[Haskell-cafe] Binary serialization, was Re: Abstraction leak

[Philip Armstrong]

On Wed, Jul 04, 2007 at 09:44:13PM +1000, Donald Bruce Stewart wrote:
>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

That's quite verbose! Plus I'm a bit concerned by the boxing implied
by those IntE / OpE constructors in get. If you were using those
values in a pattern match on the result of get, would the compiler be
able to eliminate them and refer directly to the values in the source
data?

>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,
>    http://hackage.haskell.org/packages/archive/binary/0.3/doc/html/Data-Binary.html

This doesn't seem to deal with endianness. Am I missing something?

>> >>world, you could operate on the packets in place in Haskell where
>> >>possible and save the deserialization overhead...
>> >
>> >Data.ByteString.* for this.

Ah, does Data.Binary fuse with ByteString.* then?

>Hack those bytes! Quickly! :-)

:)

It's a shame the layout definition is so verbose. Erlang's is quite
compact. I wonder if something could be done with template haskell to
translate an Erlang-style data layout definition to the Data.Binary
form?

(Bonus points for being able to parse ASN.1 and generate appropriate
Haskell datatypes & serialization primitives automatically :-) )

Phil

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