[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
-------------------------------------+-------------------------------------
              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:              |
-------------------------------------+-------------------------------------

Comment (by spacekitteh):

 Upon perusing the dictionary creation source some more, it appears that it
 could be implemented by changing adding a flag to

 {{{
 mkClassDataConOcc   = mk_simple_deriv dataName "D:"     -- We go straight
 to the "real" data con
                                                         -- for datacons
 from classes
 }}}
 in compiler/basicTypes/OccName.hs like so

 {{{
 mkClassDataConOcc True  = mk_simple_deriv dataName ""
 mkClassDataConOcc False = mk_simple_deriv dataName "D:"
 }}}

 and change buildClass in compiler/iface/BuildTyCl.hs from:

 {{{
 ...
 ; datacon_name <- newImplicitBinder tycon_name mkClassDataConOcc
 }}}

 to

 {{{
 ; datacon_name <- newImplicitBinder tycon_name (mkClassDataConOcc
 visibleConstructor)
 }}}

 This would require modifying buildClass to accept DynFlags, though.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9819#comment:10>
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