----------------------------------------------------------------------------- -- | -- Module : Data.IORef -- Copyright : (c) The University of Glasgow 2001 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : libraries@haskell.org -- Stability : experimental -- Portability : portable -- -- Mutable references in the IO monad. -- -----------------------------------------------------------------------------
module Data.IORef ( -- * IORefs IORef, -- abstract, instance of: Eq, Typeable 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 ) where import Prelude -- Explicit dependency helps 'make depend' do the right thing import Hugs.IORef -- |Mutate the contents of an 'IORef' modifyIORef :: IORef a -> (a -> a) -> IO () modifyIORef ref f = writeIORef ref . f =<< readIORef ref -- |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. -- atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b atomicModifyIORef = plainModifyIORef -- Hugs has no preemption where plainModifyIORef r f = do a <- readIORef r case f a of (a',b) -> writeIORef r a' >> return b
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