private static void TestLexer(SimpleLexer lexer)
 {
     while (lexer.HasInput)
     {
         var token = lexer.NextToken();
         Console.WriteLine("<" + token.Type + (token.HasValue?"," + token.Attribute.Value:"") + ">");
     }
 }
        static void Main(string[] args)
        {
            var lexer  = new SimpleLexer("200-250");
            var parser = new SimpleParser(lexer);
            // try {
            var res = parser.Expr();

            //Console.WriteLine(parser.Output);
            Console.WriteLine(res);
            // } catch (Exception e) {
            //     Console.WriteLine("Error: "+ e.Message);
            // }
        }