Add tests from testsuite/tests/h98

[ghc-base.git] / GHC / STRef.lhs

diff --git a/GHC/STRef.lhs b/GHC/STRef.lhs
index 7145932..9306b24 100644 (file)
--- a/GHC/STRef.lhs
+++ b/GHC/STRef.lhs
@@ -1,28 +1,47 @@
 \begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# LANGUAGE NoImplicitPrelude, MagicHash, UnboxedTuples #-}
+{-# OPTIONS_HADDOCK hide #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- 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.
+--
+-----------------------------------------------------------------------------
+
+-- #hide
 module GHC.STRef where
 
 import GHC.ST
 import GHC.Base
 
 data STRef 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@
 
+-- |Build a new 'STRef' in the current state thread
 newSTRef :: a -> ST s (STRef s a)
 newSTRef init = ST $ \s1# ->
     case newMutVar# init s1#            of { (# s2#, var# #) ->
     (# s2#, STRef var# #) }
 
+-- |Read the value of an 'STRef'
 readSTRef :: STRef s a -> ST s a
 readSTRef (STRef var#) = ST $ \s1# -> readMutVar# var# s1#
 
+-- |Write a new value into an 'STRef'
 writeSTRef :: STRef s a -> a -> ST s ()
 writeSTRef (STRef var#) val = ST $ \s1# ->
     case writeMutVar# var# val s1#      of { s2# ->
     (# s2#, () #) }
 
-modifySTRef :: STRef s a -> (a -> a) -> ST s ()
-modifySTRef ref f = readSTRef ref >>= writeSTRef ref . f
-
 -- Just pointer equality on mutable references:
 instance Eq (STRef s a) where
     STRef v1# == STRef v2# = sameMutVar# v1# v2#