I noticed that the implementation of `sum` changed from `foldl` to `foldl'` between `base-4.15` and `base-4.16`: * https://hackage.haskell.org/package/base-4.15.1.0/docs/src/GHC.List.html#sum * https://hackage.haskell.org/package/base-4.16.0.0/docs/src/GHC.List.html#sum Yet the change is not reflected in https://hackage.haskell.org/package/base-4.16.4.0/changelog. It would be nice to find out what else has changed in this area (`product`? anything else?) and write it down. Pitfalls of `sum` implemented via `foldl` used to be a common educational example, so it might be useful for posterity to document that it no longer applies in haddocks for `sum`, not only in the changelog.