Data.MRef.Instances

Description

This module exports no new symbols of its own. It defines basic class instances for creating, reading, and writing MVars, and re-exports MVar.

Synopsis

Documentation

data MVar a

An MVar (pronounced "em-var") is a synchronising variable, used for communication between concurrent threads. It can be thought of as a a box, which may be empty or full.

Instances

Eq (MVar a)
MonadIO m => PutMRef (MVar a) m a
MonadIO m => TakeMRef (MVar a) m a
MonadIO m => NewMRef (MVar a) m a
MonadIO m => NewRef (MVar a) m (Maybe a)

class Monad m => MonadIO m where

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.

Instances should satisfy the following laws, which state that liftIO is a transformer of monads:

```
liftIO . return = return
```

liftIO (m >>= f) = liftIO m >>= (liftIO . f)

Methods

liftIO :: IO a -> m a

Lift a computation from the IO monad.

Instances

MonadIO IO

data STM a

A monad supporting atomic memory transactions.

Instances

Monad STM
Functor STM
Typeable1 STM
MonadPlus STM
HasMRef STM
HasRef STM
PutMRef (TVar (Maybe a)) STM a
PutMRef (TMVar a) STM a
TakeMRef (TVar (Maybe a)) STM a
TakeMRef (TMVar a) STM a
NewMRef (TVar (Maybe a)) STM a
NewMRef (TMVar a) STM a
NewRef (TVar a) STM a
ModifyRef (TVar a) STM a
MonadIO m => ReadRef (STM a) m a
ReadRef (STM a) STM a
ReadRef (TVar a) STM a
WriteRef (TVar a) STM a
NewRef (TMVar a) STM (Maybe a)
ReadRef (TMVar a) STM (Maybe a)
PutMRef (MRef STM a) IO a
TakeMRef (MRef STM a) IO a
NewMRef (MRef STM a) IO a
MonadIO m => NewRef (Ref STM a) m a
MonadIO m => ModifyRef (Ref STM a) m a
MonadIO m => ReadRef (Ref STM a) m a
MonadIO m => WriteRef (Ref STM a) m a

data TMVar a

A TMVar is a synchronising variable, used for communication between concurrent threads. It can be thought of as a box, which may be empty or full.

Instances

Typeable1 TMVar
Eq (TMVar a)
PutMRef (TMVar a) IO a
PutMRef (TMVar a) STM a
TakeMRef (TMVar a) IO a
TakeMRef (TMVar a) STM a
NewMRef (TMVar a) IO a
NewMRef (TMVar a) STM a
MonadIO m => NewRef (TMVar a) m (Maybe a)
NewRef (TMVar a) STM (Maybe a)
MonadIO m => ReadRef (TMVar a) m (Maybe a)
ReadRef (TMVar a) STM (Maybe a)

data TVar a

Shared memory locations that support atomic memory transactions.

Instances

Typeable1 TVar
Eq (TVar a)
PutMRef (TVar (Maybe a)) IO a
PutMRef (TVar (Maybe a)) STM a
TakeMRef (TVar (Maybe a)) IO a
TakeMRef (TVar (Maybe a)) STM a
NewMRef (TVar (Maybe a)) IO a
NewMRef (TVar (Maybe a)) STM a
MonadIO m => NewRef (TVar a) m a
NewRef (TVar a) STM a
MonadIO m => ModifyRef (TVar a) m a
ModifyRef (TVar a) STM a
MonadIO m => ReadRef (TVar a) m a
ReadRef (TVar a) STM a
MonadIO m => WriteRef (TVar a) m a
WriteRef (TVar a) STM a

atomically :: STM a -> IO a

Perform a series of STM actions atomically.

You cannot use atomically inside an unsafePerformIO or unsafeInterleaveIO. Any attempt to do so will result in a runtime error. (Reason: allowing this would effectively allow a transaction inside a transaction, depending on exactly when the thunk is evaluated.)

However, see newTVarIO, which can be called inside unsafePerformIO, and which allows top-level TVars to be allocated.