p&rsquo;
argument.  &rsquo;proc&rsquo; should be a procedure taking a single argument,
namely the value yielded by the generator.  Each time &rsquo;proc&rsquo; runs it
will do so as a separate event in the event loop and so be
multi-plexed with other events.
</p>
<p>This procedure must (like the a-sync procedure) be called in the same
thread as that in which the event loop runs.
</p>
<p>This procedure is intended to be called within a waitable procedure
invoked by a-sync (which supplies the &rsquo;await&rsq