[GHC] #14319: Stuck type families can lead to lousy error messages

[GHC]

#14319: Stuck type families can lead to lousy error messages
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |             Keywords:  TypeInType,
      Resolution:                    |  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 How hard would it be to report an arity error only when we know the arity
 is wrong? And how often do we not know for sure? I don't want erosion of
 the common case either, but I don't see why it would be likely here.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14319#comment:4>
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