import "JavaBuiltin" as Java

class Functor f where
    map :: (a -> b) -> f a -> f b
    
data Foo a = Foo a

instance Functor Foo where
    map f (Foo x) = Foo (f x)
    
instance Functor Maybe where
    map f Nothing = Nothing
    map f (Just x) = Just (f x)
    
data List a = Nil | Cons a (List a)

instance Functor List where
    map f Nil = Nil
    map f (Cons h t) = Cons (f h) (map f t)
    
main = map (map (Java.iadd 1)) (Cons Nothing (Cons (Just (1 :: Integer)) Nil))
--
(Cons null (Cons 2 Nil))