[GHC] #10911: Allow left ∨ (+++) as minimal definition of ArrowChoice instance

[GHC]

#10911: Allow left ∨ (+++) as minimal definition of ArrowChoice instance
-------------------------------------+-------------------------------------
              Reporter:              |             Owner:
  mfdyck.google                      |
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  8.0.1
             Component:  Core        |           Version:  7.10.2
  Libraries                          |
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 Add default definitions of left, right in terms of (+++) to let one define
 an ArrowChoice instance in terms of (+++) rather than left, which is
 sometimes more elegant or convenient.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10911>
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