Control.Concurrent.STM.TVar.Zoom

Documentation

data TVar a where

Constructors

Leaf :: TVar x -> ALens' x a -> TVar a

Branch :: TVar x -> TVar y -> ALens' (x, y) a -> TVar a

zoomTVar :: ALens' a b -> TVar a -> TVar b

newTVar :: a -> STM (TVar a)

newTVarIO :: a -> IO (TVar a)

pairTVars :: TVar a -> TVar b -> TVar (a, b)

readTVar :: TVar a -> STM a

readTVarIO :: TVar a -> IO a

modifyTVar :: TVar a -> (a -> a) -> STM ()

modifyTVar' :: TVar a -> (a -> a) -> STM ()

writeTVar :: TVar a -> a -> STM ()

swapTVar :: TVar a -> a -> STM a

data STM a :: * -> *

A monad supporting atomic memory transactions.

Instances

Monad STM

Functor STM

Applicative STM

Alternative STM

MonadPlus STM

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.