Works like a charm! Thanks Noel. yc <div class="gmail_quote">On Thu, Jan 21, 2010 at 2:44 AM, Noel Welsh <<a href="mailto:noelwelsh@gmail.com">noelwelsh@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">You could just use a channel for this (or a semaphore, I suppose). When there is a value in the channel it will unblock. HTH, N. <div class="im"> On Thu, Jan 21, 2010 at 9:12 AM, YC <<a href="mailto:yinso.chen@gmail.com">yinso.chen@gmail.com</a>> wrote: > Hi all - > > is it possible to create an event based on whether a variable has value - if > it is #f, then the event blocks, and when the event gets set to something > else other than #f, the event unblocks? > </div>... > yc </blockquote></div>