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<pre><a name="line-1"></a><span class='hs-comment'>{-# OPTIONS_GHC -fno-warn-orphans #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE MagicHash #-}</span>
<a name="line-3"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-4"></a><span class='hs-comment'>-- |</span>
<a name="line-5"></a><span class='hs-comment'>-- Module : Control.Monad.STM</span>
<a name="line-6"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2004</span>
<a name="line-7"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-8"></a><span class='hs-comment'>-- </span>
<a name="line-9"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-10"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-11"></a><span class='hs-comment'>-- Portability : non-portable (requires STM)</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-- Software Transactional Memory: a modular composable concurrency</span>
<a name="line-14"></a><span class='hs-comment'>-- abstraction. See</span>
<a name="line-15"></a><span class='hs-comment'>--</span>
<a name="line-16"></a><span class='hs-comment'>-- * /Composable memory transactions/, by Tim Harris, Simon Marlow, Simon</span>
<a name="line-17"></a><span class='hs-comment'>-- Peyton Jones, and Maurice Herlihy, in /ACM Conference on Principles</span>
<a name="line-18"></a><span class='hs-comment'>-- and Practice of Parallel Programming/ 2005.</span>
<a name="line-19"></a><span class='hs-comment'>-- <<a href="http://research.microsoft.com/Users/simonpj/papers/stm/index.htm">http://research.microsoft.com/Users/simonpj/papers/stm/index.htm</a>></span>
<a name="line-20"></a><span class='hs-comment'>--</span>
<a name="line-21"></a><span class='hs-comment'>-- This module only defines the 'STM' monad; you probably want to </span>
<a name="line-22"></a><span class='hs-comment'>-- import "Control.Concurrent.STM" (which exports "Control.Monad.STM").</span>
<a name="line-23"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-24"></a>
<a name="line-25"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span> <span class='hs-layout'>(</span>
<a name="line-26"></a> <span class='hs-conid'>STM</span><span class='hs-layout'>,</span>
<a name="line-27"></a> <span class='hs-varid'>atomically</span><span class='hs-layout'>,</span>
<a name="line-28"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-29"></a> <span class='hs-varid'>always</span><span class='hs-layout'>,</span>
<a name="line-30"></a> <span class='hs-varid'>alwaysSucceeds</span><span class='hs-layout'>,</span>
<a name="line-31"></a> <span class='hs-varid'>retry</span><span class='hs-layout'>,</span>
<a name="line-32"></a> <span class='hs-varid'>orElse</span><span class='hs-layout'>,</span>
<a name="line-33"></a> <span class='hs-varid'>check</span><span class='hs-layout'>,</span>
<a name="line-34"></a><span class='hs-cpp'>#endif</span>
<a name="line-35"></a> <span class='hs-varid'>throwSTM</span><span class='hs-layout'>,</span>
<a name="line-36"></a> <span class='hs-varid'>catchSTM</span>
<a name="line-37"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-38"></a>
<a name="line-39"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-40"></a><span class='hs-cpp'>#if ! (MIN_VERSION_base(4,3,0))</span>
<a name="line-41"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Conc</span> <span class='hs-varid'>hiding</span> <span class='hs-layout'>(</span><span class='hs-varid'>catchSTM</span><span class='hs-layout'>)</span>
<a name="line-42"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span> <span class='hs-conid'>MonadPlus</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span> <span class='hs-layout'>)</span>
<a name="line-43"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Exts</span> <span class='hs-layout'>(</span><span class='hs-varid'>raiseIO</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-varid'>catchSTM</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span>
<a name="line-44"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span>
<a name="line-45"></a><span class='hs-cpp'>#else</span>
<a name="line-46"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Conc</span>
<a name="line-47"></a><span class='hs-cpp'>#endif</span>
<a name="line-48"></a><span class='hs-cpp'>#else</span>
<a name="line-49"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Sequential</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span>
<a name="line-50"></a><span class='hs-cpp'>#endif</span>
<a name="line-51"></a>
<a name="line-52"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-53"></a><span class='hs-cpp'>#if ! (MIN_VERSION_base(4,3,0))</span>
<a name="line-54"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadPlus</span> <span class='hs-conid'>STM</span> <span class='hs-keyword'>where</span>
