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<pre><a name="line-1"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-2"></a><span class='hs-comment'>-- |</span>
<a name="line-3"></a><span class='hs-comment'>-- Module : Data.Unique</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2001</span>
<a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-6"></a><span class='hs-comment'>-- </span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-8"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-9"></a><span class='hs-comment'>-- Portability : non-portable</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- An abstract interface to a unique symbol generator.</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-14"></a>
<a name="line-15"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Unique</span> <span class='hs-layout'>(</span>
<a name="line-16"></a> <span class='hs-comment'>-- * Unique objects</span>
<a name="line-17"></a> <span class='hs-conid'>Unique</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- instance (Eq, Ord)</span>
<a name="line-18"></a> <span class='hs-varid'>newUnique</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: IO Unique</span>
<a name="line-19"></a> <span class='hs-varid'>hashUnique</span> <span class='hs-comment'>-- :: Unique -> Int</span>
<a name="line-20"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-21"></a>
<a name="line-22"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span>
<a name="line-23"></a>
<a name="line-24"></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-25"></a>
<a name="line-26"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-27"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span>
<a name="line-28"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Num</span>
<a name="line-29"></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-30"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span>
<a name="line-31"></a><span class='hs-cpp'>#endif</span>
<a name="line-32"></a>
<a name="line-33"></a><a name="Unique"></a><span class='hs-comment'>-- | An abstract unique object. Objects of type 'Unique' may be</span>
<a name="line-34"></a><a name="Unique"></a><span class='hs-comment'>-- compared for equality and ordering and hashed into 'Int'.</span>
<a name="line-35"></a><a name="Unique"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>Unique</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Unique</span> <span class='hs-conid'>Integer</span> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Eq</span><span class='hs-layout'>,</span><span class='hs-conid'>Ord</span>
<a name="line-36"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-37"></a> <span class='hs-layout'>,</span><span class='hs-conid'>Typeable</span>
<a name="line-38"></a><span class='hs-cpp'>#endif</span>
<a name="line-39"></a> <span class='hs-layout'>)</span>
<a name="line-40"></a>
<a name="line-41"></a><a name="uniqSource"></a><span class='hs-definition'>uniqSource</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TVar</span> <span class='hs-conid'>Integer</span>
<a name="line-42"></a><span class='hs-definition'>uniqSource</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafePerformIO</span> <span class='hs-layout'>(</span><span class='hs-varid'>newTVarIO</span> <span class='hs-num'>0</span><span class='hs-layout'>)</span>
<a name="line-43"></a><span class='hs-comment'>{-# NOINLINE uniqSource #-}</span>
<a name="line-44"></a>
<a name="line-45"></a><a name="newUnique"></a><span class='hs-comment'>-- | Creates a new object of type 'Unique'. The value returned will</span>
<a name="line-46"></a><span class='hs-comment'>-- not compare equal to any other value of type 'Unique' returned by</span>
<a name="line-47"></a><span class='hs-comment'>-- previous calls to 'newUnique'. There is no limit on the number of</span>
<a name="line-48"></a><span class='hs-comment'>-- times 'newUnique' may be called.</span>
<a name="line-49"></a><span class='hs-definition'>newUnique</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-conid'>Unique</span>
<a name="line-50"></a><span class='hs-definition'>newUnique</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>atomically</span> <span class='hs-varop'>$</span> <span class='hs-keyword'>do</span>
<a name="line-51"></a> <span class='hs-varid'>val</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>uniqSource</span>
<a name="line-52"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>next</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>val</span><span class='hs-varop'>+</span><span class='hs-num'>1</span>
<a name="line-53"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>uniqSource</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>next</span>
<a name="line-54"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Unique</span> <span class='hs-varid'>next</span><span class='hs-layout'>)</span>
<a name="line-55"></a>
<a name="line-56"></a><span class='hs-comment'>-- SDM (18/3/2010): changed from MVar to STM. This fixes</span>
<a name="line-57"></a><span class='hs-comment'>-- 1. there was no async exception protection</span>
<a name="line-58"></a><span class='hs-comment'>-- 2. there was a space leak (now new value is strict)</span>
<a name="line-59"></a><span class='hs-comment'>-- 3. using atomicModifyIORef would be slightly quicker, but can</span>
<a name="line-60"></a><span class='hs-comment'>-- suffer from adverse scheduling issues (see #3838)</span>
<a name="line-61"></a><span class='hs-comment'>-- 4. also, the STM version is faster.</span>
<a name="line-62"></a>
<a name="line-63"></a><a name="hashUnique"></a><span class='hs-comment'>-- | Hashes a 'Unique' into an 'Int'. Two 'Unique's may hash to the</span>
<a name="line-64"></a><span class='hs-comment'>-- same value, although in practice this is unlikely. The 'Int'</span>
<a name="line-65"></a><span class='hs-comment'>-- returned makes a good hash key.</span>
<a name="line-66"></a><span class='hs-definition'>hashUnique</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Unique</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Int</span>
<a name="line-67"></a><span class='hs-cpp'>#if defined(__GLASGOW_HASKELL__)</span>
<a name="line-68"></a><span class='hs-definition'>hashUnique</span> <span class='hs-layout'>(</span><span class='hs-conid'>Unique</span> <span class='hs-varid'>i</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>I</span><span class='hs-cpp'>#</span> <span class='hs-layout'>(</span><span class='hs-varid'>hashInteger</span> <span class='hs-varid'>i</span><span class='hs-layout'>)</span>
<a name="line-69"></a><span class='hs-cpp'>#else</span>
<a name="line-70"></a><span class='hs-definition'>hashUnique</span> <span class='hs-layout'>(</span><span class='hs-conid'>Unique</span> <span class='hs-varid'>u</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fromInteger</span> <span class='hs-layout'>(</span><span class='hs-varid'>u</span> <span class='hs-varop'>`mod`</span> <span class='hs-layout'>(</span><span class='hs-varid'>toInteger</span> <span class='hs-layout'>(</span><span class='hs-varid'>maxBound</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span><span class='hs-layout'>)</span> <span class='hs-varop'>+</span> <span class='hs-num'>1</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-71"></a><span class='hs-cpp'>#endif</span>
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