apcomp.hs

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE InstanceSigs #-}

class ApplyCompose b c x res | b c x -> res where
  (<|) :: (b -> c) -> x -> res

instance ApplyCompose b c (a -> b) (a -> c) where
  (<|) :: (b -> c) -> (a -> b) -> a -> c
  (<|) = (.)

instance ApplyCompose b c b c where
  (<|) :: (b -> c) -> b -> c
  (<|) = ($)

infixr 1 <|

-- > isSpace <| 'a'
-- False
-- > isSpace <| toEnum @Char <| (97 :: Int)
-- False

-- > (isSpace <| toEnum <| (97 :: Int)) :: Bool
-- ambiguity error
-- > f = map <| map id
-- ambiguity error
-- > f = (map <| map id) :: [[Int]] -> [[Int]]
-- ambiguity error
-- > f = map @[Int] @[Int] <| map @Int id
-- > :t f
-- f :: [[Int]] -> [[Int]]