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<title>Sly: Agendas</title>
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<a name="Agendass"></a>
<div class="header">
<p>
Previous: <a href="Coroutines.html#Coroutines" accesskey="p" rel="prev">Coroutines</a>, Up: <a href="Time.html#Time" accesskey="u" rel="up">Time</a> [<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="Agendas-1"></a>
<h4 class="subsection">4.3.3 Agendas</h4>
<div class="example">
<pre class="example">(use-modules (sly agenda))
</pre></div>
<p>Agendas are used to schedule procedures to be called at distinct
points in time. One agenda, stored in the <code>current-agenda</code>
parameter, is active at any given time. A global agenda is initially
bound and is sufficient for most needs. When a separate scheduler is
required (see <a href="REPL.html#REPL">REPL</a> for one such case), the parameter can be
rebound using <code>parameterize</code> or <code>with-agenda</code> form.
</p>
<dl>
<dt><a name="index-make_002dagenda"></a>Scheme Procedure: <strong>make-agenda</strong></dt>
<dd><p>Create a new, empty agenda.
</p></dd></dl>
<dl>
<dt><a name="index-agenda_003f"></a>Scheme Syntax: <strong>agenda?</strong> <em><var>obj</var></em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is an agenda.
</p></dd></dl>
<dl>
<dt><a name="index-current_002dagenda"></a>Scheme Variable: <strong>current-agenda</strong></dt>
<dd><p>A parameter containing the current, dynamically scoped agenda object.
</p></dd></dl>
<dl>
<dt><a name="index-agenda_002dtime"></a>Scheme Procedure: <strong>agenda-time</strong></dt>
<dd><p>Return the time of the current agenda.
</p></dd></dl>
<dl>
<dt><a name="index-with_002dagenda"></a>Scheme Syntax: <strong>with-agenda</strong> <em><var>agenda</var> <var>body</var> …</em></dt>
<dd><p>Evaluate <var>body</var> with <code>current-agenda</code> bound to <var>agenda</var>.
</p></dd></dl>
<dl>
<dt><a name="index-agenda_002dtick_0021"></a>Scheme Procedure: <strong>agenda-tick!</strong></dt>
<dd><p>Increment time by 1 for the current agenda and run scheduled
procedures.
</p></dd></dl>
<dl>
<dt><a name="index-agenda_002dclear_0021"></a>Scheme Procedure: <strong>agenda-clear!</strong></dt>
<dd><p>Remove all scheduled procedures from the current agenda.
</p></dd></dl>
<dl>
<dt><a name="index-schedule"></a>Scheme Procedure: <strong>schedule</strong> <em><var>thunk</var> [<var>delay</var>]</em></dt>
<dd><p>Schedule <var>thunk</var> to be applied after <var>delay</var> ticks of the
current agenda. The default <var>delay</var> is one tick.
</p></dd></dl>
<dl>
<dt><a name="index-schedule_002dinterval"></a>Scheme Procedure: <strong>schedule-interval</strong> <em><var>thunk</var> <var>interval</var></em></dt>
<dd><p>Schedule <var>thunk</var> to be applied every <var>interval</var> ticks of the
current agenda, forever.
</p></dd></dl>
<dl>
<dt><a name="index-schedule_002deach"></a>Scheme Procedure: <strong>schedule-each</strong> <em><var>thunk</var></em></dt>
<dd><p>Schedule <var>thunk</var> to be applied upon every tick of the current
agenda, forever.
</p></dd></dl>
<p><a href="Coroutines.html#Coroutines">Coroutines</a> become particularly useful for game programming when
combined with the agenda. For example, a computer controller opponent
could periodically pause its AI algorithm to give the rest of the game
world a chance to do some processing. By using the <code>wait</code>
procedure, algorithms that span multiple ticks of game time can be
written in a straightforward, natural way.
</p>
<dl>
<dt><a name="index-wait"></a>Scheme Procedure: <strong>wait</strong> <em><var>delay</var></em></dt>
<dd><p>Abort the current coroutine prompt and schedule the continuation to be
run after <var>delay</var> ticks of the current agenda.
</p></dd></dl>
<hr>
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