[GHC] #9357: Kind-polymorphic type family accepts unlifted type arguments

[GHC]

#9357: Kind-polymorphic type family accepts unlifted type arguments
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              Reporter:  kosmikus    |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.2
  (Type checker)                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  accepts invalid program            |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Good point.  It's not impossible that we could accept unboxed
 ''arguments'' to type families, but unbozed ''results'' would definitely
 be problematic: how many bits does it take to represent `(F Int)`?  Is is
 held in an integer register or a floating point register.

 For now I've just made it so that we require a boxed monotype as both
 argument and result.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9357#comment:2>
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