[GHC] #9242: Implement {-# OVERLAPPABLE #-} and {-# INCOHERENT #-} pragmas

[GHC]

#9242: Implement {-# OVERLAPPABLE #-} and {-# INCOHERENT #-} pragmas
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              Reporter:  simonpj     |            Owner:  diatchki
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.2
             Component:  Compiler    |         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 simonpj):

 Replying to [comment:23 goldfire]:
 > As to comment:22, it sounds like you wish to distinguish between
 `INCOHERENTABLE` and `INCOHERENTING`. (I don't want to use those names,
 just draw the parallel to the `OVERLAP` pragmas.) Is this a reasonable
 interpretation of what you're saying?

 Yes, but I ''really'' don't want to actually have that complexity.
 Obvious alternatives:
  * Current behaviour: INCOHERENT means INCOHERNTING
  * Behaviour proposed in comment:22: INCOHERENT means INCOHERENTABLE
  * Another alternative: INCOHERENT means both INCOHERENTING and
 INCOHERENTABLE

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9242#comment:24>
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