[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 spacekitteh):

 >OK -- so it seems you want to be able to fuzz the */Constraint
 distinction.

 Sorta, yeah. More like having a data type of existential functions.

 I'm actually trying to work towards local instances (or at least, better
 library support for approximations of it like reflection). As such it is
 inappropriate for TH. Additionally, I wish for it to run on platforms
 without TH, such as ARM.

 I'm not really proposing a general language feature, but rather, allowing
 typesafe access to desugared syntax; any high level language design would
 almost certainly need access to it anyway, so this would be laying the
 foundation for experimentation in that area.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9819#comment:6>
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