[Haskell-cafe] Re: [Haskell] installing streams library

[Bulat Ziganshin]

Hello Bulat,

Sunday, May 28, 2006, 2:44:37 PM, you wrote:

>> type PtrLen a = (Ptr a, Int)
>> encodePtrLen :: (Binary a) => a -> (PtrLen a -> IO b) -> IO b
>> decodePtr :: (Binary a) => Ptr a -> IO a

Finally i've implemented the following (you then would use
'withForeignPtr' to work with contents of ForeignPtr):

-- -----------------------------------------------------------------------------
-- Encode/decode contents of memory buffer

encodePtr             :: (Binary a, Integral size) =>  a -> IO (ForeignPtr x, size)
encodePtrLE           :: (Binary a, Integral size) =>  a -> IO (ForeignPtr x, size)
encodePtrBitAligned   :: (Binary a, Integral size) =>  a -> IO (ForeignPtr x, size)
encodePtrBitAlignedLE :: (Binary a, Integral size) =>  a -> IO (ForeignPtr x, size)
encodePtr             = encodePtr' openByteAligned
encodePtrLE           = encodePtr' openByteAlignedLE
encodePtrBitAligned   = encodePtr' openBitAligned
encodePtrBitAlignedLE = encodePtr' openBitAlignedLE

decodePtr             :: (Binary a, Integral size) =>  Ptr x -> size -> IO a
decodePtrLE           :: (Binary a, Integral size) =>  Ptr x -> size -> IO a
decodePtrBitAligned   :: (Binary a, Integral size) =>  Ptr x -> size -> IO a
decodePtrBitAlignedLE :: (Binary a, Integral size) =>  Ptr x -> size -> IO a

decodePtr             = decodePtr' openByteAligned
decodePtrLE           = decodePtr' openByteAlignedLE
decodePtrBitAligned   = decodePtr' openBitAligned
decodePtrBitAlignedLE = decodePtr' openBitAlignedLE

-- Universal function what encodes data with any alignment
encodePtr' open thedata = do
    h <- createMemBuf 512 >>= open
    put_ h thedata
    vFlush h
    vRewind h
    (buf,size) <- vReceiveBuf h READING                 -- FIXME: MemBuf-implementation specific
    fptr <- newForeignPtr finalizerFree (castPtr buf)   -- FIXME: also MemBuf-implementation specific
    return (fptr,size)

-- Universal function what decodes data written with any alignment
decodePtr' open ptr size = do
    h <- openMemBuf ptr size >>= open
    result <- get h
    vClose h
    return result



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