[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:              |
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Comment (by jstolarek):

 Replying to [comment:59 goldfire]:
 > plain old injectivity for open type families.

 > more involved reasoning for closed type families, where inference is
 possible

 I'm not sure what design choices are hidden by these two statements. Do
 you mean that for open type families we would have: a) simple injectivity
 in the result only (via annotations) or b) injectivity in some of the
 arguments (also via annotations); whereas for closed type families we
 would admit the same kind of injectivity declarations as for open type
 families and perhaps also injectivity inference as proposed by me in
 comment 58?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6018#comment:61>
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