pandora-0.4.6: Pandora/Pattern/Functor/Adjoint.hs

module Pandora.Pattern.Functor.Adjoint where

import Pandora.Pattern.Functor.Covariant (Covariant)

type (-|) = Adjoint

infixl 3 -|, |-

{- |
> When providing a new instance, you should ensure it satisfies:
> * Left adjunction identity: phi cozero ≡ identity
> * Right adjunction identity: psi zero ≡ identity
> * Left adjunction interchange: phi f ≡ comap f . eta
> * Right adjunction interchange: psi f ≡ epsilon . comap f
-}

class (Covariant target source t, Covariant source target u) => Adjoint source target t u where
	(-|) :: source (t a) b -> target a (u b)
	(|-) :: target a (u b) -> source (t a) b