[GHC] #14162: Core Lint error

27 Aug 2017

      #14162: Core Lint error
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           Keywords:  TypeInType     |  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
 {-# Options_GHC -dcore-lint #-}

 {-# Language TypeOperators, KindSignatures, DataKinds, PolyKinds,
 TypeFamilies, GADTs, TypeInType #-}

 import Data.Kind

 data family Sing (a :: k)

 data
   SubList :: [a] -> [a] -> Type where
   SubNil :: SubList '[] '[]
   Keep :: SubList xs ys -> SubList (x ': xs) (x ': ys)
   Drop :: SubList xs ys -> SubList xs (x ': ys)

 data instance
   Sing (x :: SubList ys xs) where
   SSubNil :: Sing SubNil
   SKeep   :: Sing x -> Sing (Keep x)
   SDrop   :: Sing x -> Sing (Drop x)
 }}}

 running it gives a massive core lint error, attached as a `lint.log`.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14162
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler