Y-combinator and LINQ

Today I finally found an excuse to use Wes Dyer's implementation of the Y-combinator in C#:

public delegate Func<A, R> Recursive<A, R>(Recursive<A, R> r)
 
 public static Func<A, R> Y<A, R>(Func<Func<A, R>, Func<A, R>> f) {
     Recursive<A, R> rec = r => a => f(r(r))(a);
     return rec(rec);
 } 

I used it to recursively get all the files in a given directory, in a one-liner:

var RecGetFiles = Y<string, IEnumerable<string>>(f => d => Directory.GetFiles(d).Concat(Directory.GetDirectories(d).SelectMany(f)))

Nice, isn't it? Sample usage:

foreach (var f in RecGetFiles(Directory.GetCurrentDirectory()))
     Console.WriteLine(f);
 

It's probably not a good idea, though, to use this in production code, as it's not really necessary (just use regular recursion) and it harms readability.