[GHC] #11471: Kind polymorphism and unboxed types: bad things are happening

[GHC]

#11471: Kind polymorphism and unboxed types: bad things are happening
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        Reporter:  bgamari           |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |             Keywords:  TypeInType,
      Resolution:                    |  LevityPolymorphism
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 rwbarton):

 By the way, I know the name of the extension is `TypeInType`, but might it
 not make more sense to have a separate `Levity` constructor for kinds? Say
 `* :: TYPE T`. While the values of `Int` are things like `1 :: Int`, and
 they are lifted and boxed, the "values" of `*` are things like `Int :: *`,
 and... `Int` is not really represented by anything at runtime. But if it
 was, it wouldn't necessarily be a lifted, boxed pointer. Maybe you want
 lazy evaluation on the value level, but strict evaluation on the type
 level, along with a totally different runtime representation for types.

 I don't know of any reason why you would want to abstract over
 specifically (regular types of kind `*` + kinds). It seems to me that in
 such cases it would make just as much sense to allow unboxed types as
 well. On the other hand, I do realize that the name `*` is a lot more
 convenient than writing `forall (a :: RuntimeRep). ... (TYPE a)`, and
 maybe that is the real issue...?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11471#comment:9>
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