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<title>Sly: Coroutines</title>
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<a name="Coroutines"></a>
<div class="header">
<p>
Next: <a href="Agendas.html#Agendas" accesskey="n" rel="next">Agendas</a>, Previous: <a href="Signals.html#Signals" accesskey="p" rel="prev">Signals</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>
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<hr>
<a name="Coroutines-1"></a>
<h4 class="subsection">4.3.2 Coroutines</h4>
<div class="example">
<pre class="example">(use-modules (sly coroutine))
</pre></div>
<p>Coroutines are the building block for cooperative multitasking. When
used with agendas, they are a powerful mechanism for writing
algorithms that span multiple clock ticks in a straightforward, linear
fashion. Sly’s coroutines are built on top of Guile’s delimited
continuations, called prompts.
</p>
<p>To run a procedure as a coroutine, use the <code>call-with-coroutine</code>
procedure. Once inside the coroutine prompt, the <code>yield</code>
procedure can be used to pause the procedure and pass its continuation
to a callback procedure. The callback may call the continuation at
its convenience, resuming the original procedure.
</p>
<p>Coroutines are particularly useful in conjunction with <a href="Agendas.html#Agendas">Agendas</a>.
</p>
<dl>
<dt><a name="index-call_002dwith_002dcoroutine"></a>Scheme Procedure: <strong>call-with-coroutine</strong> <em><var>thunk</var></em></dt>
<dd><p>Apply <var>thunk</var> within a coroutine prompt.
</p></dd></dl>
<dl>
<dt><a name="index-coroutine"></a>Scheme Syntax: <strong>coroutine</strong> <em><var>body</var> …</em></dt>
<dd><p>Evaluate <var>body</var> within a coroutine prompt.
</p></dd></dl>
<dl>
<dt><a name="index-colambda"></a>Scheme Syntax: <strong>colambda</strong> <em><var>args</var> <var>body</var> …</em></dt>
<dd><p>Syntacic sugar for a <code>lambda</code> expression whose <var>body</var> is run
within a coroutine prompt.
</p></dd></dl>
<dl>
<dt><a name="index-codefine"></a>Scheme Syntax: <strong>codefine</strong> <em>(<var>name</var> <var>formals</var> …) <var>body</var> …</em></dt>
<dd><p>Syntacic sugar for defining a procedure called <var>name</var> with formal
arguments <var>formals</var> whose <var>body</var> is run within a coroutine
prompt.
</p></dd></dl>
<dl>
<dt><a name="index-codefine_002a"></a>Scheme Syntax: <strong>codefine*</strong> <em>(<var>name</var> <var>formals</var> …) <var>body</var> …</em></dt>
<dd><p>Syntacic sugar for defining a procedure called <var>name</var> with
optional and keyword arguments <var>formals</var> whose <var>body</var> is run
within a coroutine prompt.
</p></dd></dl>
<dl>
<dt><a name="index-yield"></a>Scheme Procedure: <strong>yield</strong> <em><var>callback</var></em></dt>
<dd><p>Yield continuation to the procedure <var>callback</var>.
</p></dd></dl>
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