Hey, that's an awesome formulation! Thanks Pedro. Any idea how much work this would be to implement in GHC, if it did garner approval?
On Tue, Oct 8, 2013 at 3:48 AM, José Pedro Magalhães <[email protected]>wrote: > 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 > >
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