JESS: Rules that count facts?

[Richard Kasperowski]

In the application we're building, we'll need rules that count facts and act when the right number of facts have been asserted. For example, we might want a rule that says

If we've sold 5 cars today, then pat ourselves on the back.

Two questions about rules like this:

1) We'll have to use something like (test (= 5 ?*n-cars-sold*)) in the LHS of a rule, right? The good advice seems to be, "avoid (test) in the LHS." Is there a better way?

2) One way to count car-sold facts is to define a query and use (count-query-results car-sold-query). Another way is to have a rule that increments a global whenever a car-sold is asserted. What is the prefered way to count facts?

Thanks,

--
Richard Kasperowski
Tel: 617-576-1552, Fax: 617-576-2441
mailto:[EMAIL PROTECTED]
http://www.altisimo.com/

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