[GHC] #12791: Superclass methods could be more aggressively specialised.

[GHC]

#12791: Superclass methods could be more aggressively specialised.
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        Reporter:  mpickering        |                Owner:  danharaj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2714
       Wiki Page:                    |
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Comment (by mpickering):

 Dan, you should open a new ticket to talk about this change as it is
 unrelated. I think it is still unclear what is going on in the case of
 reflex but let's not side track this ticket. It isn't clear that instances
 such as the strange one in your ticket help at all. If at the call site, a
 specific `t` is known then the class methods of `Reflex` should be
 suitably specialised, if not then we should understand why it is not
 happening without resorting to hacks!

 I think there are plenty of real world examples of this, that isn't a
 worry.

 A simple one is

 {{{
 foo :: MonadWriter String m => m ()
 foo = ...
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12791#comment:23>
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