C# Continuation Monad

using System;

public static class ContinuationMonad

{

    public static Func<Func<V, R>, R> SelectMany<T, U, V, R>(

             this Func<Func<T, R>, R> m,

                  Func<T, Func<Func<U, R>, R>> f,

                  Func<T, U, V> p)

    {

        return c => m(a => f(a)(x => c(p(a, x))));

    }

    public static Func<Func<T, R>, R> Return<T, R>(this T x)

    {

        return k => k(x);

    }

}

public class Program

{

    public static void Main()

    {

        Func<int, Func<Func<int, int>, int>> facCont = null;

        facCont = n => n == 0 ? 1.Return<int, int>()

                          : from x in n.Return<int, int>()

                            from y in facCont(x - 1)

                            select x * y;

        Func<int, int> fac = n => facCont(n)(x => x);

        Console.WriteLine(fac(5));

    }

}