[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 basvandijk):

 Maintainer of `monad-control` here.

 Do I get the following right (I haven't looked at this in detail yet):

 To work around not having to use the unstable `ImpredicativeTypes`  I
 should turn the [https://github.com/basvandijk/monad-
 control/blob/master/Control/Monad/Trans/Control.hs#L143 Run] type synonym
 into a `newtype`.

 Then at every call site of [https://github.com/basvandijk/monad-
 control/blob/master/Control/Monad/Trans/Control.hs#L127 liftWith] I need
 to unwrap the `newtype` to be able to apply the inner function.

 ?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9569#comment:10>
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