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<pre><a name="line-1"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-2"></a>
<a name="line-3"></a><span class='comment'>{- |
<a name="line-4"></a> Module : Control.Arrow.IOStateListArrow
<a name="line-5"></a> Copyright : Copyright (C) 2005 Uwe Schmidt
<a name="line-6"></a> License : MIT
<a name="line-7"></a>
<a name="line-8"></a> Maintainer : Uwe Schmidt (uwe\@fh-wedel.de)
<a name="line-9"></a> Stability : experimental
<a name="line-10"></a> Portability: portable
<a name="line-11"></a> Version : $Id: IOStateListArrow.hs,v 1.7 2005/09/02 17:09:39 hxml Exp $
<a name="line-12"></a>
<a name="line-13"></a> Implementation of arrows with IO and a state
<a name="line-14"></a>
<a name="line-15"></a>-}</span>
<a name="line-16"></a>
<a name="line-17"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-18"></a>
<a name="line-19"></a><span class='keyword'>module</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span><span class='varop'>.</span><span class='conid'>IOStateListArrow</span>
<a name="line-20"></a> <span class='layout'>(</span> <span class='conid'>IOSLA</span><span class='layout'>(</span><span class='keyglyph'>..</span><span class='layout'>)</span>
<a name="line-21"></a> <span class='layout'>,</span> <span class='varid'>liftSt</span>
<a name="line-22"></a> <span class='layout'>,</span> <span class='varid'>runSt</span>
<a name="line-23"></a> <span class='layout'>)</span>
<a name="line-24"></a><span class='keyword'>where</span>
<a name="line-25"></a>
<a name="line-26"></a><span class='keyword'>import</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span>
<a name="line-27"></a><span class='keyword'>import</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span><span class='varop'>.</span><span class='conid'>ArrowList</span>
<a name="line-28"></a><span class='keyword'>import</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span><span class='varop'>.</span><span class='conid'>ArrowIf</span>
<a name="line-29"></a><span class='keyword'>import</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span><span class='varop'>.</span><span class='conid'>ArrowTree</span>
<a name="line-30"></a><span class='keyword'>import</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span><span class='varop'>.</span><span class='conid'>ArrowState</span>
<a name="line-31"></a><span class='keyword'>import</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Arrow</span><span class='varop'>.</span><span class='conid'>ArrowIO</span>
<a name="line-32"></a>
<a name="line-33"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-34"></a>
<a name="line-35"></a><span class='comment'>-- | list arrow combined with a state and the IO monad</span>
<a name="line-36"></a>
<a name="line-37"></a><a name="IOSLA"></a><span class='keyword'>newtype</span> <span class='conid'>IOSLA</span> <span class='varid'>s</span> <span class='varid'>a</span> <span class='varid'>b</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='layout'>{</span> <span class='varid'>runIOSLA</span> <span class='keyglyph'>::</span> <span class='varid'>s</span> <span class='keyglyph'>-></span> <span class='varid'>a</span> <span class='keyglyph'>-></span> <span class='conid'>IO</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>b</span><span class='keyglyph'>]</span><span class='layout'>)</span> <span class='layout'>}</span>
<a name="line-38"></a>
<a name="line-39"></a><span class='keyword'>instance</span> <span class='conid'>Arrow</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-40"></a> <span class='varid'>arr</span> <span class='varid'>f</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>f</span> <span class='varid'>x</span><span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-41"></a>
<a name="line-42"></a> <span class='conid'>IOSLA</span> <span class='varid'>f</span> <span class='varop'>>>></span> <span class='conid'>IOSLA</span> <span class='varid'>g</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-43"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>ys</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-44"></a> <span class='varid'>sequence'</span> <span class='varid'>s1</span> <span class='varid'>ys</span>
<a name="line-45"></a> <span class='keyword'>where</span>
<a name="line-46"></a> <span class='varid'>sequence'</span> <span class='varid'>s'</span> <span class='conid'>[]</span> <span class='keyglyph'>=</span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s'</span><span class='layout'>,</span> <span class='conid'>[]</span><span class='layout'>)</span>
<a name="line-47"></a> <span class='varid'>sequence'</span> <span class='varid'>s'</span> <span class='layout'>(</span><span class='varid'>x'</span><span class='conop'>:</span><span class='varid'>xs'</span><span class='layout'>)</span> <span class='keyglyph'>=</span> <span class='keyword'>do</span>
<a name="line-48"></a> <span class='layout'>(</span><span class='varid'>s1'</span><span class='layout'>,</span> <span class='varid'>ys'</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>g</span> <span class='varid'>s'</span> <span class='varid'>x'</span>
