Explicit negation in boolean methods?

[Robert Goldman]

For boolean methods, is there any way to state that a frame's boolean method has the value false?  Earlier, Michael gave an example of a boolean method returning false (https://groups.google.com/a/coherentknowledge.com/g/ergoai-xsb-forum/c/8WogOXeURKE/m/bi0VW7RsCQAJ), but it appears to rely on negation as failure. Is there a way to explicitly state that a boolean method (property) returns false, without using NAF?

This is a question of interest, rather than being urgent...  A question raised by reading the manual chapter (12) on boolean methods.

[Michael Kifer]

A Boolean method in Ergo is either true or false, like a predicate is true or false.   It returns no value per se.

What you probably want to do is to define a method of type  YourMeth(...)  =>  Boolean and define 

?x:Boolean :-  isboolean{?x}.

If you want th type of that method to be checked, you can do it by setting up  type constraint  checks.

On 12/10/25 21:22, Robert Goldman wrote:

For boolean methods, is there any way to state that a frame's boolean method has the value false?  Earlier, Michael gave an example of a boolean method returning false (https://groups.google.com/a/coherentknowledge.com/g/ergoai-xsb-forum/c/8WogOXeURKE/m/bi0VW7RsCQAJ), but it appears to rely on negation as failure. Is there a way to explicitly state that a boolean method (property) returns false, without using NAF?

This is a question of interest, rather than being urgent...  A question raised by reading the manual chapter (12) on boolean methods.

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[Robert Goldman]

I think I wasn't clear enough.  The manual gives this example:

John[is_tall].

as a way of saying "John is tall."  How do I say that "Bill is not tall"?  Is not saying "Bill is tall" (NAF) the only way to do that?

Thanks,

R

[Michael Kifer]

you can state

\neg John[is_tall].

or even  

John[\neg is_tall].

But the method is_tall doesn't have any  values (truth values or other)  by itself. Rather, the statement  John[is_tall]  may be true, false, or undefined. So, you can use Boolean methods or methods that return actual values, like

John[is_tall -> yes].

Here is_tall does have a value AND the statement   John[is_tall -> yes] might be true, false or undefined.

Or you can use

John[is_tall-> \true]  (or \false) and there are thousands of other suitable alternatives. You need to choose what suits you best  in each concrete modeling situation and commit to that style.

-- michael

[Robert Goldman]

Thank you, Michael! The negated statements were something I had not thought of. Would you consider adding these examples to the manual?