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+<title>Scripts (The Chickadee Game Toolkit)</title>
+
+<meta name="description" content="Scripts (The Chickadee Game Toolkit)">
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+<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
+<link href="Scripting.html#Scripting" rel="up" title="Scripting">
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+<a name="Scripts"></a>
+<div class="header">
+<p>
+Next: <a href="Tweening.html#Tweening" accesskey="n" rel="next">Tweening</a>, Previous: <a href="Agendas.html#Agendas" accesskey="p" rel="prev">Agendas</a>, Up: <a href="Scripting.html#Scripting" 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#Index" title="Index" rel="index">Index</a>]</p>
+</div>
+<hr>
+<a name="Scripts-1"></a>
+<h4 class="subsection">2.4.2 Scripts</h4>
+
+<p>Now that we can schedule tasks, let&rsquo;s take things to the next level.
+It sure would be great if we could make procedures that described a
+series of actions that happened over time, especially if we could do
+so without contorting our code into a nest of callback procedures.
+This is where scripts come in. With scripts we can write code in a
+linear way, in a manner that appears to be synchronous, but with the
+ability to suspend periodically in order to let other scripts have a
+turn and prevent blocking the game loop. Building on top of the
+scheduling that agendas provide, here is a script that models a child
+trying to get their mother&rsquo;s attention:
+</p>
+<div class="example">
+<pre class="example">(script
+ (while #t
+ (display &quot;mom!&quot;)
+ (newline)
+ (sleep 60))) ; where 60 = 1 second of real time
+</pre></div>
+
+<p>This code runs in an endless loop, but the <code>sleep</code> procedure
+suspends the script and schedules it to be run later by the agenda.
+So, after each iteration of the loop, control is returned back to the
+game loop and the program is not stuck spinning in a loop that will
+never exit. Pretty neat, eh?
+</p>
+<p>Scripts can suspend to any capable handler, not just the agenda.
+The <code>yield</code> procedure will suspend the current script and pass
+its &ldquo;continuation&rdquo; to a handler procedure. This handler procedure
+could do anything. Perhaps the handler stashes the continuation
+somewhere where it will be resumed when the user presses a specific
+key on the keyboard, or maybe it will be resumed when the player picks
+up an item off of the dungeon floor; the sky is the limit.
+</p>
+<p>Sometimes it is necessary to abruptly terminate a script after it has
+been started. For example, when an enemy is defeated their AI routine
+needs to be shut down. When a script is spawned, a handle to that
+script is returned that can be used to cancel it when desired.
+</p>
+<div class="example">
+<pre class="example">(define script (script (while #t (display &quot;hey\n&quot;) (sleep 60))))
+;; sometime later
+(cancel-script script)
+</pre></div>
+
+<dl>
+<dt><a name="index-spawn_002dscript"></a>Procedure: <strong>spawn-script</strong> <em><var>thunk</var></em></dt>
+<dd><p>Apply <var>thunk</var> as a script and return a handle to it.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-script"></a>Syntax: <strong>script</strong> <em><var>body</var> &hellip;</em></dt>
+<dd><p>Evaluate <var>body</var> as a script and return a handle to it.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-script_003f"></a>Procedure: <strong>script?</strong> <em><var>obj</var></em></dt>
+<dd><p>Return <code>#t</code> if <var>obj</var> is a script handle.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-script_002dcancelled_003f"></a>Procedure: <strong>script-cancelled?</strong> <em><var>obj</var></em></dt>
+<dd><p>Return <code>#t</code> if <var>obj</var> has been cancelled.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-script_002drunning_003f"></a>Procedure: <strong>script-running?</strong> <em><var>obj</var></em></dt>
+<dd><p>Return <code>#t</code> if <var>obj</var> has not yet terminated or been
+cancelled.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-script_002dcomplete_003f"></a>Procedure: <strong>script-complete?</strong> <em><var>obj</var></em></dt>
+<dd><p>Return <code>#t</code> if <var>obj</var> has terminated.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-cancel_002dscript"></a>Procedure: <strong>cancel-script</strong> <em><var>co</var></em></dt>
+<dd><p>Prevent further execution of the script <var>co</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-yield"></a>Procedure: <strong>yield</strong> <em><var>handler</var></em></dt>
+<dd><p>Suspend the current script and pass its continuation to the
+procedure <var>handler</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-sleep"></a>Procedure: <strong>sleep</strong> <em><var>duration</var></em></dt>
+<dd><p>Wait <var>duration</var> before resuming the current script.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-channel_002dget"></a>Procedure: <strong>channel-get</strong> <em><var>channel</var></em></dt>
+<dd><p>Wait for a message from <var>channel</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-forever"></a>Syntax: <strong>forever</strong> <em><var>body</var> &hellip;</em></dt>
+<dd><p>Evaluate <var>body</var> in an endless loop.
+</p></dd></dl>
+
+<hr>
+<div class="header">
+<p>
+Next: <a href="Tweening.html#Tweening" accesskey="n" rel="next">Tweening</a>, Previous: <a href="Agendas.html#Agendas" accesskey="p" rel="prev">Agendas</a>, Up: <a href="Scripting.html#Scripting" 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#Index" title="Index" rel="index">Index</a>]</p>
+</div>
+
+
+
+</body>
+</html>