On the Metapundit.net site, there's a new (long) entry that takes a look at one of the programming styles, functional programming, and checks into its support in PHP. Unfortunately, it's mostly a swing and a miss.

I should just get this straight right off the bat: you can't really do much functional programing in PHP. Functions are not first class citizens and the equivalent of passing functions around is passing around strings or arrays and relying on convention. No really.

He goes on by illustrating the point that PHP can do this sort of thing but only up to a point. Once you start to get into anonymous functions and moving past things like the array_map function, you start to loose a foothold. The create_function function allows for a bit more flexibility, but still doesn't fulfill the requirements needed for full support.