Using a query to find the existing fact is one way to do it; if you're
not seeing the actual fact in the slot afterwards, it's probably just
a coding error in using the query interface. For a query like
(defquery find-some-fact
(declare (variables ?a ?b))
?f <- (some-fact (a ?a) (b ?b)))
Then you'd get the fact, if it exists, like
(bind ?result (run-query* find-some-fact A B))
(if (?result next) then
(bind ?fact (?result get ?f))
else
(bind ?fact (assert (some-fact (a A) (b B)))))
You could put all that into a deffunction so it wouldn't detract from
the flow of your other code.
An alternative way to do all this would be to have two versions of the
original rule: one with a "not" pattern for the sub-fact and one with
a positive pattern. The "not" one should create the subfact, while the
other can directly use the matched fact.
On Jun 29, 2009, at 7:12 AM, axelrad wrote:
Hello,
I have a template that has a fact as a slot.
ex)
(deftemplate mainfact
(slot subfact (type OBEJCT))
(slot index))
(deftemplate subfact
(slot name)
(slot content))
I have a rule that instantiates (assert) the mainfact and subfact if
my
condition is met. My problem is that if the subfact exists already
it gets
asserted to false. What I need is to get a handle on the fact if it
exists
and assert the mainfact with the existing subfact and a new current
index.
What I do now is along the lines of:
assert mainfact (subfact xxx) (index n)
works great if the subfact doesn't exist yet: mainfact xxx n
but if the subfact exists my result is: mainfact (false) (n)
what i need is : mainfact (existing fact) (n)
I need to compare the subfacts for when they are the same and keep
the one
with the higher index value. I've tried doing a query and putting
that value
in but i get a jess query object instead of a fact object, and later
when i
need to compare the values they are not considered the same object,
even if
the slot values are correct, so I don't get the correct results when
trying
to keep the mainfact with higher index value.
I can test if the fact exists already, but how can I get a handle on
it to
place that value in the slot?
Thanks in advance for any help!
Monica
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Ernest Friedman-Hill
Informatics & Decision Sciences Phone: (925) 294-2154
Sandia National Labs
PO Box 969, MS 9012 [email protected]
Livermore, CA 94550 http://www.jessrules.com
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