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I've used planck occasionally for years, but now it seems to be deprecated. (Won't build on homebrew.) But it sounds like its functionality has been absorbed by clj. So where can I find documentation about this, and how to run a cljs REPL?
Not sure what you mean by "absorbed by clj"?
Have you tried https://clojurescript.org/guides/quick-start to get a ClojureScript REPL up and running?
Depending on what you want to do, maybe Babashka might be appropriate? https://babashka.org/
