[GHC] #10326: ImpredicativeTypes: Unable to use in Functor etc..

[GHC]

#10326: ImpredicativeTypes: Unable to use in Functor etc..
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        Reporter:  j80JjBjVNRMajmA   |                   Owner:
            Type:  bug               |                  Status:  closed
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:  wontfix           |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Changes (by goldfire):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 `ImpredicativeTypes` is thoroughly broken and is unsupported. In the past,
 this extension was more properly implemented, but caused more grief than
 help even then.

 If you want this kind of thing, use a `newtype` instead of a `type`. It's
 surely more annoying, but it's better to have an annoying option instead
 of a totally-broken one.

 There are a number of Very Clever People working on integrating
 impredicativity with GHC-style type inference. (I'm not one of them,
 however.) In GHC's view, there has not yet been the right solution. We all
 look forward to when the right solution is found!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10326#comment:1>
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