[GHC] #7939: RHS of associated type not kind-checked

[GHC]

#7939: RHS of associated type not kind-checked
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  Reporter:  goldfire                     |          Owner:                  
      Type:  bug                          |         Status:  new             
  Priority:  normal                       |      Milestone:                  
 Component:  Compiler                     |        Version:  7.7             
Resolution:                               |       Keywords:                  
        Os:  Unknown/Multiple             |   Architecture:  Unknown/Multiple
   Failure:  GHC accepts invalid program  |     Difficulty:  Unknown         
  Testcase:  ghci/scripts/T7939           |      Blockedby:                  
  Blocking:                               |        Related:                  
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Comment(by goldfire):

 I tend to agree that generalizing the result kind (without an explicit
 annotation) is a step too far. In general, I'm happy with the current
 story that type family arguments and results default to {{{*}}}. Because
 instances aren't provided at the same place as the family declaration, any
 sort of kind inference amounts to some level of spooky action at a
 distance. Note that the kind inference for datatypes looks only at the
 declaration of the constructors, not any uses of the type. Similarly, the
 kind inference for classes only looks at the methods/other members of the
 class, not any instances. For consistency with those cases, I would expect
 for type families either (everything defaults to {{{*}}}) or (everything
 defaults to fresh kind variables). The former gives better errors in the
 common case, so I favor that one.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7939#comment:7>
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