To add to the sibling commenter - in my experience FP is not about having as little state as possible. It's about explicitly representing and tracking all state

To add to the sibling commenter - in my experience FP is not about having as little state as possible. It's about explicitly representing and tracking all state. OOP hides all state in private properties, FP displays the state as function arguments. In the end, you want a healthy mixture of both approaches. Sometimes state is better off hidden, and then in FP you need closures - might as well use an object then, instead of emulating it by creating a closure that "responds" to "messages" by manually dispatching arguments in a giant switch. I think OCaml, Scala, and Clojure got it right, on a language level, but then the problems float up into design - ie. where to use a mutable record and where to use a functional stream, etc. I don't think I saw a compelling set of guidelines how to mix the approaches in the most effective way.