We need to add role annotations for 7.8

[Austin Seipp]

Here's the bug:

https://github.com/ghc/packages-containers/blob/ghc-head/Data/Set/Base.hs#L232

Note it should be __GLASGOW_HASKELL__ with two underscores at the end.
That's why the annotation was missed for Set only.

Richard, would you mind fixing this? Or anyone, really. We should also
use the above example I showed as a test case and put it in the
containers repository so GHC can pick it up.

Johan, you'll also have to do another release. :( Sorry.

On Fri, Mar 14, 2014 at 3:54 AM, Austin Seipp <austin at well-typed.com> wrote:
> *cough* I hate to be the bearer of bad news, but something went wrong
> it seems in HEAD:
>
> $ git describe
> ghc-7.9-start-188-g337bac3
> $ grep "^version\:" libraries/containers/containers.cabal
> version: 0.5.5.0
> $ ./inplace/bin/ghc-stage2 --interactive -XSafe
> GHCi, version 7.9.20140313: http://www.haskell.org/ghc/  :? for help
> Loading package ghc-prim ... linking ... done.
> Loading package integer-gmp ... linking ... done.
> Loading package base ... linking ... done.
> Prelude> import Data.Coerce
> Prelude Data.Coerce> import Data.Map
> Prelude Data.Coerce Data.Map> import Data.Set
> Prelude Data.Coerce Data.Map Data.Set> newtype Age = MkAge Int deriving Show
> Prelude Data.Coerce Data.Map Data.Set> let _ = coerce :: Map Int Int
> -> Map Int Age
> Prelude Data.Coerce Data.Map Data.Set> let _ = coerce :: Map Int Int
> -> Map Age Int
>
> <interactive>:7:9:
>     Could not coerce from ‘Map Int Int’ to ‘Map Age Int’
>       because the constructors of ‘Map’ are not imported
>       as required in SafeHaskell mode
>       because the first type argument of ‘Map’ has role Nominal,
>       but the arguments ‘Int’ and ‘Age’ differ
>       arising from a use of ‘coerce’
>     In the expression: coerce :: Map Int Int -> Map Age Int
>     In a pattern binding: _ = coerce :: Map Int Int -> Map Age Int
> Prelude Data.Coerce Data.Map Data.Set> let _ = coerce :: Set Int -> Set Age
> Prelude Data.Coerce Data.Map Data.Set> :i Set
> data Set a
>   = containers-0.5.5.0:Data.Set.Base.Bin {-# UNPACK #-}
> !containers-0.5.5.0:Data.Set.Base.Size
>                                          !a
>                                          !(Set a)
>                                          !(Set a)
>   | containers-0.5.5.0:Data.Set.Base.Tip
>   -- Defined in ‘containers-0.5.5.0:Data.Set.Base’
> instance Eq a => Eq (Set a)
>   -- Defined in ‘containers-0.5.5.0:Data.Set.Base’
> instance Ord a => Ord (Set a)
>   -- Defined in ‘containers-0.5.5.0:Data.Set.Base’
> instance (Read a, Ord a) => Read (Set a)
>   -- Defined in ‘containers-0.5.5.0:Data.Set.Base’
> instance Show a => Show (Set a)
>   -- Defined in ‘containers-0.5.5.0:Data.Set.Base’
> Prelude Data.Coerce Data.Map Data.Set> :i Map
> type role Map nominal representational
> data Map k a
>   = containers-0.5.5.0:Data.Map.Base.Bin {-# UNPACK #-}
> !containers-0.5.5.0:Data.Map.Base.Size
>                                          !k
>                                          a
>                                          !(Map k a)
>                                          !(Map k a)
>   | containers-0.5.5.0:Data.Map.Base.Tip
>   -- Defined in ‘containers-0.5.5.0:Data.Map.Base’
> instance (Eq k, Eq a) => Eq (Map k a)
>   -- Defined in ‘containers-0.5.5.0:Data.Map.Base’
> instance Functor (Map k)
>   -- Defined in ‘containers-0.5.5.0:Data.Map.Base’
> instance (Ord k, Ord v) => Ord (Map k v)
>   -- Defined in ‘containers-0.5.5.0:Data.Map.Base’
> instance (Ord k, Read k, Read e) => Read (Map k e)
>   -- Defined in ‘containers-0.5.5.0:Data.Map.Base’
> instance (Show k, Show a) => Show (Map k a)
>   -- Defined in ‘containers-0.5.5.0:Data.Map.Base’
> Prelude Data.Coerce Data.Map Data.Set>
>
>
> --------------------------------------------------------------
>
> As you can see, Map has the proper nominal representation (:i only
> shows it when it's other than strictly representational), but Set, for
> some reason, does not.
>
> I'll look into this. We should also certainly add tests to containers
> (under tests-ghc/) to make sure this doesn't slip by again.
>
> On Thu, Mar 13, 2014 at 5:03 PM, Austin Seipp <austin at well-typed.com> wrote:
>> That's right. If you had another instance of Ord for a newtype with
>> compare = flip compare, and were allowed to coerce the keys, you can
>> break it.
>>
>> On Thu, Mar 13, 2014 at 5:00 PM, Andres Löh <andres at well-typed.com> wrote:
>>> [Sorry for the self-reply.]
>>>
>>> Oh, perhaps I actually understand this:
>>>
>>>> Please forgive my ignorance w.r.t. roles, but why aren't all of these
>>>> representational?
>>>>
>>>>> Map k v -- k: nominal, v: represententional
>>>>> Set a -- k: nominal
>>>>
>>>> AFAIK both Map and Set are "normal" datatypes. Not GADTs, no type
>>>> families involved. Why would anything need to be "nominal" then?
>>>
>>> Is this because the integrity of these types relies on the Ord
>>> instance being sane, and a newtype could have a different Ord instance
>>> defined?
>>>
>>> Cheers,
>>>   Andres
>>> _______________________________________________
>>> Libraries mailing list
>>> Libraries at haskell.org
>>> http://www.haskell.org/mailman/listinfo/libraries
>>>
>>
>>
>>
>> --
>> Regards,
>>
>> Austin Seipp, Haskell Consultant
>> Well-Typed LLP, http://www.well-typed.com/
>
>
>
> --
> Regards,
>
> Austin Seipp, Haskell Consultant
> Well-Typed LLP, http://www.well-typed.com/



-- 
Regards,

Austin Seipp, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com/