// goes well with the stage {} macro (see tok_stages)
srecord Stages2(L<Stages2.Stage> stages) is Steppable, Runnable {
  int iStage;
  Stage stage;
  
  // set this to record timing for each stage
  settable transient FunctionTimings<S> timings;
  
  { stages = new L; }
  
  record noeq Stage(S name, Runnable body) {
    run {
      if (timings != null)
        timings.do(name, body);
      else
        callF(body);
    }
    
    toString { ret or2(name, "Unnamed stage"); }
  }
  
  public bool step() {
    if (iStage >= l(stages)) false;
    var stage = stages.get(iStage++);
    stage.run();
    true;
  }
  
  Stage stage(Stage stage) {
    stages.add(stage);
    ret stage;
  }
  
  Stage stage(S name, Runnable body) {
    ret stage(new Stage(name, body));
  }
  
  run { stepAll(this); }
  
  int indexOfStage(Stage stage) {
    ret stages.indexOf(stage);
  }
  
  void stepUntilStage(Stage stage) {
    int index = indexOfStage(stage);
    while (iStage <= index && step()) {}
  }
  
  L<Stage> completedStages() {
    ret cloneTakeFirst(stages, iStage);
  }
  
  L<Stage> remainingStages() {
    ret cloneDropFirst(stages, iStage);
  }
}

Began life as a copy of #1032842