[GHC] #9183: GHC shouldn't expand constraint synonyms

[GHC]

#9183: GHC shouldn't expand constraint synonyms
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        Reporter:  Feuerbach         |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Feuerbach):

 Just tested it — doesn't seem to work.

 {{{
 {-# LANGUAGE FlexibleInstances, UndecidableInstances #-}

 class Show a => MyC a
 instance Show a => MyC a

 foo :: MyC a => a -> String
 foo = show
 }}}

 :t foo shows

 {{{
 foo :: Show a => a -> String
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9183#comment:6>
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