[GHC] #11142: Type-level skolem capture leads to core lint error

[GHC]

#11142: Type-level skolem capture leads to core lint error
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        Reporter:  goldfire          |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * cc: ekmett (added)


Comment:

 I don't think I even knew that!  The old behaviour is terribly
 inconsistent; type variables are quantified at top level, while kind
 variables are quantified locally.

 It is not at all easy to resurrect the old behaviour: the new data type
 for `HsType` simply can't express it, by design.  All the implicit binders
 are in `HsImplicitBinders` which are at the top.

 This is only going to be notice by people who using higher-rank functions
 where the nested higher-rank type is itself kind-polymorphic.  I don't
 think there are many such people.

 I'm strongly inclined not to worry.  I'm copying Edward who is the person
 on the planet most likely to have explored this particular corner.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11142#comment:6>
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