[GHC] #6018: Injective type families

[GHC]

#6018: Injective type families
-------------------------------------+-------------------------------------
              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 simonpj):

 Before embarking on the implementation, is everyone convinced that the
 proposed syntax
 {{{
 type family F a :: *
    | result -> a
 }}}
 is the best one?  I understand the desire to support injectivity in some
 parameters but not others.

 For ''closed'' type classes, can't we infer injectivity, rather than
 having to declare it?  (Although I suppose that the ability to declare is
 always a Good Thing.)

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6018#comment:45>
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