Another way (assuming that indeed a pair of facts with equal-length
multislots is to be found):
(defrule find-eql
?b1 <- (bar (list $?l1))
?b2 <- (bar (list $?l2 &:(= (length$ $?l1)(length$ $?l2))))
(test (< ?b1 ?b2))
=>
(printout t "lists " $?l1 " and " $?l2 " have equal length" crlf)
)
This doesn't require the id. If there is an id, finding pair B-A in
addition to A-B can be avoided by comparing the id's rather than the
fact-refs:
(defrule find-eql
?b1 <- (bar (id ?id1)(list $?l1))
?b2 <- (bar (id ?id2 &:(< ?id1 ?id2))
(list $?l2 &:(= (length$ $?l1)(length$ $?l2))))
=>
(printout t "lists " $?l1 " and " $?l2 " have equal length" crlf)
)
krWL
Jason Morris wrote:
Hi Hal, Peter & Wolfgang,
The proposed solution does not compare a length with foo.desired,
and binding of a multislot vaue should use a variable starting with $?.
Hal, since you said you were satisfied with Peter's solution, I never
posted my reply which anticipated Wolfgang's almost verbatim.
However, if you really want what Peter was advocating then there is a
bit more to it I think. You have to recall that Jess doesn't allow
multiple facts to have identical slot values -- that means that no two
foo facts could have the exact same multislot list and desired value.
You may need this in your application, so you'd need some other slot
like (slot id) to differentiate your facts. Also, Peter's version
would fire twice for each pair of foo facts that had the same slot
length, which is not what you want I'd think.
The implementation below addresses these issues.
Cheers,
Jason
;;;;;;;;;;;;;;;;;;
;; list-len.clp ;;
;;;;;;;;;;;;;;;;;;
(clear)
(watch all)
(deftemplate foo (slot id) (multislot my-list) (slot desired))
(deffacts init
(foo (id 1) (my-list 1 2 3 4))
(foo (id 2) (my-list a b c d))
(foo (id 3) (my-list 5 6 7 8))
(foo (id 4) (my-list e f g h)))
(defrule myrule
; Find a foo fact...
(foo (id ?id1) (my-list $?list1))
; ...and another fact of different id where the list lengths are
the same...
(foo (id ?id2&~?id1) (my-list $?list2&:(= (length$ ?list2)
(length$ ?list1))))
; ...such that we have not examined this pair of foo facts before.
(not (has-fired ?id1 ?id2))
=>
; Assert that this pair has been processed with a little logic trick.
(assert (has-fired ?id2 ?id1))
(printout t "Lists lengths in foo facts " ?id1 " and " ?id2 " are
equal!" crlf))
:: Program
(reset)
(run)
;MAIN::myrule: +1+1+1+2+1+1+2+t
; ==> Focus MAIN
; ==> f-0 (MAIN::initial-fact)
; ==> f-1 (MAIN::foo (id 1) (my-list 1 2 3 4) (desired nil))
; ==> f-2 (MAIN::foo (id 2) (my-list a b c d) (desired nil))
;==> Activation: MAIN::myrule : f-2, f-1,
;==> Activation: MAIN::myrule : f-1, f-2,
; ==> f-3 (MAIN::foo (id 3) (my-list 5 6 7 8) (desired nil))
;==> Activation: MAIN::myrule : f-3, f-1,
;==> Activation: MAIN::myrule : f-3, f-2,
;==> Activation: MAIN::myrule : f-1, f-3,
;==> Activation: MAIN::myrule : f-2, f-3,
; ==> f-4 (MAIN::foo (id 4) (my-list e f g h) (desired nil))
;==> Activation: MAIN::myrule : f-4, f-1,
;==> Activation: MAIN::myrule : f-4, f-2,
;==> Activation: MAIN::myrule : f-4, f-3,
;==> Activation: MAIN::myrule : f-1, f-4,
;==> Activation: MAIN::myrule : f-2, f-4,
;==> Activation: MAIN::myrule : f-3, f-4,
;FIRE 1 MAIN::myrule f-3, f-4,
; ==> f-5 (MAIN::has-fired 4 3)
;<== Activation: MAIN::myrule : f-4, f-3,
;Lists lengths in foo facts 3 and 4 are equal!
;FIRE 2 MAIN::myrule f-4, f-2,
; ==> f-6 (MAIN::has-fired 2 4)
;<== Activation: MAIN::myrule : f-2, f-4,
;Lists lengths in foo facts 4 and 2 are equal!
;FIRE 3 MAIN::myrule f-1, f-4,
; ==> f-7 (MAIN::has-fired 4 1)
;<== Activation: MAIN::myrule : f-4, f-1,
;Lists lengths in foo facts 1 and 4 are equal!
;FIRE 4 MAIN::myrule f-3, f-2,
; ==> f-8 (MAIN::has-fired 2 3)
;<== Activation: MAIN::myrule : f-2, f-3,
;Lists lengths in foo facts 3 and 2 are equal!
;FIRE 5 MAIN::myrule f-3, f-1,
; ==> f-9 (MAIN::has-fired 1 3)
;<== Activation: MAIN::myrule : f-1, f-3,
;Lists lengths in foo facts 3 and 1 are equal!
;FIRE 6 MAIN::myrule f-1, f-2,
; ==> f-10 (MAIN::has-fired 2 1)
;<== Activation: MAIN::myrule : f-2, f-1,
;Lists lengths in foo facts 1 and 2 are equal!
; <== Focus MAIN
--
-----------------------------------------------------------
Jason Morris
Morris Technical Solutions LLC
http://www.morris-technical-solutions.com
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