[GHC] #9112: support for deriving Vector/MVector instances

[GHC]

#9112: support for deriving Vector/MVector instances
-------------------------------------+------------------------------------
        Reporter:  jwlato            |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
-------------------------------------+------------------------------------

Comment (by bitemyapp):

 I am trying to build hackage-server on Mac OS X with GHC 7.8 and I was
 told this ticket is relevant to my problems.

 I've included the build error in this comment.

 {{{
     When deriving the instance for (VecMut.MVector
                                       VecBase.MVector DocId)

 Distribution/Server/Features/Search/DocIdSet.hs:38:13:
     Could not coerce from ‘Data.Vector.Primitive.Mutable.MVector
                              s Word32’ to ‘VecBase.MVector s DocId’
       because ‘Data.Vector.Primitive.Mutable.MVector
                  s Word32’ and ‘VecBase.MVector s DocId’ are different
 types.
       arising from the coercion of the method ‘VecMut.basicOverlaps’
                    from type
                    ‘forall s.
                     VecBase.MVector s Word32 -> VecBase.MVector s Word32
 -> Bool’
                    to type
                    ‘forall s.
                     VecBase.MVector s DocId -> VecBase.MVector s DocId ->
 Bool’
     Possible fix:
       use a standalone 'deriving instance' declaration,
         so you can specify the instance context yourself
     When deriving the instance for (VecMut.MVector
                                       VecBase.MVector DocId)

 Distribution/Server/Features/Search/DocIdSet.hs:38:13:
     Could not coerce from ‘Data.Vector.Primitive.Mutable.MVector
                              s Word32’ to ‘VecBase.MVector s DocId’
       because ‘Data.Vector.Primitive.Mutable.MVector
                  s Word32’ and ‘VecBase.MVector s DocId’ are different
 types.
       arising from the coercion of the method ‘VecMut.basicUnsafeSlice’
                    from type
                    ‘forall s.
                     Int -> Int -> VecBase.MVector s Word32 ->
 VecBase.MVector s Word32’
                    to type
                    ‘forall s.
                     Int -> Int -> VecBase.MVector s DocId ->
 VecBase.MVector s DocId’
     Possible fix:
       use a standalone 'deriving instance' declaration,
         so you can specify the instance context yourself
     When deriving the instance for (VecMut.MVector
                                       VecBase.MVector DocId)

 Distribution/Server/Features/Search/DocIdSet.hs:38:13:
     Could not coerce from ‘Data.Vector.Primitive.Mutable.MVector
                              s Word32’ to ‘VecBase.MVector s DocId’
       because ‘Data.Vector.Primitive.Mutable.MVector
                  s Word32’ and ‘VecBase.MVector s DocId’ are different
 types.
       arising from the coercion of the method ‘VecMut.basicLength’
                    from type ‘forall s. VecBase.MVector s Word32 -> Int’
 to type
                    ‘forall s. VecBase.MVector s DocId -> Int’
     Possible fix:
       use a standalone 'deriving instance' declaration,
         so you can specify the instance context yourself
     When deriving the instance for (VecMut.MVector
                                       VecBase.MVector DocId)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9112#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler