[GHC] #12976: GHCi displays the kinds of unboxed tuples incorrectly

[GHC]

#12976: GHCi displays the kinds of unboxed tuples incorrectly
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Replying to [comment:2 goldfire]:
 > I say that this behavior is correct. As you report, the kind of `(#,#)`
 is `forall (r1 :: RuntimeRep) (r2 :: RuntimeRep). TYPE r1 -> TYPE r2 ->
 TYPE 'UnboxedTupleRep`. So once you provide a type argument (`(#,#)
 Int#`), then GHC must supply both `RuntimeRep` arguments. The second one
 defaults to `PtrRepLifted`.

 Do you mind explaining your reasoning for  in a little more detail?
 Because it's not cleat at all to me why making `r1 ~ 'IntRep` would cause
 `r2` to default to `PtrRepLifted`. In particular, I would have expected:

 {{{#!hs
 (#,#) Int# :: forall (r2 :: RuntimeRep). TYPE r2 -> TYPE 'UnboxedTupleRep
 }}}

 Why would it default with an argument, but not without arguments?

 Also, do you know what's going on with:

 {{{
 λ> :k $(unboxedTupleT 2)
 $(unboxedTupleT 2) :: * -> * -> TYPE 'UnboxedTupleRep
 }}}

 Is Template Haskell causing some defaulting behavior that I'm not aware
 of?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12976#comment:3>
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