Safe Haskell	Safe-Inferred
Language	Haskell2010

Control.Carrier.Writer.Strict

Contents

Writer carrier
Writer effect

Description

A carrier for Writer effects. This carrier performs its append operations strictly and thus avoids the space leaks inherent in lazy writer monads. These appends are left-associative; as such, [] is a poor choice of monoid for computations that entail many calls to tell. The Seq or DList monoids may be a superior choice.

This implementation is based on a post Gabriel Gonzalez made to the Haskell mailing list: https://mail.haskell.org/pipermail/libraries/2013-March/019528.html

Since: 1.0.0.0

Synopsis

runWriter :: Monoid w => WriterC w m a -> m (w, a)
execWriter :: (Monoid w, Functor m) => WriterC w m a -> m w
newtype WriterC w m a = WriterC (StateC w m a)
module Control.Effect.Writer

Writer carrier

runWriter :: Monoid w => WriterC w m a -> m (w, a) Source #

Run a Writer effect with a Monoidal log, producing the final log alongside the result value.

runWriter (tell w) = pure (w, ())

runWriter (pure a) = pure (mempty, a)

execWriter :: (Monoid w, Functor m) => WriterC w m a -> m w Source #

Run a Writer effect with a Monoidal log, producing the final log and discarding the result value.

execWriter m = fmap fst (runWriter m)

newtype WriterC w m a Source #

A space-efficient carrier for Writer effects, implemented atop Control.Carrier.State.Strict.

Since: 1.0.0.0

Constructors

WriterC (StateC w m a)

Instances

Instances details

MonadTrans (WriterC w) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods lift :: Monad m => m a -> WriterC w m a #
MonadFail m => MonadFail (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods fail :: String -> WriterC w m a #
MonadFix m => MonadFix (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods mfix :: (a -> WriterC w m a) -> WriterC w m a #
MonadIO m => MonadIO (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods liftIO :: IO a -> WriterC w m a #
(Alternative m, Monad m) => Alternative (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods empty :: WriterC w m a # (<\|>) :: WriterC w m a -> WriterC w m a -> WriterC w m a # some :: WriterC w m a -> WriterC w m [a] # many :: WriterC w m a -> WriterC w m [a] #
Monad m => Applicative (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods pure :: a -> WriterC w m a # (<>) :: WriterC w m (a -> b) -> WriterC w m a -> WriterC w m b # liftA2 :: (a -> b -> c) -> WriterC w m a -> WriterC w m b -> WriterC w m c # (>) :: WriterC w m a -> WriterC w m b -> WriterC w m b # (<*) :: WriterC w m a -> WriterC w m b -> WriterC w m a #
Functor m => Functor (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods fmap :: (a -> b) -> WriterC w m a -> WriterC w m b # (<$) :: a -> WriterC w m b -> WriterC w m a #
Monad m => Monad (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods (>>=) :: WriterC w m a -> (a -> WriterC w m b) -> WriterC w m b # (>>) :: WriterC w m a -> WriterC w m b -> WriterC w m b # return :: a -> WriterC w m a #
(Alternative m, Monad m) => MonadPlus (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods mzero :: WriterC w m a # mplus :: WriterC w m a -> WriterC w m a -> WriterC w m a #
(Monoid w, Algebra sig m) => Algebra (Writer w :+: sig) (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (WriterC w m) -> (Writer w :+: sig) n a -> ctx () -> WriterC w m (ctx a) Source #

Writer effect

module Control.Effect.Writer