Modulefused-effects-1.1.2.7Haskell2010

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.

1 type
3 values

Packagefused-effects-1.1.2.7
Exports4
LanguageHaskell2010
LicenceBSD-3-Clause
SourceMaybe.hs

Empty carrier

4 declarations

valuerunEmpty :: 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)

valueevalEmpty :: 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

valueexecEmpty :: 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

newtypenewtype EmptyC (m :: Type -> Type) a

Constructors

EmptyC (MaybeT m a)

Instances8MonadTrans, Monad, Functor, MonadFix, MonadFail, Applicative, …

MonadTrans EmptyCDefined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
Monad m => Monad (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
Functor m => Functor (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
MonadFix m => MonadFix (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
MonadFail m => MonadFail (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
EmptyC passes MonadFail operations along to the underlying monad m, rather than interpreting it as a synonym for empty à la MaybeT.
Monad m => Applicative (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
MonadIO m => MonadIO (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe
Algebra sig m => Algebra (Empty :+: sig) (EmptyC m)Defined in fused-effects-1.1.2.7 · Control.Carrier.Empty.Maybe

Empty effect

0 declarations

module Control.Effect.Empty