Control.Carrier.Empty.Maybe

A carrier for an Empty effect, indicating failure with a Nothing value. Users that need access to an error message should use the Fail effect.

Note that Empty effects can, when they are the last effect in a stack, be interpreted directly to a Maybe without a call to runEmpty.

Since: 1.0.0.0

Empty carrier

runEmpty :: EmptyC m a -> m (Maybe a)

Run an Empty effect, returning Nothing for empty computations, or Just the result otherwise.

runEmpty empty = pure Nothing

runEmpty (pure a) = Just a

Since: 1.0.0.0

newtype EmptyC m a

Since: 1.0.0.0

Constructors

EmptyC (MaybeT m a)

Instances

MonadTrans EmptyC

Defined in Control.Carrier.Empty.Maybe

Methods

lift :: Monad m => m a -> EmptyC m a

Monad m => Monad (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

(>>=) :: EmptyC m a -> (a -> EmptyC m b) -> EmptyC m b

(>>) :: EmptyC m a -> EmptyC m b -> EmptyC m b

return :: a -> EmptyC m a

Functor m => Functor (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

fmap :: (a -> b) -> EmptyC m a -> EmptyC m b

(<$) :: a -> EmptyC m b -> EmptyC m a

MonadFix m => MonadFix (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

mfix :: (a -> EmptyC m a) -> EmptyC m a

MonadFail m => MonadFail (EmptyC m)

EmptyC passes MonadFail operations along to the underlying monad m, rather than interpreting it as a synonym for empty à la MaybeT.

Defined in Control.Carrier.Empty.Maybe

Methods

fail :: String -> EmptyC m a

Monad m => Applicative (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

pure :: a -> EmptyC m a

(<*>) :: EmptyC m (a -> b) -> EmptyC m a -> EmptyC m b

liftA2 :: (a -> b -> c) -> EmptyC m a -> EmptyC m b -> EmptyC m c

(*>) :: EmptyC m a -> EmptyC m b -> EmptyC m b

(<*) :: EmptyC m a -> EmptyC m b -> EmptyC m a

MonadIO m => MonadIO (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

liftIO :: IO a -> EmptyC m a

(Algebra sig m, Effect sig) => Algebra (Empty :+: sig) (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

alg :: (Empty :+: sig) (EmptyC m) a -> EmptyC m a

Empty effect

module Control.Effect.Empty