sclass Schedule<A extends Runnable> {
  Timestamp start;
  
  sclass Entry {}
  srecord Action<A>(A action) extends Entry {}
  srecord Jump (Seconds dest) extends Entry {}

  new TreeMultiMap<Seconds, Entry> entries;

  void add(double seconds, A a) {
    entries.put(Seconds(seconds), new Action<A>(a));
  }
  
  void jumpFromTo(double from, double to) {
    entries.put(Seconds(from), new Jump(Seconds(to)));
  }
  
  void speedUp(double factor) {
    entries = (TreeMultiMap) mapMultiMapKeys(entries, seconds -> seconds.div(factor));
  }
  
  run {
    start = tsNow();
    fire(first(entries));
  }
  
  scaffolded void fire(Pair<Seconds, Entry> p) {
    if (p == null) ret;
    entries.removePair(p);
    sleepUntil(start.plus(p.a));
    var e = p.b;
    if (e cast Action<A>)
      pcallF(e.action);
    else if (e cast Jump)
      start = start.plus(e.dest.minus(p.a));
    else
      fail(e);
    fire(first(entries));
  }
}