static void Main(string[] args) {
const string expression = "w x z - +";
var evaluator = new Evaluator(expression);
var sentence = new Dictionary<string, IExpression>();
sentence["w"] = new Number(5);
sentence["x"] = new Number(10);
sentence["z"] = new Number(42);
var result = evaluator.Interpret(sentence);
Console.WriteLine(result);
Console.ReadKey();
}