Safe Haskell	Safe-Inferred
Language	Haskell2010

Control.Carrier.Empty.Maybe

Contents

Empty carrier
Empty effect

Description

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

Synopsis

runEmpty :: EmptyC m a -> m (Maybe a)
evalEmpty :: Functor m => EmptyC m a -> m ()
execEmpty :: Functor m => EmptyC m a -> m Bool
newtype EmptyC m a = EmptyC (MaybeT m a)
module Control.Effect.Empty

Empty carrier

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

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 () Source #

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 Source #

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 Source #

Since: 1.0.0.0

Constructors

EmptyC (MaybeT m a)

Instances

Instances details

MonadTrans EmptyC Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods lift :: Monad m => m a -> EmptyC m a #
MonadFail m => MonadFail (EmptyC m) Source #	`EmptyC` passes `MonadFail` operations along to the underlying monad `m`, rather than interpreting it as a synonym for `empty` à la `MaybeT`.
Instance details Defined in Control.Carrier.Empty.Maybe Methods fail :: String -> EmptyC m a #
MonadFix m => MonadFix (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods mfix :: (a -> EmptyC m a) -> EmptyC m a #
MonadIO m => MonadIO (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods liftIO :: IO a -> EmptyC m a #
Monad m => Applicative (EmptyC m) Source #
Instance details 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 #
Functor m => Functor (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods fmap :: (a -> b) -> EmptyC m a -> EmptyC m b # (<$) :: a -> EmptyC m b -> EmptyC m a #
Monad m => Monad (EmptyC m) Source #
Instance details 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 #
Algebra sig m => Algebra (Empty :+: sig) (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (EmptyC m) -> (Empty :+: sig) n a -> ctx () -> EmptyC m (ctx a) Source #

Empty effect

module Control.Effect.Empty