public override void ExitRule(IParseTreeListener listener)
        {
            IInvertedPolishCalculatorListener typedListener = listener as IInvertedPolishCalculatorListener;

            if (typedListener != null)
            {
                typedListener.ExitExpression(this);
            }
        }
        public override void EnterRule(IParseTreeListener listener)
        {
            IInvertedPolishCalculatorListener typedListener = listener as IInvertedPolishCalculatorListener;

            if (typedListener != null)
            {
                typedListener.EnterOperation(this);
            }
        }