Y Combinator in Python

Of course, if you actually <i>use</i> this you can smash the stack -- Python doesn't currently have any kind of tail call optimization. (That factorial function isn't tail-recursive anyway, though.)<p>It doesn't look like Ruby has tail-call optimization, either. Lua does...what other primarily-scripting (i.e., not Scheme or Haskell) languages do?

<p><pre><code> # Ruby 1.8.7 def Y lambda { |f| f.call(f) }.call( lambda do |g| yield(lambda { |*n| g.call(g).call(*n) }) end) end Y { |this| lambda { |n| n == 0 ? 1 : n * this.call(n - 1) } }.call(5) #=&#62; 120</code></pre>

The Y combinator is just like python decorators, or generators, you just HAVE to blog about them, or you're not C001!

This must be about the 6th different 'Y Combinator in X' I have seen on this site.

That's a pretty solid butchering of the design of daringfireball.net

Perl6 ftw:<p>my $factorial = sub (Int $x) { $x &#60; 2 ?? 1 !! $x * &#38;?ROUTINE($x - 1); }