Re: [GHC] #9761: Foldable cannot be derived by GND due to redundant contexts

5 Nov 2014

      #9761: Foldable cannot be derived by GND due to redundant contexts
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              Reporter:  dfeuer      |            Owner:  dfeuer
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:
             Component:  Core        |          Version:  7.9
  Libraries                          |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  rejects valid program              |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D425   |
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Comment (by Herbert Valerio Riedel ):

 In [changeset:"0a8e8995fd31dd46fa9bdbc7f65984b51c8c13dc/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="0a8e8995fd31dd46fa9bdbc7f65984b51c8c13dc"
 Remove redundant contexts from Foldable methods

 New `Foldable` methods accidentally had `Foldable` contexts, which led
 to type roles being assigned incorrectly and preventing GND from
 deriving `Foldable` instances. Removing those fixes #9761.

 Moreover, this patch takes advantage of this fix by deriving
 `Foldable` (and `Eq`) for `UniqFM`.

 Differential Revision: https://phabricator.haskell.org/D425
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9761#comment:6
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