[GHC] #13244: Error Dealing with Unboxed Types and Type Families

[GHC]

#13244: Error Dealing with Unboxed Types and Type Families
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        Reporter:  sgschlesinger     |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  LevityPolymorphism
Operating System:  Linux             |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * keywords:  pprIfaceCo => LevityPolymorphism


Comment:

 OK I can reproduce this.  It fails with a Lint error in the GHC 8.0
 branch:
 {{{
 *** Core Lint errors : in result of Tidy Core ***
 <no location info>: warning:
     In the type ‘Unboxed x_aws[sk] -> x_aws[sk]’
     Ill-kinded argument
       in type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’
     type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’ kind: TYPE
                                                           (Rep x_aws[sk])
 <no location info>: warning:
     In the type ‘Unboxed x_aws[sk] -> x_aws[sk]’
     Ill-kinded argument
       in type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’
     type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’ kind: TYPE
                                                           (Rep x_aws[sk])
 <no location info>: warning:
     In the type ‘Unboxed x_aws[sk] -> x_aws[sk]’
     Ill-kinded argument
       in type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’
     type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’ kind: TYPE
                                                           (Rep x_aws[sk])
 <no location info>: warning:
     In the type ‘forall x_aws[sk].
                  Unbox x_aws[sk] =>
                  Unboxed x_aws[sk] -> x_aws[sk]’
     Ill-kinded argument
       in type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’
     type or kind ‘Unboxed x_aws[sk] -> x_aws[sk]’ kind: TYPE
                                                           (Rep x_aws[sk])
 *** Offending Program ***
 }}}
 But the recent round of improvements to levity polymorphism make this OK
 in HEAD (and hence in 8.2).  I'll add a regression test.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13244#comment:6>
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