Day.hs

{-# LANGUAGE UndecidableInstances #-}

module Pandora.Paradigm.Primary.Transformer.Day where

import Pandora.Pattern.Category ((#))
import Pandora.Pattern.Functor.Covariant (Covariant ((-<$>-)))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Extractable (Extractable (extract))
import Pandora.Pattern.Functor.Extendable (Extendable ((<<=)))
import Pandora.Pattern.Transformer.Lowerable (Lowerable (lower))
import Pandora.Pattern.Transformer.Hoistable (Hoistable ((/|\)))
import Pandora.Paradigm.Primary.Algebraic.Exponential ((!..), (-.#..-))

data Day t u a = forall b c . Day (t b) (u c) (b -> c -> a)

instance Covariant (Day t u) (->) (->) where
	f -<$>- Day tb uc g = Day tb uc # f -.#..- g

instance (Pointable t (->), Pointable u (->)) => Pointable (Day t u) (->) where
	point x = Day # point () # point () # (x !..)

instance (Extractable t (->), Extractable u (->)) => Extractable (Day t u) (->) where
	extract (Day tb uc bcad) = bcad # extract tb # extract uc

instance (Extendable t (->), Extendable u (->)) => Extendable (Day t u) (->) where
	f <<= day@(Day tb uc _) = Day tb uc (f day !..)

instance Extractable t (->) => Lowerable (Day t) where
	lower (Day tb uc bca) = bca (extract tb) -<$>- uc

instance Hoistable (Day t) where
	g /|\ Day tb uc bca = Day tb # g uc # bca

data Day_ category source target t u r = forall a b .
	Day_ (target (category (source a b) r) (target (t a) (u b)))