hxt-8.0.0: doc/hdoc/src/Control-Monad-MonadStateIO.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<!-- Generated by HsColour, http://www.cs.york.ac.uk/fp/darcs/hscolour/ -->
<title>Haskell Code by HsColour</title>
<link type='text/css' rel='stylesheet' href='hscolour.css' />
</head>
<body>
<pre><a name="line-1"></a><span class='comment'>-- |</span>
<a name="line-2"></a><span class='comment'>-- general usefull state monad for a local state and IO</span>
<a name="line-3"></a><span class='comment'>--</span>
<a name="line-4"></a><span class='comment'>-- Version : $Id: MonadStateIO.hs,v 1.1 2004/09/02 19:11:55 hxml Exp $</span>
<a name="line-5"></a>
<a name="line-6"></a>
<a name="line-7"></a><span class='keyword'>module</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Monad</span><span class='varop'>.</span><span class='conid'>MonadStateIO</span>
<a name="line-8"></a> <span class='layout'>(</span> <span class='keyword'>module</span> <span class='conid'>Control</span><span class='varop'>.</span><span class='conid'>Monad</span><span class='varop'>.</span><span class='conid'>MonadStateIO</span>
<a name="line-9"></a> <span class='layout'>)</span>
<a name="line-10"></a><span class='keyword'>where</span>
<a name="line-11"></a>
<a name="line-12"></a><span class='keyword'>import</span> <span class='conid'>System</span><span class='varop'>.</span><span class='conid'>IO</span>
<a name="line-13"></a>
<a name="line-14"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-15"></a>
<a name="line-16"></a><a name="StateIO"></a><span class='keyword'>newtype</span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='varid'>res</span> <span class='keyglyph'>=</span> <span class='conid'>STIO</span> <span class='layout'>{</span> <span class='varid'>trans</span> <span class='keyglyph'>::</span> <span class='varid'>state</span> <span class='keyglyph'>-></span> <span class='conid'>IO</span> <span class='layout'>(</span><span class='varid'>res</span><span class='layout'>,</span> <span class='varid'>state</span><span class='layout'>)</span> <span class='layout'>}</span>
<a name="line-17"></a>
<a name="line-18"></a><span class='keyword'>instance</span> <span class='conid'>Monad</span> <span class='layout'>(</span><span class='conid'>StateIO</span> <span class='varid'>state</span><span class='layout'>)</span> <span class='keyword'>where</span>
<a name="line-19"></a> <span class='varid'>return</span> <span class='varid'>v</span>
<a name="line-20"></a> <span class='keyglyph'>=</span> <span class='conid'>STIO</span> <span class='layout'>(</span> <span class='keyglyph'>\</span><span class='varid'>s</span> <span class='keyglyph'>-></span> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>v</span><span class='layout'>,</span> <span class='varid'>s</span><span class='layout'>)</span><span class='layout'>)</span>
<a name="line-21"></a>
<a name="line-22"></a> <span class='conid'>STIO</span> <span class='varid'>cmd</span> <span class='varop'>>>=</span> <span class='varid'>f</span>
<a name="line-23"></a> <span class='keyglyph'>=</span> <span class='conid'>STIO</span> <span class='layout'>(</span> <span class='keyglyph'>\</span><span class='varid'>s</span> <span class='keyglyph'>-></span>
<a name="line-24"></a> <span class='varid'>cmd</span> <span class='varid'>s</span> <span class='varop'>>>=</span> <span class='keyglyph'>\</span> <span class='layout'>(</span><span class='varid'>rl</span><span class='layout'>,</span> <span class='varid'>s'</span><span class='layout'>)</span> <span class='keyglyph'>-></span>
<a name="line-25"></a> <span class='layout'>(</span><span class='varid'>trans</span> <span class='varop'>.</span> <span class='varid'>f</span><span class='layout'>)</span> <span class='varid'>rl</span> <span class='varid'>s'</span>
<a name="line-26"></a> <span class='layout'>)</span>
<a name="line-27"></a>
<a name="line-28"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-29"></a><span class='comment'>-- |</span>
<a name="line-30"></a><span class='comment'>-- lift IO command to 'StateIO'</span>
<a name="line-31"></a>
<a name="line-32"></a><a name="io"></a><span class='definition'>io</span> <span class='keyglyph'>::</span> <span class='conid'>IO</span> <span class='varid'>a</span> <span class='keyglyph'>-></span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='varid'>a</span>
<a name="line-33"></a><span class='definition'>io</span> <span class='varid'>iocmd</span>
<a name="line-34"></a> <span class='keyglyph'>=</span> <span class='conid'>STIO</span> <span class='layout'>(</span> <span class='keyglyph'>\</span><span class='varid'>s</span> <span class='keyglyph'>-></span>
<a name="line-35"></a> <span class='keyword'>do</span>
<a name="line-36"></a> <span class='varid'>a</span> <span class='keyglyph'><-</span> <span class='varid'>iocmd</span>
<a name="line-37"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>a</span><span class='layout'>,</span> <span class='varid'>s</span><span class='layout'>)</span>
<a name="line-38"></a> <span class='layout'>)</span>
<a name="line-39"></a>
<a name="line-40"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-41"></a>
<a name="line-42"></a><span class='comment'>-- |</span>
<a name="line-43"></a><span class='comment'>-- state inspection command: a \"show\"-like function is applied to the state</span>
<a name="line-44"></a><span class='comment'>-- and the result is written to stderr.</span>
<a name="line-45"></a>
