storing values in clips into variable

Question

I am having a template of

(deftemplate Product
(slot productId (type INTEGER))
(slot uom (default EA))
(slot quantity (type INTEGER))
(slot amount))

I'm using the code for

(defrule sum_of_quantity
   (exists (Product (productId 1 | 2 | 3)(amount ?amount)))
   =>
   (bind ?totalQuantity 0)
   (do-for-all-facts ((?p Product))
                     (or (eq ?p:productNumber 1)
                         (eq ?p:productNumber 2)
                         (eq ?p:productNumber 3))
      (bind ?totalQuantity (+ ?totalQuantity ?p:quantity)))
     (if (>= ?amount 5000) then
   (printout t "TotalQuantity is " ?totalQuantity crlf)))

Here i am getting an error saying that: Undefined variable amount referenced in RHS of defrule.

I have to check if the amount of each product is greater than 5000. How do we do that.

Answer 1

A simple fact pattern that can be matched by several different facts can cause multiple activations of a rule:

CLIPS> 
(deftemplate product
   (slot id)
   (slot amount))
CLIPS>    
(deffacts products
   (product (id 1) (amount 1000))
   (product (id 2) (amount 3000))
   (product (id 3) (amount 6000)))
CLIPS> 
(defrule print-amount
   (product (id ?id) (amount ?amount))
   =>
   (printout t ?id ": " ?amount crlf))
CLIPS> (reset)
CLIPS> (agenda)
0      print-amount: f-3
0      print-amount: f-2
0      print-amount: f-1
For a total of 3 activations.
CLIPS> (run)
3: 6000
2: 3000
1: 1000
CLIPS> 

When each activation is allowed to executed, the variable amount is retrieved from the product fact associated with activation. So there are three rule firings where amount is 6000, 3000, and 1000 respectively.

An exists conditional element is matched just once regardless of the number of time the fact patterns it contains are matched:

CLIPS> 
(defrule exists
   (exists (product (id ?id) (amount ?amount)))
   =>)
CLIPS> (agenda)
0      exists: *
For a total of 1 activation.
CLIPS>

When the agenda is listed, an * is displayed indicating that the pattern is matched, but not by a specific fact. If you tried accessing the variable amount in the actions of the rule, you'd get an error. This is because the variable amount has no meaning outside of the pattern because it has no specific value. You'd get unpredictable behavior if one of the facts matching the fact pattern was arbitrarily chosen to provide the value for amount.

The simplest way to rewrite your rule is to move the amount check from the actions of the rule to the exists pattern:

(defrule sum_of_quantity
   (exists (Product (productId 1 | 2 | 3)
                    (amount ?amount&:(>= ?amount 5000))))
   =>
   (bind ?totalQuantity 0)
   (do-for-all-facts ((?p Product))
                     (or (eq ?p:productId 1)
                         (eq ?p:productId 2)
                         (eq ?p:productId 3))
      (bind ?totalQuantity (+ ?totalQuantity ?p:quantity)))
   (printout t "TotalQuantity is " ?totalQuantity crlf))

Your do-for-all-facts query was also referencing productNumber rather than productId.