Hi all,

Can anyone help me with some Haskell de/serialisation woes I'm encountering? What I'm trying to do it implement a proprietary network protocol which will enable me to talk to a network Java/Tuple Space.

Specifically, I'm trying to serialise a "TypeStructurePreamble" and send that down the Handle (my network stream), I'm then expecting the Space to send me a TypeStructurePreamble back again, but with different data. So I need to de/serialise this type. I've not got all the code together yet, because I'm trying to figure out the concepts rather than any particular coding problem.

Here's some code I have so far;

import System.IO (hGetLine,hClose,hPutStrLn,hSetBuffering,BufferMode(..),Handle,stdout)

import Data.Binary.Get
import qualified Data.ByteString.Lazy as L

type TypeStructurePreamble = (String,Int,[String])

-- This function I know works because it was spoon-fed to me by someone on this list! :-)

readStrings :: Int -> Get [String]

readStrings n = replicateM n $ do

len <- getWord32be

name <- getByteString $ fromIntegral len

return $ UTF.toString name

deserialisePreamble :: Get(String, Int, [String])

deserialisePreamble = do

len <- getWord32be

typename <- getByteString $ fromIntegral len

c <- getWord32be

numFields <- getWord32be

fields <- readStrings (fromIntegral numfields)

return (typename,c,numFields)

-- not sure what this type should be

serialisePreamble :: Handle -> TypeStructurePreamble -> ??

serialisePreamble h (n,c,fs) = do

L.hPut h (encode (0xFAB1000A :: Word32))

L.hPut h (encode (length n))

L.hPut h (encode n)

L.hPut h (encode (c :: Word32))

L.hPut h (encode (length fs))

-- not sure how I would L.hPut out every String in fs

It is my (maybe wrong) understanding that these de/serialise functions don't actually do the work, they basically just form a description of what must be done in order to get the work done, so I'm slightly confused on how I should use it.

For example;

main = do

-- set up Handle called h here, I know how to do this

serialisePreamble h ("MyType",0,["field1","field2"])

--now I'm expecting to be able to read a modified TypeStructurePreamble from h

(n,c,fs) <- deserialisePreamble -- but according to the type of deserialisePreamble, how does the h get into it?

print "c was "+c -- can I just slot sout style statements into here?

evaluate (n,c,fs)

hClose h

return (n,c,fs)

Does this make sense? Can someone help me fill in the blanks of serialisePreamble and main? I've read the tutorials on the Get monad which google turns up, am I missing some really good ones? Is there some other resource which I'm missing? I'm been thrown a lot of the Hackage documentation on these things but (assuming I'm looking in the right place) they seem to work more like JavaDocs and give the "what it does", rather than the "how it should be used".

Many thanks,

Tom