Re: JESS: How to match slot values in LHS?

[Richard Kasperowski]

Thanks, that's exactly the clarification I needed.

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



First, note the following two general rules:
1) Don't use "test" if you don't need to, and
2) direct matching is more efficient than function calls.

Therefore, I'd recomment rewriting your rule above as:

(defrule find-different-years
(automobile (model ?model) (year ?year-1))
(automobile (model ?model) (year ?year-2&~?year-1))

Note that using "?model" to match both facts means that both facts
must contain the same slot value. This rule says exactly the same
thing as the original, but does a lot less work during pattern
matching.

Now, as written, the rule matches any time the two years are
different, which means that any pair will match twice: 1,2 and 2,1 are
both valid matches. To remove the duplicates, just pick one specific
ordering. Since "year" is numeric, this is easy here:

(defrule find-different-years
(automobile (model ?model) (year ?year-1))
(automobile (model ?model) (year ?year-2&:(> ?year-1 ?year-2)))

i.e., the rule matches only one of the two possible orderings, when
?year-1 comes after ?year-2.

---------------------------------------------------------
Ernest Friedman-Hill
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