Реализовать функцию, которая для заданного элемента считает количество его повторений в списке

(defun count-n (l n)
  (apply #'+
    (mapcar #'(lambda (x) (if (equal x n) 1 0)) l)))
 
(count-n '(1 5 3 4 5) '5) 
 
==> 2
 
(defun count-n (l n)
  (length
    (remove-if-not #'(lambda (x) (equal x n)) l)))
 
(count-n '(1 5 3 4 5) '5) 
 
==> 2
 
(defun count-n (l n)
    (reduce #'+ l :key (lambda (x) (if (equal x n) 1 0))))
 
(count-n '(1 5 3 4 5) '5)
 
==> 2

(defun counter! (lst item)
  (let ((c 0))
   (iter (for i in lst) (when (eq i item) (counting i into c))) c))
 
==> counter!
 
(counter! '(1 5 3 4 5 5 5) 5)
 
==> 4
 
(defun counter!! (lst item)
  (- (length lst) (length (remove item lst))))
 
==> counter!!
 
(counter!! '(1 5 3 4 5 5 5) 5)
 
==> 4

(defun count-elm (a w &optional (n 0))
  (cond ((null w) n)
        ((equalp (car w) a) (count-elm a (cdr w) (1+ n)))
        (t (count-elm a (cdr w) n))))
 
> (count-elm 'b '(a b b a b a b))
4

(defun count-elm (a w) (count a w))
 
> (count-elm 'b '(a b b a b a b))
4

(defun count-elm (a w)
  (loop for e in w when (equalp e a) count e))
 
> (count-elm 'b '(a b b a b a b))
4

(defun count-elm (a w &optional (n 0))
  (if w
      (count-elm a
                 (cdr w)
                 (if (equalp (car w) a)
                     (1+ n)
                     n))
      n))
 
> (count-elm 'b '(a b b a b a b))
4