[GHC] #11736: Allow unsaturated uses of unlifted types in Core

[GHC]

#11736: Allow unsaturated uses of unlifted types in Core
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        Reporter:  bgamari           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 What about unboxed tuples? Right now, we have, e.g., `(# , #) :: forall
 (r1 :: RuntimeRep) (r2 :: RuntimeRep). TYPE r1 -> TYPE r2 -> TYPE
 'UnboxedTupleRep`. Of course, `UnboxedTupleRep` is a lie, because unboxed
 tuples have all sorts of representations. There is an explicit check for
 this along with the check for runtime representation polymorphism.
 With those checks in place, what can go wrong even if we unsaturate
 unboxed tuples? I think it's OK.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11736#comment:4>
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