[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:
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Comment (by simonpj):

 Well, remember that even if Ptr has a phantom role, the two types (Ptr
 Int) and (Ptr Double) would be different types.  It's just that you could
 *coerce* between them.  Which is perhaps not unreasonable.  Indeed that is
 precisely what castPtr does.  It’s not silent or implicit.

 I still don't see why it would be bad to make `Ptr` phantom.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9163#comment:3>
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