Can you list those same features that it provides? My understanding of Scala's philosophy is it provides as many features as it can. A Maybe type, immutable state, separation of IO, etc. isn't very useful if my coworker can choose not to use it.
Even in Haskell you can cast out of your type system, or unsafePerformIO, no?
Also, if you need a language to dictate your coworker's behavior, that says something more about your coworker than the language. Why doesn't he just choose to write good code? (barring arguments regarding the activation energy of good versus bad code)
Since I recently went through coworkers writing "bad" (by which I mean non-idiomatic) Scala, and repairing the situation, I can say that it was surprisingly easy to lay down "functional constructs" and the result was amazing. The code became reliable, well-structured, and easy to leverage. Switching to Scala for our projects -- including introducing procedurally minded programmers to it -- was a huge win for us.
- Don't do any processing after the pattern match within a function; break into smaller functions
- Reach for pattern matching before if/else
- Avoid the use of var
- Avoid dropping through to wildcard pattern. (This tip was from Yaron Minsky of OCaml fame)
In conjunction with preferring the use of combinators over loops, and using Option (and being forced to think about None), we got surprisingly functional Scala code in a short time.
But idiomatic writers do feel like natives!
Haskell goes out of its way to make it hard to do "dangerous" things by accident.