<a name="line-49"></a> <span class='layout'>(</span><span class='varid'>s2'</span><span class='layout'>,</span> <span class='varid'>zs'</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>sequence'</span> <span class='varid'>s1'</span> <span class='varid'>xs'</span>
<a name="line-50"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s2'</span><span class='layout'>,</span> <span class='varid'>ys'</span> <span class='varop'>++</span> <span class='varid'>zs'</span><span class='layout'>)</span>
<a name="line-51"></a>
<a name="line-52"></a> <span class='varid'>first</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='layout'>(</span><span class='varid'>x1</span><span class='layout'>,</span> <span class='varid'>x2</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-53"></a> <span class='layout'>(</span><span class='varid'>s'</span><span class='layout'>,</span> <span class='varid'>ys1</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x1</span>
<a name="line-54"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s'</span><span class='layout'>,</span> <span class='keyglyph'>[</span> <span class='layout'>(</span><span class='varid'>y1</span><span class='layout'>,</span> <span class='varid'>x2</span><span class='layout'>)</span> <span class='keyglyph'>|</span> <span class='varid'>y1</span> <span class='keyglyph'><-</span> <span class='varid'>ys1</span> <span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-55"></a>
<a name="line-56"></a> <span class='comment'>-- just for efficiency</span>
<a name="line-57"></a> <span class='varid'>second</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>g</span><span class='layout'>)</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='layout'>(</span><span class='varid'>x1</span><span class='layout'>,</span> <span class='varid'>x2</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-58"></a> <span class='layout'>(</span><span class='varid'>s'</span><span class='layout'>,</span> <span class='varid'>ys2</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>g</span> <span class='varid'>s</span> <span class='varid'>x2</span>
<a name="line-59"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s'</span><span class='layout'>,</span> <span class='keyglyph'>[</span> <span class='layout'>(</span><span class='varid'>x1</span><span class='layout'>,</span> <span class='varid'>y2</span><span class='layout'>)</span> <span class='keyglyph'>|</span> <span class='varid'>y2</span> <span class='keyglyph'><-</span> <span class='varid'>ys2</span> <span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-60"></a>
<a name="line-61"></a> <span class='comment'>-- just for efficiency</span>
<a name="line-62"></a> <span class='conid'>IOSLA</span> <span class='varid'>f</span> <span class='varop'>***</span> <span class='conid'>IOSLA</span> <span class='varid'>g</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='layout'>(</span><span class='varid'>x1</span><span class='layout'>,</span> <span class='varid'>x2</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-63"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>ys1</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x1</span>
<a name="line-64"></a> <span class='layout'>(</span><span class='varid'>s2</span><span class='layout'>,</span> <span class='varid'>ys2</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>g</span> <span class='varid'>s1</span> <span class='varid'>x2</span>
<a name="line-65"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s2</span><span class='layout'>,</span> <span class='keyglyph'>[</span> <span class='layout'>(</span><span class='varid'>y1</span><span class='layout'>,</span> <span class='varid'>y2</span><span class='layout'>)</span> <span class='keyglyph'>|</span> <span class='varid'>y1</span> <span class='keyglyph'><-</span> <span class='varid'>ys1</span><span class='layout'>,</span> <span class='varid'>y2</span> <span class='keyglyph'><-</span> <span class='varid'>ys2</span> <span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-66"></a>
<a name="line-67"></a> <span class='comment'>-- just for efficiency</span>
<a name="line-68"></a> <span class='conid'>IOSLA</span> <span class='varid'>f</span> <span class='varop'>&&&</span> <span class='conid'>IOSLA</span> <span class='varid'>g</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-69"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>ys1</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-70"></a> <span class='layout'>(</span><span class='varid'>s2</span><span class='layout'>,</span> <span class='varid'>ys2</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>g</span> <span class='varid'>s1</span> <span class='varid'>x</span>
<a name="line-71"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s2</span><span class='layout'>,</span> <span class='keyglyph'>[</span> <span class='layout'>(</span><span class='varid'>y1</span><span class='layout'>,</span> <span class='varid'>y2</span><span class='layout'>)</span> <span class='keyglyph'>|</span> <span class='varid'>y1</span> <span class='keyglyph'><-</span> <span class='varid'>ys1</span><span class='layout'>,</span> <span class='varid'>y2</span> <span class='keyglyph'><-</span> <span class='varid'>ys2</span> <span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-72"></a>
