event Request { integer requestId; ... }
event Response { integer requestId; ... }

monitor Client {
   action doWork() {
      //do some processing
      ...
      integer id := integer.getUnique();
      route Request(id, ... );
      Response r;
      on Response(requestId=id):r {
      // continue processing
      ...
      // Beware! Any code here will execute immediately
      // (before processing the response)
   }
}
 
monitor Server {
   action processRequests() {
      Request r;
      on all Request():r {
         // evaluate response
         route Response(r.id,...);
      }
   }
}