Copyright	(c) Philipp Pfeiffer 2016
License	MIT
Maintainer	pfiff@hax-f.net
Stability	experimental
Portability	POSIX
Safe Haskell	Safe
Language	Haskell2010

Control.Monad.Backend

Description

Defines the BackendT transformer, which is a variant of the StateT transformer, such that the state is within an MVar.

Synopsis

Documentation

newtype BackendT s m a Source #

The BackendT transformer is a StateT, where the state is encapsulated into a MVar. We have

BackendT s m a

where s is the state and m is a monad, usually with a MonadIO constraint. The state is only unwrapped, when get, set or state is used. A bind will not unwrap.

Constructors

BackendT (MVar s -> m (MVar s, a))

Instances

(Monad m, MonadIO m) => MonadState s (BackendT s m) Source #
Methods get :: BackendT s m s # put :: s -> BackendT s m () # state :: (s -> (a, s)) -> BackendT s m a #
Monad m => Monad (BackendT s m) Source #
Methods (>>=) :: BackendT s m a -> (a -> BackendT s m b) -> BackendT s m b # (>>) :: BackendT s m a -> BackendT s m b -> BackendT s m b # return :: a -> BackendT s m a # fail :: String -> BackendT s m a #
Functor m => Functor (BackendT s m) Source #
Methods fmap :: (a -> b) -> BackendT s m a -> BackendT s m b # (<$) :: a -> BackendT s m b -> BackendT s m a #
Monad m => Applicative (BackendT s m) Source #
Methods pure :: a -> BackendT s m a # (<>) :: BackendT s m (a -> b) -> BackendT s m a -> BackendT s m b # (>) :: BackendT s m a -> BackendT s m b -> BackendT s m b # (<*) :: BackendT s m a -> BackendT s m b -> BackendT s m a #
(Monad m, MonadIO m) => MonadIO (BackendT s m) Source #
Methods liftIO :: IO a -> BackendT s m a #

runBackendT :: (Monad m, MonadIO m) => BackendT s m a -> s -> m (MVar s, a) Source #

runBackendT unwraps the BackendT monad on a given initial state. This given state is wrapped into an MVar.

rawRunBackendT :: BackendT s m a -> MVar s -> m (MVar s, a) Source #

rawRunBackendT unwraps then BackendT monad on a given initial state, where this state is wrapped into an MVar. **The MVar shouldn't be empty, otherwise every state reading/writing is blocking.** Usually, one should use runBackendT.