Как найти декартово произведение

(cart '(a b) '(с d))
 
==> ((a c) (a d) (b c) (b d))

(defun cartesian-product (w v) 
  (when w (nconc (mi (car w) v) (cartesian-product (cdr w) v)))) 
 
(defun mi (a v) 
  (when v (cons (list a (car v)) (mi a (cdr v))))) 
 
> (cartesian-product '(a b c d) '(1 2 3))
((A 1) (A 2) (A 3) (B 1) (B 2) (B 3) (C 1) (C 2) (C 3) (D 1) (D 2) (D 3))

(defun cartesian-product (w v) 
  (when w 
    (append
     (maplist
      #'(lambda (e) (list (car w) (car e))) v)
     (cartesian-product (cdr w) v))))
 
> (cartesian-product '(a b c d) '(1 2 3))
((A 1) (A 2) (A 3) (B 1) (B 2) (B 3) (C 1) (C 2) (C 3) (D 1) (D 2) (D 3))

(defun cartesian-product (w v)
  (apply
   #'nconc
   (mapcar
    #'(lambda (e) (mapcar #'(lambda (a) (list e a)) v)) w)))
 
> (cartesian-product '(a b c d) '(1 2 3))
((A 1) (A 2) (A 3) (B 1) (B 2) (B 3) (C 1) (C 2) (C 3) (D 1) (D 2) (D 3))

(автор – Max Vasin)
(defun cartesian-product (w v)
  (mapcan (lambda (e) (mapcar (lambda (a) `(,a ,e)) w)) v))
 
> (cartesian-product '(a b c d) '(1 2 3))
((A 1) (B 1) (C 1) (D 1) (A 2) (B 2) (C 2) (D 2) (A 3) (B 3) (C 3) (D 3))

(defun cart! (x y)
  (let ((r nil))
       (dolist (i x r)
          (dolist (j y t)
             (setq r (cons (list i j) r))))))
 
 
==> cart!
 
(cart! '(1 2 3) '(c v b))
 
==> ((3 b) (3 v) (3 c) (2 b) (2 v) (2 c) (1 b) (1 v) (1 c))