[GHC] #11467: Panic while type checking expression using function with context holes

[GHC]

#11467: Panic while type checking expression using function with context holes
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           Reporter:  HairyDude      |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       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
 module Bug where

 holey :: _ => _
 holey = undefined

 useHoley = holey True
 }}}

 {{{
 $ ghc Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:3:10:
     Found hole ‘_’ with inferred constraints: ()
     To use the inferred type, enable PartialTypeSignatures
     In the type signature for ‘holey’: _ => _

 Bug.hs:3:15:
     Found hole ‘_’ with type: w_1
     Where: ‘w_1’ is a rigid type variable bound by
                  the inferred type of holey :: w_1 at Bug.hs:4:1
     To use the inferred type, enable PartialTypeSignatures
     In the type signature for ‘holey’: _ => _

 Bug.hs:6:12:
     Couldn't match expected type ‘Bool -> t0’ with actual type ‘w_’
       ‘w_’ is untouchable
         inside the constraints ()
         bound by the inferred type of useHoley :: t0
         at Bug.hs:6:1-21ghc: panic! (the 'impossible' happened)
   (GHC version 7.10.3 for x86_64-unknown-linux):
         No skolem info: w__alO[sk]

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

 $ ghc --version
 The Glorious Glasgow Haskell Compilation System, version 7.10.3
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11467>
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