[GHC] #9819: Create typesafe method of obtaining dictionary types from class definitions, and constraint objects from dictionary types

[GHC]

#9819: Create typesafe method of obtaining dictionary types from class
definitions, and constraint objects from dictionary types
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              Reporter:              |            Owner:
  spacekitteh                        |           Status:  new
                  Type:  feature     |        Milestone:
  request                            |          Version:
              Priority:  normal      |         Keywords:
             Component:  Compiler    |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Moderate (less
      Operating System:              |  than a day)
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 Replying to [comment:9 spacekitteh]:
 > Right. I'm not requesting local instances as a whole; rather, just
 access to the desugared typeclass dictionary types. Basically, adding a
 Dictionary kind, and a type function from Constraint kinds to Dictionary
 kinds (local instances could involve adding a type function in the reverse
 direction). Additionally, a Coercible instance for the class and the
 dictionary would be useful too.
 >
 > This seems like it would be fairly straightforward to implement and not
 involve much design work; the problems seem to only arise when going from
 Dictionary -> Constraint.

 Ah. This makes sense.

 But, before diving into implementation, we need a clear specification of
 the feature, preferably on a wiki page. The page should contain motivation
 and examples of programs that you wish to be accepted. Then, we'll all
 have a better idea of what we're discussing.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9819#comment:11>
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