[GHC] #9293: GHCI :unset -XLanguageExtension returns "don't know how to reverse -XLanguageExtension"

[GHC]

#9293: GHCI :unset -XLanguageExtension returns "don't know how to reverse
-XLanguageExtension"
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              Reporter:  jfeltz            |            Owner:  leroux
                  Type:  bug               |           Status:  patch
              Priority:  normal            |        Milestone:
             Component:  GHCi              |          Version:  7.8.2
            Resolution:                    |         Keywords:  newcomer
      Operating System:  Unknown/Multiple  |     Architecture:  x86
       Type of failure:  None/Unknown      |       Difficulty:  Unknown
             Test Case:  T9293             |       Blocked By:
              Blocking:                    |  Related Tickets:
Differential Revisions:  Phab:D516         |
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Changes (by leroux):

 * status:  new => patch
 * differential:   => Phab:D516


Comment:

 Patch that essentially rewrites {{{:unset -X<ext>}}} to {{{:set
 -XNo<ext>}}}.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9293#comment:5>
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