Proposal: GHC.Generics marked UNSAFE for SafeHaskell
José Pedro Magalhães
Tue Oct 8 07:48:51 UTC 2013
On Mon, Oct 7, 2013 at 10:32 AM, Dag Odenhall <dag.odenhall at gmail.com>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
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