[GHC] #4455: Add Applicative instance for ST

[GHC]

#4455: Add Applicative instance for ST
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    Reporter:  pumpkin           |       Owner:                
        Type:  proposal          |      Status:  new           
    Priority:  normal            |   Component:  libraries/base
     Version:  6.12.3            |    Keywords:                
    Testcase:                    |   Blockedby:                
          Os:  Unknown/Multiple  |    Blocking:                
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown  
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 ST has a Functor and a Monad instance, but no Applicative instance. This
 patch by Bas van Dijk adds such an instance.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4455>
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