{-# LANGUAGE UndecidableInstances #-}

module Pandora.Paradigm.Primary.Transformer.Jet where

import Pandora.Pattern.Functor.Covariant (Covariant ((<$>)), (<$$>), Covariant_ ((-<$>-)), (-<$$>-))
import Pandora.Pattern.Functor.Avoidable (Avoidable (empty))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Extractable (Extractable (extract))
import Pandora.Pattern.Functor.Applicative (Applicative ((<*>)))
import Pandora.Pattern.Functor.Traversable (Traversable ((->>), (->>>)))

data Jet t a = Jet a (Jet t (t a))

instance Covariant t => Covariant (Jet t) where
	f <$> Jet x xs = Jet (f x) (f <$$> xs)

instance Covariant_ t (->) (->) => Covariant_ (Jet t) (->) (->) where
	f -<$>- Jet x xs = Jet (f x) (f -<$$>- xs)

instance Traversable t => Traversable (Jet t) where
	Jet x xs ->> f = Jet <$> f x <*> xs ->>> f

instance (forall u . Avoidable u, Covariant_ t (->) (->)) => Pointable (Jet t) (->) where
	point x = Jet x empty

instance Covariant_ t (->) (->) => Extractable (Jet t) (->) where
	extract (Jet x _) = x