10:15 , Jefferson Heard wrote:
>
>  checking for path to top of build tree... pwd: timer_create: Invalid
>> argument
>>
>
> Translated into plain English, this means "your glibc is too old for this
> binary distribution".
> You will probably have to build from source with an older gcc as the
> bootstrap compiler.
>
> --
> brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
> system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
> electrical and computer engineering, carnegie mellon university    KF8NH
>
>
>


-- 
I try to take things like a crow; war and chaos don't always ruin a picnic,
they just mean you have to be careful what you swallow.

-- Jessica Edwards
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From allbery at ece.cmu.edu  Fri Jun 27 16:04:59 2008
From: allbery at ece.cmu.edu (Brandon S. Allbery KF8NH)
Date: Fri Jun 27 15:56:22 2008
Subject: [Haskell-cafe] Error in configure script for GHC
In-Reply-To: <4165d3a70806271204x74e2f680o61b420b3af746d79@mail.gmail.com>
References: <4165d3a70806270715pab9937egc40f0c631680b817@mail.gmail.com>
	<A79B2455-CFAA-44C9-A0B0-80419AA3B5D8@ece.cmu.edu>
	<4165d3a70806271204x74e2f680o61b420b3af746d79@mail.gmail.com>
Message-ID: <1D9DFB6A-8AD4-4711-A340-82B191EAB73C@ece.cmu.edu>


On Jun 27, 2008, at 15:04 , Jefferson Heard wrote:

> Linux version 2.6.9-34.0.2.ELsmp (buildcentos@x8664- 
> build.centos.org) (gcc version 3.4.5 20051201 (Red Hat 3.4.5-2)) #1  
> SMP Fri Jul 7 18:22:55 CDT 2006


I can't help with much of anything Linux aside form having run into  
that error on SuSE 9.3.  But in any case, that's the kernel version.   
for glibc version, run /lib/libc.so.6.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


From qdunkan at gmail.com  Fri Jun 27 16:53:24 2008
From: qdunkan at gmail.com (Evan Laforge)
Date: Fri Jun 27 16:44:45 2008
Subject: [Haskell-cafe] ghci vi mode?
In-Reply-To: <00D43556-2F67-4BF4-8524-2F8BF2E9A159@gmail.com>
References: <00D43556-2F67-4BF4-8524-2F8BF2E9A159@gmail.com>
Message-ID: <2518b95d0806271353k31c7e339h71c5e6f8de188458@mail.gmail.com>

On Fri, Jun 27, 2008 at 12:04 PM, Adam Smyczek <adam.smyczek@gmail.com> wrote:
> If I remember correctly, ghci uses readline framework on Linux/OS X.
> Is it possible to change ghci editing mode to vi?

Here's what I have:

% cat ~/.inputrc
set editing-mode vi
set keymap vi
set bell-style none
From john at repetae.net  Fri Jun 27 20:08:04 2008
From: john at repetae.net (John Meacham)
Date: Fri Jun 27 19:59:25 2008
Subject: Haskell on ARM (was Re: [Haskell-cafe] ANN: Topkata)
In-Reply-To: <20080626142619.GA4743@matrix.chaos.earth.li>
References: <87zlpoguqh.fsf@elefant.olsbruecken.local>
	<4B3E7353-F7F2-4D2D-A335-30D2D3883A4A@gmail.com>
	<200806170851.22718.valgarv@gmx.net>
	<87ej6ww9dy.fsf_-_@columbia.edu>
	<20080617201233.GD19304@scytale.galois.com>
	<871w2mit8o.wl%jeremy@n-heptane.com>
	<20080626142619.GA4743@matrix.chaos.earth.li>
Message-ID: <20080628000804.GI12977@sliver.repetae.net>

Just a random note. jhc works fine on ARM, I have successfully run
Haskell programs on on iPhone and a nokia n800 tablet compiled with it.
jhc is, of course, still pretty unstable. but new developers are always
welcome.

