Control.Monad.Writer.Concurrent.Strict

A monad whose actions produce an output.

This module builds output strictly. For a lazy version, see Control.Monad.Writer.Concurrent.Lazy.

Documentation

module Control.Monad.Writer

The WriterC monad transformer

data WriterC w m a

A concurrent monad transformer collecting output of type w.

This is very similar to transformers' WriterT, with the exception of the MonadIO constraint on every instance, which is necessary to perform STM actions.

Instances

(Monoid w, MonadReader r m) => MonadReader r (WriterC w m)

(Monoid w, MonadIO m) => MonadWriter w (WriterC w m)

MonadTrans (WriterC w)

Monad m => Monad (WriterC w m)

Functor m => Functor (WriterC w m)

MonadFix m => MonadFix (WriterC w m)

MonadPlus m => MonadPlus (WriterC w m)

(Functor m, Monad m) => Applicative (WriterC w m)

(Functor m, MonadPlus m) => Alternative (WriterC w m)

(MonadIO m, MonadCatch m) => MonadCatch (WriterC w m)

MonadIO m => MonadIO (WriterC w m)

(Monoid w, MonadFork m) => MonadFork (WriterC w m)

Running WriterC actions

runWriterC

Arguments

:: MonadIO m

=> WriterC w m a

computation to execute

-> TVar w

output channel

-> m (a, w)

return value and collected output

Unwrap a concurrent Writer monad computation as a function.

execWriterC

Arguments

:: MonadIO m

=> WriterC w m a

computation to execute

-> TVar w

output channel

-> m w

collected output

Unwrap a concurrent Writer monad computation as a function, discarding the return value.

• execWriterC m w = liftM snd (runWriterC m w)

mapWriterC :: (m (a, TVar w) -> n (b, TVar w)) -> WriterC w m a -> WriterC w n b

Map both the return value and output of a computation using the given function.

Running concurrent operations on a single input

runWritersC

Arguments

:: (MonadFork m, Monoid w)

=> [WriterC w m a]

writer computations to execute

-> m ([a], w)

return values and output

Run multiple Writer operations on the same value, returning the resultant output and the value produced by each operation.

execWritersC

Arguments

:: (MonadFork m, Monoid w)

=> [WriterC w m a]

writer computations to execute

-> m w

output

Run multiple Writer operations on the same value, returning the resultant output.

Lifting other operations

liftCallCC :: ((((a, TVar w) -> m (b, TVar w)) -> m (a, TVar w)) -> m (a, TVar w)) -> ((a -> WriterC w m b) -> WriterC w m a) -> WriterC w m a

Lift a callCC operation to the new monad.

liftCatch :: (m (a, TVar w) -> (e -> m (a, TVar w)) -> m (a, TVar w)) -> WriterC w m a -> (e -> WriterC w m a) -> WriterC w m a

Lift a catchError operation to the new monad.