[GHC] #6018: Injective type families

[GHC]

#6018: Injective type families
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              Reporter:  lunaris     |            Owner:  jstolarek
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  7.4.1
             Component:  Compiler    |         Keywords:  TypeFamilies,
            Resolution:              |  Injective
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:  #4259
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D202   |
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Comment (by goldfire):

 Replying to [comment:76 simonpj]:
 >  * My brain is too small to think about verifying injectivity for closed
 families. Richard?

 I've put some comments on the wiki page. But the whole thing makes me a
 little nervous, as closed type families are really squirrelly. I would
 want something resembling a proof before feeling truly confident. As a
 first pass, we could always treat the equations of a closed family as
 independent (like an open family). I believe that such a treatment would
 be fully conservative.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6018#comment:81>
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