[GHC] #9163: Ptr should have a phantom role

[GHC]

#9163: Ptr should have a phantom role
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        Reporter:  simonpj           |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #9164
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Comment (by nomeata):

 I agree with rwbarton: The `Ptr`’s parameter is, in a sense, a convenience
 for the user. The API could just use `Ptr` without an argument, and users
 could use `Tagged a Ptr` if they want to track types. By that reasoning,
 `Ptr`’s argument should be phantom, as nothing in `Foreign.Ptr` takes `a`
 into account.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9163#comment:15>
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