        John

-- 
John Meacham - ?repetae.net?john?
From aeyakovenko at gmail.com  Fri Jun 27 21:20:51 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Fri Jun 27 21:12:13 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <20080618170543.GK32397@darcs.net>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<c290c4f20806180811uf0fa029w6af06a33a352749@mail.gmail.com>
	<e26d18e40806180916h59f9c577qb0fccb0d501ad763@mail.gmail.com>
	<20080618170543.GK32397@darcs.net>
Message-ID: <e26d18e40806271820p271c9c37i350d4f8846e6f9dd@mail.gmail.com>

> I suspect that it is your initialization that is the difference.  For
> one thing, you've initialized the arrays to different values, and in
> your C code you've fused what are two separate loops in your Haskell
> code.  So you've not only given the C compiler an easier loop to run
> (since you're initializing the array to a constant rather than to a
> sequence of numbers), but you've also manually optimized that
> initialization.  In fact, this fusion could be precisely the factor of
> two.  Why not see what happens in Haskell if you create just one
> vector and dot it with itself? (of course, that'll also make the blas
> call faster, so you'll need to be careful in your interpretation of
> your results.)

The difference cant be in the initialization.   I am calling the dot
product a million times, the malloc and init in both cases are
insignificant.  Also, "fusing" the two loops in C probably wont help,
if anything having each loop run separate is likely to be faster and
result in less cache misses.

In this case, i am using vectors of size 10 only, and calling the loop
10 million times, haskell is far far slower, or 35 times.  That's
pretty crappy.


$ cat htestdot.hs
{-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
-fglasgow-exts -fbang-patterns -lcblas#-}
module Main where

import Data.Vector.Dense.IO
import Control.Monad

main = do
   let size = 10
   let times = 10*1000*1000
   v1::IOVector Int Double <- newListVector size $ replicate size 0.1
   v2::IOVector Int Double <- newListVector size $ replicate size 0.1
   sum <- foldM (\ ii zz -> do
      rv <- v1 `getDot` v2
      return $ zz + rv
      ) 0.0 [0..times]
   print $ sum


$ ghc --make htestdot.hs
$ time ./htestdot
1.00000001e7

real    0m17.328s
user    0m17.320s
sys     0m0.010

$ cat testdot.c
#include <cblas.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main() {
   int size = 10;
   int times = 10*1000*1000;
   int ii = 0;
   double dd = 0.0;
   double* v1 = malloc(sizeof(double) * (size));
   double* v2 = malloc(sizeof(double) * (size));
   for(ii = 0; ii < size; ++ii) {
      v1[ii] = 0.1;
   }
   for(ii = 0; ii < size; ++ii) {
      v2[ii] = 0.1;
   }
   for(ii = 0; ii < times; ++ii) {
      dd += cblas_ddot(size, v1, 1, v2, 1);
   }
   free(v1);
   free(v2);
   printf("%f\n", dd);
   return 0;
}

$ gcc -O2 testdot.c -lcblas -o testdot
$ time ./testdot
999999.999839

real    0m0.491s
user    0m0.480s
sys     0m0.020s


Just to make sure that fold isnt causing the slowdown, i reverted the
haskell program to use the mapM_, i still got almost the same
performance:

$ cat htestdot.hs
{-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
-fglasgow-exts -fbang-patterns -lcblas#-}
module Main where

import Data.Vector.Dense.IO
import Control.Monad

main = do
   let size = 10
   let times = 10*1000*1000
   v1::IOVector Int Double <- newListVector size $ replicate size 0.1
   v2::IOVector Int Double <- newListVector size $ replicate size 0.1
   mapM_ (\ ii -> do v1 `getDot` v2) [0..times]
$ ghc --make htestdot

$ time ./htestdot

real    0m15.660s
user    0m15.630s
sys     0m0.030s

This is what the profiler has to say:

 $ cat htestdot.prof
        Fri Jun 27 18:06 2008 Time and Allocation Profiling Report  (Final)

           htestdot +RTS -p -RTS

        total time  =       22.00 secs   (1100 ticks @ 20 ms)
        total alloc = 3,320,010,716 bytes  (excludes profiling overheads)

COST CENTRE                    MODULE               %time %alloc

main                           Main                 100.0  100.0



                        individual    inherited
COST CENTRE              MODULE
       no.    entries  %time %alloc   %time %alloc

MAIN                     MAIN
         1           0   0.0    0.0   100.0  100.0
 main                    Main
       222           1  93.6   88.0    93.6   88.0
 CAF                     Main
       216           5   0.0    0.0     6.4   12.0
  main                   Main
       223           0   6.4   12.0     6.4   12.0
 CAF                     GHC.Handle
       168           3   0.0    0.0     0.0    0.0
From dan.doel at gmail.com  Fri Jun 27 22:41:51 2008
From: dan.doel at gmail.com (Dan Doel)
Date: Fri Jun 27 22:33:18 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806271820p271c9c37i350d4f8846e6f9dd@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<20080618170543.GK32397@darcs.net>
	<e26d18e40806271820p271c9c37i350d4f8846e6f9dd@mail.gmail.com>
Message-ID: <200806272241.51624.dan.doel@gmail.com>

