Discussion: forM for Data.Set

This was posted a year ago already, but without many comments: https://mail.haskell.org/pipermail/libraries/2019-January/029335.html So after cleaning up the PR a bit, adding tests and benchmarks, let's give it another go. PR is at: https://github.com/haskell/containers/pull/592 New functions are: forM, mapM, for, traverse This follows the other Data.Set exported functions, overwriting Prelude ones like foldr etc, so I think that's exactly what we want. Cheers, Julian Ospald