[GHC] #8566: Panic with kindFunResult

[GHC]

#8566: Panic with kindFunResult
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        Reporter:  dreixel           |            Owner:
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.7
      Resolution:  fixed             |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:  polykinds/T8566   |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by goldfire):

 I would say that `unA` in Pedro's (dreixel's) most recent example is
 indeed ill-typed -- it's an existential record selector, much like

 {{{
 data Ex where
   MkEx :: { unEx :: [a] } -> Ex
 }}}

 The error message, though, could be improved. With `unEx`, GHC accepts the
 declaration but then prevents any use of `unEx` in an expression position.
 I propose that the same be done with `unA`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8566#comment:6>
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