Question

I get a ‘-Program stack overflow’ prompt in clisp when I try to execute the following recursive function that, I believe, returns the most common element in a list:

(defun greater-member (lst)
  (cond  ((null (cdr lst))
                (cons (car lst) (count-if #'(lambda (x) (eql x (car lst))) lst)))
         ((>= (count-if #'(lambda (x) (eql x (car lst))) lst)
              (count-if #'(lambda (x) (eql x (car (remove (car lst) lst)))) lst))
                (greater-member (remove (car (remove (car lst) lst)) lst)))
         (t (greater-member (remove (car lst) lst)))))

e.g greater-number should return as follows:

>(greater-number '(a a a b b b b c))
(b . 4)  

May I ask, what is causing the overflow? I’ve gotten rid of all the little syntax errors
by repeatedly executing greater-number in clisp- the function seems to hold logically.

Answer 1

I’ve realized my error now.

Looking at my null test, rather than

(null (cdr lst)) 

I should have

(null (remove (car lst) lst))

So that the redundant, lesser occurring unique elements are removed.