!752

answer {
  if "which users have you had" {
    L history = cast get(getMainBot(), "history");
    new TreeSet<S> users;
    
    for (O dialog : history) {
      S user = getString(dialog, "user");
      if (user != null)
        users.add(user);
    }
    
    ret structure(list(users));
  }
}