[GHC] #9371: Overlapping type families, segafult

[GHC]

#9371: Overlapping type families, segafult
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              Reporter:  pingu          |            Owner:
                  Type:  bug            |           Status:  new
              Priority:  normal         |        Milestone:
             Component:  Compiler       |          Version:  7.8.3
            Resolution:                 |         Keywords:
      Operating System:  Linux          |     Architecture:  x86_64 (amd64)
       Type of failure:  Runtime crash  |       Difficulty:  Unknown
             Test Case:                 |       Blocked By:
              Blocking:                 |  Related Tickets:
Differential Revisions:                 |
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Comment (by simonpj):

 OK I agree that the same issue arises if `IdentityT` was a data type, so
 my point about newtype unwrapping for `IdentityT` was a bit of a red
 herring.

 And yes I agree that this "silly example" is indeed a case where eta-
 reduction of newtype axioms (and data/newtype instance!) axioms is useful.
 And since the code is implemented, I suppose that the shortest path is to
 fix the conflict detector.

 But it does hurt me that we have NO formalised description of the eta-
 reduction story in any of our papers.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9371#comment:7>
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