Do they need to be functions? Because this seems a lot like handling [:a :keyword :vector :for :navigating :trees] in Clojure and passing it to either update-in or get-in functions, which is a pattern ubiquitous in re-frame, but not sure is can be called a lens).

What you're saying sounds similar. But my question and your post are both missing the "composition" aspect. Somehow lenses are composable, and I guess to grok that we'd need to look deeper.

Sounds about right.