uo; and &rsquo;resume&rsquo; arguments).
It is the single-threaded corollary of await-generator-in-thread!.
This means that (unlike with await-generator-in-thread!) while
&rsquo;generator&rsquo; is running other events in the event loop will not make
progress, so blocking calls (other than to the yield procedure) should
not be made in &rsquo;generator&rsquo;.  This procedure can be useful for the
purpose of implementing co-operative multi-tasking, say by composing
tasks with compose-a-sync (see compose.scm)