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<title>XMonad/Util/SpawnOnce.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE DeriveDataTypeable #-}</span>
<a name="line-2"></a>
<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 : XMonad.Util.SpawnOnce</span>
<a name="line-6"></a><span class='hs-comment'>-- Copyright : (c) Spencer Janssen 2009</span>
<a name="line-7"></a><span class='hs-comment'>-- License : BSD3-style (see LICENSE)</span>
<a name="line-8"></a><span class='hs-comment'>--</span>
<a name="line-9"></a><span class='hs-comment'>-- Maintainer : spencerjanssen@gmail.com</span>
<a name="line-10"></a><span class='hs-comment'>-- Stability : unstable</span>
<a name="line-11"></a><span class='hs-comment'>-- Portability : not portable</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-- A module for spawning a command once, and only once. Useful to start</span>
<a name="line-14"></a><span class='hs-comment'>-- status bars and make session settings inside startupHook.</span>
<a name="line-15"></a><span class='hs-comment'>--</span>
<a name="line-16"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
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<a name="line-18"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>XMonad</span><span class='hs-varop'>.</span><span class='hs-conid'>Util</span><span class='hs-varop'>.</span><span class='hs-conid'>SpawnOnce</span> <span class='hs-layout'>(</span><span class='hs-varid'>spawnOnce</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-19"></a>
<a name="line-20"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>XMonad</span>
<a name="line-21"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Set</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Set</span>
<a name="line-22"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>XMonad</span><span class='hs-varop'>.</span><span class='hs-conid'>Util</span><span class='hs-varop'>.</span><span class='hs-conid'>ExtensibleState</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>XS</span>
<a name="line-23"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span>
<a name="line-24"></a>
<a name="line-25"></a><a name="SpawnOnce"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>SpawnOnce</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SpawnOnce</span> <span class='hs-layout'>{</span> <span class='hs-varid'>unspawnOnce</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>Set</span> <span class='hs-conid'>String</span><span class='hs-layout'>)</span> <span class='hs-layout'>}</span>
<a name="line-26"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Read</span><span class='hs-layout'>,</span> <span class='hs-conid'>Show</span><span class='hs-layout'>,</span> <span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-27"></a>
<a name="line-28"></a><a name="instance%20ExtensionClass%20SpawnOnce"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-conid'>SpawnOnce</span> <span class='hs-keyword'>where</span>
<a name="line-29"></a> <span class='hs-varid'>initialValue</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SpawnOnce</span> <span class='hs-conid'>Set</span><span class='hs-varop'>.</span><span class='hs-varid'>empty</span>
<a name="line-30"></a> <span class='hs-varid'>extensionType</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>PersistentExtension</span>
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<a name="line-32"></a><a name="spawnOnce"></a><span class='hs-comment'>-- | The first time 'spawnOnce' is executed on a particular command, that</span>
<a name="line-33"></a><span class='hs-comment'>-- command is executed. Subsequent invocations for a command do nothing.</span>
<a name="line-34"></a><span class='hs-definition'>spawnOnce</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>String</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-conid'>()</span>
<a name="line-35"></a><span class='hs-definition'>spawnOnce</span> <span class='hs-varid'>xs</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-36"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-conid'>XS</span><span class='hs-varop'>.</span><span class='hs-varid'>gets</span> <span class='hs-layout'>(</span><span class='hs-conid'>Set</span><span class='hs-varop'>.</span><span class='hs-varid'>member</span> <span class='hs-varid'>xs</span> <span class='hs-varop'>.</span> <span class='hs-varid'>unspawnOnce</span><span class='hs-layout'>)</span>
<a name="line-37"></a> <span class='hs-varid'>when</span> <span class='hs-layout'>(</span><span class='hs-varid'>not</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span> <span class='hs-keyword'>do</span>
<a name="line-38"></a> <span class='hs-varid'>spawn</span> <span class='hs-varid'>xs</span>
<a name="line-39"></a> <span class='hs-conid'>XS</span><span class='hs-varop'>.</span><span class='hs-varid'>modify</span> <span class='hs-layout'>(</span><span class='hs-conid'>SpawnOnce</span> <span class='hs-varop'>.</span> <span class='hs-conid'>Set</span><span class='hs-varop'>.</span><span class='hs-varid'>insert</span> <span class='hs-varid'>xs</span> <span class='hs-varop'>.</span> <span class='hs-varid'>unspawnOnce</span><span class='hs-layout'>)</span>
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