anchor.diff:  }
   
   
  +bool checkCurrentIsolate() {
  +  if (currentIsolate != null) {
  +    return true;
  +  }
  +  print("Need valid current isolate");
  +  return false;
  +}
  +
  +
  +bool checkPaused() {
  +  if (!checkCurrentIsolate()) return false;
  +  if (currentIsolate.isPaused) return true;
  +  print("Current isolate must be paused");
  +  return false;
  +}
  +
   typedef void HandlerType(Map response);
   
   HandlerType showPromptAfter(void handler(Map response)) {
  
positive.code:     if (args.length == 3) {
        cmd = { "id": seqNum,
                "command": "getListElements",
                "params": { "isolateId" : isolate_id,
                            "objectId": int.parse(args[1]),
                            "index": int.parse(args[2]) } };
      } else {
        cmd = { "id": seqNum,
                "command": "getListElements",
                "params": { "isolateId" : isolate_id,
                            "objectId": int.parse(args[1]),
                            "index": int.parse(args[2]),
                            "length": int.parse(args[3]) } };
  
negative.code: 
  void handleGetIsolatesResponse(Map response) {
    Map result = response["result"];
    List ids = result["isolateIds"];
    assert(ids != null);
    print("List of isolates:");
    for (int id in ids) {
      TargetIsolate isolate = targetIsolates[id];
      var state = (isolate != null) ? "running" : "<unknown isolate>";
      if (isolate != null && isolate.isPaused) {
        var loc = formatLocation(isolate.pausedLocation);
        state = "paused at $loc";
      }
      var marker = " ";
      if (currentIsolate != null && id == currentIsolate.id) {
        marker = "*";
      }
      print("$marker $id $state");
    }
  }
  
  
  