[GHC] #16248: ImplicitParams does not imply FlexibleContexts or FlexibleInstances

[GHC]

#16248: ImplicitParams does not imply FlexibleContexts or FlexibleInstances
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        Reporter:  NeilMitchell      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Documentation     |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by AntC):

 `instance Foo XI ...` in the first case needs `TypeSynonymInstances`. That
 expands `XI` to `X Int`, then needs `FlexibleInstances`.

 `FlexibleInstances` is supposed to imply `TypeSynonymInstances`. I wonder
 if `ImplicitParams` switches on `FlexibleInstances` OK, but fails to also
 switch on `TypeSynonymInstances`?

 IOW try the code with `ImplicitParams` and `TypeSynonymInstances`, but not
 `FlexibleInstances`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16248#comment:1>
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