[GHC] #8177: Roles for type families

[GHC]

#8177: Roles for type families
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              Reporter:  simonpj     |            Owner:  goldfire
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.6.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 Roles for data families (associated or not) cannot be inferred, because
 they are open. But, theoretically, they can be declared and then checked.
 That is the subject of this ticket. So, it conceivable to give the roles
 you ask for.

 But, you don't seem to need those roles, because you seem interested in
 coercing in and out of the newtype, not among different instantiations of
 the newtype. This is possible as long as the newtype constructor
 (`Quantity'`) is in scope. Roles aren't a part of the story, in your case.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8177#comment:21>
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