From corentin.dupont at gmail.com  Mon Oct 29 06:09:43 2007
From: corentin.dupont at gmail.com (Dupont Corentin)
Date: Mon Oct 29 06:07:17 2007
Subject: [Haskell-fr] Fractional etc...
Message-ID: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>

Salut,
J'ai vraiment du mal ? mettre au point un petit programme...
Il me sort souvent des probl?mes du style :

  No instance for (Fractional Integer)
     arising from use of `/' at <interactive>:1:4-7
  Possible fix: add an instance declaration for (Fractional Integer)

Par exemple sous ghci si je fait:

map (/5) [0..10]

tout se passe bien.
Mais si je me dit "tiens je voudrais bien param?trer le 5":

let m = 5
map (/m) [0..10]

il me sort:
    No instance for (Fractional Integer)
      arising from use of `/' at <interactive>:1:4-7
    Possible fix: add an instance declaration for (Fractional Integer)
    In the first argument of `map', namely `(/ m)'
    In the expression: map ((/ m)) ([0 .. 10])
    In the definition of `it': it = map ((/ m)) ([0 .. 10])


Pourtant les 2 codes me sembles assez ?quivalents!!!
Je peux utiliser des "fromInteger", ce qui r?sout temporairement le probl?me.

Je me retrouve par la suite avec des (de m?moire)
Infered type : Int
Expected type : Integer

Ce qui me laisse dans le flou...

a+
Corentin
From corentin.dupont at gmail.com  Mon Oct 29 07:02:50 2007
From: corentin.dupont at gmail.com (Dupont Corentin)
Date: Mon Oct 29 07:00:21 2007
Subject: [Haskell-fr] Re: Fractional etc...
In-Reply-To: <20071029104150.GA26568@nic.fr>
References: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>
	<20071029104150.GA26568@nic.fr>
Message-ID: <18a05e6b0710290402i3cfcb163r264d0ce27e0acc86@mail.gmail.com>

J'ai ghci 6.6.1.
Ce code ne passe pas:

*Prelude> let m = 5
Prelude> map (/m) [0..10]

<interactive>:1:4:
    No instance for (Fractional Integer)
      arising from use of `/' at <interactive>:1:4-7

*par contre ?a ?a passe dans ghci:

*Prelude> let foo m = map (/m) [0..10]
Prelude> foo 5
[0.0,0.2,0.4,0.6,0.8,1.0,1.2,1.4,1.6,1.8,2.0]*

Mais... Bien sur:

*Prelude> let n = 5*
*Prelude> let foo m = map (/m) [0..10]
Prelude> foo n*

Ne passe pas plus!

*
*



On 10/29/07, Stephane Bortzmeyer <bortzmeyer@nic.fr> wrote:
> On Mon, Oct 29, 2007 at 11:09:43AM +0100,
>  Dupont Corentin <corentin.dupont@gmail.com> wrote
>  a message of 43 lines which said:
>
> > let m = 5
> > map (/m) [0..10]
> >
> > il me sort:
> >     No instance for (Fractional Integer)
>
> Quelle version ? Avec ghci 6.6, c'est accept? sans probl?me. (J'ai
> essay? avec let et aussi avec :
>
> foobar m =
>  map (/m) [0..10]
>
> main = do
>  print (foobar 5)
>
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From chaddai.fouche at gmail.com  Mon Oct 29 07:44:44 2007
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Mon Oct 29 07:42:14 2007
Subject: [Haskell-fr] Fractional etc...
In-Reply-To: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>
References: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>
Message-ID: <e9350eaf0710290444y25640340o2c7b7d67440ed39@mail.gmail.com>

Le 29/10/07, Dupont Corentin<corentin.dupont@gmail.com> a ?crit :
>
> let m = 5
> map (/m) [0..10]
>
> il me sort:
>     No instance for (Fractional Integer)
>       arising from use of `/' at <interactive>:1:4-7
>     Possible fix: add an instance declaration for (Fractional Integer)
>     In the first argument of `map', namely `(/ m)'
>     In the expression: map ((/ m)) ([0 .. 10])
>     In the definition of `it': it = map ((/ m)) ([0 .. 10])
>

C'est normal, car GHCi est oblig? de typer 5 sans autres informations,
il lui donne donc le type par d?faut pour un litt?ral entier :
Integer. Comme ensuite tu utilises (/) qui ne prend pas un Integer
comme op?rande...

Par contraste :
map (/5) [0..10]
L?, GHCi a plus d'information sur le typage de 5, il sait qu'il doit
s'agir d'un Fractional, il lui donne donc le type Fractional par
d?faut, c'est ? dire Double.

Dans un v?ritable programme, ce probl?me n'appara?t pas, car GHC
dispose toujours de meilleures contraintes de typage (ou la variable
n'est pas utilis?e). Il n'y a pas vraiment de rem?de au probl?me,
except? de mettre un devin dans GHCi, ou peut-?tre de retarder la
compilation des lets... (mais jusqu'? quand ?)

