[GHC] #8165: Use GeneralizedNewtypeDeriving to automatically create associated type families

[GHC]

#8165: Use GeneralizedNewtypeDeriving to automatically create associated type
families
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        Reporter:  MikeIzbicki       |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      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 goldfire):

 This auto-generation seems to be rather different from the way
 `GeneralizedNewtypeDeriving` works in other contexts. In particular, the
 instances that you're generating are not directly related to any existing
 instances. Are you proposing that type families used on derived instances
 should just "look through" the newtype and be applied to the base type? Or
 only in cases with type variables? And, where does the `HasRing a =>`
 constraint come from?

 Without those constraints, I can see more of a coherent and general
 picture here... but it doesn't seem like `GeneralizedNewtypeDeriving` to
 me. Perhaps you're really proposing a new extension for generation of type
 family instances for newtypes?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8165#comment:4>
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