Cartesian product

cartesian.clj

(defn cartesian-product
  "All the ways to take one item from each sequence"
  [& seqs]
  (let [v-original-seqs (vec seqs)
  step
  (fn step [v-seqs]
    (let [increment
   (fn [v-seqs]
      (loop [i (dec (count v-seqs)), v-seqs v-seqs]
        (if (= i -1) nil
      (if-let [rst (next (v-seqs i))]
        (assoc v-seqs i rst)
        (recur (dec i) (assoc v-seqs i (v-original-seqs i)))))))]
      (when v-seqs
         (cons (map first v-seqs)
         (lazy-seq (step (increment v-seqs)))))))]
    (when (every? seq seqs)
      (lazy-seq (step v-original-seqs)))))