Unboxed tuples as values

Consider

  type T a = Int -> (# Int, Int #)

  f :: T a -> T a
  f t = \x -> case t x of r -> r

gives the following error message:

  ghc-5.04.1: panic! (the `impossible' happened, GHC 
version 5.04.1):
	  codeGen/CgRetConv.lhs:83: Non-exhaustive 
patterns in function
	  dataReturnConvPrim

Trouble is that 'r' is bound to an unboxed tuple.  This 
should fail, but in 5.04.1 it crashes the compiler.  In 6.0 
it's worse: the code will core dump because it enters R1.

But it should be rejected in the type checker.

Trac metadata

Trac field	Value
Version	None
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedFixed
Component	Compiler (Type checker)
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