[GHC] #12709: GHC panic

[GHC]

#12709: GHC panic
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nfrisby):

 I don't know if it's exactly the same as this ticket, but I get a similar
 panic from the following minimization.

 {{{#!hs
 {-# Language TypeFamilies, TypeInType #-}

 import Data.Kind (Type)

 data U = U

 type family A (k :: Type) :: Type where
   A U = Type

 type family B (ty :: k) :: A k

 bad :: B 'U -> U
 bad _ = U
 }}}

 That gives the following panic when loaded in GHCi.

 {{{
 ghc.exe: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-mingw32):
         kindPrimRep.go U
 }}}

 It does not panic when ''compiling'' with GHC.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12709#comment:2>
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