[GHC] #9220: type roles for unboxed arrays

[GHC]

#9220: type roles for unboxed arrays
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              Reporter:  rwbarton    |            Owner:  goldfire
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Core        |          Version:  7.8.1
  Libraries                          |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 Sorry for missing the second question.

 If we change roles from representational to nominal, then some uses of GND
 will no longer type check. This is correct behavior. With `UArray` having
 its representational role back, the code in comment:11 will type check.

 I think a fuller answer is that, according to Reid's analysis in
 comment:3, we don't want to be able to coerce a `StorableArray i Int` to a
 `StorableArray i Age`, because `Age` and `Int` might have different
 `Storable` instances. So, if GND fails, that's correct behavior.

 In any case, I will wait for Reid (or someone else knowledgeable about
 `array`) to give explicit instructions on what to do.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9220#comment:15>
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