In this new post to his blog Fabien Potencier looks at two of the much-hyped features of the upcoming PHP 5.x series release (5.3) - closures and lambda functions.

I won't talk too much about what lambda functions or closures are, as you can find many good blog posts describing them in great details. To sum up, a lambda function is an anonymous PHP function that can be stored in a variable and passed as an argument to other functions or methods. A closure is a lambda function that is aware of its surrounding context.

He includes several examples including how they would work with a few of the array functions, an implementation of the Y-combinator method (as written by Stanislav Malyshev) and how they can be used to create dependency injection functionality.

New from the PHP 10.0 blog today is this look at trying to set up recursive closures in the upcoming PHP 5.3 release (it includes closures, but it doesn't look like this is possible). Instead, Stas suggests the Y combinator method as an alternative.

One of the ways to do it is to use Y combinator function, which allows, by application of dark magic and friendly spirits from other dimensions, to convert non-recursive code to recursive code. [...] Doing Y-combinator in PHP was attempted before (and here), but now I think it works better. It could be even nicer if PHP syntax allowed chaining function invocations - ($foo($bar))($baz) - but for now it doesn't.

His (less than ideal) first method throws in some variable variables and a separate factoral function and his second passes in a factoral value of itself to call itself the correct number of times.