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-<title>Scripts (The Chickadee Game Toolkit)</title>
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-<link href="Scripting.html" rel="up" title="Scripting" />
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-<span id="Scripts"></span><div class="header">
-<p>
-Next: <a href="Tweening.html" accesskey="n" rel="next">Tweening</a>, Previous: <a href="Agendas.html" accesskey="p" rel="prev">Agendas</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="Scripts-1"></span><h4 class="subsection">5.5.2 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="lisp">
-<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">script</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">while</span> <span class="syntax-symbol">#t</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">display</span> <span class="syntax-string">"mom!"</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">newline</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">sleep</span> <span class="syntax-symbol">60</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span> <span class="syntax-comment">; where 60 = 1 second of real time
-</span></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="lisp">
-<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">script</span> <span class="syntax-open">(</span><span class="syntax-symbol">script</span> <span class="syntax-open">(</span><span class="syntax-symbol">while</span> <span class="syntax-symbol">#t</span> <span class="syntax-open">(</span><span class="syntax-symbol">display</span> <span class="syntax-string">"hey\n"</span><span class="syntax-close">)</span> <span class="syntax-open">(</span><span class="syntax-symbol">sleep</span> <span class="syntax-symbol">60</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
-<span class="syntax-comment">;; sometime later
-</span><span class="syntax-open">(</span><span class="syntax-symbol">cancel-script</span> <span class="syntax-symbol">script</span><span class="syntax-close">)</span>
-</pre></div>
-
-<dl>
-<dt id="index-spawn_002dscript">Procedure: <strong>spawn-script</strong> <em>thunk</em></dt>
-<dd><p>Apply <var>thunk</var> as a script and return a handle to it.
-</p></dd></dl>
-
-<dl>
-<dt id="index-script">Syntax: <strong>script</strong> <em>body &hellip;</em></dt>
-<dd><p>Evaluate <var>body</var> as a script and return a handle to it.
-</p></dd></dl>
-
-<dl>
-<dt id="index-script_003f">Procedure: <strong>script?</strong> <em>obj</em></dt>
-<dd><p>Return <code>#t</code> if <var>obj</var> is a script handle.
-</p></dd></dl>
-
-<dl>
-<dt id="index-script_002dcancelled_003f">Procedure: <strong>script-cancelled?</strong> <em>obj</em></dt>
-<dd><p>Return <code>#t</code> if <var>obj</var> has been cancelled.
-</p></dd></dl>
-
-<dl>
-<dt id="index-script_002drunning_003f">Procedure: <strong>script-running?</strong> <em>obj</em></dt>
-<dd><p>Return <code>#t</code> if <var>obj</var> has not yet terminated or been
-cancelled.
-</p></dd></dl>
-
-<dl>
-<dt id="index-script_002dcomplete_003f">Procedure: <strong>script-complete?</strong> <em>obj</em></dt>
-<dd><p>Return <code>#t</code> if <var>obj</var> has terminated.
-</p></dd></dl>
-
-<dl>
-<dt id="index-cancel_002dscript">Procedure: <strong>cancel-script</strong> <em>co</em></dt>
-<dd><p>Prevent further execution of the script <var>co</var>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-yield">Procedure: <strong>yield</strong> <em>handler</em></dt>
-<dd><p>Suspend the current script and pass its continuation to the
-procedure <var>handler</var>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-join">Procedure: <strong>join</strong> <em>script</em></dt>
-<dd><p>Suspend the current script until <var>script</var> has terminated.
-</p></dd></dl>
-
-<dl>
-<dt id="index-sleep">Procedure: <strong>sleep</strong> <em>duration</em></dt>
-<dd><p>Wait <var>duration</var> before resuming the current script.
-</p></dd></dl>
-
-<dl>
-<dt id="index-wait_002duntil">Syntax: <strong>wait-until</strong> <em>condition</em></dt>
-<dd><p>Wait until <var>condition</var> is met before resuming the current script.
-</p>
-<div class="lisp">
-<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">script</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">wait-until</span> <span class="syntax-open">(</span><span class="syntax-symbol">key-pressed?</span> <span class="syntax-symbol">'z</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">display</span> <span class="syntax-string">"you pressed the Z key!\n"</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
-</pre></div>
-
-</dd></dl>
-
-<dl>
-<dt id="index-forever">Syntax: <strong>forever</strong> <em>body &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" accesskey="n" rel="next">Tweening</a>, Previous: <a href="Agendas.html" accesskey="p" rel="prev">Agendas</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>
-
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-</html>