On Friday 27 June 2008, Anatoly Yakovenko wrote:
> $ cat htestdot.hs
> {-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
> -fglasgow-exts -fbang-patterns -lcblas#-}
> module Main where
>
> import Data.Vector.Dense.IO
> import Control.Monad
>
> main = do
>    let size = 10
>    let times = 10*1000*1000
>    v1::IOVector Int Double <- newListVector size $ replicate size 0.1
>    v2::IOVector Int Double <- newListVector size $ replicate size 0.1
>    sum <- foldM (\ ii zz -> do
>       rv <- v1 `getDot` v2
>       return $ zz + rv
>       ) 0.0 [0..times]
>    print $ sum

Hackage is down for the time being, so I can't install blas and look at the 
core for your program. However, there are still some reasons why this code 
would be slow.

For instance, a brief experiment seems to indicate that foldM is not a good 
consumer in the foldr/build sense, so no deforestation occurs. Your program 
is iterating over a 10-million element lazy list. That's going to add 
overhead. I wrote a simple test program which just adds 0.1 in each 
iteration:

---- snip ----

{-# LANGUAGE BangPatterns #-}

module Main (main) where

import Control.Monad

main = do
  let times = 10*1000*1000
  sum <- foldM (\_ zz -> return $ zz + 0.1) 0.0 [0..times]
--  sum <- foo 0 times 0.0
  print $ sum

foo :: Int -> Int -> Double -> IO Double
foo k m !zz
  | k <= m     = foo (k+1) m (zz + 0.1)
  | otherwise = return zz

---- snip ----

With foldM, it takes 2.5 seconds on my machine. If you comment that line, and 
use foo instead, it takes around .1 seconds. So that's a factor of what, 250? 
That loop allows for a lot more unboxing, which allows much better code to be 
generated.

When Hackage comes back online, I'll take a look at your code, and see if I 
can make it run faster, but you might want to try it yourself in the time 
being. Strictifying the addition of the accumulator is probably a good idea, 
for instance.

Cheers,
-- Dan
From pgavin at gmail.com  Fri Jun 27 23:19:01 2008
From: pgavin at gmail.com (Peter Gavin)
Date: Fri Jun 27 23:10:25 2008
Subject: [Haskell-cafe] ANN: Gtk2Hs 0.9.13 released
Message-ID: <4865ADA5.3070103@gmail.com>

Hello everyone,

Gtk2Hs version 0.9.13 is now available. [1]

New features:

     * bindings for Gnome VFS and GStreamer
     * a new Gtk+ tutorial has been adapted by Hans van Thiel
     * cairo image stride support
     * many new demos
     * compiles with GHC 6.8.3
     * lots of bug fixes

This release has been tested on a variety of platforms with different 
versions of Gtk+ and GHC, so you should have no trouble compiling it if 
you're using an older version of Gtk+.

Note that the binaries for Win32 for this release are only provided for 
GHC 6.8.3 and Gtk+ 2.12.  As with older releases, all the C libraries 
needed are included in the installer, so you don't need to download 
anything else to get up an running.  I've also created zip files 
containing only the C libraries that can be used for redistribution. 
The sources for these binaries are available at [2]

Links:
[1] 
http://sourceforge.net/project/showfiles.php?group_id=49207&package_id=42440
[2] http://ftp.gnome.org/pub/GNOME/sources/


--
Pete
From aeyakovenko at gmail.com  Sat Jun 28 01:29:22 2008
From: aeyakovenko at gmail.com (Anatoly Yakovenko)
Date: Sat Jun 28 01:20:43 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <200806272241.51624.dan.doel@gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<20080618170543.GK32397@darcs.net>
	<e26d18e40806271820p271c9c37i350d4f8846e6f9dd@mail.gmail.com>
	<200806272241.51624.dan.doel@gmail.com>
Message-ID: <e26d18e40806272229t5eab9d83gb13330697121384@mail.gmail.com>

i get the same crappy performance with:

