[GHC] #8883: FlexibleContexts checking should happen also on inferred signature

[GHC]

#8883: FlexibleContexts checking should happen also on inferred signature
------------------------------------------------+--------------------------
        Reporter:  Blaisorblade                 |            Owner:
            Type:  bug                          |  jstolarek
        Priority:  normal                       |           Status:  closed
       Component:  Compiler                     |        Milestone:
      Resolution:  fixed                        |          Version:  7.6.3
Operating System:  Unknown/Multiple             |         Keywords:
 Type of failure:  None/Unknown                 |     Architecture:
       Test Case:  typecheck/should_fail/T8883  |  Unknown/Multiple
        Blocking:                               |       Difficulty:
                                                |  Unknown
                                                |       Blocked By:
                                                |  Related Tickets:
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Comment (by Lemming):

 You can rewrite the constraint
 {{{
  (Functor (PF a), Regular a)
 }}}
 to
 {{{
  (PF a ~ pfa, Functor pfa, Regular a)
 }}}
 and then it is no longer a FlexibleContext. However, this trick does not
 work in superclasses since you must only use class parameters there and
 you cannot introduce new variables.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8883#comment:15>
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