Code reviews. Let developers peer-review each other's code changes and share knowledge about the functional programming practices used in the codebase. This is not a technical problem and has nothing to do with Scala.
Language design can discourage those bad practices and lessen the workload of code reviews.
Catching bad practices and anti-patterns in code review sounds fine on paper, but I'm sure we've all been in the situation where there simply isn't enough time in the day to do intensive code reviews while still maintaining the pace needed for delivery.
