Overlapping, undecidable, incoherent -- or worse?

[Alex Ferguson]

On Thu, May 20, 2004 at 11:06:44PM +0100, MR K P SCHUPKE wrote:
> I agree, I have made it not terminate myself with undecidable-instances,

Congratulations. ;-)


> I also think prolog style backtacking would be a good idea... I think I said
> that  you either want full backtracking or you want to leave it how it is
> (with dependancies ignored) - I have yet to be convinced that any partial
> solution would have the elegance of full backtracking, yet would complicate
> the implementation and syntax. 

Oh, I don't think what I'm suggesting is a 'partial solution', short of
full dependency-based backtracking: I think it almost requires the
latter.  But having done such a thing, I'd imagine one is yet more
likely to encounter situations where it's ambiguous which of a number of
possible instance derivation routes is possible, which in turn is likely
to make specifying which is wanted more important -- the alternative
would seem to be verifying that only one possible instance can be
arrived at, or examing the possibilities in some arbitrary order (such as
that of the program text).

(I belatedly found the more full description of 'incoherent instances'
in the documentation, having initially only noticed the 'flags' section,
and can see that it indeed does nothing like what I was needing...)

Cheers,
Alex.