[GHC] #11427: TypeSynonyms not deduced

[GHC]

#11427: TypeSynonyms not deduced
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        Reporter:  phadej            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by phadej):

 Ok, so this is special case which has a elegent-enough workaround. I guess
 the error message could be better:

 {{{
     • Could not deduce (SListI xss)
         arising from the superclasses of an instance declaration
       from the context: All SListI xss
         bound by the instance declaration at foo.hs:39:3-40

     Note: superclasses of (All SListI xss) aren't considered,
           because it's no smaller then the instance head.
 }}}

 or some variation of that.

 ''arising from the superclasses of an instance'' is a bit misleading in
 this case.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11427#comment:5>
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