public void Visit(AdditionExpression obj)
{
sb.Append("(");
obj.Left.Accept(this);
sb.Append("+");
obj.Right.Accept(this);
sb.Append(")");
}
static void Main(string[] args)
{
var e = new AdditionExpression(
left: new DoubleExpression(3),
right: new AdditionExpression(
left: new DoubleExpression(4),
right: new DoubleExpression(7)));
var ep = new ExpressionPrinter();
ep.Visit(e);
WriteLine(ep);
ReadKey();
}