[GHC] #7854: Constrained method type accepted in Haskell 98 mode

[GHC]

#7854: Constrained method type accepted in Haskell 98 mode
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        Reporter:  refold            |                   Owner:  thomie
            Type:  bug               |                  Status:  closed
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler (Type    |                 Version:  7.6.3
  checker)                           |                Keywords:  newcomer
      Resolution:  fixed             |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |  module/mod39
 Related Tickets:  #10118, #10119    |                Blocking:
                                     |  Differential Revisions:  Phab:D688
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Comment (by simonpj):

 Two thoughts
  * I'm relaxed about what we choose here.  It really matters little; and
 it's been a long-standing bug in GHC.

  * You do have a point: that `FlexibleContexts` sounds as if it has to do
 with type-signature contexts (and it does); and so does
 `ConstrainedClassMethods`.  So perhaps it would be more intuitive to make
 `FlexibleContexts` imply `ConstrainedClassMethods` than
 `MultiParamTypeClasses`?

 But I bet there are packages that use `MultiParamTypeClasses` but not
 `FlexibleContexts`.  So

  * Perhaps we should try making `FlexibleContexts` imply
 `ConstrainedClassMethods`, but ''not'' `MultiParamTypeClasses`, just to
 see what happens.
  * If it's painful, then maybe the path of least resistance is to make
 both imply `ConstrainedClassMethods`.

 Any views from others?  Would someone like to try the experiment?


 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7854#comment:22>
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