Control.Monad.State.Concurrent.Lazy

Concurrent state monad, providing a State-like interface but allowing for multiple threads to operate on the same value simultaneously.

This module performs state computations lazily. For a strict version, see Control.Monad.State.Concurrent.Strict.

Documentation

module Control.Monad.State

The StateC monad transformer

data StateC s m a

A concurrent state transformer monad parameterized by:

• s - The state. This is contained in a TVar.
• m - The inner monad.

The return function leaves the state unchanged, while >>= performs actions atomically on the held TVar.

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

Instances

(Functor m, MonadIO m) => MonadState s (StateC s m)

MonadTrans (StateC s)

MonadIO m => Monad (StateC s m)

(Functor m, MonadIO m) => Functor (StateC s m)

(MonadIO m, MonadFix m) => MonadFix (StateC s m)

(MonadPlus m, MonadIO m) => MonadPlus (StateC s m)

(Functor m, MonadIO m) => Applicative (StateC s m)

(MonadIO m, Functor m, MonadPlus m) => Alternative (StateC s m)

(MonadIO m, MonadCatch m) => MonadCatch (StateC s m)

MonadIO m => MonadIO (StateC s m)

Concurrent state operations

runStateC

Arguments

:: MonadIO m

=> StateC s m a

state-passing computation to execute

-> TVar s

initial state

-> m (a, s)

return value and final state

Unwrap a concurrent state monad computation as a function.

evalStateC

Arguments

:: MonadIO m

=> StateC s m a

state-passing computation to execute

-> TVar s

initial state

-> m a

return value

Evaluate a concurrent state computation with the given initial state and return the final value, discarding the final state.

• evalStateC m s = liftM fst (runStateC m s)

execStateC

Arguments

:: MonadIO m

=> StateC s m a

state-passing computation to execute

-> TVar s

initial state

-> m s

final state

Execute a concurrent state computation with the given initial state and return the final state, discarding the final value.

• execStateC m s = liftM snd (runStateC m s)

Lifting other operations

liftCallCCC :: ((((a, TVar s) -> m (b, TVar s)) -> m (a, TVar s)) -> m (a, TVar s)) -> ((a -> StateC s m b) -> StateC s m a) -> StateC s m a

Uniform lifting of a callCC operation to the new monad. This version rolls back to the original TVar upon entering the continuation.

liftCallCCC' :: ((((a, TVar s) -> m (b, TVar s)) -> m (a, TVar s)) -> m (a, TVar s)) -> ((a -> StateC s m b) -> StateC s m a) -> StateC s m a

In-situ lifting of a callCC operation to the new monad. This version uses the current TVar upon entering the continuation. It does not satisfy the laws of a monad transformer.

liftCatchC :: (m (a, TVar s) -> (e -> m (a, TVar s)) -> m (a, TVar s)) -> StateC s m a -> (e -> StateC s m a) -> StateC s m a

Lift a catchError operation to the new monad.

liftListenC :: Monad m => (m (a, TVar s) -> m ((a, TVar s), w)) -> StateC s m a -> StateC s m (a, w)

Lift a listen operation to the new monad.

liftPassC :: Monad m => (m ((a, TVar s), b) -> m (a, TVar s)) -> StateC s m (a, b) -> StateC s m a

Lift a pass operation to the new monad.