On Thu, Jul 17, 2008 at 11:34 AM, Rafael Gustavo da Cunha Pereira
Pinto
f::[Integer]->Integer f a = x a - y a where x=sum y=foldr max 0
Using double f g x = (f x, g x), f a = x a - y a f a = uncurry (-) (x a, y a) f a = uncurry (-) (double x y a) f = uncurry (-) . double sum (foldr max 0) Now, note that, from Control.Arrow, (&&&) :: Arrow a => a b c -> a b c' -> a b (c, c') and that (->) is an instance of Arrow, so that when (&&&) is specilized to (->) we get (***) :: (b -> c) -> (b -> c') -> (b -> (c, c')) exactly the type of double! (verify that) So, we may write your function as f = uncurry (-) . (&&&) sum (foldr max 0) f = sum &&& foldr max 0 >>> uncurry (-) ------ Final (point-free) code: import Control.Arrow f = sum &&& foldr max 0 >>> uncurry (-) -- Felipe.