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

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

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