cartesian-product.lisp

(defun distl (m N)
  (cond
   ((null N) nil)
   (t (cons (list m (car N))
            (distl m (cdr N))))))
(print (distl 'b '(x y z)))

(defun cartesian (M N)
  (cond
   ((null M) nil)
   (t (append (distl (car M) N)
              (cartesian (cdr M) N)))))

user> (= (reduce concat (map (fn [m] (map (fn [n] (list m n)) (range 10))) (range 10))) 
         (for [x (range 10) y (range 10)] (list x y)))
true
user> (reduce concat (map (fn [m] (map (fn [n] (list m n)) (range 10))) (range 10)))
((0 0) (0 1) (0 2) (0 3) (0 4) (0 5) (0 6) (0 7) (0 8) (0 9)
 (1 0) (1 1) (1 2) (1 3) (1 4) (1 5) (1 6) (1 7) (1 8) (1 9)
 (2 0) (2 1) (2 2) (2 3) (2 4) (2 5) (2 6) (2 7) (2 8) (2 9)
 (3 0) (3 1) (3 2) (3 3) (3 4) (3 5) (3 6) (3 7) (3 8) (3 9)
 (4 0) (4 1) (4 2) (4 3) (4 4) (4 5) (4 6) (4 7) (4 8) (4 9)
 (5 0) (5 1) (5 2) (5 3) (5 4) (5 5) (5 6) (5 7) (5 8) (5 9)
 (6 0) (6 1) (6 2) (6 3) (6 4) (6 5) (6 6) (6 7) (6 8) (6 9)
 (7 0) (7 1) (7 2) (7 3) (7 4) (7 5) (7 6) (7 7) (7 8) (7 9)
 (8 0) (8 1) (8 2) (8 3) (8 4) (8 5) (8 6) (8 7) (8 8) (8 9)
 (9 0) (9 1) (9 2) (9 3) (9 4) (9 5) (9 6) (9 7) (9 8) (9 9))
user> (count (map (fn [m] (map (fn [n] (list m n)) (range 10))) (range 10)))
10
user> (map count (map (fn [m] (map (fn [n] (list m n)) (range 10))) (range 10)))
(10 10 10 10 10 10 10 10 10 10)
user> (count (reduce concat (map (fn [m] (map (fn [n] (list m n)) (range 10))) (range 10))))
100
user> (count (for [x (range 10) y (range 10)] (list x y)))
100