[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 simonpj):

 I'm concentrating on the section "Base proposal".  It says "Expose the
 constructor of the dictionary datatype created by desugaring typeclasses".
 But what does that mean?

  * Is there any new syntax? If so what, precisely?
  * Are there any new types available? How are they declared and used?
  * Are there any new functions available? If so which, and with what
 types?
  * Does type inference change at all? If so how?
  * Could you give some examples of usage?

 I know it's hard, but you can't define a language feature in one
 paragraph!

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9819#comment:17>
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