At work, we are pondering on a new way to split our game levels editing code, and persistent data structures came to me as one idea, in order to handle UNDO in generic way, and they by diff, or other means visualize the changes. I've read Okasaki's book long time ago, but seeing this implemented in a imperative language is really helpful.
Also pretty much enjoyed the post-modern talk too :) - hehehe
Thank you!