// Note: Service providers schedule actions.
// Only puzzle runners call step().
// interface for ProbabilisticScheduler (#1031949)
sinterface IProbabilisticScheduler extends Steppable {
  // schedule an action at an absolute probability
  void at(double probability, Runnable action);
  
  // schedule an action at a probability relative to
  // currentProbability()
  default void atRelative aka schedule(double probability, Runnable action) {
    at(currentProbability()*probability, action);
  }
  
  double currentProbability(); // for thread, only while running a step
  long stepCount();
  
  double lastExecutedProbability();
  
  default void run aka schedule aka at(Runnable x) {
    if (x == null) ret;
    initAction(x);
    x.run();
  }
  
  default void scheduleAll(Iterable<WithProbability<? extends Runnable>> l) {
    fOr (var x : l)
      at(x.probability(), x!);
  }

  default void initAction(O action) {  
    if (action cast IProbabilistic)
      action.setScheduler(this);
  }
}