[GHC] #13146: Doc for RealWorld refers to non-existent "ptrArg"

[GHC]

#13146: Doc for RealWorld refers to non-existent "ptrArg"
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           Reporter:  chris-martin   |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Prelude        |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The haddock for `RealWorld` says:

 > `RealWorld` is deeply magical. It is ''primitive'', but it is not
 ''unlifted'' (hence `ptrArg`). We never manipulate values of type
 `RealWorld`; it's only used in the type system, to parameterise `State#`.

 The "(hence `ptrArg`)" doesn't seem to make any sense. There is no
 identifer named `ptrArg` anywhere in the GHC repository. Is this a typo,
 or a reference to something that no longer exists?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13146>
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