module Pandora.Paradigm.Primary.Functor.Edges where

import Pandora.Pattern.Category (($))
import Pandora.Pattern.Functor.Covariant (Covariant ((-<$>-)))
import Pandora.Pattern.Functor.Traversable (Traversable ((<<-)))
import Pandora.Paradigm.Primary.Algebraic.Exponential ()
import Pandora.Paradigm.Primary.Algebraic (point)

data Edges a = Empty | Leap a | Connect a | Overlay a

instance Covariant (->) (->) Edges where
	_ -<$>- Empty = Empty
	f -<$>- Connect x = Connect $ f x
	f -<$>- Overlay x = Overlay $ f x
	f -<$>- Leap x = Leap $ f x

instance Traversable (->) (->) Edges where
	_ <<- Empty = point Empty
	f <<- Connect x = Connect -<$>- f x
	f <<- Overlay x = Overlay -<$>- f x
	f <<- Leap x = Leap -<$>- f x

edges :: r -> (a -> r) -> (a -> r) -> (a -> r) -> Edges a -> r
edges r _ _ _ Empty = r
edges _ f _ _ (Connect x) = f x
edges _ _ g _ (Overlay y) = g y
edges _ _ _ h (Leap z) = h z