data Stream a = Cons a (Stream a)

chop :: Int -> Stream a -> [a]
chop 0 _ = []
chop n (Cons x s) = x : chop (n-1) s

decode :: Stream (a, Int) -> Stream a
decode (Cons (x, 0) s) = decode s
decode (Cons (x, n) s) = Cons x $ decode $ Cons (x, n-1) s

encode :: Eq a => Stream a -> Stream (a, Int)
encode (Cons x s) = accumulate x 1 s
    where accumulate :: Eq a => a -> Int -> Stream a -> Stream (a, Int)
          accumulate x n (Cons y s) | x == y    = accumulate x (n+1) s
                                    | otherwise = Cons (x,n) (accumulate y 1 s)