[grease]

All your points (1 through 4) matched with what was looking for. I chose Clojure. It's Lispy, focuses on immutable data (but not necessarily pure functions), has a version (cljs) that compiles to javascript (if you're writing web-apps, its great to write both your front-end and backend code in one langauage). I've broadly found clojure to be a "practical" functional language to work in.

(If it helps, I'm primarily a python/js developer before picking Clojure).

[fulafel]

For someone coming from JS/Python, I think a major familiar property of Clojure is the dynamic nature. You can quickly try something out or iterate and it runs right away, without asking you to specify the program completely type-wise.

Clojure's data checking and testing stories are good too, with spec and the various test libs - including generative tests from specs. And of course you can share the same specs on front and back end, demonstrating a payoff of the front/back code sharing.