[GHC] #10325: Clearify status of ImpredicativeTypes Extension

[GHC]

#10325: Clearify status of ImpredicativeTypes Extension
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              Reporter:              |             Owner:
  j80JjBjVNRMajmA                    |            Status:  new
                  Type:  bug         |         Milestone:
              Priority:  normal      |           Version:  7.10.1
             Component:              |  Operating System:  Unknown/Multiple
  Documentation                      |   Type of failure:  None/Unknown
              Keywords:              |        Blocked By:
          Architecture:              |   Related Tickets:
  Unknown/Multiple                   |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 There seem to be many statements about this extension and its problems
 floating around in the internet. But a user of GHC will first fall into a
 possibly large number of traps and problems before he finds them.

 I think it would help, if the GHC manual
 [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/other-
 type-extensions.html#impredicative-polymorphism] and the compiler warned
 about this extension (instead of suggesting it!).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10325>
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