-- 
Jeda?
From popavdan at yahoo.com  Mon Oct 29 14:21:04 2007
From: popavdan at yahoo.com (Dan Popa)
Date: Mon Oct 29 14:18:38 2007
Subject: [Haskell-fr] Fractional etc...
In-Reply-To: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>
Message-ID: <392608.60401.qm@web36506.mail.mud.yahoo.com>

Why don't you try :
> map (/5.0) [0.0 .. 10.0]
> 
> let m = 5.0
> map (/m) [0.0 .. 10.0]
> 
I have a similar problem trying a divison by a  length
of a list. Finaly I have to build a version of length
called len:

len [] = 0.0
len (h:t)  = 1.0 + len t

Dan 


--- Dupont Corentin <corentin.dupont@gmail.com> wrote:

> Salut,
> J'ai vraiment du mal ? mettre au point un petit
> programme...
> Il me sort souvent des probl?mes du style :
> 
>   No instance for (Fractional Integer)
>      arising from use of `/' at <interactive>:1:4-7
>   Possible fix: add an instance declaration for
> (Fractional Integer)
> 
> Par exemple sous ghci si je fait:
> 
> map (/5) [0..10]
> 
> tout se passe bien.
> Mais si je me dit "tiens je voudrais bien param?trer
> le 5":
> 
> let m = 5
> map (/m) [0..10]
> 
> il me sort:
>     No instance for (Fractional Integer)
>       arising from use of `/' at <interactive>:1:4-7
>     Possible fix: add an instance declaration for
> (Fractional Integer)
>     In the first argument of `map', namely `(/ m)'
>     In the expression: map ((/ m)) ([0 .. 10])
>     In the definition of `it': it = map ((/ m)) ([0
> .. 10])
> 
> 
> Pourtant les 2 codes me sembles assez ?quivalents!!!
> Je peux utiliser des "fromInteger", ce qui r?sout
> temporairement le probl?me.
> 
> Je me retrouve par la suite avec des (de m?moire)
> Infered type : Int
> Expected type : Integer
> 
> Ce qui me laisse dans le flou...
> 
> a+
> Corentin
> _______________________________________________
> Haskell-fr mailing list
> Haskell-fr@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-fr
> 


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From corentin.dupont at gmail.com  Tue Oct 30 04:49:03 2007
From: corentin.dupont at gmail.com (Dupont Corentin)
Date: Tue Oct 30 04:46:31 2007
Subject: [Haskell-fr] Fractional etc...
In-Reply-To: <392608.60401.qm@web36506.mail.mud.yahoo.com>
References: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>
	<392608.60401.qm@web36506.mail.mud.yahoo.com>
Message-ID: <18a05e6b0710300149w36ae5389l63747faf5ef09aa9@mail.gmail.com>

There must be a way to divide a real by an integer??
My integer is eventually a "number of elements" as in the exemple of Dan.
How would you compute a mean then?


On 10/29/07, Dan Popa <popavdan@yahoo.com> wrote:
>
> Why don't you try :
> > map (/5.0) [0.0 .. 10.0]
> >
> > let m = 5.0
> > map (/m) [0.0 .. 10.0]
> >
> I have a similar problem trying a divison by a  length
> of a list. Finaly I have to build a version of length
> called len:
>
> len [] = 0.0
> len (h:t)  = 1.0 + len t
>
> Dan
>
>
> --- Dupont Corentin <corentin.dupont@gmail.com> wrote:
>
> > Salut,
> > J'ai vraiment du mal ? mettre au point un petit
> > programme...
> > Il me sort souvent des probl?mes du style :
> >
> >   No instance for (Fractional Integer)
> >      arising from use of `/' at <interactive>:1:4-7
> >   Possible fix: add an instance declaration for
> > (Fractional Integer)
> >
> > Par exemple sous ghci si je fait:
> >
> > map (/5) [0..10]
> >
> > tout se passe bien.
> > Mais si je me dit "tiens je voudrais bien param?trer
> > le 5":
> >
> > let m = 5
> > map (/m) [0..10]
> >
> > il me sort:
> >     No instance for (Fractional Integer)
> >       arising from use of `/' at <interactive>:1:4-7
> >     Possible fix: add an instance declaration for
> > (Fractional Integer)
> >     In the first argument of `map', namely `(/ m)'
> >     In the expression: map ((/ m)) ([0 .. 10])
> >     In the definition of `it': it = map ((/ m)) ([0
> > .. 10])
> >
> >
> > Pourtant les 2 codes me sembles assez ?quivalents!!!
> > Je peux utiliser des "fromInteger", ce qui r?sout
> > temporairement le probl?me.
> >
> > Je me retrouve par la suite avec des (de m?moire)
> > Infered type : Int
> > Expected type : Integer
> >
> > Ce qui me laisse dans le flou...
> >
> > a+
> > Corentin
> > _______________________________________________
> > Haskell-fr mailing list
> > Haskell-fr@haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-fr
> >
>
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam?  Yahoo! Mail has the best spam protection around
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>
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From chaddai.fouche at gmail.com  Tue Oct 30 06:50:47 2007
From: chaddai.fouche at gmail.com (=?ISO-8859-1?Q?Chadda=EF_Fouch=E9?=)
Date: Tue Oct 30 06:48:15 2007
Subject: [Haskell-fr] Fractional etc...
In-Reply-To: <18a05e6b0710300149w36ae5389l63747faf5ef09aa9@mail.gmail.com>
References: <18a05e6b0710290309qff6a121wb06ce746fadb25d2@mail.gmail.com>
	<392608.60401.qm@web36506.mail.mud.yahoo.com>
	<18a05e6b0710300149w36ae5389l63747faf5ef09aa9@mail.gmail.com>
Message-ID: <e9350eaf0710300350g28c54b07lc671bf668ed8146d@mail.gmail.com>

Le 30/10/07, Dupont Corentin<corentin.dupont@gmail.com> a ?crit :
>
> There must be a way to divide a real by an integer??
> My integer is eventually a "number of elements" as in the exemple of Dan.
> How would you compute a mean then?
>

No, you can't "divide a real by an integer", but you can introduce the
integer in the reals and divide by this.

divideByI :: (Fractional a, Integral b) => a -> b -> a
divideByI a b = a / fromIntegral b

-- 
Jeda?