[GHC] #13998: Default Signature messes up arity of type constructor

[GHC]

#13998: Default Signature messes up arity of type constructor
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        Reporter:  andrewthad        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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 simonpj):

 > The problem is that the Class data type....

 But the `classTyCon` has everything.  The `classTyVars` are redundant,
 just there for convenience.

 I'm fixing it by using the visiblity of the class (tycon) parameters and
 using that consistently.   `mkSpecSigmaTy` is deeply suspect.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13998#comment:7>
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