"Functional But In Place" languages according to the comments: Roc, Lean, Koka.

Koka is the one I got hits on when I tried to remember what Roc was called, as Koka seems to have been the first or most well-known to have been used for a paper with a functional-looking in-place-executing quicksort.

‌‌#FunctionalButInPlace #FBIP #LeanLang #KokaLang #Koka