[GHC] #11516: Panic, "falls into a hole"

30 Jan 2016

      #11516: Panic, "falls into a hole"
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             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:
-------------------------------------+-------------------------------------
 {{{#!hs
 {-# language PolyKinds #-}
 {-# language FlexibleContexts #-}
 {-# language ConstraintKinds #-}
 {-# language FlexibleInstances #-}
 {-# language FunctionalDependencies #-}

 import GHC.Types (Constraint)

 class Ríki (p :: i -> i -> *)
 class (Ríki p) => Varpi p q f | f -> p q
 instance Varpi () () f => Varpi (->) (->) (Either f) where
 }}}

 causes

 {{{
 % ghci -ignore-dot-ghci /tmp/testing.hs
 GHCi, version 8.1.20160117: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( /tmp/testing.hs, interpreted )

 /tmp/testing.hs:11:10: error:ghc: panic! (the 'impossible' happened)
   (GHC version 8.1.20160117 for x86_64-unknown-linux):
         fvProv falls into a hole {a13R}

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

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11516
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler