{-# LANGUAGE Unsafe #-} {-# LANGUAGE NoImplicitPrelude, MagicHash, DeriveDataTypeable #-} {-# OPTIONS_GHC -funbox-strict-fields #-} {-# OPTIONS_HADDOCK hide #-} ----------------------------------------------------------------------------- -- | -- Module : GHC.IORef -- Copyright : (c) The University of Glasgow 2008 -- License : see libraries/base/LICENSE -- -- Maintainer : cvs-ghc@haskell.org -- Stability : internal -- Portability : non-portable (GHC Extensions) -- -- The IORef type -- ----------------------------------------------------------------------------- module GHC.IORef ( IORef(..), newIORef, readIORef, writeIORef, atomicModifyIORef ) where import GHC.Base import GHC.STRef import GHC.IO import Data.Typeable.Internal( Typeable ) -- --------------------------------------------------------------------------- -- IORefs -- |A mutable variable in the 'IO' monad newtype IORef a = IORef (STRef RealWorld a) deriving( Typeable ) -- explicit instance because Haddock can't figure out a derived one instance Eq (IORef a) where IORef x == IORef y = x == y -- |Build a new 'IORef' newIORef :: a -> IO (IORef a) newIORef v = stToIO (newSTRef v) >>= \ var -> return (IORef var) -- |Read the value of an 'IORef' readIORef :: IORef a -> IO a readIORef (IORef var) = stToIO (readSTRef var) -- |Write a new value into an 'IORef' writeIORef :: IORef a -> a -> IO () writeIORef (IORef var) v = stToIO (writeSTRef var v) atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b atomicModifyIORef (IORef (STRef r#)) f = IO $ \s -> atomicModifyMutVar# r# f s