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Add Cochoice instances for Joker and Star #31

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Add Cochoice instances for Joker and Star #31

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10 changes: 9 additions & 1 deletion src/Data/Profunctor/Joker.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,13 @@ module Data.Profunctor.Joker where

import Prelude

import Data.Either (Either(..))
import Control.Alternative (empty)
import Control.MonadPlus (class MonadZero)
import Data.Either (Either(..), either)
import Data.Newtype (class Newtype, un)
import Data.Profunctor (class Profunctor)
import Data.Profunctor.Choice (class Choice)
import Data.Profunctor.Cochoice (class Cochoice)

-- | Makes a trivial `Profunctor` for a covariant `Functor`.
newtype Joker f a b = Joker (f b)
Expand Down Expand Up @@ -38,5 +41,10 @@ instance bindJoker :: Bind f => Bind (Joker f a) where

instance monadJoker :: Monad m => Monad (Joker m a)

instance cochoiceJoker :: MonadZero f => Cochoice (Joker f)
where
unleft (Joker fa) = Joker $ fa >>= either pure (const empty)
unright (Joker fb) = Joker $ fb >>= either (const empty) pure

hoistJoker :: forall f g a b. (f ~> g) -> Joker f a b -> Joker g a b
hoistJoker f (Joker a) = Joker (f a)
5 changes: 5 additions & 0 deletions src/Data/Profunctor/Star.purs
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Expand Up @@ -15,6 +15,7 @@ import Data.Newtype (class Newtype)
import Data.Profunctor (class Profunctor)
import Data.Profunctor.Choice (class Choice)
import Data.Profunctor.Closed (class Closed)
import Data.Profunctor.Cochoice (class Cochoice)
import Data.Profunctor.Strong (class Strong)
import Data.Tuple (Tuple(..))

Expand Down Expand Up @@ -75,6 +76,10 @@ instance choiceStar :: Applicative f => Choice (Star f) where
left (Star f) = Star $ either (map Left <<< f) (pure <<< Right)
right (Star f) = Star $ either (pure <<< Left) (map Right <<< f)

instance cochoiceStar :: MonadZero f => Cochoice (Star f) where
unleft (Star f) = Star $ \a -> (=<<) (either pure (const empty)) $ f (Left a)
unright (Star f) = Star $ \a -> (=<<) (either (const empty) pure) $ f (Right a)

instance closedStar :: Distributive f => Closed (Star f) where
closed (Star f) = Star \g -> distribute (f <<< g)

Expand Down