squo; (obtained from a call to a-sync) to the
return value of &rsquo;proc&rsquo;.  &rsquo;file&rsquo; can be a port or a file descriptor
(and if it is a file descriptor, the revealed count is not
incremented).  &rsquo;proc&rsquo; should take a single argument which will be set
by the event loop to &rsquo;in or &rsquo;excpt (see the documentation on
event-loop-add-read-watch! for further details).  It is intended to be
called within a waitable procedure invoked by a-sync (which supplies
the &rsquo;await&rsqu