You're in luck, David, since both of your requests are currently things that GHC will do. Specifically,
> 1. Prefer GND to the built-in derivations for Functor and Foldable, and > probably also Eq and Ord. GHC will always derive Eq and Ord instances for newtypes using GND, and will prefer GND when deriving Functor and Foldable instances for newtypes when (1) the -XGeneralizedNewtypeDeriving extension is on, and (2) eta-reducing the type variable is allowed. See [1] for the full details on how GHC chooses when to pick GND behind the scenes. > 2. Make DeriveTraversable imply DeriveFunctor and DeriveFoldable. That's already the case, thanks to Trac #9069. [2] Ryan S. ----- [1] https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/DerivingStrategies#Thederivingstrategyresolutionalgorithm [2] https://ghc.haskell.org/trac/ghc/ticket/9069 _______________________________________________ ghc-devs mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
