[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):

 Thanks. I have not been following the thread in detail, because I've been
 hoping it would reach a conclusion in the form of a wiki page summarising
 the proposal.

 Thank you for making a start on it. But I can't understand it (yet) I'm
 afraid.  Could you have a go at clarifying.  In particular:

  * What, precisely, IS the proposal? Perhaps you can add a section heading
 "The proposal" that says, as precisely as possible, what the changes (from
 the point of view of the user) are.

  Is there any new syntax? Are there any new system-provided functions?
 Does type inference change?  (For example, the wiki page mentions `using`,
 but I have no idea what it is.)

  * You could have a sub-section "What this proposal is NOT", covering the
 bit about overlapping instances.

  * Several examples of using the new facility. Again a section "Examples
 of use".

  * Then (and only then) some discussion about implementation.

 Thanks.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9819#comment:14>
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