[eyelidlessness]

Also worth mentioning in terms of mixing functional/imperative techniques: it can be very helpful to use languages (and frameworks, libraries, interfaces) which are functional-first/-by default, not necessarily pure but which provide specific affordances for managing side effects. This can be seen in languages like Clojure (with reference types distinct from most of the rest of the language/stdlib). It’s also a hallmark of many projects with a reactive paradigm (which in some form or another have dedicated APIs for isolating state and/or effects).

These aren’t strictly necessary for effectively using functional techniques in an imperative environment, but they can go a long way toward providing useful guardrails you don’t have to figure out yourself.