module Pandora.Paradigm.Primary.Functor.Endo where

import Pandora.Pattern.Semigroupoid ((.))
import Pandora.Pattern.Category (identity, (#))
import Pandora.Pattern.Functor.Invariant (Invariant ((<$<)))
import Pandora.Pattern.Functor.Divariant ((>->))
import Pandora.Pattern.Object.Semigroup (Semigroup ((+)))
import Pandora.Pattern.Object.Monoid (Monoid (zero))
import Pandora.Paradigm.Controlflow.Effect.Interpreted (Interpreted (Primary, run, unite, (||=)))
import Pandora.Paradigm.Primary.Algebraic.Exponential ()

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

instance Interpreted Endo where
	type Primary Endo a = a -> a
	run ~(Endo x) = x
	unite = Endo

instance Invariant Endo where
	f <$< g = (g >-> f ||=)

instance Semigroup (Endo a) where
	Endo f + Endo g = Endo # g . f

instance Monoid (Endo a) where
	zero = Endo identity