New paper by Mitchell Riley, putting optics - the technique popularised in Haskell for accessing and modifying state in a highly general way - on a sound categorical footing.

https://arxiv.org/abs/1809.00738

Despite being familiar with lens/optics usage in Haskell, I'm finding this paper very difficult, although this course has certainly helped. Profunctors feature heavily of course, as do end/coends, which I have so far found impenetrable.