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<title>System/Console/Haskeline/Monads.hs</title>
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<pre><a name="line-1"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>Console</span><span class='hs-varop'>.</span><span class='hs-conid'>Haskeline</span><span class='hs-varop'>.</span><span class='hs-conid'>Monads</span><span class='hs-layout'>(</span>
<a name="line-2"></a> <span class='hs-keyword'>module</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>Console</span><span class='hs-varop'>.</span><span class='hs-conid'>Haskeline</span><span class='hs-varop'>.</span><span class='hs-conid'>MonadException</span><span class='hs-layout'>,</span>
<a name="line-3"></a> <span class='hs-conid'>MonadTrans</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-4"></a> <span class='hs-conid'>MonadIO</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-5"></a> <span class='hs-conid'>ReaderT</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-6"></a> <span class='hs-varid'>runReaderT'</span><span class='hs-layout'>,</span>
<a name="line-7"></a> <span class='hs-varid'>mapReaderT</span><span class='hs-layout'>,</span>
<a name="line-8"></a> <span class='hs-varid'>asks</span><span class='hs-layout'>,</span>
<a name="line-9"></a> <span class='hs-conid'>StateT</span><span class='hs-layout'>,</span>
<a name="line-10"></a> <span class='hs-varid'>runStateT</span><span class='hs-layout'>,</span>
<a name="line-11"></a> <span class='hs-varid'>evalStateT'</span><span class='hs-layout'>,</span>
<a name="line-12"></a> <span class='hs-varid'>mapStateT</span><span class='hs-layout'>,</span>
<a name="line-13"></a> <span class='hs-varid'>gets</span><span class='hs-layout'>,</span>
<a name="line-14"></a> <span class='hs-varid'>modify</span><span class='hs-layout'>,</span>
<a name="line-15"></a> <span class='hs-varid'>update</span><span class='hs-layout'>,</span>
<a name="line-16"></a> <span class='hs-conid'>MonadReader</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-17"></a> <span class='hs-conid'>MonadState</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-18"></a> <span class='hs-conid'>MaybeT</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-19"></a> <span class='hs-varid'>orElse</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'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-varid'>liftM</span><span class='hs-layout'>)</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><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadIO</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-24"></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-conid'>MonadTrans</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-25"></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'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-conid'>MaybeT</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-26"></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'>Reader</span> <span class='hs-varid'>hiding</span> <span class='hs-layout'>(</span><span class='hs-varid'>ask</span><span class='hs-layout'>,</span><span class='hs-varid'>asks</span><span class='hs-layout'>)</span>
<a name="line-27"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</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'>Reader</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Reader</span>
<a name="line-28"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>IORef</span>
<a name="line-29"></a><span class='hs-cpp'>#if __GLASGOW_HASKELL__ < 705</span>
<a name="line-30"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span> <span class='hs-varid'>hiding</span> <span class='hs-layout'>(</span><span class='hs-varid'>catch</span><span class='hs-layout'>)</span>
<a name="line-31"></a><span class='hs-cpp'>#endif</span>
<a name="line-32"></a>
<a name="line-33"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>Console</span><span class='hs-varop'>.</span><span class='hs-conid'>Haskeline</span><span class='hs-varop'>.</span><span class='hs-conid'>MonadException</span>
<a name="line-34"></a>
<a name="line-35"></a><a name="MonadReader"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-keyword'>where</span>
<a name="line-36"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span>
<a name="line-37"></a>
<a name="line-38"></a><a name="instance%20MonadReader%20r%20(ReaderT%20r%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>ReaderT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-39"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Reader</span><span class='hs-varop'>.</span><span class='hs-varid'>ask</span>
<a name="line-40"></a>
<a name="line-41"></a><a name="instance%20MonadReader%20s%20(StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-42"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>get</span>
<a name="line-43"></a>
<a name="line-44"></a><a name="instance%20MonadReader%20r%20(t%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadTrans</span> <span class='hs-varid'>t</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-varid'>t</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-varid'>t</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-45"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-46"></a>
<a name="line-47"></a><a name="asks"></a><span class='hs-definition'>asks</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-48"></a><span class='hs-definition'>asks</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>liftM</span> <span class='hs-varid'>f</span> <span class='hs-varid'>ask</span>
<a name="line-49"></a>
<a name="line-50"></a><a name="MonadState"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-keyword'>where</span>
