[m-dev.] Re: assertions (was: Assocative predicates)

[David Glen JEFFERY]

On 23-Apr-1998, Zoltan Somogyi <zs at cs.mu.OZ.AU> wrote:
> David Jeffery wrote:
> It may not be quite so simple. One reason why you may want prescriptive
> assertions is to make sure that the predicate never gets called with arguments
> that would cause a runtime abort, 

Yes.

> and the conditions required to ensure this
> may be different in different modes.

I'm not convinced. Could you give me an example?

The way I see it, a prescriptive constraint would be a constraint over some set
of variables from the clause head. This constraint would only need to be 
satisfied if all of those variables were sufficiently instantiated to check
the constraint. In that way, you effectively get different constraints in
different modes, but the constraints for a particular mode are a well defined
subset of the whole predicate's prescriptive constraints.

Anyhow, I guess we've strayed quite a bit from the original topic --- how to
assert abstract properties of predicates such as associativity. I suspect that
any mechanism of input/output assertion should be a different mechanism to 
this. Thoughts, anyone?


love and cuddles,
dgj
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