Maybe.hs

module Control.Joint.Effects.Maybe where

import Control.Joint.Abilities.Composition (Composition (Primary, run))
import Control.Joint.Abilities.Transformer (Transformer (Schema, embed, build, unite))
import Control.Joint.Abilities.Liftable (Liftable (lift))
import Control.Joint.Schemes.TU (TU (TU))
import Control.Joint.Schemes.TUT (TUT (TUT))
import Control.Joint.Schemes.UT (UT (UT))

instance Functor u => Functor (UT Maybe u) where
	fmap f (UT x) = UT $ (fmap . fmap) f x

instance Applicative u => Applicative (UT Maybe u) where
	pure = UT . pure . pure
	UT f <*> UT x = UT $ (<*>) <$> f <*> x

instance (Applicative u, Monad u) => Monad (UT Maybe u) where
	UT x >>= f = UT $ x >>= maybe (pure Nothing) (run . f)

instance Composition Maybe where
	type Primary Maybe a = Maybe a
	run x = x

instance Transformer Maybe where
	type Schema Maybe u = UT Maybe u
	embed x = UT $ Just <$> x
	build x = UT . pure $ x
	unite = UT

type Optional = Liftable Maybe