Wedge.hs

module Pandora.Paradigm.Primary.Functor.Wedge where

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

data Wedge e a = Nowhere | Here e | There a

instance Covariant (Wedge e) where
	_ <$> Nowhere = Nowhere
	_ <$> Here x = Here x
	f <$> There x = There $ f x

instance Covariant_ (Wedge e) (->) (->) where
	_ -<$>- Nowhere = Nowhere
	_ -<$>- Here x = Here x
	f -<$>- There x = There $ f x

instance Pointable (Wedge e) (->) where
	point = There

instance Traversable (Wedge e) (->) (->) where
	_ <<- Nowhere = point Nowhere
	_ <<- Here x = point $ Here x
	f <<- There x = There -<$>- f x

wedge :: (e -> r) -> (a -> r) -> r -> Wedge e a -> r
wedge f _ _ (Here x) = f x
wedge _ g _ (There x) = g x
wedge _ _ r Nowhere = r