<a name="line-73"></a>
<a name="line-74"></a>
<a name="line-75"></a><span class='keyword'>instance</span> <span class='conid'>ArrowZero</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-76"></a> <span class='varid'>zeroArrow</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='keyglyph'>-></span> <span class='varid'>const</span> <span class='layout'>(</span><span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='conid'>[]</span><span class='layout'>)</span><span class='layout'>)</span>
<a name="line-77"></a>
<a name="line-78"></a>
<a name="line-79"></a><span class='keyword'>instance</span> <span class='conid'>ArrowPlus</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-80"></a> <span class='conid'>IOSLA</span> <span class='varid'>f</span> <span class='varop'><+></span> <span class='conid'>IOSLA</span> <span class='varid'>g</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-81"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>rs1</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-82"></a> <span class='layout'>(</span><span class='varid'>s2</span><span class='layout'>,</span> <span class='varid'>rs2</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>g</span> <span class='varid'>s1</span> <span class='varid'>x</span>
<a name="line-83"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s2</span><span class='layout'>,</span> <span class='varid'>rs1</span> <span class='varop'>++</span> <span class='varid'>rs2</span><span class='layout'>)</span>
<a name="line-84"></a>
<a name="line-85"></a><span class='keyword'>instance</span> <span class='conid'>ArrowChoice</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-86"></a> <span class='varid'>left</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='keyglyph'>-></span> <span class='varid'>either</span>
<a name="line-87"></a> <span class='layout'>(</span><span class='keyglyph'>\</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-88"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>y</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-89"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>map</span> <span class='conid'>Left</span> <span class='varid'>y</span><span class='layout'>)</span>
<a name="line-90"></a> <span class='layout'>)</span>
<a name="line-91"></a> <span class='layout'>(</span><span class='keyglyph'>\</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='conid'>Right</span> <span class='varid'>x</span><span class='keyglyph'>]</span><span class='layout'>)</span><span class='layout'>)</span>
<a name="line-92"></a>
<a name="line-93"></a> <span class='varid'>right</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='keyglyph'>-></span> <span class='varid'>either</span>
<a name="line-94"></a> <span class='layout'>(</span><span class='keyglyph'>\</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='conid'>Left</span> <span class='varid'>x</span><span class='keyglyph'>]</span><span class='layout'>)</span><span class='layout'>)</span>
<a name="line-95"></a> <span class='layout'>(</span><span class='keyglyph'>\</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-96"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>y</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-97"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>map</span> <span class='conid'>Right</span> <span class='varid'>y</span><span class='layout'>)</span>
<a name="line-98"></a> <span class='layout'>)</span>
<a name="line-99"></a>
<a name="line-100"></a><span class='keyword'>instance</span> <span class='conid'>ArrowApply</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-101"></a> <span class='varid'>app</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>,</span> <span class='varid'>x</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-102"></a>
<a name="line-103"></a><span class='keyword'>instance</span> <span class='conid'>ArrowList</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-104"></a> <span class='varid'>arrL</span> <span class='varid'>f</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='layout'>(</span><span class='varid'>f</span> <span class='varid'>x</span><span class='layout'>)</span><span class='layout'>)</span>
<a name="line-105"></a> <span class='varid'>arr2A</span> <span class='varid'>f</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='layout'>(</span><span class='varid'>x</span><span class='layout'>,</span> <span class='varid'>y</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='varid'>runIOSLA</span> <span class='layout'>(</span><span class='varid'>f</span> <span class='varid'>x</span><span class='layout'>)</span> <span class='varid'>s</span> <span class='varid'>y</span>
<a name="line-106"></a> <span class='varid'>constA</span> <span class='varid'>c</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='keyglyph'>-></span> <span class='varid'>const</span> <span class='layout'>(</span><span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>c</span><span class='keyglyph'>]</span><span class='layout'>)</span><span class='layout'>)</span>
