[GHC] #11524: Something is amiss with quantification in pattern synonym type signatures

[GHC]

#11524: Something is amiss with quantification in pattern synonym type signatures
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by bgamari):

 * cc: niteria (added)


Comment:

 > It's a bug in the pretty-printer.

 Actually, I'm not entirely sure that this is the whole story.

 After pulling I'm now seeing,
 {{{
 $ inplace/bin/ghc-stage1 hi.hs
 [1 of 1] Compiling Main             ( hi.hs, hi.o )
 ghc-stage1: panic! (the 'impossible' happened)
   (GHC version 8.1.20160124 for x86_64-unknown-linux):
         ASSERT failed!
   file compiler/types/TyCoRep.hs line 1919
   in_scope InScope {k_aB4 k_aJd a_aJe b_aJf}
   tenv [auE :-> a_aJe[tau:5], auF :-> b_aJf[tau:5],
         aB3 :-> k_aJd[tau:5]]
   cenv []
   tys [fun_auD[sk] ~ a_auE[sk] b_auF[sk]]
   cos []
   needInScope [auD :-> fun_auD[sk], aB4 :-> k_aB4[tau:1]]

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

 Presumably this is niteria's in-scope set checks in action.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11524#comment:2>
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