SandBox.hs

class BuildList r  where
    type Build r :: * -> *
    build' :: [a] -> a -> Build r a

instance BuildList a [a] where
    type Build [a] = [a]
    build' l x = reverse $ x:l

instance BuildList a r => BuildList a (a -> r) where
    build' l x  = \ y -> build'(x:l) y

--build :: forall r a. (BuildList a r) => a -> r
build :: (BuildList a r) => a -> r
build x = build' [] x