[GHC] #8185: Change role annotation syntax

[GHC]

#8185: Change role annotation syntax
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        Reporter:           |            Owner:  goldfire
  goldfire                  |           Status:  new
            Type:  feature  |        Milestone:  7.8.1
  request                   |          Version:  7.7
        Priority:  normal   |         Keywords:
       Component:           |     Architecture:  Unknown/Multiple
  Compiler                  |       Difficulty:  Moderate (less than a day)
      Resolution:           |       Blocked By:
Operating System:           |  Related Tickets:
  Unknown/Multiple          |
 Type of failure:           |
  None/Unknown              |
       Test Case:           |
        Blocking:           |
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Comment (by carter):

 Theres really two types of code folks will be writing in 7.8

 1. Code that should be backwards compatible with prior GHCs, and in some
 cases even be (essentially) Haskell98

 2. code that is unconditionally using ghc features only available in 7.8
 and newer.

 It sounds like theres sound arguments for both the Pragma approach, and a
 clear "its part of the type, lets embrace that" approach.
 Having both would create its own complexity, but is that perhaps the best
 approach?


 terrible strawman that probably is a bad idea : a simpler solution is just
 to use the GHC CPP pass and have a different data / type declaration for
 the with vs without roles codes. This might result in a A LOT of CPP
 though for certain libraries.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8185#comment:6>
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