@open class Error(msg: String): Throwable(msg) {
  @override fun printStackTrace() {
    if super.getMessage() !== nil {
      println("Error: " + super.getMessage());
    } else {
      println("Error");
    }

    let x = self.getStackTrace();

    var i = 0;

    while i < x.length() {
      println(i.toString() + ": " + x.get(i).toString());
      i = i + 1;
    }
  }
}