Variable unbinding

[iancu denis]

Let's say for example I have the following facts

(deffacts num
    (number 4)
    (number 5)
    (number 9)
)

Create an empty variable

(bind ?numbers (create$)
)

And have the following rule to try to add each number to the variable

(defrule build-numbers
    ?number-fact<-(number ?c)
    =>
    (bind ?numbers (insert$ ?numbers 999 ?c))
    (retract ?number-fact)
)

If I check before runing if the variable is properly bound by printing it, i get no error

(printout t   "Numbers "  ?numbers crlf
)

However when I run the example, I get the following error

[PRCCODE5] Variable numbers unbound.

[PRCCODE4] Execution halted during the actions of defrule build-numbers.

I notice the variable getting unbound after doing a (reset), so I bind it afterwards, but why does it also unbind when doing (run)? Is there a way around this?

[CLIPS Support]

Variables bound at the Read-Eval-Print-Loop (REPL) are local to the REPLL will not be in the scope of any code within other constructs. You can define a defglobal if you want to create a variable with global scope. In your code, rather than using a global variable, you could just create a fact for storing the numbers:

         CLIPS (6.31 6/12/19)

CLIPS> 

(deffacts num

    (number 4)

    (number 5)

    (number 9)

    (numbers)

)

CLIPS> 

(defrule build-numbers

    ?number-fact<-(number ?c)

    ?numbers <- (numbers $?n)

    =>

    (retract ?numbers ?number-fact)

    (assert (numbers ?n ?c)))

CLIPS> (reset)

CLIPS> (run)

CLIPS> (facts)

f-0     (initial-fact)

f-7     (numbers 4 5 9)

For a total of 2 facts.

CLIPS>