fraction-clojure

(defn parse-int [s]
   (Integer. (re-find  #"\d+" s )))

(defn mult [x y]
  "Умножение в столбик двух чисел в виде строки"
  (let [x (map #(parse-int (str %)) (reverse x))
        y (map #(parse-int (str %)) (reverse y))
        summarize-it (atom [])]
    (loop [current-multiplier (last x)]
      (when (not= current-multiplier nil)
        (swap! summarize-it
          (into @summarize-it
            (reduce
            (fn [coll-sum unit-of-y]
              (let [leftover (atom 0)
              multiple (fn [multiplier left] (+ (* unit-of-y multiplier) left))]
              (swap! leftover (quot (multiple unit-of-y @leftover) 10))
              (if (= unit-of-y (last y))
                (do
                  (into coll-sum (rem (multiple unit-of-y @leftover) 10))
                  (into coll-sum (quot (multiple unit-of-y @leftover) 10)))
                (into coll-sum (rem (multiple unit-of-y @leftover) 10))))
              ) [] y)))
            (recur (drop-last x))))))

(mult "547" "83")