Indeed, typeclasses in languages such as Haskell and Mercury can be (ab)used for many of the same uses as functors. I've used both and there are merits to each

Indeed, typeclasses in languages such as Haskell and Mercury can be (ab)used for many of the same uses as functors. I've used both and there are merits to each, but I still can't put my finger on when one is better than the other.