階乗の計算 in Clojure

factorial.clj

;;; 普通の再帰版
(defn fact-1 [n]
  (if (= n 0) 1
      (*' n (fact-1 (dec n)))))

;;; 末尾再帰版
(defn fact-2
  ([n] (fact-2 n 1))
  ([n acc]
     (if (= n 0) acc
         (fact-2 (dec n) (*' n acc)))))

;;; loop - recur 版
(defn fact-3 [n]
  (loop [cnt n acc 1]
    (if (= cnt 0) acc
        (recur (dec cnt) (*' cnt acc)))))

;;; fact (multimethod 普通の再帰版)
(defmulti fact-4 identity)
(defmethod fact-4 0 [n] 1)
(defmethod fact-4 :default [n] (*' n (fact-4 (dec n))))