[GHC] #14292: Coercing between constraints of newtypes

[GHC]

#14292: Coercing between constraints of newtypes
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  Roles
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 I started a
 [https://www.reddit.com/r/haskell/comments/72zdwm/use_cases_for_type_classes_with_representational/
 reddit discussion].

 * `type role Coercible representational representational` is an example of
 a "type class" with representational roles.
 * [http://www.well-typed.com/blog/2015/07/checked-exceptions/ Well-Typed]
 has a `representational` example that could be `phantom` (`class Throws
 e`).
 *
 [https://www.reddit.com/r/haskell/comments/2iqrr5/video_simon_peyton_jones_zerocost_coercions_in/cl6k9ik/
 Sjoerd Visscher] wants this as early as 2 years ago.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14292#comment:10>
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