I'm having difficulty finding resources on how to write programs in a functional style. The most advanced topic I could find discussed online was using structural typing to cut down on class hierarchies; most just deal with how to use map/fold/reduce/etc to replace imperative loops.

What I would really like to find is an in-depth discussion of an OOP implementation of a non-trivial program, its limitations, and how to refactor it in a functional style. Not just an algorithm or a data structure, but something with several different roles and aspects - a video game perhaps. By the way I did read Real-World Functional Programming by Tomas Petricek, but I'm left wanting more.