No, I mean mostly code generation using closures and string eval. If you write code that writes code then you can usually make that generated code extremely efficient. A good example for me was a system that processes large volumes of records based on a config file of rules that were strongly influenced by file type. Instead of making a machine in perl that processed the records according to the rules I made a machine in perl that created perl programs that were equivelent to the rules for each type of file. Each closure was constructed to handle only the rules for each file and in an optimised way. The end result has proved to be extremely fast.

Im not sure if im abusing the term functional programming here, but it seems to me that this kind of thing is indeed a form of it. Anyway, hope this makes some sense, im not feeling particularly expressive right now. :-)