<a name="line-51"></a> <span class='hs-varid'>get</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>s</span>
<a name="line-52"></a> <span class='hs-varid'>put</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-conid'>()</span>
<a name="line-53"></a>
<a name="line-54"></a><a name="gets"></a><span class='hs-definition'>gets</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-55"></a><span class='hs-definition'>gets</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>liftM</span> <span class='hs-varid'>f</span> <span class='hs-varid'>get</span>
<a name="line-56"></a>
<a name="line-57"></a><a name="modify"></a><span class='hs-definition'>modify</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-conid'>()</span>
<a name="line-58"></a><span class='hs-definition'>modify</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>get</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>put</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span>
<a name="line-59"></a>
<a name="line-60"></a><a name="update"></a><span class='hs-definition'>update</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>s</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-61"></a><span class='hs-definition'>update</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-62"></a> <span class='hs-varid'>s</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>get</span>
<a name="line-63"></a> <span class='hs-keyword'>let</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span>
<a name="line-64"></a> <span class='hs-varid'>put</span> <span class='hs-varid'>s'</span>
<a name="line-65"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>x</span>
<a name="line-66"></a>
<a name="line-67"></a><a name="runReaderT'"></a><span class='hs-definition'>runReaderT'</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ReaderT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-68"></a><span class='hs-definition'>runReaderT'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>flip</span> <span class='hs-varid'>runReaderT</span>
<a name="line-69"></a>
<a name="line-70"></a><a name="StateT"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-layout'>{</span> <span class='hs-varid'>getStateTFunc</span>
<a name="line-71"></a> <span class='hs-keyglyph'>::</span> <span class='hs-keyword'>forall</span> <span class='hs-varid'>r</span> <span class='hs-varop'>.</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span><span class='hs-layout'>}</span>
<a name="line-72"></a>
<a name="line-73"></a><a name="instance%20Monad%20(StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-74"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>f</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span> <span class='hs-varid'>s</span>
<a name="line-75"></a> <span class='hs-conid'>StateT</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-76"></a> <span class='hs-varid'>useX</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span>
<a name="line-77"></a> <span class='hs-varid'>useX</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>x</span> <span class='hs-varid'>s'</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>getStateTFunc</span> <span class='hs-layout'>(</span><span class='hs-varid'>g</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-varid'>s'</span>
<a name="line-78"></a>
<a name="line-79"></a><a name="instance%20MonadTrans%20(StateT%20s)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadTrans</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-80"></a> <span class='hs-varid'>lift</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-81"></a> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>m</span>
<a name="line-82"></a> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>f</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span> <span class='hs-varid'>s</span>
<a name="line-83"></a>
<a name="line-84"></a><a name="instance%20MonadIO%20(StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadIO</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-85"></a> <span class='hs-varid'>liftIO</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>liftIO</span>
<a name="line-86"></a>
<a name="line-87"></a><a name="mapStateT"></a><span class='hs-definition'>mapStateT</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-keyword'>forall</span> <span class='hs-varid'>b</span> <span class='hs-varop'>.</span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>n</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>n</span> <span class='hs-varid'>a</span>
<a name="line-88"></a><span class='hs-definition'>mapStateT</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-varid'>m</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-89"></a>
<a name="line-90"></a><a name="runStateT"></a><span class='hs-definition'>runStateT</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span>
<a name="line-91"></a><span class='hs-definition'>runStateT</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-92"></a> <span class='hs-varid'>useXS</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>getStateTFunc</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span>
<a name="line-93"></a> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-varid'>useXS</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>x</span> <span class='hs-varid'>s'</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span>
<a name="line-94"></a>
<a name="line-95"></a><a name="makeStateT"></a><span class='hs-definition'>makeStateT</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>s</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-96"></a><span class='hs-definition'>makeStateT</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-97"></a> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span>
