простые рекурсивные функции для обработки списков

(defun -member (a w)
    (cond ((null w) nil)
    ((equalp a (car w)) (cons (car w) (cdr w)))
    ((-member a (cdr w)))))
 
(defun sine-twins (w)
  (cond ((null w) nil)
        ((-member (car w) (cdr w)) (sine-twins (cdr w)))
        ((cons (car w) (sine-twins (cdr w))))))
 
> (sine-twins '((a b) c d (a b) c e))
(D (A B) C E)

(defun sum-sequence (n m w)
  (reduce #'+ (subseq w n (1+ m))))
 
> (sum-sequence 3 5 '(1 2 3 4 5 6 7))
15

(defun sum-sequence (n m w)
  (reduce #'+ (subseq w (1- n) m)))
 
> (sum-sequence 3 5 '(1 2 3 4 5 6 7))
12

(defun sum-sequence (w n m)
  (cond ((= m 0) 0)
        ((= n 1) (+ (car w) (sum-sequence (cdr w) n (1- m))))
        ((sum-sequence (cdr w) (1- n) (1- m)))))
 
> (sum-sequence '(1 2 3 4 5 6 7) 3 5)
12

(defun del-dup (lst &optional r f)
  (cond ((null f) (del-dup (reverse lst) nil t))
        ((null lst) r)
        ((not (member (car lst) r)) (del-dup (cdr lst) (cons (car lst) r) t))
        (t (del-dup (cdr lst)  r t))))
 
  
 
==> del-dup
 
(del-dup '((a b) c d (a b) c e))
 
==> (d (a b) c e)

(defun sum3 (n m lst)
  (let ((c 0))
       (apply '+ (mapcar #'(lambda (x) (setq c (+ 1 c)) (if (and (>= c n) (<= c m)) x 0) ) lst))))
 
==> sum3
 
(sum3 3 5 '(1 2 3 4 5 6 7))
 
==> 12