Hi Richard, I've been guilty of slipping in similar instances myself. In fact, I like OrdList better than Bag precisely because it has more instances and thus a far better interface. Not being able to see whether mempty denotes a Bag should be as simple as a mouse hover with HLS set up. So a +99 from me.
Cheers, Sebastian Am Mi., 14. Apr. 2021 um 20:28 Uhr schrieb Richard Eisenberg < r...@richarde.dev>: > Hi devs, > > In the work on simplifying the error-message infrastructure (heavy lifting > by Alfredo, in cc), I've been tempted (twice!) to add > > > instance Semigroup (Bag a) where > > (<>) = unionBags > > > > instance Monoid (Bag a) where > > mempty = emptyBag > > to GHC.Data.Bag. > > The downside to writing these is that users might be tempted to write e.g. > mempty instead of emptyBag, while the latter gives more information to > readers and induces less manual type inference (to a human reader). The > upside is that it means Bags work well with Monoid-oriented functions, like > foldMap. > > I favor adding them, and slipped them into !5509 (a big commit with lots > of other stuff). Alfredo rightly wondered whether this decision deserved > more scrutiny, and so I'm asking the question here. > > What do we think? > > Thanks, > Richard > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >
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