use of role macro

os2-example.rkt

@@ -9,11 +9,11 @@
 
 (define (sleep n k)
   (transition k
-    (add-role (topic-subscriber (super-alarm (+ (current-inexact-milliseconds) n)))
-	      (handlers #f #f (lambda (eid topic now)
-				(lambda (k)
-				  (extend-transition (k)
-				    (delete-role eid))))))))
+    (role (topic-subscriber (super-alarm (+ (current-inexact-milliseconds) n)))
+      #:state k
+      #:id id
+      #:on-ready (begin (write `(ready ,id)) (newline) k)
+      [now (extend-transition (k) (delete-role id))])))
 
 (define (example-process delay)
   (write `(sleeping for ,delay milliseconds))