$ cat htestdot.hs
{-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
-fglasgow-exts -fbang-patterns -lcblas#-}
module Main where

import Data.Vector.Dense.IO
import Control.Monad

main = do
   let size = 10
   let times = 10*1000*1000
   v1::IOVector Int Double <- newListVector size $ replicate size 0.1
   v2::IOVector Int Double <- newListVector size $ replicate size 0.1
   replicateM_ times $ v1 `getDot` v2



On Fri, Jun 27, 2008 at 7:41 PM, Dan Doel <dan.doel@gmail.com> wrote:
> On Friday 27 June 2008, Anatoly Yakovenko wrote:
>> $ cat htestdot.hs
>> {-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
>> -fglasgow-exts -fbang-patterns -lcblas#-}
>> module Main where
>>
>> import Data.Vector.Dense.IO
>> import Control.Monad
>>
>> main = do
>>    let size = 10
>>    let times = 10*1000*1000
>>    v1::IOVector Int Double <- newListVector size $ replicate size 0.1
>>    v2::IOVector Int Double <- newListVector size $ replicate size 0.1
>>    sum <- foldM (\ ii zz -> do
>>       rv <- v1 `getDot` v2
>>       return $ zz + rv
>>       ) 0.0 [0..times]
>>    print $ sum
>
> Hackage is down for the time being, so I can't install blas and look at the
> core for your program. However, there are still some reasons why this code
> would be slow.
>
> For instance, a brief experiment seems to indicate that foldM is not a good
> consumer in the foldr/build sense, so no deforestation occurs. Your program
> is iterating over a 10-million element lazy list. That's going to add
> overhead. I wrote a simple test program which just adds 0.1 in each
> iteration:
>
> ---- snip ----
>
> {-# LANGUAGE BangPatterns #-}
>
> module Main (main) where
>
> import Control.Monad
>
> main = do
>  let times = 10*1000*1000
>  sum <- foldM (\_ zz -> return $ zz + 0.1) 0.0 [0..times]
> --  sum <- foo 0 times 0.0
>  print $ sum
>
> foo :: Int -> Int -> Double -> IO Double
> foo k m !zz
>  | k <= m     = foo (k+1) m (zz + 0.1)
>  | otherwise = return zz
>
> ---- snip ----
>
> With foldM, it takes 2.5 seconds on my machine. If you comment that line, and
> use foo instead, it takes around .1 seconds. So that's a factor of what, 250?
> That loop allows for a lot more unboxing, which allows much better code to be
> generated.
>
> When Hackage comes back online, I'll take a look at your code, and see if I
> can make it run faster, but you might want to try it yourself in the time
> being. Strictifying the addition of the accumulator is probably a good idea,
> for instance.
>
> Cheers,
> -- Dan
>
From dons at galois.com  Sat Jun 28 01:51:09 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun 28 01:42:35 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806272229t5eab9d83gb13330697121384@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<20080618170543.GK32397@darcs.net>
	<e26d18e40806271820p271c9c37i350d4f8846e6f9dd@mail.gmail.com>
	<200806272241.51624.dan.doel@gmail.com>
	<e26d18e40806272229t5eab9d83gb13330697121384@mail.gmail.com>
Message-ID: <20080628055109.GA28148@liouville.galois.com>

aeyakovenko:
> i get the same crappy performance with:
> 
> $ cat htestdot.hs
> {-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
> -fglasgow-exts -fbang-patterns -lcblas#-}
> module Main where
> 
> import Data.Vector.Dense.IO
> import Control.Monad
> 
> main = do
>    let size = 10
>    let times = 10*1000*1000
>    v1::IOVector Int Double <- newListVector size $ replicate size 0.1
>    v2::IOVector Int Double <- newListVector size $ replicate size 0.1
>    replicateM_ times $ v1 `getDot` v2

replicateM_ is using a list underneath for control as well,

    replicateM n x    = sequence (replicate n x)

Try writing a simple recursive loop, as Dan suggested. No list node
forcing overhead, so in a very tight loop you'll just want the index in
a register.

See here for more examples of tight register loops,

    http://cgi.cse.unsw.edu.au/~dons/blog/2008/05/16#fast

In general, if you're chasing C performance for a loop, your best bet is
to write a loop first. Then later see if you can get the same kind of
code from higher order, lazy, monadic functions.

