how to get the index of facts in RHS of rule? - clips

Question

I'm asking if there is a possibility of accessing a get the index of fact in RHS of defrule ?
It gives me that undefined every time I try to index a fact in a RHS of defrule.
because I have a while loop , I want to be able to modify elevator fact depending on my input data.
(deftemplate elevator
(slot goal))
(deffacts elevator
(elevator (goal 0)))
(defrule read-data
=>
?f1 <- (elevator)
(modify ?f2 (goal 1))
)
this an example of my code , since I can't put all online :
(deftemplate data
(slot data)
)
(deffacts data
(data (data 1))
)
(defrule rule1
?f1 <-(data)
=>
(bind ?value (readline input) )
(while (neq ?value EOF)
do
(bind ?data (fact-slot-value ?f1 data))
(printout t "data " ?data crlf )
(retract ?f1)
(modify ?f1 (data ?value))
(bind ?value (readline input)
)
)
)
this is my input file :
2
3
4
5
6
7
this is what I'm getting :
CLIPS> (run)
data 1
data FALSE
data FALSE
data FALSE
data FALSE
data FALSE
CLIPS>
I want it to print out
data 2
data 3
data 4 ..ect

Answer 1

You can do it this way from the RHS of a rule, but if your rule actually has no LHS conditions, it's pointless to use a rule to change the value of the fact. Just use a function.
CLIPS>
(deftemplate elevator
(slot goal))
CLIPS>
(deffacts elevator
(elevator (goal 0)))
CLIPS>
(defrule read-data
=>
(do-for-fact ((?f elevator)) TRUE
(modify ?f (goal 1))))
CLIPS> (watch facts)
CLIPS> (reset)
<== f-0 (initial-fact)
==> f-0 (initial-fact)
==> f-1 (elevator (goal 0))
CLIPS> (run)
<== f-1 (elevator (goal 0))
==> f-2 (elevator (goal 1))
CLIPS>
Alternately, you can bind the fact you want to modify in the conditions of the rule:
CLIPS> (clear)
CLIPS>
(deftemplate elevator
(slot goal))
CLIPS>
(deffacts elevator
(elevator (goal 0)))
CLIPS>
(defrule read-data
?f <- (elevator (goal 0))
=>
(modify ?f (goal 1)))
CLIPS> (watch facts)
CLIPS> (reset)
<== f-0 (initial-fact)
==> f-0 (initial-fact)
==> f-1 (elevator (goal 0))
CLIPS> (run)
<== f-1 (elevator (goal 0))
==> f-2 (elevator (goal 1))
CLIPS>
Updated:
You can get your original rule to "work" by removing the retract and rebinding ?f1 to the value returned by modify:
CLIPS> (clear)
CLIPS>
(deftemplate data
(slot data))
CLIPS>
(deffacts data
(data (data 1)))
CLIPS>
(defrule rule1
?f1 <- (data)
=>
(bind ?value (readline input))
(while (neq ?value EOF)
(bind ?data (fact-slot-value ?f1 data))
(printout t "data " ?data crlf )
(bind ?f1 (modify ?f1 (data ?value)))
(bind ?value (readline input))))
CLIPS> (reset)
CLIPS> (open input.txt input)
TRUE
CLIPS> (run)
data 1
data 2
data 3
data 4
data 5
data 6
CLIPS> (close input)
TRUE
CLIPS>
It's still suspiciously complicated to be modifying the same fact multiple times on the RHS.