Haskell Monads - The List Monad

This topic is for the [The List Monad][] exercise in the [Haskell Monads][] trail. Post any questions, corrections, or pointers you have to share with other Upcase subscribers.
[The List Monad]: https://exercises.upcase.com/exercises/the-list-monad
[Haskell Monads]: https://thoughtbot.com/upcase/haskell-monads