Hi everyone, Ed Kmett recently pointed me towards his usage of Backpack to write some code in the tagless final style, and I've been playing with it and riffing on it for a while. There's a solution to the expression problem in there involving classy Prisms (and now Backpacky Prisms) that seems pretty neat. I've written it up here: https://qfpl.io/posts/backpack-for-initial-and-final-encodings/ Hopefully some of you find it interesting. Cheers, Dave