[GHC] #9515: Deprecate -XExplicitForAll

[GHC]

#9515: Deprecate -XExplicitForAll
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              Reporter:  dfeuer      |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Specifically, apart from `-XScopedTypeVariables`, the following flags
 imply `-XExplicitForAll`:
  * `-XRankNTypes`
  * `-XLiberalTypeSynonyms`
  * `-XExistentialQuantification`

 So the concrete proposal is:
  * Abolish `-XExplicitForAll`
  * Make the above three flags imply `-XScopedTypeVariables`, which in turn
 would switch on the `forall` keyword, and make type variables have lexical
 scope.

 I would be fine with this. I'd like to hear more opinions.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9515#comment:6>
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