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) = pure (Just a)

Since: 1.0.0.0

evalEmpty :: Functor m => EmptyC m a -> m ()

Run an Empty effect, discarding its result.

This is convenient for using empty to signal early returns without needing to know whether control exited normally or not.

evalEmpty = void . runEmpty

Since: 1.1.0.0

execEmpty :: Functor m => EmptyC m a -> m Bool

Run an Empty effect, replacing its result with a Bool indicating whether control exited normally.

This is convenient for using empty to signal early returns when all you need to know is whether control exited normally or not, and not what value it exited with.

execEmpty = fmap isJust . runEmpty

execEmpty (pure a) = pure True

execEmpty empty = pure False

Since: 1.1.0.0

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

fail :: String -> 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 => Algebra (Empty :+: sig) (EmptyC m)

Defined in Control.Carrier.Empty.Maybe

Methods

alg :: Functor ctx => Handler ctx n (EmptyC m) -> (Empty :+: sig) n a -> ctx () -> EmptyC m (ctx a)

Empty effect

module Control.Effect.Empty