[GHC] #9618: Undocument ImpredicativeTypes

[GHC]

#9618: Undocument ImpredicativeTypes
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              Reporter:  dfeuer      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:              |          Version:  7.8.3
  Documentation                      |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  Documentation bug                  |  Related Tickets:  #8808
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 I'm not convinced `ImpredicativeTypes` should be removed from the manual.
 Sometimes^[''citation needed'']^ I have needed `ImpredicativeTypes` to get
 my code to type check. `ImpredicativeTypes` isn't ''wrong'' -- it's just
 very, very rough around the edges. It won't (as far as I know) cause your
 code to segfault or otherwise go astray. The extension just doesn't work
 in all the contexts we might like it to.

 So, instead of removing it altogether, I think we should label it as
 experimental and very limited.

 That all said, I don't feel terribly strongly about this and am happy
 enough if the majority disagrees with me here.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9618#comment:3>
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