Maybe monad in C#

Maybe.cs

using System;

namespace Maybe
{
    interface Maybe<T>
    {
        T Value();
        bool HasValue();
        Maybe<T> Bind(Func<T, Maybe<T>> f);
    }

    class Just<T> : Maybe<T>
    {
        private T _val;

        public Just(T val) // <- Unit
        {
            _val = val;
        }

        #region Maybe implementation
        public T Value ()
        {
            return _val;
        }

        public bool HasValue() { return true; }

        public Maybe<T> Bind (Func<T, Maybe<T>> f) // <- Bind
        {
            return f (_val);
        }
        #endregion
    }

    class Nothing<T> : Maybe<T>
    {
        public Nothing() {} // <- Unit

        #region Maybe implementation
        public T Value ()
        {
            return default(T);
        }

        public bool HasValue() { return false; }

        public Maybe<T> Bind (Func<T, Maybe<T>> f)
        {
            return new Nothing<T>(); // don't care
        }
        #endregion
    }

    class MainClass
    {
        public static void Main (string[] args)
        {
            Maybe<int> m = new Just<int> (20); // <- unit, technical the constructor

            var res = m.Bind (x => new Just<int> (x + 4))
                .Bind (x => new Just<int> (x * 100))
                .Bind (x => {
                    Console.WriteLine ("Value at this stage is: " + x.ToString()); // did something but didn't change the value...
                    return new Just<int> (x);
                })
                .Bind (x => x >= 2400 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x));

            if (res.HasValue())
                Console.WriteLine (res.Value());
            else
                Console.WriteLine ("no value present");
            
            Maybe<int> m2 = new Just<int> (20);

            var res2 = m2.Bind (x => new Just<int>(x - 10))
                .Bind (x => new Just<int>(x * 100))
                .Bind (x => {
                    Console.WriteLine ("Value at this stage is: " + x.ToString());
                    return new Just<int> (x);
                })
                .Bind (x => x >= 2400 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x));
            
            if (res2.HasValue())
                Console.WriteLine (res2.Value());
            else
                Console.WriteLine ("no value present");

            Maybe<int> m3 = new Just<int> (0);

            var res3 = m3.Bind (x => x == 0 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x))
                .Bind (x => new Just<int> (50 / x));

            if (res3.HasValue ())
                Console.WriteLine (res3.Value ());
            else
                Console.WriteLine ("Failed to divide by 0");

            Maybe<int> m4 = new Just<int> (10);

            var res4 = m4.Bind (x => x == 0 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x))
                .Bind (x => new Just<int> (50 / x));

            if (m4.HasValue ())
                Console.WriteLine (res4.Value ());
            else
                Console.WriteLine ("Failed to divide by 10");

            /*
            Value at this stage is: 2400
            no value present
            Value at this stage is: 1000
            1000
            Failed to divide by 0
            5
            */

        }
    }
}