data List a = Nil | Cons a (List a)

map :: (a -> b) -> List a -> List b
map f Nil        = Nil
map f (Cons h t) = Cons (f h) (map f t)

constMap :: a -> List b -> List a
constMap c = map (\x -> c)

main = constMap (5 :: Integer) (Cons (1 :: Integer) (Cons (2 :: Integer) (Cons (3 :: Integer) Nil)))
--
(Cons 5 (Cons 5 (Cons 5 Nil)))