Functional recursion and tail recursion

gistfile1.txt

using System;

namespace Factorial
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("factorial of 3 using simple recursion: " + Factorial(3));
            Console.WriteLine("factorial of 3 using accumulator passing style: " + FactorialAcc(3));
            Console.WriteLine("factorial of 3 using continuation passing style: " + FactorialCps(3));
            Console.ReadLine();
        }

        /// <summary>
        /// This function calculates the factorial of the given number using a naive approach
        /// </summary>
        public static int Factorial(int number)
        {
            return number == 0 ? 1 : number * Factorial(number - 1);
        }

        /// <summary>
        /// This function calculates the factorial of the given number using a tail recursive approach, namely accumulator passing
        /// </summary>
        public static int FactorialAcc(int number)
        {
            Func<int, int, int> acc = null;

            acc = (val, accVal) => val == 0 ? accVal : acc(val - 1, accVal * val);
            return acc(number, 1);
        }

        /// <summary>
        /// This function calculates the factorial of the given number using a tail recursive approach, namely continuation passing
        /// </summary>
        public static int FactorialCps(int number)
        {
            Func<int, Func<int, int>, int> cps = null;

            cps = (val, continuation) => val == 0 ? continuation(1) : cps(val - 1, y => continuation(val*y));
            return cps(number, y => y);
        }
    }
}