[GHC] #10503: The impossible happened (no skolem info) - untouchable kind variable

9 Jun 2015


      #10503: The impossible happened (no skolem info) - untouchable kind variable
-------------------------------------+-------------------------------------
              Reporter:              |             Owner:
  AlekseyKliger                      |            Status:  new
                  Type:  bug         |         Milestone:
              Priority:  normal      |           Version:  7.10.1
             Component:  Compiler    |  Operating System:  Unknown/Multiple
              Keywords:              |   Type of failure:  Compile-time
          Architecture:              |  crash
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 {{{#!hs
 {-# LANGUAGE RankNTypes, PolyKinds, DataKinds, TypeFamilies #-}
 module GHCBug where

 data Proxy p = Proxy

 data KProxy (a :: *) = KProxy

 h :: forall r . (Proxy ('KProxy :: KProxy k) ~ Proxy ('KProxy :: KProxy *)
 => r) -> r
 h = undefined
 }}}

 GHC reports

 {{{
 GHCBug.hs:8:6:
     Couldn't match kind ‘k’ with ‘*’
       ‘k’ is untouchable
         inside the constraints (Proxy 'KProxy ~ Proxy 'KProxy)
         bound by the type signature for
                    h :: (Proxy 'KProxy ~ Proxy 'KProxy) => r
         at GHCBug.hs:8:6-87ghc: panic! (the 'impossible' happened)
   (GHC version 7.10.1 for x86_64-unknown-linux):
         No skolem info: k_amc[sk]
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10503
GHC http://www.haskell.org/ghc/
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