pandora-0.1.3: Pandora/Paradigm/Basis/Endo.hs

module Pandora.Paradigm.Basis.Endo (Endo (..)) where

import Pandora.Core.Morphism ((.), identity)
import Pandora.Pattern.Functor.Invariant (Invariant (invmap))
import Pandora.Pattern.Object.Semigroup (Semigroup ((<>)))
import Pandora.Pattern.Object.Monoid (Monoid (unit))

newtype Endo a = Endo { endo :: a -> a }

instance Invariant Endo where
	invmap f g (Endo x) = Endo (f . x . g)

instance Semigroup (Endo a) where
	Endo f <> Endo g = Endo (g . f)

instance Monoid (Endo a) where
	unit = Endo identity