{-# LANGUAGE TypeOperators #-}

import Prelude hiding (foldl)

infixr 1 :->

newtype a :-> b = S {unS :: a -> b}

infixl 9 #

class Fun f where
  lam :: (a -> b) -> f a b
  (#) :: f a b -> (a -> b)

instance Fun (->) where
  lam = id
  (#) = ($)

instance Fun (:->) where
  lam = S
  (#) = \f x -> unS f $! x

foldl :: (Fun i, Fun j) => i b (j a b) -> i b ([a] :-> b)
foldl = lam $ \f -> lam $ \e -> lam $ \l -> case l of
          []     -> e
          x : xs -> foldl # f # (f # e # x) # xs

lplus :: Int -> Int -> Int
lplus = (+)

splus :: Int :-> Int :-> Int
splus = lam $ \m -> lam $ \n -> ((+) $! m) $! n