[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:  goldfire
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.2
  (Type checker)                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  rejects valid program              |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Is it ok to remove the para about "non-parametric" equations?

 Re your question, no that `S` doesn't have a CUSK, any more than
 {{{
 data T a b = MkT (T a b) a b
 }}}
 does.  It's "obvious" that `S`'s RHS has kind `*`, but only because you
 have mentally done kind inference on `S`'s right hand side.

 Of course, the example you give would be accepted in fact.  Neither has a
 CUSK, but normal inference and generalisation suffices.  There is no
 polymorphic recursion.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9200#comment:35>
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