Outline.hs

{-# LANGUAGE UndecidableInstances #-}

module Pandora.Paradigm.Primary.Transformer.Outline where

import Pandora.Pattern.Semigroupoid ((.))
import Pandora.Pattern.Category (identity, ($), (#))
import Pandora.Pattern.Functor.Covariant (Covariant ((-<$>-)))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Extractable (Extractable (extract))
import Pandora.Pattern.Transformer.Liftable (Liftable (lift))
import Pandora.Pattern.Transformer.Hoistable (Hoistable ((/|\)))
import Pandora.Paradigm.Primary.Algebraic.Exponential ()

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 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 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