[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 goldfire):

 That syntax precludes the possibility of `result` being the name of an
 argument to the function. Using `Result` avoids this problem, but that
 would be a capitalized keyword, which is strange. The other possibility
 that avoids stealing the name `result` is to use the type family itself to
 represent the result: `type family F a | F -> a`, but that's a little
 strange. I guess I favor the last syntax the most.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6018#comment:46>
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