Http-tower-hs — A Rust Tower-inspired middleware library for Haskell

You implemented all the instances by hand. I would recommend always using deriving via if possible. In this case, your type is isomorphic to Kleisli (ExceptT ServiceError IO), and all the instances (including others that we haven’t talked about like Alternative) come from there. This way you (and readers of your code) can be sure all the instances are correct.