[GHC] #10607: Auto derive from top to bottom

[GHC]

#10607: Auto derive from top to bottom
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        Reporter:  songzh            |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:  deriving,
Operating System:  Unknown/Multiple  |  typeclass, auto
 Type of failure:  None/Unknown      |            Architecture:
      Blocked By:                    |  Unknown/Multiple
 Related Tickets:                    |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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Comment (by goldfire):

 Yes -- TH struggles a bit with instance lookup and such. Implementing new
 querying features shouldn't be hard though, if you can suggest an API.

 Why do you need fancy querying capabilities for your use case? Where does
 `reifyInstances` fail for you? As for type synonyms, you can check out the
 `th-expand-syns` package. `th-desugar` also does (limited) type family
 expansion (among other, larger features).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10607#comment:5>
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