list.mana

------------------------------------------------------------------------------
--
--  List
--
------------------------------------------------------------------------------

namespace List

  import Primitive

  ------------------------------------------------------------------------------
  --  List
  ------------------------------------------------------------------------------

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

  head : List a -> Maybe a
  head (Nil      ) = None
  head (Cons x xs) = Some x

  map : (a -> b) -> List a -> List b
  map f (Nil      ) = Nil
  map f (Cons x xs) = Cons (f x) (map f xs)

  zipWith : (a -> b -> c) -> List a -> List b -> List c
  zipWith f (Cons x xs) (Cons y ys) = Cons (f x y) (zipWith f xs ys)
  zipWith f _           _           = Nil

  ------------------------------------------------------------------------------
  --  main
  ------------------------------------------------------------------------------

  xs : List Int
  xs = Cons 3 (Cons 5 Nil)

  main = do
    print <| xs
    print <| head (Nil : List Bool)
    print <| head xs
    print <| map square xs
    print <| zipWith (+) xs (map square xs)