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<pre><a name="line-1"></a><span class='hs-comment'>{-# OPTIONS_GHC -Wall -fwarn-tabs #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE CPP, DeriveDataTypeable #-}</span>
<a name="line-3"></a>
<a name="line-4"></a><span class='hs-comment'>-- HACK: in GHC 7.10, Haddock complains about Control.Monad.STM and</span>
<a name="line-5"></a><span class='hs-comment'>-- System.IO.Unsafe being imported but unused. However, if we use</span>
<a name="line-6"></a><span class='hs-comment'>-- CPP to avoid including them under Haddock, then it will fail to</span>
<a name="line-7"></a><span class='hs-comment'>-- compile!</span>
<a name="line-8"></a><span class='hs-cpp'>#ifdef __HADDOCK__</span>
<a name="line-9"></a><span class='hs-comment'>{-# OPTIONS_GHC -fno-warn-unused-imports #-}</span>
<a name="line-10"></a><span class='hs-cpp'>#endif</span>
<a name="line-11"></a>
<a name="line-12"></a><span class='hs-cpp'>#if __GLASGOW_HASKELL__ >= 701</span>
<a name="line-13"></a><span class='hs-cpp'># ifdef __HADDOCK__</span>
<a name="line-14"></a><span class='hs-comment'>{-# LANGUAGE Trustworthy #-}</span>
<a name="line-15"></a><span class='hs-cpp'># else</span>
<a name="line-16"></a><span class='hs-comment'>{-# LANGUAGE Safe #-}</span>
<a name="line-17"></a><span class='hs-cpp'># endif</span>
<a name="line-18"></a><span class='hs-cpp'>#endif</span>
<a name="line-19"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-20"></a><span class='hs-comment'>-- 2015.03.29</span>
<a name="line-21"></a><span class='hs-comment'>-- |</span>
<a name="line-22"></a><span class='hs-comment'>-- Module : Control.Concurrent.STM.TMQueue</span>
<a name="line-23"></a><span class='hs-comment'>-- Copyright : Copyright (c) 2011--2015 wren gayle romano</span>
<a name="line-24"></a><span class='hs-comment'>-- License : BSD</span>
<a name="line-25"></a><span class='hs-comment'>-- Maintainer : wren@community.haskell.org</span>
<a name="line-26"></a><span class='hs-comment'>-- Stability : provisional</span>
<a name="line-27"></a><span class='hs-comment'>-- Portability : non-portable (GHC STM, DeriveDataTypeable)</span>
<a name="line-28"></a><span class='hs-comment'>--</span>
<a name="line-29"></a><span class='hs-comment'>-- A version of "Control.Concurrent.STM.TQueue" where the queue is</span>
<a name="line-30"></a><span class='hs-comment'>-- closeable. This is similar to a @TQueue (Maybe a)@ with a</span>
<a name="line-31"></a><span class='hs-comment'>-- monotonicity guarantee that once there's a @Nothing@ there will</span>
<a name="line-32"></a><span class='hs-comment'>-- always be @Nothing@.</span>
<a name="line-33"></a><span class='hs-comment'>--</span>
<a name="line-34"></a><span class='hs-comment'>-- /Since: 2.0.0/</span>
<a name="line-35"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-36"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Concurrent</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span><span class='hs-varop'>.</span><span class='hs-conid'>TMQueue</span>
<a name="line-37"></a> <span class='hs-layout'>(</span>
<a name="line-38"></a> <span class='hs-comment'>-- * The TMQueue type</span>
<a name="line-39"></a> <span class='hs-conid'>TMQueue</span><span class='hs-conid'>()</span>
<a name="line-40"></a> <span class='hs-comment'>-- ** Creating TMQueues</span>
<a name="line-41"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newTMQueue</span>
<a name="line-42"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newTMQueueIO</span>
<a name="line-43"></a> <span class='hs-comment'>-- ** Reading from TMQueues</span>
<a name="line-44"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>readTMQueue</span>
<a name="line-45"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryReadTMQueue</span>
<a name="line-46"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>peekTMQueue</span>
<a name="line-47"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryPeekTMQueue</span>
<a name="line-48"></a> <span class='hs-comment'>-- ** Writing to TMQueues</span>
<a name="line-49"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>writeTMQueue</span>
<a name="line-50"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>unGetTMQueue</span>
<a name="line-51"></a> <span class='hs-comment'>-- ** Closing TMQueues</span>
<a name="line-52"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>closeTMQueue</span>
<a name="line-53"></a> <span class='hs-comment'>-- ** Predicates</span>
<a name="line-54"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isClosedTMQueue</span>
<a name="line-55"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isEmptyTMQueue</span>
<a name="line-56"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-57"></a>
<a name="line-58"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-59"></a><span class='hs-cpp'>#if __GLASGOW_HASKELL__ < 710</span>
<a name="line-60"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Applicative</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varop'><$></span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-61"></a><span class='hs-cpp'>#endif</span>
