/*
 * Created by SharpDevelop.
 * User: zeonni
 * Date: 29.09.2016
 * Time: 16:07
 *
 * To change this template use Tools | Options | Coding | Edit Standard Headers.
 */
using System;

namespace Maybe
{
    class Program
    {
        public static void Main(string[] args)
        {
            welcome(new Maybe<String>("Onni"));
            welcome(new Maybe<String>(null));

            Console.ReadKey();
        }

        public static void welcome(Maybe<String> user) {
            Console.WriteLine(
                user.Take<String>(
                    (name) => String.Format("Welcome, {0}!", name),
                    () => "User not auth"
                )
            );
        }
    }

    class Maybe<T> {

        public delegate R Just<R>(T value);
        public delegate R Nothing<R>();

        private T value;

        public Maybe(T value) {
            this.value = value;
        }

        public R Take<R>(Just<R> just, Nothing<R> nothing) {
            return value == null ? nothing() : just(value);
        }

    }
}