[GHC] #9200: Milner-Mycroft failure at the kind level

[GHC]

#9200: Milner-Mycroft failure at the kind level
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        Reporter:  ekmett                     |            Owner:
            Type:  bug                        |           Status:  new
        Priority:  normal                     |        Milestone:
       Component:  Compiler (Type checker)    |          Version:  7.8.2
      Resolution:                             |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  GHC rejects valid program  |  Unknown/Multiple
       Test Case:                             |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:
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Comment (by goldfire):

 By "2) Allow more flexible partial kind signatures", I meant that, under
 (NEWCUSK), the kind of un-annotated type variables ''can'' unify with
 lexically-scoped kind variables, allowing the following to type-check:

 {{{
 data Q f (a :: k) where
   MkQ :: f a -> Q f a
 -- fails under (PARTIAL) and (PARGEN)
 -- succeeds under (BASELINE) and (NEWCUSK)
 }}}

 If partial type signatures on terms are so useful (and I think they will
 be), then partial kind signatures, like the one on `Q`, would be, too.

 Yes, I am agreed with the examples in comment:21.

 (NEWCUSK) description was already on wiki page, and I have now added rules
 for closed type families. These rules are a breaking change from today's
 closed type families, but a "good" breakage, in that it tightens up the
 specification from the current wonky state of affairs. See the example
 from comment:18, which would no longer type-check.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9200#comment:22>
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