[GHC] #5498: Generalized newtype deriving allows creating of instances I can't create by hand

[GHC]

#5498: Generalized newtype deriving allows creating of instances I can't create by
hand
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        Reporter:  dterei            |            Owner:
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:  7.6.2
       Component:  Compiler          |          Version:  7.3
      Resolution:  fixed             |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:  1496
        Blocking:                    |  Related Tickets:
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Changes (by nomeata):

 * status:  new => closed
 * resolution:   => fixed


Comment:

 This should not be possible any more: In the type `intIso :: forall c. c t
 -> c Int`, `c`’s type parameter is considered to be nominal, so `coerce`
 will not allow changing `c (Down a)` to `c a` any more. And GND is now
 based on `Coercible`...

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5498#comment:9>
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