Comment made by: alexmiller
I'd leave the first sentence as is.
All of these collection ops are kind of tricky in being able to succinctly state the intent, while also covering special cases (which are often related to Java types). Here I think the intent is to cover lookup in "associative data structures" which covers Clojure maps, records, vectors, Java maps, and other less obvious things like weird ILookup impls.
The non-obvious inclusions for me are: Clojure sets (I haven't reviewed but undoubtedly this is implicitly used in a bunch of special cases), and the Java special cases which are Strings and arrays. For an example of wording, I would point to
nth, which are similarly weird.
So maybe a sentence like: "get also works on sets to return contained values, and on strings and arrays for value by index." ?
We'll need to answer these same questions in the spec too btw. I expect the act of spec'ing core fns to drive more of these tricky questions.