Ross Paterson wrote:
On Sat, Aug 08, 2009 at 10:09:38AM +0100, Iavor Diatchki wrote:
I thought that the intended semantics was supposed to be that the only
element is bottom (hence the proposal to add a related empty case
construct)?
If that were the case, a compiler could legitimately discard any value
of such a type, because it could be easily reconstructed. I don't
think that is what is intended.
Actually, I think it is. I think that's a natural consequence of the
way Haskell is specified. GHC tries to pick the kind of bottom that you
expected, but it doesn't always work really well, because it's not
actually specified in any sort of formal way...
Now, with imprecise exceptions, I'm not sure a compiler could
legitimately discard the value.
(by the way, for a type that you can unsafeCoerce anything to, GHC has a
special type named "Any". Which is not the same as a data type with no
constructors.)
-Isaac
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