Y-Combinator in C#

Anay — Wed, 08 Apr 2009 14:19:26 +0000

For last few days, I was trying to use lambda feature of C# to implement Y-Combinator. After few trial and errors, I was able to implement it in C# 3.5. I’m currently posting the code here and in my next blog, I’ll explain how I derived it.

In this code, Y-Combinator function, is used to implement anonymous recursive-factorial function called ‘factorial’.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace YCombinator
{
    class Program
    {
        delegate Func RecursiveFunction(RecursiveFunction f);

        static void Main(string[] args)
        {

            Func, Func>, Func> Y = (f) =>
            {
                RecursiveFunction function = (h) =>
                {
                    return (x) =>
                    {
                        return f(h(h))(x);
                    };
                };
                return function(function);
            };

            Func factorial = Y(function=>
            {
                return x =>
                {
                    return x == 0 ? 1 : x * function(x - 1);
                };
            });
            Console.WriteLine(factorial(5));
            Console.ReadLine();
        }
    }
}

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Y-Combinator in C#