hen the generator has
finished or, if &rsquo;handler&rsquo; is provided, upon the generator throwing an
exception.  This procedure will return #f if the generator completes
normally, or &rsquo;guile-a-sync-thread-error if the generator throws an
exception and &rsquo;handler&rsquo; is run (the &rsquo;guile-a-sync-thread-error symbol
is reserved to the implementation and should not be yielded by the
generator).
</p>
<p>This procedure is intended to be called within a waitable procedure
invoked by a-sync (whic