[GHC] #12811: GHC tells me to use RankNTypes when it's already enabled

[GHC]

#12811: GHC tells me to use RankNTypes when it's already enabled
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Yes indeed.  Perhaps someone can arrange to suppress the suggestion if
 `RankNTypes` is already on?  That would help a bit, by removing the
 confusing suggestion.

 But it's hard to come up with a good error message for
 {{{
 a b . c d
 }}}
 as a type.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12811#comment:1>
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