[mercury-users] full and empty lists

[David Overton]

On Mon, Jan 14, 2002 at 11:00:41PM +1100, Dave Slutzkin wrote:
> 
> The mode benefits only come from full_timeline 'promising' a non-empty list. 
> The other benefits I was hoping for were modularity, and implementation
> hiding.  So I could theoretically change the implementation of timeline from
> list to something else (which is likely) without having to change any
> existing code.
>  
> > As Ralph pointed out, the determinism analysis won't currently detect
> > that empty_timeline and full_timeline are mutually exclusive and
> > exhaustive (although there is someone working on allowing you to promise
> > this).  However, as far as _modes_ are concerned, using the constructors
> > directly instead of wrapping them in appropriately declared predicates
> > should make no difference.
> 
> So if I have:
> 
>     Line = [_|_]
> 
> then I still get the mode benefit?

Yes.

> I suppose the compiler still knows that
> it must be a non_empty_list...  I hadn't tried that, but that would be a
> part-solution to my problem.  (And I'll try it as soon as I get back to my
> machine.)
> 
> So I've got the mode benefits, but still sorta without the hidden
> implementation that would be the ultimate.

Yes, you will need to wait until the exclusive/exhaustive declarations
are implemented before you can do what you want.



David
-- 
David Overton      Department of Computer Science & Software Engineering
PhD Student        The University of Melbourne, Victoria 3010, Australia
+61 3 8344 9159    http://www.cs.mu.oz.au/~dmo
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