[GHC] #10190: Add a Monad instance for ((,) w)

[GHC]

#10190: Add a Monad instance for ((,) w)
-------------------------------------+-------------------------------------
              Reporter:  fumieval    |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:              |           Version:  7.8.4
  libraries/base                     |  Operating System:  Unknown/Multiple
              Keywords:              |   Type of failure:  None/Unknown
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
 Now Monoid is defined in GHC.Base; We can define a reasonable Monad
 instance for `(,) w`, as a writer monad.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10190>
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