Proposal: GHC.Generics marked UNSAFE for SafeHaskell

[Ryan Newton]

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 <dreixel at gmail.com>wrote:

> Hi,
>
> 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
> LVish?
>
>
> Cheers,
> Pedro
>
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