It doesn't help that Scala takes a lax attitude towards functional principles whenever it's convenient -- for instance, you can map over a set, and certain maps

It doesn't help that Scala takes a lax attitude towards functional principles whenever it's convenient -- for instance, you can map over a set, and certain maps will get you a different type back. Haskell it's not. It's more like a terse Java with optional types and pure functions added on.