結合Lambda的階乘累加方法

/// <summary>
    /// 階乘、累加
    /// Func<int, int>中前一個是委托方法參數類型，後一個是委托的返回類型
    /// </summary>
    public class Factorial
    {
        /// <summary>
        /// 階乘方法委托調用
        /// </summary>
        public static Func<int, int> functirial = RFunc<int, int>((m,n)=>n==1?1:n*m(n-1));

        public static Func<int, int> cumulative = RFunc<int, int>((m, n) => n == 0 ? 0 : n +m (n- 1));

        /// <summary>
        /// 單參數有返回值遞歸方法生成器。
        /// </summary>
        /// <typeparam name="T">參數類型。</typeparam>
        /// <typeparam name="TResult">返回值類型。</typeparam>
        /// <param name="f">遞歸運算實現</param>
        /// <returns></returns>
        public static Func<T, TResult> RFunc<T, TResult>(Func<Func<T, TResult>, T, TResult> f)
        {
            return x => f(RFunc(f), x);
        }
    }

外部調用

Factorial.functirial(4)