I've not tried this module out.

But if functional programming is what you're looking for, MapReduce isn't exactly it. It's more of a large-scale job control framework for computations that are what a functional program would be more likely to be designed upon (that is, pure functions). If you want to experience the kinds of tools that are associated with more day-to-day stuff, like using (probably lazy) lists, abstract datatypes, pattern matching, type inference, curried functions, composition, folds etc., this isn't where you'll find them.

Two CPAN modules for Perl 5 that bring some of the goodies (incidentally both at version 0.03 right now) are fp and Language::Functional.