<a name="line-107"></a> <span class='varid'>isA</span> <span class='varid'>p</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyword'>if</span> <span class='varid'>p</span> <span class='varid'>x</span> <span class='keyword'>then</span> <span class='keyglyph'>[</span><span class='varid'>x</span><span class='keyglyph'>]</span> <span class='keyword'>else</span> <span class='conid'>[]</span><span class='layout'>)</span>
<a name="line-108"></a> <span class='conid'>IOSLA</span> <span class='varid'>f</span> <span class='varop'>>>.</span> <span class='varid'>g</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-109"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>ys</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-110"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>g</span> <span class='varid'>ys</span><span class='layout'>)</span>
<a name="line-111"></a> <span class='comment'>-- just for efficency</span>
<a name="line-112"></a> <span class='varid'>perform</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-113"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='sel'>_ys</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-114"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>x</span><span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-115"></a>
<a name="line-116"></a><span class='keyword'>instance</span> <span class='conid'>ArrowIf</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-117"></a> <span class='varid'>ifA</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>p</span><span class='layout'>)</span> <span class='varid'>ta</span> <span class='varid'>ea</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-118"></a> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>res</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>p</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-119"></a> <span class='varid'>runIOSLA</span> <span class='layout'>(</span> <span class='keyword'>if</span> <span class='varid'>null</span> <span class='varid'>res</span>
<a name="line-120"></a> <span class='keyword'>then</span> <span class='varid'>ea</span>
<a name="line-121"></a> <span class='keyword'>else</span> <span class='varid'>ta</span>
<a name="line-122"></a> <span class='layout'>)</span> <span class='varid'>s1</span> <span class='varid'>x</span>
<a name="line-123"></a>
<a name="line-124"></a> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span> <span class='varop'>`orElse`</span> <span class='varid'>g</span>
<a name="line-125"></a> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-126"></a> <span class='varid'>r</span><span class='keyglyph'>@</span><span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>res</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s</span> <span class='varid'>x</span>
<a name="line-127"></a> <span class='keyword'>if</span> <span class='varid'>null</span> <span class='varid'>res</span>
<a name="line-128"></a> <span class='keyword'>then</span> <span class='varid'>runIOSLA</span> <span class='varid'>g</span> <span class='varid'>s1</span> <span class='varid'>x</span>
<a name="line-129"></a> <span class='keyword'>else</span> <span class='varid'>return</span> <span class='varid'>r</span>
<a name="line-130"></a>
<a name="line-131"></a>
<a name="line-132"></a><span class='keyword'>instance</span> <span class='conid'>ArrowIO</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-133"></a> <span class='varid'>arrIO</span> <span class='varid'>cmd</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-134"></a> <span class='varid'>res</span> <span class='keyglyph'><-</span> <span class='varid'>cmd</span> <span class='varid'>x</span>
<a name="line-135"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>res</span><span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-136"></a>
<a name="line-137"></a><span class='keyword'>instance</span> <span class='conid'>ArrowIOIf</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-138"></a> <span class='varid'>isIOA</span> <span class='varid'>p</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-139"></a> <span class='varid'>res</span> <span class='keyglyph'><-</span> <span class='varid'>p</span> <span class='varid'>x</span>
<a name="line-140"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyword'>if</span> <span class='varid'>res</span> <span class='keyword'>then</span> <span class='keyglyph'>[</span><span class='varid'>x</span><span class='keyglyph'>]</span> <span class='keyword'>else</span> <span class='conid'>[]</span><span class='layout'>)</span>
<a name="line-141"></a>
<a name="line-142"></a><span class='keyword'>instance</span> <span class='conid'>ArrowState</span> <span class='varid'>s</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-143"></a> <span class='varid'>changeState</span> <span class='varid'>cf</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>let</span> <span class='varid'>s'</span> <span class='keyglyph'>=</span> <span class='varid'>cf</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyword'>in</span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>seq</span> <span class='varid'>s'</span> <span class='varid'>s'</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>x</span><span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-144"></a> <span class='varid'>accessState</span> <span class='varid'>af</span> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s</span><span class='layout'>,</span> <span class='keyglyph'>[</span><span class='varid'>af</span> <span class='varid'>s</span> <span class='varid'>x</span><span class='keyglyph'>]</span><span class='layout'>)</span>
