Haskell Fundamentals - Fill In The Types

This topic is for the [Fill In The Types] exercise in the [Haskell Fundamentals] trail. Post any questions, corrections, or pointers you have to share with other Upcase subscribers.
[Fill In The Types]: https://exercises.upcase.com/exercises/fill-in-the-types
[Haskell Fundamentals]: Learn Haskell Fundamentals | Haskell Online Tutorial by thoughtbot