asclass Probabilistic implements IProbabilistic, Steppable {
  IProbabilisticScheduler ps;

  void initScheduler {
    if (ps == null) ps = new ProbabilisticScheduler;
  }
  
  public void setScheduler(IProbabilisticScheduler ps) {
    this.ps = ps;
  }
  
  void schedule(double probability, Runnable action) {
    initScheduler();
    ps.at(probability, action);
  }
  
  void scheduleAll(double probability, Iterable<? extends Runnable> actions) {
    forEach(actions, a -> schedule(probability, a));
  }
  
  // call run() before
  void stepAll() {
    initScheduler();
    main stepAll(ps);
  }
  
  // call run() before
  public bool step() {
    initScheduler();
    ret ps.step();
  }
}