T_U.hs

module Pandora.Paradigm.Schemes.T_U where

import Pandora.Core.Functor (type (:=))
import Pandora.Pattern.Functor.Covariant (Covariant ((<$>)))
import Pandora.Pattern.Functor.Contravariant (Contravariant ((>$<)))
import Pandora.Pattern.Functor.Bivariant (Bivariant ((<->)))
import Pandora.Pattern.Functor.Divariant (Divariant ((>->)))
import Pandora.Paradigm.Controlflow.Effect.Interpreted (Interpreted (Primary, run, unite, (||=)))

newtype T_U ct cu p t u a = T_U (p (t a) (u a))

infixr 2 <:.:>, >:.:>, <:.:<, >:.:<

type (<:.:>) t u p = T_U Covariant Covariant p t u
type (>:.:>) t u p = T_U Contravariant Covariant p t u
type (<:.:<) t u p = T_U Covariant Contravariant p t u
type (>:.:<) t u p = T_U Contravariant Contravariant p t u

instance Interpreted (T_U ct cu p t u) where
	type Primary (T_U ct cu p t u) a = p (t a) (u a)
	run ~(T_U x) = x
	unite = T_U

instance (Bivariant p, Covariant t, Covariant u) => Covariant (t <:.:> u := p) where
	f <$> x = ((f <$>) <-> (f <$>)) ||= x

instance (Divariant p, Contravariant t, Covariant u) => Covariant (t >:.:> u := p) where
	f <$> x = ((f >$<) >-> (f <$>)) ||= x

instance (Bivariant p, Contravariant t, Contravariant u) => Contravariant (t >:.:< u := p) where
	f >$< x = ((f >$<) <-> (f >$<)) ||= x