Re: [GHC] #15076: Typed hole with higher-rank kind causes GHC to panic (No skolem info)

31 May 2018

      #15076: Typed hole with higher-rank kind causes GHC to panic (No skolem info)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |             Keywords:  TypedHoles,
      Resolution:                    |  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14040, #14880    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Another example of this bug, discovered in
 https://github.com/goldfirere/ghc/issues/57 :

 {{{#!hs
 {-# LANGUAGE PolyKinds, MultiParamTypeClasses, GADTs, ScopedTypeVariables,
              TypeOperators #-}
 {-# OPTIONS_GHC -fno-warn-redundant-constraints #-}

 module Super where

 import Data.Proxy
 import GHC.Prim

 class (a ~ b) => C a b
 data SameKind :: k -> k -> * where
   SK :: SameKind a b

 bar :: forall (a :: *) (b :: *). C a b => Proxy a -> Proxy b -> ()
 bar _ _ = const () (undefined :: forall (x :: a) (y :: b). SameKind x y)
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15076#comment:7
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