[C#]再帰的四則演算（加減乗除）

KPF第四回勉強会でやったネタのC#版ですね。

The Little Schemerの4章のNumbers Gamesのコード片です。

 

download - NumbersGames.cs

using System; using System.Collections.Generic; using System.Linq; using System.Text;   // The Little Schemer // chapter 4 // ISBN:0262560992 namespace NumbersGames {     class Program     {         static void Main(string[] args)         {             /* 再帰で加減乗除（四足演算） */             //インクリメント             var inc = new Func<int, int>(n => ++n);             Console.WriteLine("inc(1) -> {0}", inc(1));// -> 2               //デクリメント             var dec = new Func<int, int>(n => --n);             Console.WriteLine("dec(1) -> {0}", dec(1));// -> 0               //加算             Func<int, int, int> add = null;             add = (n, m) =>                 {                     return m == 0                         ? n                         : inc(add(n, dec(m)));                 };             Console.WriteLine("add(2, 3) -> {0}", add(2, 3));// -> 5               //減算             Func<int, int, int> sub = null;             sub = (n, m) =>                 {                     return m == 0                         ? n                         : dec(sub(n, dec(m)));                 };             Console.WriteLine("sub(3, 2) -> {0}", sub(3, 2));// -> 1               //大なり             Func<int, int, bool> bgr = null;             bgr = (n, m) =>                 {                     return n == 0                         ? false : m == 0                         ? true : bgr(dec(n), dec(m));                 };             Console.WriteLine("bgr(3, 2) -> {0}", bgr(3, 2));// -> True               //小なり             Func<int, int, bool> sml = null;             sml = (n, m) =>                 {                     return m == 0                         ? false : n == 0                         ? true : sml(dec(n), dec(m));                 };             Console.WriteLine("sml(2, 3) -> {0}", sml(2, 3));// -> True               //乗算             Func<int, int, int> mul = null;             mul = (n, m) =>                 {                     return m == 0                         ? m                         : add(n, mul(n, dec(m)));                 };             Console.WriteLine("mul(2, 3) -> {0}", mul(2, 3));// -> 6               //除算             Func<int, int, int> div = null;             div = (n, m) =>                 {                     return sml(n, m)                         ? 0                         : inc(div(sub(n, m), m));                 };             Console.WriteLine("div(15, 3) -> {0}", div(15, 3));// -> 5               Console.ReadLine();         }     } }