[GHC] #12017: GHC panics on pattern synonym ‘kindPrimRep’

5 May 2016

      #12017: GHC panics on pattern synonym ‘kindPrimRep’
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           Reporter:  Iceland_jack   |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternSynonyms                    |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!hs
 {-# Language PatternSynonyms, GADTs #-}

 data Ty a where
   B :: Ty Bool

 class (Eq a, Ord a, Show a) => GetTy a where
   getTy :: Ty a

 instance GetTy Bool where
   getTy = B

 data Exp a where
   Constant :: GetTy a => Ty a -> a -> Exp a

 pattern MkBool :: () => (GetTy t, Bool ~ t) => t -> Exp t
 pattern MkBool bool = Constant B bool

 pattern Tru :: () => Bool ~ t => Exp t
 pattern Tru = MkBool True
 }}}

 with head:

 {{{
 $ ghci -ignore-dot-ghci /tmp/tywM.hs
 GHCi, version 8.1.20160503: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( /tmp/tywM.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.1.20160503 for x86_64-unknown-linux):
         kindPrimRep.go rep_a2tC

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
...
}}}

 {{{#!hs
 pattern Tru :: () => Bool ~ t => Exp t
 pattern Tru = Constant B True
 }}}

 works fine

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12017
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