[GHC] #6018: Injective type families

[GHC]

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

 It's a little hard to say whether or not injective type families would
 actually help with what I'm doing - it could well be that I don't just
 understand this type level magic enough! However, in a few cases where
 I've got stuck I've moved things to a GADT to witness the relation between
 types instead, which I believe does get me injectivity and from that
 points things seemed to "just work" - albeit requiring a bit more effort.
 I'll keep my eyes out, and try and provide examples here if I find
 anything concrete.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6018#comment:24>
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