[GHC] #8177: Roles for type families

[GHC]

#8177: Roles for type families
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        Reporter:  simonpj           |            Owner:  goldfire
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by jwlato):

 It's only outside the scope of this request if you insist on the rule that
 parameters at role R can't be matched against.  I think I agree with
 Richard's analysis that this would entail a data family that does
 representational matching.

 I do think this is a valuable feature as ghc-7.8 broke code some code in
 the wild, so I'll make a new ticket.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8177#comment:15>
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