manuals/chickadee/Channels.html


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* Chickadee: (chickadee).     Game programming toolkit for Guile.

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<span id="Channels"></span><div class="header">
<p>
Previous: <a href="Tweening.html" accesskey="p" rel="prev">Tweening</a>, Up: <a href="Scripting.html" accesskey="u" rel="up">Scripting</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
</div>
<hr />
<span id="Channels-1"></span><h4 class="subsection">5.5.4 Channels</h4>

<p>Channels are a tool for communicating amongst different scripts.  One
script can write a value to the channel and another can read from it.
Reading or writing to a channel suspends that script until there is
someone on the other end of the line to complete the transaction.
</p>
<p>Here&rsquo;s a simplistic example:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">c</span> <span class="syntax-open">(</span><span class="syntax-symbol">make-channel</span><span class="syntax-close">)</span><span class="syntax-close">)</span>

<span class="syntax-open">(</span><span class="syntax-symbol">script</span>
 <span class="syntax-open">(</span><span class="syntax-symbol">forever</span>
  <span class="syntax-open">(</span><span class="syntax-special">let</span> <span class="syntax-open">(</span><span class="syntax-open">(</span><span class="syntax-symbol">item</span> <span class="syntax-open">(</span><span class="syntax-symbol">channel-get</span> <span class="syntax-symbol">c</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
    <span class="syntax-open">(</span><span class="syntax-symbol">pk</span> <span class="syntax-symbol">'got</span> <span class="syntax-symbol">item</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span>

<span class="syntax-open">(</span><span class="syntax-symbol">script</span>
 <span class="syntax-open">(</span><span class="syntax-symbol">channel-put</span> <span class="syntax-symbol">c</span> <span class="syntax-symbol">'sword</span><span class="syntax-close">)</span>
 <span class="syntax-open">(</span><span class="syntax-symbol">channel-put</span> <span class="syntax-symbol">c</span> <span class="syntax-symbol">'shield</span><span class="syntax-close">)</span>
 <span class="syntax-open">(</span><span class="syntax-symbol">channel-put</span> <span class="syntax-symbol">c</span> <span class="syntax-symbol">'potion</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
</pre></div>

<dl>
<dt id="index-make_002dchannel">Procedure: <strong>make-channel</strong></dt>
<dd><p>Return a new channel
</p></dd></dl>

<dl>
<dt id="index-channel_003f">Procedure: <strong>channel?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a channel.
</p></dd></dl>

<dl>
<dt id="index-channel_002dget">Procedure: <strong>channel-get</strong> <em>channel</em></dt>
<dd><p>Retrieve a value from <var>channel</var>.  The current script suspends
until a value is available.
</p></dd></dl>

<dl>
<dt id="index-channel_002dput">Procedure: <strong>channel-put</strong> <em>channel data</em></dt>
<dd><p>Send <var>data</var> to <var>channel</var>.  The current script suspends until
another script is available to retrieve the value.
</p></dd></dl>

<p>A low-level API also exists for using channels outside of a script via
callback procedures:
</p>
<dl>
<dt id="index-channel_002dget_0021">Procedure: <strong>channel-get!</strong> <em>channel proc</em></dt>
<dd><p>Asynchronously retrieve a value from <var>channel</var> and call <var>proc</var>
with that value.
</p></dd></dl>

<dl>
<dt id="index-channel_002dput_0021">Procedure: <strong>channel-put!</strong> <em>channel data [thunk]</em></dt>
<dd><p>Asynchronously send <var>data</var> to <var>channel</var> and call <var>thunk</var>
after it has been received.
</p></dd></dl>

<dl>
<dt id="index-channel_002dclear_0021">Procedure: <strong>channel-clear!</strong> <em>channel</em></dt>
<dd><p>Clear all messages and scripts awaiting messages in <var>channel</var>.
</p></dd></dl>


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