[m-rev.] for review: add `any_is_bound' pragma

[David Overton]

On Thu, Jul 24, 2003 at 03:46:24PM +1000, Fergus Henderson wrote:
> 
> Also, regarding the comment about `nonvar': I'm quite dubious about
> adding `nonvar' in the future.  Given that we have no_tag types,
> and that the `nonvar' value could just be a no_tag wrapper around a solver
> type with inst `any', I don't see how `nonvar' could provide any useful
> information.

Yes, you're right, it's not useful in this situation because it doesn't
give you any more information than `any'.

However, I've been asked to implement it for Mercury because it is
useful for increasing the precision of mode analysis in other
situations.  E.g. for herbrand types, HAL provides an impure predicate

	:- impure pred nonvar(T) <= solver(T).

It would be useful to be able to give this a mode declarations of

	:- mode nonvar(any >> nonvar) is semidet.

(rather than `any >> any').  This can avoid unnecessary tag tests and
dereferences, among other things.


David
-- 
David Overton                  Uni of Melbourne     +61 3 8344 1354
dmo at cs.mu.oz.au                Monash Uni (Clayton) +61 3 9905 5779
http://www.cs.mu.oz.au/~dmo    Mobile Phone         +61 4 0337 4393
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