Modifying the current fact that fires a rule

Question

Say I have defined a template and some facts as shown below:

(deftemplate student
    (slot name (type SYMBOL) (default ?NONE))
    (slot grade (type SYMBOL) (default C) (allowed-symbols A B C D))
    (slot graduated (type SYMBOL) (default no) (allowed-symbols yes no))
)

(deffacts insert-facts
    (student (name George) (grade A))
    (student (name Nick) (grade C))
    (student (name Bob))
    (student (name Mary) (grade B))
)

Say that I want to create a rule that checks the grade of each student and sets the corresponding graduated variable to the symbol 'yes'. How could I do this?

Answer 1

Here's a slightly less verbose version of the rule you came up with to solve your problem:

CLIPS> 
(deftemplate student
    (slot name (type SYMBOL) (default ?NONE))
    (slot grade (type SYMBOL) (default C) (allowed-symbols A B C D))
    (slot graduated (type SYMBOL) (default no) (allowed-symbols yes no)))
CLIPS> 
(deffacts insert-facts
    (student (name George) (grade A))
    (student (name Nick) (grade C))
    (student (name Bob))
    (student (name Mary) (grade B)))
CLIPS> 
(defrule rule-1
   ?s <- (student (grade A|B) (name ?n) (graduated ~yes))
   =>
   (modify ?s (graduated yes))
   (printout t "Congratulations " ?n "!" crlf))
CLIPS> (reset)
CLIPS> (run)
Congratulations Mary!
Congratulations George!
CLIPS>