<a name="line-55"></a> <span class='hs-varid'>mzero</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>retry</span>
<a name="line-56"></a> <span class='hs-varid'>mplus</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>orElse</span>
<a name="line-57"></a><span class='hs-cpp'>#endif</span>
<a name="line-58"></a>
<a name="line-59"></a><a name="check"></a><span class='hs-definition'>check</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Bool</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-varid'>a</span>
<a name="line-60"></a><span class='hs-definition'>check</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-varid'>undefined</span> <span class='hs-keyword'>else</span> <span class='hs-varid'>retry</span>
<a name="line-61"></a><span class='hs-cpp'>#endif</span>
<a name="line-62"></a>
<a name="line-63"></a><span class='hs-cpp'>#if ! (MIN_VERSION_base(4,3,0))</span>
<a name="line-64"></a><a name="catchSTM"></a><span class='hs-comment'>-- |Exception handling within STM actions.</span>
<a name="line-65"></a><span class='hs-definition'>catchSTM</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>STM</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-varid'>a</span>
<a name="line-66"></a><span class='hs-definition'>catchSTM</span> <span class='hs-layout'>(</span><span class='hs-conid'>STM</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-varid'>handler</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>STM</span> <span class='hs-varop'>$</span> <span class='hs-varid'>catchSTM</span><span class='hs-cpp'>#</span> <span class='hs-varid'>m</span> <span class='hs-varid'>handler'</span>
<a name="line-67"></a> <span class='hs-keyword'>where</span>
<a name="line-68"></a> <span class='hs-varid'>handler'</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>case</span> <span class='hs-varid'>fromException</span> <span class='hs-varid'>e</span> <span class='hs-keyword'>of</span>
<a name="line-69"></a> <span class='hs-conid'>Just</span> <span class='hs-varid'>e'</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>case</span> <span class='hs-varid'>handler</span> <span class='hs-varid'>e'</span> <span class='hs-keyword'>of</span> <span class='hs-conid'>STM</span> <span class='hs-varid'>m'</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m'</span>
<a name="line-70"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>raiseIO</span><span class='hs-cpp'>#</span> <span class='hs-varid'>e</span>
<a name="line-71"></a>
<a name="line-72"></a><a name="throwSTM"></a><span class='hs-comment'>-- | A variant of 'throw' that can only be used within the 'STM' monad.</span>
<a name="line-73"></a><span class='hs-comment'>--</span>
<a name="line-74"></a><span class='hs-comment'>-- Throwing an exception in @STM@ aborts the transaction and propagates the</span>
<a name="line-75"></a><span class='hs-comment'>-- exception.</span>
<a name="line-76"></a><span class='hs-comment'>--</span>
<a name="line-77"></a><span class='hs-comment'>-- Although 'throwSTM' has a type that is an instance of the type of 'throw', the</span>
<a name="line-78"></a><span class='hs-comment'>-- two functions are subtly different:</span>
<a name="line-79"></a><span class='hs-comment'>--</span>
<a name="line-80"></a><span class='hs-comment'>-- > throw e `seq` x ===> throw e</span>
<a name="line-81"></a><span class='hs-comment'>-- > throwSTM e `seq` x ===> x</span>
<a name="line-82"></a><span class='hs-comment'>--</span>
<a name="line-83"></a><span class='hs-comment'>-- The first example will cause the exception @e@ to be raised,</span>
<a name="line-84"></a><span class='hs-comment'>-- whereas the second one won\'t. In fact, 'throwSTM' will only cause</span>
<a name="line-85"></a><span class='hs-comment'>-- an exception to be raised when it is used within the 'STM' monad.</span>
<a name="line-86"></a><span class='hs-comment'>-- The 'throwSTM' variant should be used in preference to 'throw' to</span>
<a name="line-87"></a><span class='hs-comment'>-- raise an exception within the 'STM' monad because it guarantees</span>
<a name="line-88"></a><span class='hs-comment'>-- ordering with respect to other 'STM' operations, whereas 'throw'</span>
<a name="line-89"></a><span class='hs-comment'>-- does not.</span>
<a name="line-90"></a><span class='hs-definition'>throwSTM</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Exception</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-varid'>a</span>
<a name="line-91"></a><span class='hs-definition'>throwSTM</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>STM</span> <span class='hs-varop'>$</span> <span class='hs-varid'>raiseIO</span><span class='hs-cpp'>#</span> <span class='hs-layout'>(</span><span class='hs-varid'>toException</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span>
<a name="line-92"></a><span class='hs-cpp'>#endif</span>
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