Just to double down on the points of some other commenters here: &quot;Functional&quot; is a pretty difficult word to pin down these days. That said, there seems to be a clear camp in what might be better called &quot;denotational&quot; programming which centers around the ML-alike languages, the dependently typed languages, and Scala.<p>Lisp is not much at all like these languages. Nor is Erlang, though it is vastly closer.