[GHC] #9569: Tuple constraints don't work right

[GHC]

#9569: Tuple constraints don't work right
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              Reporter:  simonpj     |            Owner:
                  Type:  bug         |           Status:  closed
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.2
            Resolution:  fixed       |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
  polykinds/T9569,                   |
  typecheck/should_compile/T9569a    |
              Blocking:              |
Differential Revisions:              |
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Comment (by luite):

 I just wanted to check if this is not an unexpected side effect of the
 patch, since I didn't see any mention of this.

 I avoid `-XImpredicativeTypes` in my own code, but GHCJS indirectly
 depends on the `monad-control` and `lifted-base` packages, which fail to
 build now because they do use it, so I can't test GHCJS anymore on the
 latest head. I haven't found a workaround yet.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9569#comment:7>
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