Hi, On Mon, Oct 7, 2013 at 10:32 AM, Dag Odenhall <[email protected]>wrote:
> Here‘s a thought: doesn’t Generic already have an unused phantom type > that's only there “just in case we need to add something in the future”? > No, it doesn't. Just a thought: what if we had a type family type family Derives (t :: k1) (c :: k2) :: Bool which would automatically be instantiated by GHC appropriately? E.g., if the user had the following code: data MyData = MyData deriving (Eq, Generic) deriving instance Show MyData instance Ord MyData GHC would automatically instantiate: type instance Derives MyData Eq = True type instance Derives MyData Generic = True type instance Derives MyData Show = True type instance Derives MyData Ord = False Would this be something Ryan could use for detecting safe instances for LVish? Cheers, Pedro
_______________________________________________ ghc-devs mailing list [email protected] http://www.haskell.org/mailman/listinfo/ghc-devs
