My first Haskell program

gistfile1.hs

{- learning haskell by "porting" Construct from python -}

import Data.Int
import Data.Word
import qualified Data.ByteString.Lazy as LBS
import Data.Char
import Control.Monad
import Data.Binary.Get

data Packer t = Packer {
                    unpack :: Get t
                }

bytes :: Int64 -> Packer LBS.ByteString
bytes len = Packer {
                unpack = do
                    bs <- getLazyByteString len
                    return bs
            }

struct :: [Packer t] -> Packer [t]
struct packers = Packer {
                     unpack = do
                            res <- mapM unpack packers     -- that was a wild guess, but it works :)
                            return res
                 }


x = struct [bytes 4, bytes 3]

main :: IO ()
main = do
    print $ runGet (unpack $ x) rawData
    where
        rawData = LBS.pack . map (fromIntegral . ord) $ "AAAABBBBCCCC"

-- prints ["AAAA", "BBB"]