[GHC] #9667: Type inference is weaker for GADT than analogous Data Family

[GHC]

#9667: Type inference is weaker for GADT than analogous Data Family
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              Reporter:  carter      |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
  (Type checker)                     |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:  GHC         |
  rejects valid program              |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 Can you create a minimal example? I can't run your example in the original
 post because it has unstated dependencies, and the attached file has a lot
 of stuff that's presumably unrelated.

 But, it sounds like you want some sort of type-level injectivity guarantee
 on a GADT. Interesting thought.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9667#comment:3>
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