add two lists of arbitrary bytes

bytesum.hs

byteSum :: [Word8] -> [Word8] -> [Word8]
byteSum = byteSum' 0
  where
    byteSum' 0 [] [] = []
    byteSum' 1 [] [] = [1]
    byteSum' carry (x:xs) (y:ys) =
        let v = x + y + carry
        in v : byteSum' (if v < x || v < y then 1 else 0) xs ys