That's not even the worst part. Even since GHC 8.0, WrappedMonad's Applicative instance doesn't define pure in terms of return (see [1]), so at the moment, it's completely unusable for DerivingVia in the way that's been proposed. If we we decide we want to keep WrappedMonad after all, we would need to once again change the semantics of this Applicative instance, since it is indeed not terribly useful the way it's currently defined. Ryan S. ----- [1] https://ghc.haskell.org/trac/ghc/ticket/13876