[GHC] #13178: Generalize type of runRW#

[GHC]

#13178: Generalize type of runRW#
-------------------------------------+-------------------------------------
           Reporter:  dfeuer         |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Currently, we have

 {{{#!hs
 runRW# :: (State# RealWorld -> (# State# RealWorld, o #)) -> (# State#
 RealWorld, o #)
 }}}

 where `o` is open-kinded. This type is a bit annoying, because `runRW#` is
 very often used in contexts where we want to discard the state token. I
 think it should be easy to generalize, however:

 {{{#!hs
 runRW# :: (State# RealWorld -> o) -> o
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13178>
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