[GHC] #9111: base should export Typeable instances of its promoted data constructors

[GHC]

#9111: base should export Typeable instances of its promoted data constructors
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        Reporter:  goldfire          |            Owner:
            Type:  feature request   |           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 dreixel):

 Replying to [comment:11 goldfire]:
 > Would universally deriving `Typeable` break some abstraction guarantees?
 That is, if a library wanted to hide some types, could they be gotten
 through their (unhideable) `Typeable` instances? Template Haskell can
 surely do this, but I might be willing to ignore that particular attack.
 Are there others? What if a type is known but not the constructors? (I
 don't think `Typeable` can do this.) What about if a type synonym is known
 but the RHS isn't exported? (I bet it can do this.)

 `Typeable` knows nothing about the RHS of its type, so constructors are
 safe. Also, if you don't export a type nor any of its constructors, I
 don't see how you could use its |typeRep|, so I guess you're safe too
 (ignoring Template Haskell, of course).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9111#comment:12>
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