<a name="line-62"></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-varop'>.</span><span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>STM</span><span class='hs-layout'>)</span>
<a name="line-63"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Concurrent</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span><span class='hs-varop'>.</span><span class='hs-conid'>TVar</span>
<a name="line-64"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Concurrent</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span><span class='hs-varop'>.</span><span class='hs-conid'>TQueue</span> <span class='hs-comment'>-- N.B., GHC only</span>
<a name="line-65"></a>
<a name="line-66"></a><span class='hs-comment'>-- N.B., we need a Custom cabal build-type for this to work.</span>
<a name="line-67"></a><span class='hs-cpp'>#ifdef __HADDOCK__</span>
<a name="line-68"></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-varop'>.</span><span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-varid'>atomically</span><span class='hs-layout'>)</span>
<a name="line-69"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Unsafe</span> <span class='hs-layout'>(</span><span class='hs-varid'>unsafePerformIO</span><span class='hs-layout'>)</span>
<a name="line-70"></a><span class='hs-cpp'>#endif</span>
<a name="line-71"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-72"></a>
<a name="line-73"></a><a name="TMQueue"></a><span class='hs-comment'>-- | @TMQueue@ is an abstract type representing a closeable FIFO</span>
<a name="line-74"></a><a name="TMQueue"></a><span class='hs-comment'>-- queue.</span>
<a name="line-75"></a><a name="TMQueue"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>TMQueue</span>
<a name="line-76"></a> <span class='hs-comment'>{-# UNPACK #-}</span> <span class='hs-varop'>!</span><span class='hs-layout'>(</span><span class='hs-conid'>TVar</span> <span class='hs-conid'>Bool</span><span class='hs-layout'>)</span>
<a name="line-77"></a> <span class='hs-comment'>{-# UNPACK #-}</span> <span class='hs-varop'>!</span><span class='hs-layout'>(</span><span class='hs-conid'>TQueue</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-78"></a> <span class='hs-keyword'>deriving</span> <span class='hs-conid'>Typeable</span>
<a name="line-79"></a>
<a name="line-80"></a>
<a name="line-81"></a><a name="newTMQueue"></a><span class='hs-comment'>-- | Build and returns a new instance of @TMQueue@.</span>
<a name="line-82"></a><span class='hs-definition'>newTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-83"></a><span class='hs-definition'>newTMQueue</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-84"></a> <span class='hs-varid'>closed</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVar</span> <span class='hs-conid'>False</span>
<a name="line-85"></a> <span class='hs-varid'>queue</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTQueue</span>
<a name="line-86"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span>
<a name="line-87"></a>
<a name="line-88"></a>
<a name="line-89"></a><a name="newTMQueueIO"></a><span class='hs-comment'>-- | @IO@ version of 'newTMQueue'. This is useful for creating</span>
<a name="line-90"></a><span class='hs-comment'>-- top-level @TMQueue@s using 'unsafePerformIO', because using</span>
<a name="line-91"></a><span class='hs-comment'>-- 'atomically' inside 'unsafePerformIO' isn't possible.</span>
<a name="line-92"></a><span class='hs-definition'>newTMQueueIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-93"></a><span class='hs-definition'>newTMQueueIO</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-94"></a> <span class='hs-varid'>closed</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVarIO</span> <span class='hs-conid'>False</span>
<a name="line-95"></a> <span class='hs-varid'>queue</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTQueueIO</span>
<a name="line-96"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span>
<a name="line-97"></a>
<a name="line-98"></a>
<a name="line-99"></a><a name="readTMQueue"></a><span class='hs-comment'>-- | Read the next value from the @TMQueue@, retrying if the queue</span>
<a name="line-100"></a><span class='hs-comment'>-- is empty (and not closed). We return @Nothing@ immediately if</span>
<a name="line-101"></a><span class='hs-comment'>-- the queue is closed and empty.</span>
<a name="line-102"></a><span class='hs-definition'>readTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-103"></a><span class='hs-definition'>readTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-104"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-105"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-106"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>tryReadTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-107"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>readTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-108"></a><span class='hs-comment'>{-
<a name="line-109"></a>-- The above is lazier reading from @queue@, and slightly optimized, compared to the clearer:
