 the &rsquo;worker&rsquo; event loop, and whenever &rsquo;generator&rsquo; yields a value
this will cause &rsquo;proc&rsquo; to execute in the event loop specified by the
&rsquo;waiter&rsquo; argument, or in the default event loop if no &rsquo;waiter&rsquo;
argument is provided or if #f is provided as the &rsquo;waiter&rsquo; argument.
&rsquo;proc&rsquo; should be a procedure taking a single argument, namely the
value yielded by the generator.
</p>
<p>This procedure is intended to be called within a waitabl