Modify a fact using a variable like slot name

[pron]

Is it possible to modify the fact "?u" using a variable like the slot name, instead of a symbol?

(defrule R-1
     ?u <- (user)
     ?f <-  (question
                 (answered no)
                 (the-question ?q)
                 (attribute ?attribute))
     =>
     (modify ?f (answered yes))
     (modify ?u (?attribute 5))
)

[Gary Riley]

You can't do this with facts, but you can with instances since the message argument to the send function can be a constant, variable, or expression.

CLIPS> 
(defclass EXAMPLE (is-a USER)
   (slot x)
   (slot y)
   (slot z))
CLIPS> (make-instance [x] of EXAMPLE (x 1) (y 2) (z 3))
[x]
CLIPS> (send [x] print)
[x] of EXAMPLE
(x 1)
(y 2)
(z 3)
CLIPS> (send [x] (sym-cat put- x) 5)
5
CLIPS> (send [x] print)
[x] of EXAMPLE
(x 5)
(y 2)
(z 3)
CLIPS>