[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 simonpj):

 I really don't see what we can reasonably do here.  e.g.
 {{{
 type Foo a = (Eq a, Ix a)
 }}}
 Now if you instantiate and re-generalise it's really not possible to
 reconstruct the `Foo a`. I suppose you could have a magical special case
 when there is a type synonym for a single constraint.  That might, just,
 be possible.  But it'd be a bit of effort to push it through, so I propose
 to wait until more people yell.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9183#comment:10>
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