[Haskell-cafe] Re: Abstraction leak
Donald Bruce Stewart
dons at cse.unsw.edu.au
Wed Jul 4 07:44:13 EDT 2007
> On Wed, Jul 04, 2007 at 09:02:15PM +1000, Donald Bruce Stewart wrote:
> >>On Sun, Jul 01, 2007 at 06:07:13PM +0100, Andrew Coppin wrote:
> >>>I haven't actually tried, but presumably a TCP connection is represented
> >>>in the same way as a file, and so has the same problems.
> >>>Basically doing binary I/O seems to be one of those things that in
> >>Haskell >falls into the class of "it's possibly but annoyingly messy"...
> >>In an ideal world there would be a 'deriving Serializable' you
> >derive Binary
> > (use an external tool for this)
> such as?
Binary instances are pretty easy to write. For a simple data type:
> instance Binary Exp where
> put (IntE i) = do put (0 :: Word8)
> put i
> put (OpE s e1 e2) = do put (1 :: Word8)
> put s
> put e1
> put e2
> get = do tag <- getWord8
> case tag of
> 0 -> liftM IntE get
> 1 -> liftM3 OpE get get get
The Data.Binary comes with one tool to derive these. The DrIFT preprocessor
also can, as can Stefan O'Rear's SYB deriver.
I just write them by hand, or use the tool that comes with the lib.
More docs here,
> >>could do on datatypes which would get this right. In a really ideal
> >>world, you could specify the data layout somehow[2a], which would
> >Directly in Haskell data type decls -- see the ICFP 05 paper on the
> >House OS, which added packing annotations, and bit syntax. In current
> >Haskell, you specify the layout in instances Storable or Binary.
> I'll have a look.
> >>make integrating Haskell code into a wider distributed network of
> >>processes exchanging binary data a cinch. In a super really ideal
> >Definitely. See things like the zlib or iconv
> >Data.Binary/Data.ByteString bindings, for prototypes. The 'tar'
> >reader/writer on hackage.haskell.org is also a good example.
> OK. Maybe this is the sort of stuff which ought to go into the new
> Haskell book? 'Integrating Haskell with external data sources' or
> >>world, you could operate on the packets in place in Haskell where
> >>possible and save the deserialization overhead...
> >Data.ByteString.* for this.
> >>Anyone trying to do any of this?
> >Yeah, its a bit of a hot topic currently. :)
> >Gotta chase Erlang for hacking network data.
> Absolutely. Ta for the pointers anyway.
Hack those bytes! Quickly! :-)
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