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

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)))