sclass Stage implements Runnable {
  S name;
  bool done;
  O result;
  PersistableThrowable error;
  //long started, done; // timestamps
  //S log;
  IF0 code;
  
  sS _fieldOrder = "name done result";
  
  *() {}
  *(S *name) {}
  *(S *name, IF0 *code) {}
  
  event computed;
  
  run {
    if (done || code == null) ret;
    try {
      result = code!;
      computed();
    } catch print e {
      error = persistableThrowable(e);
    } finally {
      done = true;
    }
  }
}