Hi,
I was strugling with the following code, until I remembered that rule
activations are only affected when you assert/retract or modify facts
that can match a rule's patterns. Anyway, I think I'd better share this
problem and get further advice.
; I have 3 deftemplates:
(deftemplate a (slot b)) ; This slot _b_ will contain a reference to a
fact _b_.
(deftemplate b (slot s)) ; I want to check if there are facts _b_ and
_c_ with the same slot _s_,
(deftemplate c (slot s)) ; where _b_ will be referred to in a fact _a_.
; Then I have a rule to get a matching of slot _s_ of both _b_ and _c_
facts, where _b_ must be referred to by an _a_ fact:
(defrule r2
(a (b ?b))
?b <- (b) ; Apparently useless
(c (s ?b.s)) ; Using dot notation
=>
(printout t "abc! " ?b.s crlf) )
; Some initial facts:
(deffacts my-facts
(b (s 1))
(a (b (fact-id 1))) ; This is a shortcut to have slot _b_ of fact
_a_ refer to fact _b_ in the line above.
(c (s 1)) )
; Let's do it:
(reset)
(facts)
(modify 1 (s 2)) ; Here I modify fact _b_, changing its slot _s_ to 2.
(facts)
(run)
Now, this version works as expected: rule r2 does *not* fire. However,
if I comment the "Apparently useless" pattern binding, the rule *will
fire*, although slots _s_ of both _c_ and _b_ facts no longer have the
same value!
Does this mean that when using dotted variables a pattern binding should
always be included before they are used?
Thanks.
Henrique
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