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<title>Data/Conduit/Util/Source.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE RankNTypes #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE FlexibleContexts #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE TypeFamilies #-}</span>
<a name="line-4"></a><span class='hs-comment'>{-# LANGUAGE CPP #-}</span>
<a name="line-5"></a><span class='hs-comment'>-- | Utilities for constructing and converting 'Source', 'Source' and</span>
<a name="line-6"></a><span class='hs-comment'>-- 'BSource' types. Please see "Data.Conduit.Types.Source" for more information</span>
<a name="line-7"></a><span class='hs-comment'>-- on the base types.</span>
<a name="line-8"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Conduit</span><span class='hs-varop'>.</span><span class='hs-conid'>Util</span><span class='hs-varop'>.</span><span class='hs-conid'>Source</span>
<a name="line-9"></a> <span class='hs-layout'>(</span> <span class='hs-varid'>sourceState</span>
<a name="line-10"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>sourceStateIO</span>
<a name="line-11"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>SourceStateResult</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-12"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>sourceIO</span>
<a name="line-13"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>SourceIOResult</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-14"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>transSource</span>
<a name="line-15"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-16"></a>
<a name="line-17"></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'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Resource</span>
<a name="line-18"></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'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span><span class='hs-varid'>lift</span><span class='hs-layout'>)</span>
<a name="line-19"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Conduit</span><span class='hs-varop'>.</span><span class='hs-conid'>Types</span><span class='hs-varop'>.</span><span class='hs-conid'>Source</span>
<a name="line-20"></a>
<a name="line-21"></a><a name="SourceStateResult"></a><span class='hs-comment'>-- | The return value when pulling in the @sourceState@ function. Either</span>
<a name="line-22"></a><a name="SourceStateResult"></a><span class='hs-comment'>-- indicates no more data, or the next value and an updated state.</span>
<a name="line-23"></a><a name="SourceStateResult"></a><span class='hs-comment'>--</span>
<a name="line-24"></a><a name="SourceStateResult"></a><span class='hs-comment'>-- Since 0.2.0</span>
<a name="line-25"></a><a name="SourceStateResult"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>SourceStateResult</span> <span class='hs-varid'>state</span> <span class='hs-varid'>output</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateOpen</span> <span class='hs-varid'>state</span> <span class='hs-varid'>output</span> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>StateClosed</span>
<a name="line-26"></a>
<a name="line-27"></a><a name="sourceState"></a><span class='hs-comment'>-- | Construct a 'Source' with some stateful functions. This function addresses</span>
<a name="line-28"></a><span class='hs-comment'>-- threading the state value for you.</span>
<a name="line-29"></a><span class='hs-comment'>--</span>
<a name="line-30"></a><span class='hs-comment'>-- Since 0.2.0</span>
<a name="line-31"></a><span class='hs-definition'>sourceState</span>
<a name="line-32"></a> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Resource</span> <span class='hs-varid'>m</span>
<a name="line-33"></a> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>state</span> <span class='hs-comment'>-- ^ Initial state</span>
<a name="line-34"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>state</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ResourceT</span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-conid'>SourceStateResult</span> <span class='hs-varid'>state</span> <span class='hs-varid'>output</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ Pull function</span>
<a name="line-35"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Source</span> <span class='hs-varid'>m</span> <span class='hs-varid'>output</span>
<a name="line-36"></a><span class='hs-definition'>sourceState</span> <span class='hs-varid'>state0</span> <span class='hs-varid'>pull0</span> <span class='hs-keyglyph'>=</span>
<a name="line-37"></a> <span class='hs-varid'>src</span> <span class='hs-varid'>state0</span>
<a name="line-38"></a> <span class='hs-keyword'>where</span>
<a name="line-39"></a> <span class='hs-varid'>src</span> <span class='hs-varid'>state</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Source</span> <span class='hs-layout'>(</span><span class='hs-varid'>pull</span> <span class='hs-varid'>state</span><span class='hs-layout'>)</span> <span class='hs-varid'>close</span>
<a name="line-40"></a>
<a name="line-41"></a> <span class='hs-varid'>pull</span> <span class='hs-varid'>state</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-42"></a> <span class='hs-varid'>res</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>pull0</span> <span class='hs-varid'>state</span>
<a name="line-43"></a> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-keyword'>case</span> <span class='hs-varid'>res</span> <span class='hs-keyword'>of</span>
<a name="line-44"></a> <span class='hs-conid'>StateOpen</span> <span class='hs-varid'>state'</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Open</span> <span class='hs-layout'>(</span><span class='hs-varid'>src</span> <span class='hs-varid'>state'</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span>