-- Don
From dons at galois.com  Sat Jun 28 03:44:51 2008
From: dons at galois.com (Don Stewart)
Date: Sat Jun 28 03:36:16 2008
Subject: [Haskell-cafe] blas bindings, why are they so much slower the C?
In-Reply-To: <e26d18e40806272229t5eab9d83gb13330697121384@mail.gmail.com>
References: <e26d18e40806172100q327f0947x59f3a09bd1a272df@mail.gmail.com>
	<20080618170543.GK32397@darcs.net>
	<e26d18e40806271820p271c9c37i350d4f8846e6f9dd@mail.gmail.com>
	<200806272241.51624.dan.doel@gmail.com>
	<e26d18e40806272229t5eab9d83gb13330697121384@mail.gmail.com>
Message-ID: <20080628074451.GA29980@liouville.galois.com>

so I had a look at the code. The loops are all fine. replicateM_ isn't 
a problem, but getDot is decidedly non trivial. Lots of pattern matching
on different vector forms, and to top it off ffi calls.

With some inlining in the blas library I was able to cut a few seconds
off the running time, but getDot looks to be fundamentally a bit
complicated in the current implementation.

I wonder if you'll get different results with hmatrix?

Anyway, this is a library issue. Better take it up with Patrick.
Pass on to the library author the C code, the Haskell you think should
be compiled identically.

-- Don

aeyakovenko:
> i get the same crappy performance with:
> 
> $ cat htestdot.hs
> {-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
> -fglasgow-exts -fbang-patterns -lcblas#-}
> module Main where
> 
> import Data.Vector.Dense.IO
> import Control.Monad
> 
> main = do
>    let size = 10
>    let times = 10*1000*1000
>    v1::IOVector Int Double <- newListVector size $ replicate size 0.1
>    v2::IOVector Int Double <- newListVector size $ replicate size 0.1
>    replicateM_ times $ v1 `getDot` v2
> 
> 
> 
> On Fri, Jun 27, 2008 at 7:41 PM, Dan Doel <dan.doel@gmail.com> wrote:
> > On Friday 27 June 2008, Anatoly Yakovenko wrote:
> >> $ cat htestdot.hs
> >> {-# OPTIONS_GHC -O2 -fexcess-precision -funbox-strict-fields
> >> -fglasgow-exts -fbang-patterns -lcblas#-}
> >> module Main where
> >>
> >> import Data.Vector.Dense.IO
> >> import Control.Monad
> >>
> >> main = do
> >>    let size = 10
> >>    let times = 10*1000*1000
> >>    v1::IOVector Int Double <- newListVector size $ replicate size 0.1
> >>    v2::IOVector Int Double <- newListVector size $ replicate size 0.1
> >>    sum <- foldM (\ ii zz -> do
> >>       rv <- v1 `getDot` v2
> >>       return $ zz + rv
> >>       ) 0.0 [0..times]
> >>    print $ sum
> >
> > Hackage is down for the time being, so I can't install blas and look at the
> > core for your program. However, there are still some reasons why this code
> > would be slow.
> >
> > For instance, a brief experiment seems to indicate that foldM is not a good
> > consumer in the foldr/build sense, so no deforestation occurs. Your program
> > is iterating over a 10-million element lazy list. That's going to add
> > overhead. I wrote a simple test program which just adds 0.1 in each
> > iteration:
> >
> > ---- snip ----
> >
> > {-# LANGUAGE BangPatterns #-}
> >
> > module Main (main) where
> >
> > import Control.Monad
> >
> > main = do
> >  let times = 10*1000*1000
> >  sum <- foldM (\_ zz -> return $ zz + 0.1) 0.0 [0..times]
> > --  sum <- foo 0 times 0.0
> >  print $ sum
> >
> > foo :: Int -> Int -> Double -> IO Double
> > foo k m !zz
> >  | k <= m     = foo (k+1) m (zz + 0.1)
> >  | otherwise = return zz
> >
> > ---- snip ----
> >
> > With foldM, it takes 2.5 seconds on my machine. If you comment that line, and
> > use foo instead, it takes around .1 seconds. So that's a factor of what, 250?
> > That loop allows for a lot more unboxing, which allows much better code to be
> > generated.
> >
> > When Hackage comes back online, I'll take a look at your code, and see if I
> > can make it run faster, but you might want to try it yourself in the time
> > being. Strictifying the addition of the accumulator is probably a good idea,
> > for instance.
> >
> > Cheers,
> > -- Dan
> >
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