#include "share/atspre_staload.hats" datatype list (a:t@ype) = | Nil (a) of () | Cons (a) of (a, list a) #define :: Cons datatype maybe (a:t@ype) = | Nothing (a) of () | Just (a) of a (* type class *) sortdef tycon = t@ype -> type extern fun {f:tycon} {a,b:t@ype} fmap (a -<cloref1> b): f(a) -<cloref1> f(b) (* instance list *) implement (a,b:t@ype) fmap<list><a,b> (f) = lam (xs: list a): list b => case+ xs of | Cons (x, xs) => Cons (f x, (fmap<list><a,b> f) xs) | _ => Nil () (* instance maybe *) implement (a,b:t@ype) fmap<maybe><a,b> (f) = lam (x: maybe a): maybe b => case+ x of | Just a => Just (f a) | Nothing () => Nothing () implement main0 () = let val xs = 1 :: 2 :: 3 :: Nil() : list int val ys = fmap<list><int,int> (lam (x:int):int => x + 1) (xs) val zs = fmap<list><int,int> (lam (x:int):int => let val _ = println! x in x end) (ys) val mx = Just 1 : maybe int val my = fmap<maybe><int,string> (lam (x:int):string => "hello") (mx) val mz = fmap<maybe><string,string> (lam (x:string):string => let val _ = println! x in x end) (my) in end