<a name="line-45"></a> <span class='hs-conid'>StateClosed</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Closed</span>
<a name="line-46"></a>
<a name="line-47"></a> <span class='hs-varid'>close</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span>
<a name="line-48"></a>
<a name="line-49"></a><a name="SourceIOResult"></a><span class='hs-comment'>-- | The return value when pulling in the @sourceIO@ function. Either indicates</span>
<a name="line-50"></a><a name="SourceIOResult"></a><span class='hs-comment'>-- no more data, or the next value.</span>
<a name="line-51"></a><a name="SourceIOResult"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>SourceIOResult</span> <span class='hs-varid'>output</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IOOpen</span> <span class='hs-varid'>output</span> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>IOClosed</span>
<a name="line-52"></a>
<a name="line-53"></a><a name="sourceIO"></a><span class='hs-comment'>-- | Construct a 'Source' based on some IO actions for alloc/release.</span>
<a name="line-54"></a><span class='hs-comment'>--</span>
<a name="line-55"></a><span class='hs-comment'>-- Since 0.2.0</span>
<a name="line-56"></a><span class='hs-definition'>sourceIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ResourceIO</span> <span class='hs-varid'>m</span>
<a name="line-57"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>state</span> <span class='hs-comment'>-- ^ resource and/or state allocation</span>
<a name="line-58"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>state</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ resource and/or state cleanup</span>
<a name="line-59"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>state</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-conid'>SourceIOResult</span> <span class='hs-varid'>output</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ Pull function. Note that this need not explicitly perform any cleanup.</span>
<a name="line-60"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Source</span> <span class='hs-varid'>m</span> <span class='hs-varid'>output</span>
<a name="line-61"></a><span class='hs-definition'>sourceIO</span> <span class='hs-varid'>alloc</span> <span class='hs-varid'>cleanup</span> <span class='hs-varid'>pull0</span> <span class='hs-keyglyph'>=</span>
<a name="line-62"></a> <span class='hs-conid'>Source</span>
<a name="line-63"></a> <span class='hs-layout'>{</span> <span class='hs-varid'>sourcePull</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-64"></a> <span class='hs-layout'>(</span><span class='hs-varid'>key</span><span class='hs-layout'>,</span> <span class='hs-varid'>state</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>withIO</span> <span class='hs-varid'>alloc</span> <span class='hs-varid'>cleanup</span>
<a name="line-65"></a> <span class='hs-varid'>pull</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span>
<a name="line-66"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>sourceClose</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span>
<a name="line-67"></a> <span class='hs-layout'>}</span>
<a name="line-68"></a> <span class='hs-keyword'>where</span>
<a name="line-69"></a> <span class='hs-varid'>src</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Source</span> <span class='hs-layout'>(</span><span class='hs-varid'>pull</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>release</span> <span class='hs-varid'>key</span><span class='hs-layout'>)</span>
<a name="line-70"></a>
<a name="line-71"></a> <span class='hs-varid'>pull</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-72"></a> <span class='hs-varid'>res</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>$</span> <span class='hs-varid'>pull0</span> <span class='hs-varid'>state</span>
<a name="line-73"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>res</span> <span class='hs-keyword'>of</span>
<a name="line-74"></a> <span class='hs-conid'>IOClosed</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-75"></a> <span class='hs-varid'>release</span> <span class='hs-varid'>key</span>
<a name="line-76"></a> <span class='hs-varid'>return</span> <span class='hs-conid'>Closed</span>
<a name="line-77"></a> <span class='hs-conid'>IOOpen</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-conid'>Open</span> <span class='hs-layout'>(</span><span class='hs-varid'>src</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span>
<a name="line-78"></a>
<a name="line-79"></a><a name="sourceStateIO"></a><span class='hs-comment'>-- | A combination of 'sourceIO' and 'sourceState'.</span>
<a name="line-80"></a><span class='hs-comment'>--</span>
<a name="line-81"></a><span class='hs-comment'>-- Since 0.2.1</span>
<a name="line-82"></a><span class='hs-definition'>sourceStateIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ResourceIO</span> <span class='hs-varid'>m</span>
<a name="line-83"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>state</span> <span class='hs-comment'>-- ^ resource and/or state allocation</span>
<a name="line-84"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>state</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ resource and/or state cleanup</span>
<a name="line-85"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>state</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-conid'>SourceStateResult</span> <span class='hs-varid'>state</span> <span class='hs-varid'>output</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ Pull function. Note that this need not explicitly perform any cleanup.</span>
