[GHC] #9822: Add displayException to Exception typeclass

[GHC]

#9822: Add displayException to Exception typeclass
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              Reporter:  snoyberg    |            Owner:  snoyberg
                  Type:  feature     |           Status:  patch
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:
             Component:  Core        |         Keywords:  base
  Libraries                          |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Easy (less than 1
      Operating System:              |  hour)
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D517   |
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"3222b7ae347be092bdd414f7b43bee18861b0e1e/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="3222b7ae347be092bdd414f7b43bee18861b0e1e"
 Add displayException method to Exception (#9822)

 Defaults to using `show` to prevent any breakage of existing code.  Also
 provide a custom implementation for `SomeException` which uses the
 underlying exception's `displayException`.

 Differential Revision: https://phabricator.haskell.org/D517
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9822#comment:4>
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