<a name="line-98"></a> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>g</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>g</span> <span class='hs-varid'>x</span> <span class='hs-varid'>s'</span>
<a name="line-99"></a>
<a name="line-100"></a><a name="instance%20MonadState%20s%20(StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-101"></a> <span class='hs-varid'>get</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>f</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span> <span class='hs-varid'>s</span>
<a name="line-102"></a> <span class='hs-varid'>put</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>s</span> <span class='hs-varop'>`seq`</span> <span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>f</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>f</span> <span class='hs-conid'>()</span> <span class='hs-varid'>s</span>
<a name="line-103"></a>
<a name="line-104"></a><a name="instance%20MonadState%20s%20(t%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadTrans</span> <span class='hs-varid'>t</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-varid'>t</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-varid'>t</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-105"></a> <span class='hs-varid'>get</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>get</span>
<a name="line-106"></a> <span class='hs-varid'>put</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>put</span>
<a name="line-107"></a>
<a name="line-108"></a><a name="instance%20MonadState%20s%20(ReaderT%20(IORef%20s)%20m)"></a><span class='hs-comment'>-- ReaderT (IORef s) is better than StateT s for some applications,</span>
<a name="line-109"></a><a name="instance%20MonadState%20s%20(ReaderT%20(IORef%20s)%20m)"></a><span class='hs-comment'>-- since StateT loses its state after an exception such as ctrl-c.</span>
<a name="line-110"></a><a name="instance%20MonadState%20s%20(ReaderT%20(IORef%20s)%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadIO</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>ReaderT</span> <span class='hs-layout'>(</span><span class='hs-conid'>IORef</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-111"></a> <span class='hs-varid'>get</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ask</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>liftIO</span> <span class='hs-varop'>.</span> <span class='hs-varid'>readIORef</span>
<a name="line-112"></a> <span class='hs-varid'>put</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ask</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>liftIO</span> <span class='hs-varop'>.</span> <span class='hs-varid'>flip</span> <span class='hs-varid'>writeIORef</span> <span class='hs-varid'>s</span>
<a name="line-113"></a>
<a name="line-114"></a><a name="evalStateT'"></a><span class='hs-definition'>evalStateT'</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-115"></a><span class='hs-definition'>evalStateT'</span> <span class='hs-varid'>s</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>liftM</span> <span class='hs-varid'>fst</span> <span class='hs-varop'>$</span> <span class='hs-varid'>runStateT</span> <span class='hs-varid'>f</span> <span class='hs-varid'>s</span>
<a name="line-116"></a>
<a name="line-117"></a><a name="instance%20MonadException%20(StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadException</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadException</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-118"></a> <span class='hs-varid'>controlIO</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>makeStateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>controlIO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>run</span> <span class='hs-keyglyph'>-></span>
<a name="line-119"></a> <span class='hs-varid'>fmap</span> <span class='hs-layout'>(</span><span class='hs-varid'>flip</span> <span class='hs-varid'>runStateT</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span> <span class='hs-varid'>f</span> <span class='hs-varop'>$</span> <span class='hs-varid'>stateRunIO</span> <span class='hs-varid'>s</span> <span class='hs-varid'>run</span>
<a name="line-120"></a> <span class='hs-keyword'>where</span>
<a name="line-121"></a> <span class='hs-varid'>stateRunIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RunIO</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>RunIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span>
<a name="line-122"></a> <span class='hs-varid'>stateRunIO</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>RunIO</span> <span class='hs-varid'>run</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>RunIO</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>fmap</span> <span class='hs-layout'>(</span><span class='hs-varid'>makeStateT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>const</span><span class='hs-layout'>)</span>
<a name="line-123"></a> <span class='hs-varop'>$</span> <span class='hs-varid'>run</span> <span class='hs-layout'>(</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>m</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-124"></a>
<a name="line-125"></a><a name="orElse"></a><span class='hs-definition'>orElse</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MaybeT</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-126"></a><span class='hs-definition'>orElse</span> <span class='hs-layout'>(</span><span class='hs-conid'>MaybeT</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>maybe</span> <span class='hs-varid'>g</span> <span class='hs-varid'>return</span>
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