[GHC] #8978: Type synonyms in class associated types behave strangely

[GHC]

#8978: Type synonyms in class associated types behave strangely
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        Reporter:  joelteon                   |            Owner:
            Type:  bug                        |           Status:  new
        Priority:  normal                     |        Milestone:
       Component:  Compiler                   |          Version:  7.8.1
      Resolution:                             |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  GHC rejects valid program  |  Unknown/Multiple
       Test Case:                             |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:
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Changes (by goldfire):

 * cc: eir@… (added)


Comment:

 I just got bit by this, too, on code that worked with 7.8.1 RC2. A perusal
 through a `-ddump-tc-trace` makes it look like something in the constraint
 solver, but I could be wrong.

 An easy workaround (if you wrote the type synonym) is to use a one-
 equation type family instead.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8978#comment:2>
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