public void Visit(AdditionExpression5 obj)
 {
     sb.Append("(");
     obj.Left.Accept(this);
     sb.Append("+");
     obj.Right.Accept(this);
     sb.Append(")");
 }
        // change to Main to run.
        public static void none()
        {
            var e = new AdditionExpression5(
                left: new DoubleExpression5(1),
                right: new AdditionExpression5(
                    left: new DoubleExpression5(2),
                    right: new DoubleExpression5(3)));
            var ep = new ExpressionPrinter4();

            ep.Visit(e);
            Console.WriteLine(ep.ToString());
        }