static async Task Main(string[] args)
{
    //defining expression
    var addition = new Addition(
        new Literal(5.0), new Literal(6.0));

    var sb = new StringBuilder();
    //create visitor
    var expressionPrinter = new InfixExpressionPrinter(sb);
    //addition will be "visited" by our visitor
    addition.Accept(expressionPrinter);
    Console.WriteLine(sb);   //outputs (5+6)
    Console.ReadLine();
}