[Aqueous]

While I agree that the ability to fall back on stateful imperative code makes it not a pure functional language, once you get into an immutable pattern it becomes less and less convenient or desirable to fall back on mutable data structures. I can't remember the last time I was even tempted to make something mutable. Also, in my experience it's required very little effort to convince new hires that are new to Scala to adopt this pattern.