<a name="line-110"></a>readTMQueue (TMQueue closed queue) = do
<a name="line-111"></a> b <- isEmptyTQueue queue
<a name="line-112"></a> b' <- readTVar closed
<a name="line-113"></a> if b && b'
<a name="line-114"></a> then return Nothing
<a name="line-115"></a> else Just <$> readTQueue queue
<a name="line-116"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-117"></a>-}</span>
<a name="line-118"></a>
<a name="line-119"></a>
<a name="line-120"></a><a name="tryReadTMQueue"></a><span class='hs-comment'>-- | A version of 'readTMQueue' which does not retry. Instead it</span>
<a name="line-121"></a><span class='hs-comment'>-- returns @Just Nothing@ if the queue is open but no value is</span>
<a name="line-122"></a><span class='hs-comment'>-- available; it still returns @Nothing@ if the queue is closed</span>
<a name="line-123"></a><span class='hs-comment'>-- and empty.</span>
<a name="line-124"></a><span class='hs-definition'>tryReadTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-125"></a><span class='hs-definition'>tryReadTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-126"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-127"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-128"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>fmap</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>tryReadTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-129"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>tryReadTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-130"></a><span class='hs-comment'>{-
<a name="line-131"></a>-- The above is lazier reading from @queue@ (and removes an extraneous isEmptyTQueue when using the compatibility layer) than the clearer:
<a name="line-132"></a>tryReadTMQueue (TMQueue closed queue) = do
<a name="line-133"></a> b <- isEmptyTQueue queue
<a name="line-134"></a> b' <- readTVar closed
<a name="line-135"></a> if b && b'
<a name="line-136"></a> then return Nothing
<a name="line-137"></a> else Just <$> tryReadTQueue queue
<a name="line-138"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-139"></a>-}</span>
<a name="line-140"></a>
<a name="line-141"></a>
<a name="line-142"></a><a name="peekTMQueue"></a><span class='hs-comment'>-- | Get the next value from the @TMQueue@ without removing it,</span>
<a name="line-143"></a><span class='hs-comment'>-- retrying if the queue is empty.</span>
<a name="line-144"></a><span class='hs-definition'>peekTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-145"></a><span class='hs-definition'>peekTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-146"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-147"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-148"></a> <span class='hs-keyword'>then</span> <span class='hs-keyword'>do</span>
<a name="line-149"></a> <span class='hs-varid'>b'</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>isEmptyTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-150"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b'</span>
<a name="line-151"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span>
<a name="line-152"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>peekTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-153"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>peekTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-154"></a><span class='hs-comment'>{-
<a name="line-155"></a>-- The above is lazier reading from @queue@ than the clearer:
<a name="line-156"></a>peekTMQueue (TMQueue closed queue) = do
<a name="line-157"></a> b <- isEmptyTQueue queue
<a name="line-158"></a> b' <- readTVar closed
<a name="line-159"></a> if b && b'
<a name="line-160"></a> then return Nothing
<a name="line-161"></a> else Just <$> peekTQueue queue
<a name="line-162"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-163"></a>-}</span>
<a name="line-164"></a>
<a name="line-165"></a>
<a name="line-166"></a><a name="tryPeekTMQueue"></a><span class='hs-comment'>-- | A version of 'peekTMQueue' which does not retry. Instead it</span>
<a name="line-167"></a><span class='hs-comment'>-- returns @Just Nothing@ if the queue is open but no value is</span>
<a name="line-168"></a><span class='hs-comment'>-- available; it still returns @Nothing@ if the queue is closed</span>
<a name="line-169"></a><span class='hs-comment'>-- and empty.</span>
<a name="line-170"></a><span class='hs-definition'>tryPeekTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-171"></a><span class='hs-definition'>tryPeekTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-172"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-173"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-174"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>fmap</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>tryPeekTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-175"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>tryPeekTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-176"></a><span class='hs-comment'>{-