<a name="line-46"></a><a name="trcState"></a><span class='definition'>trcState</span> <span class='keyglyph'>::</span> <span class='layout'>(</span><span class='varid'>state</span> <span class='keyglyph'>-></span> <span class='conid'>String</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='conid'>()</span>
<a name="line-47"></a><span class='definition'>trcState</span> <span class='varid'>fct</span>
<a name="line-48"></a> <span class='keyglyph'>=</span> <span class='conid'>STIO</span> <span class='layout'>(</span> <span class='keyglyph'>\</span><span class='varid'>s</span> <span class='keyglyph'>-></span>
<a name="line-49"></a> <span class='keyword'>do</span>
<a name="line-50"></a> <span class='varid'>hPutStr</span> <span class='varid'>stderr</span> <span class='varop'>$</span> <span class='varid'>fct</span> <span class='varid'>s</span>
<a name="line-51"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='conid'>()</span><span class='layout'>,</span> <span class='varid'>s</span><span class='layout'>)</span>
<a name="line-52"></a> <span class='layout'>)</span>
<a name="line-53"></a>
<a name="line-54"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-55"></a><span class='comment'>--</span>
<a name="line-56"></a><span class='comment'>-- state access commands</span>
<a name="line-57"></a>
<a name="line-58"></a><span class='comment'>-- |</span>
<a name="line-59"></a><span class='comment'>-- change the state with a given function and return the new state</span>
<a name="line-60"></a>
<a name="line-61"></a><a name="changeState"></a><span class='definition'>changeState</span> <span class='keyglyph'>::</span> <span class='layout'>(</span><span class='varid'>state</span> <span class='keyglyph'>-></span> <span class='varid'>state</span><span class='layout'>)</span> <span class='keyglyph'>-></span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='varid'>state</span>
<a name="line-62"></a><span class='definition'>changeState</span> <span class='varid'>f</span>
<a name="line-63"></a> <span class='keyglyph'>=</span> <span class='conid'>STIO</span> <span class='layout'>(</span> <span class='keyglyph'>\</span><span class='varid'>s</span> <span class='keyglyph'>-></span>
<a name="line-64"></a> <span class='keyword'>let</span> <span class='varid'>s'</span> <span class='keyglyph'>=</span> <span class='varid'>f</span> <span class='varid'>s</span>
<a name="line-65"></a> <span class='keyword'>in</span>
<a name="line-66"></a> <span class='varid'>return</span> <span class='layout'>(</span><span class='varid'>s'</span><span class='layout'>,</span> <span class='varid'>s'</span><span class='layout'>)</span>
<a name="line-67"></a> <span class='layout'>)</span>
<a name="line-68"></a>
<a name="line-69"></a><span class='comment'>-- |</span>
<a name="line-70"></a><span class='comment'>-- set the state</span>
<a name="line-71"></a>
<a name="line-72"></a><a name="setState"></a><span class='definition'>setState</span> <span class='keyglyph'>::</span> <span class='varid'>state</span> <span class='keyglyph'>-></span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='varid'>state</span>
<a name="line-73"></a><span class='definition'>setState</span> <span class='varid'>s</span>
<a name="line-74"></a> <span class='keyglyph'>=</span> <span class='varid'>changeState</span> <span class='layout'>(</span> <span class='keyglyph'>\</span><span class='keyword'>_</span> <span class='keyglyph'>-></span> <span class='varid'>s</span> <span class='layout'>)</span>
<a name="line-75"></a>
<a name="line-76"></a><span class='comment'>-- |</span>
<a name="line-77"></a><span class='comment'>-- read the state</span>
<a name="line-78"></a>
<a name="line-79"></a><a name="getState"></a><span class='definition'>getState</span> <span class='keyglyph'>::</span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='varid'>state</span>
<a name="line-80"></a><span class='definition'>getState</span>
<a name="line-81"></a> <span class='keyglyph'>=</span> <span class='varid'>changeState</span> <span class='varid'>id</span>
<a name="line-82"></a>
<a name="line-83"></a><span class='comment'>-- ------------------------------------------------------------</span>
<a name="line-84"></a><span class='comment'>-- |</span>
<a name="line-85"></a><span class='comment'>-- run a 'StateIO' command with an initial state</span>
<a name="line-86"></a>
<a name="line-87"></a><a name="run"></a><span class='definition'>run</span> <span class='keyglyph'>::</span> <span class='varid'>state</span> <span class='keyglyph'>-></span> <span class='conid'>StateIO</span> <span class='varid'>state</span> <span class='varid'>res</span> <span class='keyglyph'>-></span> <span class='conid'>IO</span> <span class='varid'>res</span>
<a name="line-88"></a><span class='definition'>run</span> <span class='varid'>initialState</span> <span class='layout'>(</span><span class='conid'>STIO</span> <span class='varid'>cmd</span><span class='layout'>)</span>
<a name="line-89"></a> <span class='keyglyph'>=</span> <span class='keyword'>do</span>
<a name="line-90"></a> <span class='layout'>(</span><span class='varid'>res</span><span class='layout'>,</span> <span class='sel'>_finalState</span><span class='layout'>)</span> <span class='keyglyph'><-</span> <span class='varid'>cmd</span> <span class='varid'>initialState</span>
<a name="line-91"></a> <span class='varid'>return</span> <span class='varid'>res</span>
<a name="line-92"></a>
<a name="line-93"></a>
<a name="line-94"></a><span class='comment'>-- ------------------------------------------------------------</span>
</pre></body>
</html>