In principle, I'm very much predisposed to collections that are purely functional. I know that Apache Arrow (https://arrow.apache.org/ https://arrow.apache.org/

In principle, I'm very much predisposed to collections that are purely functional. I know that Apache Arrow (https://arrow.apache.org/ https://arrow.apache.org/) aims to create an interoperable in-memory dataframe structure that tries to take into account CPU caches and other dark-magic-from-my-perspective things. Any reason why a purely functional data structure shouldn't be able to achieve the aims that something like Arrow is attempting? Incidentally fset looks really impressive.