public void Visit(AdditionExpression ae)
{
sb.Append("(");
ae.Left.Accept(this);
sb.Append("+");
ae.Right.Accept(this);
sb.Append(")");
}
static void Main(string[] args)
{
AdditionExpression ae = new AdditionExpression(
new DoubleExpression(1),
new AdditionExpression(
new DoubleExpression(2),
new DoubleExpression(3)
));
ExpressionPrinter ep = new ExpressionPrinter();
ep.Visit(ae);
Console.WriteLine(ep);
ExpressionCalculator ec = new ExpressionCalculator();
ec.Visit(ae);
Console.WriteLine($"{ep} = {ec.Result}");
}