@open @abstract class Throwable(let msg: String) {
  var backtrace: Array[Int] = nil;
  var elements: Array[StackTraceElement] = nil;

  self.retrieveStackTrace();

  fun getStackTrace() -> Array[StackTraceElement] {
    if self.elements !== nil {
      return self.elements;
    }

    if self.backtrace === nil {
      self.elements = arrayEmpty[StackTraceElement]();
      return self.elements;
    }

    var i = 0;
    let len = self.backtrace.length() / 2;
    self.elements = Array[StackTraceElement](len);

    while i < len {
      self.elements.set(i, self.getStackTraceElement(i));
      i = i + 1;
    }

    return self.elements;
  }

  fun getMessage() -> String {
    return self.msg;
  }

  @abstract fun printStackTrace();

  @internal fun retrieveStackTrace();
  @internal fun getStackTraceElement(idx: Int) -> StackTraceElement;
}

class StackTraceElement(let name: String, let line: Int) {
  fun toString() -> String = self.name + ": " + self.line.toString();
}