<a name="line-145"></a>
<a name="line-146"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-147"></a>
<a name="line-148"></a><span class='comment'>-- |</span>
<a name="line-149"></a><span class='comment'>-- lift the state of an IOSLA arrow to a state with an additional component.</span>
<a name="line-150"></a><span class='comment'>--</span>
<a name="line-151"></a><span class='comment'>-- This is uesful, when running predefined IO arrows, e.g. for document input,</span>
<a name="line-152"></a><span class='comment'>-- in a context with a more complex state component.</span>
<a name="line-153"></a>
<a name="line-154"></a><a name="liftSt"></a><span class='definition'>liftSt</span> <span class='keyglyph'>::</span> <span class='conid'>IOSLA</span> <span class='varid'>s1</span> <span class='varid'>b</span> <span class='varid'>c</span> <span class='keyglyph'>-></span> <span class='conid'>IOSLA</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>s2</span><span class='layout'>)</span> <span class='varid'>b</span> <span class='varid'>c</span>
<a name="line-155"></a><span class='definition'>liftSt</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span>
<a name="line-156"></a> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>s2</span><span class='layout'>)</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-157"></a> <span class='layout'>(</span><span class='varid'>s1'</span><span class='layout'>,</span> <span class='varid'>ys</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='varid'>s1</span> <span class='varid'>x</span>
<a name="line-158"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='layout'>(</span><span class='varid'>s1'</span><span class='layout'>,</span> <span class='varid'>s2</span><span class='layout'>)</span><span class='layout'>,</span> <span class='varid'>ys</span><span class='layout'>)</span>
<a name="line-159"></a>
<a name="line-160"></a>
<a name="line-161"></a><span class='comment'>-- |</span>
<a name="line-162"></a><span class='comment'>-- run an arrow with augmented state in the context of a simple state arrow.</span>
<a name="line-163"></a><span class='comment'>-- An initial value for the new state component is needed.</span>
<a name="line-164"></a><span class='comment'>--</span>
<a name="line-165"></a><span class='comment'>-- This is useful, when running an arrow with an extra environment component, e.g.</span>
<a name="line-166"></a><span class='comment'>-- for namespace handling in XML.</span>
<a name="line-167"></a>
<a name="line-168"></a><a name="runSt"></a><span class='definition'>runSt</span> <span class='keyglyph'>::</span> <span class='varid'>s2</span> <span class='keyglyph'>-></span> <span class='conid'>IOSLA</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>s2</span><span class='layout'>)</span> <span class='varid'>b</span> <span class='varid'>c</span> <span class='keyglyph'>-></span> <span class='conid'>IOSLA</span> <span class='varid'>s1</span> <span class='varid'>b</span> <span class='varid'>c</span>
<a name="line-169"></a><span class='definition'>runSt</span> <span class='varid'>s2</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>f</span><span class='layout'>)</span>
<a name="line-170"></a> <span class='keyglyph'>=</span> <span class='conid'>IOSLA</span> <span class='varop'>$</span> <span class='keyglyph'>\</span> <span class='varid'>s1</span> <span class='varid'>x</span> <span class='keyglyph'>-></span> <span class='keyword'>do</span>
<a name="line-171"></a> <span class='layout'>(</span><span class='layout'>(</span><span class='varid'>s1'</span><span class='layout'>,</span> <span class='sel'>_s2'</span><span class='layout'>)</span><span class='layout'>,</span> <span class='varid'>ys</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>f</span> <span class='layout'>(</span><span class='varid'>s1</span><span class='layout'>,</span> <span class='varid'>s2</span><span class='layout'>)</span> <span class='varid'>x</span>
<a name="line-172"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s1'</span><span class='layout'>,</span> <span class='varid'>ys</span><span class='layout'>)</span>
<a name="line-173"></a>
<a name="line-174"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-175"></a>
<a name="line-176"></a><span class='keyword'>instance</span> <span class='conid'>ArrowTree</span> <span class='layout'>(</span><span class='conid'>IOSLA</span> <span class='varid'>s</span><span class='layout'>)</span>
<a name="line-177"></a>
<a name="line-178"></a>
<a name="line-179"></a><span class='comment'>-- ------------------------------------------------------------</span>
</pre></body>
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