Sample Haskell module compiling into .so

A.hs

{-# LANGUAGE ForeignFunctionInterface #-}

module A (encodeCrockford, decodeCrockford) where

import Foreign.Marshal.Utils
import Foreign.Ptr
import Foreign.C.String
import Foreign.C.Types
import Foreign.Marshal.Array
import Codec.Crockford
import Codec.Text.Raw
import Codec.Utils
import qualified Data.ByteString as BS
import qualified Data.ByteString.Char8 as BS8

encodeCrockford :: CString -> IO CString
encodeCrockford cs = do
	os <- peekArray0 0 cs
	let bs = BS8.pack $ Codec.Crockford.encode $ fromOctets 256 $ map (fromIntegral) os
	BS.useAsCString bs (\ cs' -> do
		len <- lengthArray0 0 cs'
		csNew <- mallocArray0 len
		copyArray csNew cs' (len + 1)
		return csNew
		)

decodeCrockford :: CString -> IO CString
decodeCrockford cs = do
	pt <- new (fromIntegral 0 :: CInt)
	s <- peekCString cs
	let bs = BS.pack $ maybe [] (toOctets 256) $ Codec.Crockford.decode s
	BS.useAsCString bs (\ cs' -> do
		len <- lengthArray0 0 cs'
		csNew <- mallocArray0 len
		copyArray csNew cs' (len + 1)
		return csNew
		)

foreign export ccall encodeCrockford :: CString -> IO CString
foreign export ccall decodeCrockford :: CString -> IO CString

Makefile

clean:
	rm -f *_stub* *.hi *.o *.so

rnacrockford.so: A.hs
	ghc -package Crypto -package crockford -package bytestring -c -O A.hs
	ghc -package Crypto -package crockford -package bytestring -optc-O -I. -L. -optc-Wl,-Bstatic -optc-Wl,-Bdynamic -optl '-shared' -no-hs-main A.o -o rnacrockford.so