{-# LANGUAGE Unsafe #-}{-# LANGUAGE NoImplicitPrelude, MagicHash, UnboxedTuples #-}{-# OPTIONS_HADDOCK not-home #-}------------------------------------------------------------------------------- |-- Module : GHC.STRef-- Copyright : (c) The University of Glasgow, 1994-2002-- License : see libraries/base/LICENSE---- Maintainer : cvs-ghc@haskell.org-- Stability : internal-- Portability : non-portable (GHC Extensions)---- References in the 'ST' monad.-------------------------------------------------------------------------------moduleGHC.STRef(STRef (..),newSTRef ,readSTRef ,writeSTRef )whereimportGHC.ST importGHC.Base -- $setup-- import PreludedataSTRef s a =STRef (MutVar#s a )-- ^ a value of type @STRef s a@ is a mutable variable in state thread @s@,-- containing a value of type @a@---- >>> :{-- runST (do-- ref <- newSTRef "hello"-- x <- readSTRef ref-- writeSTRef ref (x ++ "world")-- readSTRef ref )-- :}-- "helloworld"-- |Build a new 'STRef' in the current state threadnewSTRef ::a ->ST s (STRef s a )newSTRef :: a -> ST s (STRef s a)
newSTRef a
init =STRep s (STRef s a) -> ST s (STRef s a)
forall s a. STRep s a -> ST s a
ST (STRep s (STRef s a) -> ST s (STRef s a))
-> STRep s (STRef s a) -> ST s (STRef s a)
forall a b. (a -> b) -> a -> b
$ \State# s
s1# ->casea -> State# s -> (# State# s, MutVar# s a #)
forall a d. a -> State# d -> (# State# d, MutVar# d a #)
newMutVar#a
init State# s
s1# of{(#State# s
s2# ,MutVar# s a
var# #)->(#State# s
s2# ,MutVar# s a -> STRef s a
forall s a. MutVar# s a -> STRef s a
STRef MutVar# s a
var# #)}-- |Read the value of an 'STRef'readSTRef ::STRef s a ->ST s a readSTRef :: STRef s a -> ST s a
readSTRef (STRef MutVar# s a
var# )=STRep s a -> ST s a
forall s a. STRep s a -> ST s a
ST (STRep s a -> ST s a) -> STRep s a -> ST s a
forall a b. (a -> b) -> a -> b
$ \State# s
s1# ->MutVar# s a -> STRep s a
forall d a. MutVar# d a -> State# d -> (# State# d, a #)
readMutVar#MutVar# s a
var# State# s
s1# -- |Write a new value into an 'STRef'writeSTRef ::STRef s a ->a ->ST s ()writeSTRef :: STRef s a -> a -> ST s ()
writeSTRef (STRef MutVar# s a
var# )a
val =STRep s () -> ST s ()
forall s a. STRep s a -> ST s a
ST (STRep s () -> ST s ()) -> STRep s () -> ST s ()
forall a b. (a -> b) -> a -> b
$ \State# s
s1# ->caseMutVar# s a -> a -> State# s -> State# s
forall d a. MutVar# d a -> a -> State# d -> State# d
writeMutVar#MutVar# s a
var# a
val State# s
s1# of{State# s
s2# ->(#State# s
s2# ,()#)}-- | Pointer equality.---- @since 2.01instanceEq(STRef s a )whereSTRef MutVar# s a
v1# == :: STRef s a -> STRef s a -> Bool
==STRef MutVar# s a
v2# =Int# -> Bool
isTrue#(MutVar# s a -> MutVar# s a -> Int#
forall d a. MutVar# d a -> MutVar# d a -> Int#
sameMutVar#MutVar# s a
v1# MutVar# s a
v2# )