Lambda表达式编写递归函数

    class Program
    {
       

        //Fix求出的是函数f的不动点，它就是我们所需要的递归函数：
        static Func<T, TResult> Fix<T, TResult>(Func<Func<T, TResult>, Func<T, TResult>> f)
        {
            return x => f(Fix(f))(x);
        }

        static Func<T1, T2, TResult> Fix<T1, T2, TResult>(Func<Func<T1, T2, TResult>, Func<T1, T2, TResult>> f)
        {
            return (x, y) => f(Fix(f))(x, y);
        }

        static void Main(string[] args)
        {
           

            //最大公约数
            var fac = Fix<int, int>(f => x => x <= 1 ? 1 : x * f(x - 1));
            //fibonacci数列
            var fib = Fix<int, int>(f => x => x <= 1 ? 1 : f(x - 1) + f(x - 2));
            //阶乘
            var gcd = Fix<int, int, int>(f => (x, y) => y == 0 ? x : f(y, x % y));
            //函数式链表快速排序
            var qsort = Fix<IEnumerable<int>, IEnumerable<int>>(f => l => l.Any() ? f(l.Skip(1).Where(e => e < l.First())).Concat(Enumerable.Repeat(l.First(), 1)).Concat(f(l.Skip(1).Where(e => e >= l.First()))) : Enumerable.Empty<int>());

            Console.WriteLine(gcd(10, 8));
            Console.WriteLine(fib(10));   
            Console.WriteLine(fac(5));   
          
            List<int> lTest = new List<int>();
            lTest.AddRange(new int[] { 4,5,1,23,3,43,8,7,1});
   
            foreach (int item in qsort(lTest))
            {
                Console.WriteLine(item);
            }

            Console.Read();
        }

    }

    更详细的去看：
    http://www.cnblogs.com/JeffreyZhao/archive/2009/08/31/recursive-lambda-expressions.html