<a name="line-177"></a>-- The above is lazier reading from @queue@ (and removes an extraneous isEmptyTQueue when using the compatibility layer) than the clearer:
<a name="line-178"></a>tryPeekTMQueue (TMQueue closed queue) = do
<a name="line-179"></a> b <- isEmptyTQueue queue
<a name="line-180"></a> b' <- readTVar closed
<a name="line-181"></a> if b && b'
<a name="line-182"></a> then return Nothing
<a name="line-183"></a> else Just <$> tryPeekTQueue queue
<a name="line-184"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-185"></a>-}</span>
<a name="line-186"></a>
<a name="line-187"></a>
<a name="line-188"></a><a name="writeTMQueue"></a><span class='hs-comment'>-- | Write a value to a @TMQueue@. If the queue is closed then the</span>
<a name="line-189"></a><span class='hs-comment'>-- value is silently discarded. Use 'isClosedTMQueue' to determine</span>
<a name="line-190"></a><span class='hs-comment'>-- if the queue is closed before writing, as needed.</span>
<a name="line-191"></a><span class='hs-definition'>writeTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>()</span>
<a name="line-192"></a><span class='hs-definition'>writeTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-193"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-194"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-195"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span> <span class='hs-comment'>-- discard silently</span>
<a name="line-196"></a> <span class='hs-keyword'>else</span> <span class='hs-varid'>writeTQueue</span> <span class='hs-varid'>queue</span> <span class='hs-varid'>x</span>
<a name="line-197"></a>
<a name="line-198"></a>
<a name="line-199"></a><a name="unGetTMQueue"></a><span class='hs-comment'>-- | Put a data item back onto a queue, where it will be the next</span>
<a name="line-200"></a><span class='hs-comment'>-- item read. If the queue is closed then the value is silently</span>
<a name="line-201"></a><span class='hs-comment'>-- discarded; you can use 'peekTMQueue' to circumvent this in certain</span>
<a name="line-202"></a><span class='hs-comment'>-- circumstances.</span>
<a name="line-203"></a><span class='hs-definition'>unGetTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>()</span>
<a name="line-204"></a><span class='hs-definition'>unGetTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-205"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-206"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-207"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span> <span class='hs-comment'>-- discard silently</span>
<a name="line-208"></a> <span class='hs-keyword'>else</span> <span class='hs-varid'>unGetTQueue</span> <span class='hs-varid'>queue</span> <span class='hs-varid'>x</span>
<a name="line-209"></a>
<a name="line-210"></a>
<a name="line-211"></a><a name="closeTMQueue"></a><span class='hs-comment'>-- | Closes the @TMQueue@, preventing any further writes.</span>
<a name="line-212"></a><span class='hs-definition'>closeTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>()</span>
<a name="line-213"></a><span class='hs-definition'>closeTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-214"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>closed</span> <span class='hs-conid'>True</span>
<a name="line-215"></a>
<a name="line-216"></a>
<a name="line-217"></a><a name="isClosedTMQueue"></a><span class='hs-comment'>-- | Returns @True@ if the supplied @TMQueue@ has been closed.</span>
<a name="line-218"></a><span class='hs-definition'>isClosedTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Bool</span>
<a name="line-219"></a><span class='hs-definition'>isClosedTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-220"></a> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-221"></a>
<a name="line-222"></a><span class='hs-comment'>{-
<a name="line-223"></a>-- | Returns @True@ if the supplied @TMQueue@ has been closed.
<a name="line-224"></a>isClosedTMQueueIO :: TMQueue a -> IO Bool
<a name="line-225"></a>isClosedTMQueueIO (TMQueue closed _queue) =
<a name="line-226"></a> readTVarIO closed
<a name="line-227"></a>-}</span>
<a name="line-228"></a>
<a name="line-229"></a>
<a name="line-230"></a><a name="isEmptyTMQueue"></a><span class='hs-comment'>-- | Returns @True@ if the supplied @TMQueue@ is empty.</span>
<a name="line-231"></a><span class='hs-definition'>isEmptyTMQueue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TMQueue</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Bool</span>
<a name="line-232"></a><span class='hs-definition'>isEmptyTMQueue</span> <span class='hs-layout'>(</span><span class='hs-conid'>TMQueue</span> <span class='hs-sel'>_closed</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-233"></a> <span class='hs-varid'>isEmptyTQueue</span> <span class='hs-varid'>queue</span>
<a name="line-234"></a>
<a name="line-235"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-236"></a><span class='hs-comment'>----------------------------------------------------------- fin.</span>
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