JESS: How to match slot values in LHS?

[Richard Kasperowski]

I'm looking for help writing a rule that can match facts by slot value. For example, given:

(deftemplate automobile
"A specific car."
(slot make)
(slot model)
(slot year (type INTEGER))
(slot color (default white)))

(assert (automobile (make Chrysler) (model LeBaron) (year 1997)))
(assert (automobile (make Chrysler) (model LeBaron) (year 1998)))
(assert (automobile (make Chrysler) (model SomethingElse) (year 1998)))

how would I find the two automobiles that have the same model but different years?

This rule almost does what I want:

(defrule find-different-years
(automobile (model ?model-1) (year ?year-1))
(automobile (model ?model-2) (year ?year-2))
(test (eq ?model-1 ?model-2))
(test (not (eq ?year-1 ?year-2)))
=>
(printout t "model-1=" ?model-1
", year-1=" ?year-1
", model-2=" ?model-2
", year-2=" ?year-2
crlf))

The output of running this rule with those facts is:

model-1=LeBaron, year-1=1997, model-2=LeBaron, year-2=1998
model-1=LeBaron, year-1=1998, model-2=LeBaron, year-2=1997

What I really want is output like this:

model-1=LeBaron, year-1=1997, model-2=LeBaron, year-2=1998

from a rule looks for a second automobile, the model of which is equal to ?model-1, with no duplicate results. What's the best way to write a rule to do that?

Thanks,

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

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