Shrink the role macro, using #:defaults and a local expander

os2.rkt

@@ -116,44 +116,30 @@
 	  (~or (~optional (~seq #:on-presence presence) #:name "#:on-presence handler")
 	       (~optional (~seq #:on-absence absence) #:name "#:on-absence handler")
 	       (~optional (~seq #:on-ready ready) #:name "#:on-ready handler")
-	       (~optional (~seq #:id eid) #:name "#:id")
+	       (~optional (~seq #:id eid) #:defaults ([eid #'e0]) #:name "#:id")
-	       (~optional (~seq #:topic topic) #:name "#:topic")
+	       (~optional (~seq #:topic topic) #:defaults ([topic #'t0]) #:name "#:topic")
-	       (~optional (~seq #:reason reason) #:name "#:reason"))
+	       (~optional (~seq #:reason reason) #:defaults ([reason #'r0]) #:name "#:reason"))
 	  ...
 	  [message-pattern clause-body ...]
 	  ...)
-       (with-syntax ([eid (if (attribute eid) #'eid #'dummy-eid)]
+       (define-syntax-rule (build-handler args e-attr)
-		     [topic (if (attribute topic) #'topic #'dummy-topic)]
+	 (if (not (attribute e-attr))
-		     [reason (if (attribute reason) #'reason #'dummy-reason)])
+	     #'#f
-	 (with-syntax ([presence-handler (if (not (attribute presence))
+	     #`(lambda (eid . args) (match-lambda [state-pattern e-attr]))))
-					     #'#f
+       (with-syntax ([presence-handler (build-handler (topic) presence)]
-					     #'(lambda (eid topic)
+		     [absence-handler (build-handler (topic reason) absence)]
-						 (lambda (state)
+		     [ready-handler (build-handler () ready)]
-						   (match state
+		     [message-handler #'(lambda (eid topic message-body)
-						     [state-pattern presence]))))]
+					  (lambda (state)
-		       [absence-handler (if (not (attribute absence))
+					    (match state
-					    #'#f
+					      [state-pattern
-					    #'(lambda (eid topic reason)
+					       (match message-body
-						(lambda (state)
+						 [message-pattern clause-body ...]
-						  (match state
+						 ...
-						    [state-pattern absence]))))]
+						 [_ state])])))])
-		       [ready-handler (if (not (attribute ready))
+	 #'(add-role topic-expr
-					  #'#f
+		     (handlers presence-handler absence-handler message-handler)
-					  #'(lambda (eid)
+		     ready-handler))])))
-					      (lambda (state)
-						(match state
-						  [state-pattern ready]))))]
-		       [message-handler #'(lambda (eid topic message-body)
-					    (lambda (state)
-					      (match state
-						[state-pattern
-						 (match message-body
-						   [message-pattern clause-body ...]
-						   ...
-						   [_ state])])))])
-	   #'(add-role topic-expr
-		       (handlers presence-handler absence-handler message-handler)
-		       ready-handler)))])))
 
 ;;---------------------------------------------------------------------------
 ;; Smarter constructors for transitions and preactions.