op if no &rsquo;loop&rsquo; argument is provided or if #f is
provided as the &rsquo;loop&rsquo; argument (pattern matching is used to detect
the type of the third argument).  This procedure calls &rsquo;await&rsquo; and
will return the thunk&rsquo;s return value.  It is intended to be called
within a waitable procedure invoked by a-sync (which supplies the
&rsquo;await&rsquo; and &rsquo;resume&rsquo; arguments).  It will normally be necessary to
call event-loop-block! before invoking this procedure.  If the