[GHC] #8993: Fold NullaryTypeClasses into MPTC

[GHC]

#8993: Fold NullaryTypeClasses into MPTC
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        Reporter:  owst              |            Owner:
            Type:  bug               |           Status:  patch
        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'm fine with this, but I think the error message could be better.  "Too
 many args" is better than "Invalid number of args".  It would be easy to
 generate the same messages as before, by passing `arity` to
 `classArityErr`.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8993#comment:2>
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