Portability | portable |
---|---|

Stability | unstable |

Maintainer | mail@n-sch.de |

MState: A consistent State monad for concurrent applications.

- data MState t m a
- runMState :: Forkable m => MState t m a -> t -> m (a, t)
- evalMState :: Forkable m => MState t m a -> t -> m a
- execMState :: Forkable m => MState t m a -> t -> m t
- mapMState :: (MonadIO m, MonadIO n) => (m (a, t) -> n (b, t)) -> MState t m a -> MState t n b
- withMState :: MonadIO m => (t -> t) -> MState t m a -> MState t m a
- modifyM :: MonadIO m => (t -> t) -> MState t m ()
- class MonadIO m => Forkable m where
- forkM :: Forkable m => MState t m () -> MState t m ThreadId

# The MState Monad

The MState is an abstract data definition for a State monad which can be
used in concurrent applications. It can be accessed with `evalMState`

and
`execMState`

. To start a new state thread use `forkM`

.

MonadReader r m => MonadReader r (MState t m) | |

MonadIO m => MonadState t (MState t m) | |

MonadError e m => MonadError e (MState t m) | |

MonadWriter w m => MonadWriter w (MState t m) | |

MonadTrans (MState t) | |

Monad m => Monad (MState t m) | |

Monad m => Functor (MState t m) | |

MonadFix m => MonadFix (MState t m) | |

MonadPlus m => MonadPlus (MState t m) | |

MonadCont m => MonadCont (MState t m) | |

MonadIO m => MonadIO (MState t m) |

Run the MState and return both, the function value and the state value

Evaluate the MState monad with the given initial state, throwing away the final state stored in the MVar.

Execute the MState monad with a given initial state. Returns the value of the final state.

mapMState :: (MonadIO m, MonadIO n) => (m (a, t) -> n (b, t)) -> MState t m a -> MState t n bSource

Map a stateful computation from one `(return value, state)`

pair to
another. See `Control.Monad.State.Lazy.mapState`

for more information.

withMState :: MonadIO m => (t -> t) -> MState t m a -> MState t m aSource

Apply this function to this state and return the resulting state.

modifyM :: MonadIO m => (t -> t) -> MState t m ()Source

Modify the MState. Block all other threads from accessing the state.

# Concurrency

class MonadIO m => Forkable m whereSource

The class which is needed to start new threads in the MState monad. Don't
confuse this with `forkM`

which should be used to fork new threads!

Start a new thread, using `forkIO`

. The main process will wait for all
child processes to finish.

# Example

Example usage:

import Control.Concurrent import Control.Concurrent.MState import Control.Monad.State type MyState a = MState Int IO a -- Expected state value: 2 main = print =<< execMState incTwice 0 incTwice :: MyState () incTwice = do -- First inc inc -- This thread should get killed before it can "inc" our state: kill =<< forkM incDelayed -- This thread should "inc" our state forkM incDelayed return () where inc = get >>= put . (+1) kill = liftIO . killThread incDelayed = do liftIO $ threadDelay 2000000 inc