Enjoyed the post with plenty of great information contained inside, but felt the conclusion was either something that went over my head or was too obvious to state (for the likely reader of this post). Of course, Haskell can't prove that your code satisfies the necessary laws to call some class a functor. I thought we were going to get something a bit more insightful given the title of the post. However, as I said I did really enjoy the other content in the blog and maybe it could have just worked to a different conclusion with an alternative title.