pandora-0.4.8: Pandora/Pattern/Functor/Contravariant.hs

module Pandora.Pattern.Functor.Contravariant where

import Pandora.Pattern.Category (Category)

infixl 4 >-|-, >$<

{- |
> When providing a new instance, you should ensure it satisfies:
> * Identity morphism: (identity >-|-) ≡ identity
> * Interpreted of morphisms: (f >-|-) . (g >-|-) ≡ (g . f >-|-)
-}

class (Category source, Category target) => Contravariant source target t where
	(>-|-) :: source a b -> target (t b) (t a)

(>$<) :: Contravariant source target t => source a b -> target (t b) (t a)
(>$<) = (>-|-)