thinking objectively vs. functionally

As I try to increase my knowledge of functional programming, I'm finding it quite difficult to re-imagine the solutions to problems I've solved in an OOP language in terms of functions, particularly where widgets are involved. Sites like Project Euler and 4Clojure are great for learning core functions and techniques for manipulating primitive data, but what I'd really like is a resource that discusses how to idiomatically translate OOP constructs into FP, with particular attention to identifying when and how to use state. (To use a concrete example, what is the best way to implement a piano keyboard in Clojure?)