[GHC] #13879: Strange interaction between higher-rank kinds and type synonyms

[GHC]

#13879: Strange interaction between higher-rank kinds and type synonyms
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"fae672f647fe00c303d8fb56971563c1a76ad04e/ghc" fae672f/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="fae672f647fe00c303d8fb56971563c1a76ad04e"
 Fix constraint solving for forall-types

 Trac #13879 showed that when we were trying to solve

   (forall z1 (y1::z1). ty1)  ~  (forall z2 (y2:z2). ty2)

 we'd end up spitting out z1~z2 with no binding site for them.
 Those kind equalities need to be inside the implication.

 I ended up re-factoring the code for solving forall-equalities.
 It's quite nice now.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13879#comment:4>
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