public override void Visit(AdditionExpression additionExpression)
 {
     _sb.Append("(");
     additionExpression.LHS.Accept(this);
     _sb.Append("+");
     additionExpression.RHS.Accept(this);
     _sb.Append(")");
 }
        public void Run()
        {
            var e = new AdditionExpression(
                new DoubleExpression(1),
                new AdditionExpression(
                    new DoubleExpression(2),
                    new DoubleExpression(3)
                    )
                );

            var sb = new StringBuilder();

            e.Print(sb);
            Console.WriteLine(sb);
        }