{-# LANGUAGE UndecidableInstances #-}

module Pandora.Paradigm.Primary.Transformer.Outline where

import Pandora.Pattern.Category (identity, (.), ($), (#))
import Pandora.Pattern.Functor.Covariant (Covariant ((<$>)), Covariant_ ((-<$>-)))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Extractable (Extractable (extract))
import Pandora.Pattern.Functor.Applicative (Applicative ((<*>)))
import Pandora.Pattern.Transformer.Liftable (Liftable (lift))
import Pandora.Pattern.Transformer.Hoistable (Hoistable ((/|\)))
import Pandora.Paradigm.Controlflow.Effect.Interpreted (Interpreted (Primary, run, unite))
import Pandora.Paradigm.Primary.Functor.Function ((%))

data Outline t a where
	Line :: a -> Outline t a
	Outlined :: t a -> Outline t (a -> b) -> Outline t b

instance Covariant (Outline t) where
	f <$> Line a = Line $ f a
	f <$> Outlined x y = Outlined x # (.) f <$> y

instance Covariant_ (Outline t) (->) (->) where
	f -<$>- Line a = Line $ f a
	f -<$>- Outlined x y = Outlined x # (.) f -<$>- y

instance Pointable (Outline t) (->) where
	point = Line

instance Extractable t (->) => Extractable (Outline t) (->) where
	extract (Line x) = x
	extract (Outlined x y) = extract y # extract x

instance Applicative (Outline f) where
	Line f <*> y = f <$> y
	Outlined x y <*> z = Outlined x # (%) <$> y <*> z

instance Liftable Outline where
	lift t = Outlined t (Line identity)

instance Hoistable Outline where
	_ /|\ Line x = Line x
	f /|\ Outlined x y = Outlined # f x # f /|\ y

instance (Extractable t (->), Pointable t (->), Applicative t) => Interpreted (Outline t) where
	type Primary (Outline t) a = t a
	run (Line x) = point x
	run (Outlined t f) = run f <*> t
	unite = Line . extract