public override BaseExpression VisitUnary([NotNull] ExpressionParser.UnaryContext context)
        {
            BaseExpression ret = Visit(context.factor());

            if (context.MINUS() != null)
            {
                ret = new BinaryOpExpression(new NumberExpression(decimal.MinusOne), BinaryOp.Multiply, ret);
            }
            return(ret);
        }