Thanks. I've opened a PR on GitHub to update the docs: https://github.com/ghc/ghc/pull/48
On Mon, Jun 26, 2017 at 2:05 PM David Feuer <david.fe...@gmail.com> wrote: > In the old days, DeriveDataTypeable enabled deriving both Data and > Typeable. As of a fairly recent GHC version (7.10? 8.0?), Typeable > instances are indeed derived automatically for all types that can get > such instances, so DeriveDataTypeable is only used for deriving Data > instances. I can't say whether it will ever be an error to write an > explicit `deriving Typeable` clause, but I don't see much point in > making it one. > > Unrelatedly, 8.2 has a complete overhaul of Typeable that you should > take a look at if you're interested in the class. The new > Type.Reflection API is much more powerful than the old Data.Typeable > one. > > On Mon, Jun 26, 2017 at 1:17 PM, Chris Martin <ch.mar...@gmail.com> wrote: > > Exhibit A: > > > >> With -XDeriveDataTypeable, you can derive instances of the class Data, > >> defined in Data.Data. See "Deriving Typeable instances" for deriving > >> Typeable. > > > > Exhibit B: > > > >> -XDeriveDataTypeable > >> Enable automatic deriving of instances for the Typeable typeclass > > > > Exhibit C: > > > >> Derived instances of Typeable are ignored, and may be reported as an > error > >> in a later version of the compiler. > > > > ---------------- > > > > A and B seem contradictory: Is this extension for deriving Data, or for > > deriving Typeable? > > > > B and C seem... not technically contradictory, but why is there an > extension > > that enables the deriving of instances that will just be ignored? > > > > Is this extension meant to be deprecated? > > > > From experimentation, it seems like all types automatically get Typeable > > instances whether you declare it or not. Is that accurate? > > > > _______________________________________________ > > Glasgow-haskell-users mailing list > > Glasgow-haskell-users@haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users > > >
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