Sample for using the maybe monad in C#.

HaskelDict

   public static class MaybeConcat
   {
         public static Maybe<T> Concat<T>(this Maybe<T> source1, Func<Maybe<T>> source2F)
        {
            return source1.IsNone ? source2F() : source1;
        }
    }

    public class HaskellLookupSample
    {
        private static readonly Dictionary<string, string> FullNamesDb =
            new Dictionary<string, string>
                {
                    { "Bill Gates", "[email protected]" },
                    { "Bill Clinton", "[email protected]" },
                    { "Michael Jackson", "[email protected]" }
                };

        private static readonly Dictionary<string, string> NickNamesDb =
            new Dictionary<string, string>
                {
                    { "billy", "[email protected]" },
                    { "slick willy", "[email protected]" },
                    { "jacko", "[email protected]" }
                };

        private static readonly Dictionary<string, string> PrefsDb =
            new Dictionary<string, string>
                {
                    { "[email protected]", "HTML" },
                    { "[email protected]", "Plain" },
                    { "[email protected]", "HTML" }
                };

        [Fact]
        public void DictionaryLookup()
        {
            Assert.Equal("HTML", LookUp("billy").Some);
            Assert.Equal("HTML", LookUp("Bill Gates").Some);
            Assert.True(LookUp("Steffen").IsNone);
        }

        private static Maybe<string> LookUp(string text)
        {
            return
                FullNamesDb.TryFind(text)
                    .Concat(() => NickNamesDb.TryFind(text))   // Lazy 
                    .SelectMany(y => PrefsDb.TryFind(y));
        }
    }