[GHC] #11399: Ill-kinded instance head involving -XTypeInType can invoke GHC panic

10 Jan 2016


      #11399: Ill-kinded instance head involving -XTypeInType can invoke GHC panic
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           Reporter:  RyanGlScott    |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
  (Type checker)                     |
           Keywords:  TypeInType     |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This code:

 {{{#!hs
 {-# LANGUAGE FlexibleInstances, TypeInType #-}
 module FvProvFallsIntoAHole where

 import Data.Kind

 newtype UhOh (k :: * -> *) (a :: k *) = UhOh (k *)
 instance Functor k => Functor (UhOh k) where
 }}}

 produces this GHC panic:

 {{{
 $ /opt/ghc/head/bin/ghc FvProvFallsIntoAHole.hs
 [1 of 1] Compiling FvProvFallsIntoAHole ( FvProvFallsIntoAHole.hs,
 FvProvFallsIntoAHole.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.1.20160108 for x86_64-unknown-linux):
         fvProv falls into a hole {aq6}

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

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11399
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