haskell module to process XOR encryption/decryption

XORcoder.hs

module Coder(encode,decode) where
import Data.Word
import Data.Char(ord,chr)
import Data.Bits(xor)
import qualified Data.ByteString.Char8 as C
import qualified Data.ByteString as B

tp n ls = takeWhile(not.null) $ map(take n.flip drop ls) [0,n..]

conv_key key = [fromIntegral $ ord x | x <- key]
xored a b = [xor x y | x <- a, y <- b]
process chunked bin_key = foldl (++) [] [xored bin_key x | x <- chunked]

encode::String -> [Word8] -> [Word8]
encode key bin =
  let
    chunked   = tp (length key) bin
    bin_key   = conv_key key
  in
    process chunked bin_key


decode::String -> [Word8] -> String
decode key bin =
  let
    chunked = tp (length key) bin
    bin_key = conv_key key
  in
    C.unpack $ B.pack $process chunked bin_key