<a name="line-86"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Source</span> <span class='hs-varid'>m</span> <span class='hs-varid'>output</span>
<a name="line-87"></a><span class='hs-definition'>sourceStateIO</span> <span class='hs-varid'>alloc</span> <span class='hs-varid'>cleanup</span> <span class='hs-varid'>pull0</span> <span class='hs-keyglyph'>=</span>
<a name="line-88"></a> <span class='hs-conid'>Source</span>
<a name="line-89"></a> <span class='hs-layout'>{</span> <span class='hs-varid'>sourcePull</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-90"></a> <span class='hs-layout'>(</span><span class='hs-varid'>key</span><span class='hs-layout'>,</span> <span class='hs-varid'>state</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>withIO</span> <span class='hs-varid'>alloc</span> <span class='hs-varid'>cleanup</span>
<a name="line-91"></a> <span class='hs-varid'>pull</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span>
<a name="line-92"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>sourceClose</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span>
<a name="line-93"></a> <span class='hs-layout'>}</span>
<a name="line-94"></a> <span class='hs-keyword'>where</span>
<a name="line-95"></a> <span class='hs-varid'>src</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Source</span> <span class='hs-layout'>(</span><span class='hs-varid'>pull</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>release</span> <span class='hs-varid'>key</span><span class='hs-layout'>)</span>
<a name="line-96"></a>
<a name="line-97"></a> <span class='hs-varid'>pull</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-98"></a> <span class='hs-varid'>res</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>$</span> <span class='hs-varid'>pull0</span> <span class='hs-varid'>state</span>
<a name="line-99"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>res</span> <span class='hs-keyword'>of</span>
<a name="line-100"></a> <span class='hs-conid'>StateClosed</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-101"></a> <span class='hs-varid'>release</span> <span class='hs-varid'>key</span>
<a name="line-102"></a> <span class='hs-varid'>return</span> <span class='hs-conid'>Closed</span>
<a name="line-103"></a> <span class='hs-conid'>StateOpen</span> <span class='hs-varid'>state'</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-conid'>Open</span> <span class='hs-layout'>(</span><span class='hs-varid'>src</span> <span class='hs-varid'>key</span> <span class='hs-varid'>state'</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span>
<a name="line-104"></a>
<a name="line-105"></a><a name="transSource"></a><span class='hs-comment'>-- | Transform the monad a 'Source' lives in.</span>
<a name="line-106"></a><span class='hs-comment'>--</span>
<a name="line-107"></a><span class='hs-comment'>-- Note that this will /not/ thread the individual monads together, meaning</span>
<a name="line-108"></a><span class='hs-comment'>-- side effects will be lost. This function is most useful for transformers</span>
<a name="line-109"></a><span class='hs-comment'>-- only providing context and not producing side-effects, such as @ReaderT@.</span>
<a name="line-110"></a><span class='hs-comment'>--</span>
<a name="line-111"></a><span class='hs-comment'>-- Since 0.2.0</span>
<a name="line-112"></a><span class='hs-definition'>transSource</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>Base</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>~</span> <span class='hs-conid'>Base</span> <span class='hs-varid'>n</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span>
<a name="line-113"></a> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-keyword'>forall</span> <span class='hs-varid'>a</span><span class='hs-varop'>.</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>n</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-114"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Source</span> <span class='hs-varid'>m</span> <span class='hs-varid'>output</span>
<a name="line-115"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Source</span> <span class='hs-varid'>n</span> <span class='hs-varid'>output</span>
<a name="line-116"></a><span class='hs-definition'>transSource</span> <span class='hs-varid'>f</span> <span class='hs-varid'>c</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>c</span>
<a name="line-117"></a> <span class='hs-layout'>{</span> <span class='hs-varid'>sourcePull</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>transResourceT</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-varid'>fmap</span> <span class='hs-varid'>go2</span> <span class='hs-varop'>$</span> <span class='hs-varid'>sourcePull</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span>
<a name="line-118"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>sourceClose</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>transResourceT</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-varid'>sourceClose</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span>
<a name="line-119"></a> <span class='hs-layout'>}</span>
<a name="line-120"></a> <span class='hs-keyword'>where</span>
<a name="line-121"></a> <span class='hs-varid'>go2</span> <span class='hs-layout'>(</span><span class='hs-conid'>Open</span> <span class='hs-varid'>p</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Open</span> <span class='hs-layout'>(</span><span class='hs-varid'>transSource</span> <span class='hs-varid'>f</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span>
<a name="line-122"></a> <span class='hs-varid'>go2</span> <span class='hs-conid'>Closed</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Closed</span>
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