More thoughts on new lazy pure functional programming language to run on JVM

gistfile1.txt

class List implements Monad {
  (:), nil, (++), null public;

  (:), nil constructor;
  (:) :: forall a. a -> this a -> this a;
  nil :: forall a. this a;

  (++) :: forall a. List a -> List a -> List a;
  (x:?xs) ++ ys = x : (xs ++ ys);
  nil? ++ ys = ys;

  null :: forall a. List a -> Bool;
  null nil? = true;
  null (x:?xs) = false;

  return, join implementation;
  return a = cons a nil;

  join nil? = [];
  join (x:?xs) = x ++ join xs;
}

interface Functor {
  fmap :: (a -> b) -> (this a -> this b)
}

interface Monad extends Functor {
  return :: forall a. this a;

  join :: forall a. this (this a) -> this a;
  join = (>>= id)

  (>>=) infix right 5;
  (>>=) :: forall a b. this a -> (a -> this b) -> this b;
  a >>= f = join (fmap f a)

  fmap implementation
  fmap f = (>>= (return . f))
}