Filter function in CLIPS

Question

I tried to define this function that takes multiple integers and keeps those that are different from 0. It does not work, apparently, the recursive call (filter $?tail) does not match with the parameter list. Can this be done in CLIPS?

(deffunction filter (?head $?tail)
    (if (= (length $?tail) 0) then
        (if (!= ?head 0) then (return ?head))
        (return $?tail))
    (if (= ?head 0) then
        (return (filter $?tail)))
    (bind $?result ?head (filter $?tail)) 
    (return $?result)
)

Answer 1

The function filter is declared with 2 parameters filter(?head $?tail) but you are calling it with only one (filter $?tail)

Is the recursion needed? This problem can be solved easily with the function delete-member$:

(delete-member$ $?list 0)

Example:

CLIPS> (delete-member$ (create$ 6 7 0 8 0 7) 0)
(6 7 8 7)
CLIPS>