sync bug eliminated

collects/2htdp/private/last.rkt

@@ -16,7 +16,7 @@
     
     ;; -> World
     (define/public (last) 
-      (define result (sync #;yield end:ch)) ;; bug? 
+      (define result (yield end:ch))
       (if (exn? result) (raise result) result))
     
     (field [dr:cust (current-custodian)])

collects/2htdp/universe.rkt

@@ -5,7 +5,6 @@
 #| TODO: 
    -- check that on-release is only defined if on-key is defined 
 
-   -- yield instead of sync
    -- run callbacks in user eventspace
    -- make timer fire just once; restart after on-tick callback finishes
    -- take out counting; replace by 0.25 delay
@@ -338,5 +337,8 @@
   (define esp (make-eventspace))
   (define thd (eventspace-handler-thread esp))
   (with-handlers ((exn:break? (lambda (x) (break-thread thd))))
+    (define obj:ch (make-channel))
     (parameterize ([current-eventspace esp])
-      (send (o) last))))
+      (queue-callback (lambda () (channel-put obj:ch (o)))))
+    (send (channel-get obj:ch) last)))
+