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Data.IORef

Portability | portable
Stability | experimental
Maintainer | libraries@haskell.org

Contents

IORefs

Description
Mutable references in the IO monad.
Synopsis

data IORef a
newIORef :: a -> IO (IORef a)
readIORef :: IORef a -> IO a
writeIORef :: IORef a -> a -> IO ()
modifyIORef :: IORef a -> (a -> a) -> IO ()
atomicModifyIORef :: IORef a -> (a -> (a, b)) -> IO b
mkWeakIORef :: IORef a -> IO () -> IO (Weak (IORef a))

IORefs
data IORef a

A mutable variable in the `IO` monad
Instances

Typeable a => Typeable (IORef a)
Eq (IORef a)

newIORef :: a -> IO (IORef a)
Build a new `IORef`
readIORef :: IORef a -> IO a
Read the value of an `IORef`
writeIORef :: IORef a -> a -> IO ()
Write a new value into an `IORef`
modifyIORef :: IORef a -> (a -> a) -> IO ()
Mutate the contents of an `IORef`
atomicModifyIORef :: IORef a -> (a -> (a, b)) -> IO b

Atomically modifies the contents of an `IORef`.

This function is useful for using `IORef` in a safe way in a multithreaded program. If you only have one `IORef`, then using `atomicModifyIORef` to access and modify it will prevent race conditions.

Extending the atomicity to multiple `IORef`s is problematic, so it is recommended that if you need to do anything more complicated then using `MVar` instead is a good idea.

mkWeakIORef :: IORef a -> IO () -> IO (Weak (IORef a))
Make a `Weak` pointer to an `IORef`
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