Re: [GHC] #11534: Allow class associated types to reference functional dependencies

2 Mar 2016

      #11534: Allow class associated types to reference functional dependencies
-------------------------------------+-------------------------------------
        Reporter:  ekmett            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |             Keywords:  TypeFamilies,
      Resolution:                    |  FunctionalDependencies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ekmett):

 Using the rough elaboration scheme I mentioned above, isn't it just this?

 {{{#!hs
 instance Foo a b => Foo [a] [b] where
     type Foo_FD1 [a] = [Foo_FD1 a]
 }}}

 After all:

 {{{#!hs
 type Foo_FD1 [a] = [b] = [Foo_FD1 a]
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11534#comment:26
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