Re: [GHC] #11062: Type families + hs-boot files = panic (type family consistency check too early)

15 Dec 2016

      #11062: Type families + hs-boot files = panic (type family consistency check too
early)
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:  TypeFamilies
                                     |  hs-boot
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2215
       Wiki Page:                    |
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Comment (by ezyang):

 There is a technical difficulty with (1): we need to be able to
 distinguish between imported families and families which we are going to
 define. Unfortunately, these families are all bundled together in a
 `FamInstEnv`, and the only indication if it's local or external is in the
 `Name` of the `CoAxiom`, but we're not allowed to actually poke the
 `CoAxiom` to get this `Name` (since that will force the thunk.) So we need
 to carry along the `Name` of the `FamInstEnv`, or separate out
 local/external while we're typechecking the interface. The latter sounds
 less intrusive; we'll just end up with two FamInstEnvs in this case.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11062#comment:13
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