• Ryan Scott's avatar
    Add Bifoldable and Bitraversable to base · 270d545d
    Ryan Scott authored
    This adds `Data.Bifoldable` and `Data.Bitraversable` from the
    `bifunctors` package to `base`, completing the migration started in
    D336.  This is fairly straightforward, although there were a suprising
    amount of reinternal organization in `base` that was needed for this to
    happen:
    
    * `Data.Foldable`, `Data.Traversable`, `Data.Bifoldable`, and
      `Data.Bitraversable` share some nonexported datatypes (e.g., `StateL`,
      `StateR`, `Min`, `Max`, etc.) to implement some instances. To avoid
      code duplication, I migrated this internal code to a new hidden
      module, `Data.Functor.Utils` (better naming suggestions welcome).
    
    * `Data.Traversable` and `Data.Bitraversable` also make use of an
      identity newtype, so I modified them to use
      `Data.Functor.Identity.Identity`. This has a ripple effect on several
      other modules, since I had to move instances around in order to avoid
      dependency cycles.
    
    Fixes #10448.
    
    Reviewers: ekmett, hvr, austin, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D2284
    
    GHC Trac Issues: #9682, #10448
    270d545d
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