[GHC] #8827: Inferring Safe mode with GeneralizedNewtypeDeriving is wrong

[GHC]

#8827: Inferring Safe mode with GeneralizedNewtypeDeriving is wrong
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        Reporter:  goldfire          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc1
      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):

 OK, but what does "access the symbols" mean, exactly?  The kind of a type
 constructor may change if you change its implementation; and similarly its
 roles.  I think it should be fine to coerce `T Age` to `T Int`, even if
 T's constructors are not visible, unless T's author declares T's role to
 be nominal.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8827#comment:3>
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