Don't include invisible members in membership summary.

conversation.rkt

@@ -3,6 +3,7 @@
 (require racket/bool)
 (require racket/match)
 (require racket/class)
+(require racket/list)
 
 (require "functional-queue.rkt")
 (require "blocking-box.rkt")
@@ -223,8 +224,9 @@
       (broadcast (remove-binding state b) b (departed (binding-name b) why))))
 
 (define (membership-summary state)
-  (map (lambda (member) (arrived (binding-name member)))
-       (room-state-members state)))
+  (filter-map (lambda (member) (and (not (binding-invisible? member))
+				    (arrived (binding-name member))))
+	      (room-state-members state)))
 
 (define (add-binding state b)
   (struct-copy room-state state