factorial.clj

(defn how-not-to-factorial [x]
  (condp #(< %2 %1) x
    1 (throw (IllegalArgumentException.))
    3 x
    (loop [acc (bigint x) prev (dec x)]
      (if (= prev 2) (* acc 2) (recur (* acc prev) (dec prev))))))

;; when you want to factorial...
(defn just-factorial [n] (apply * (range 1N (inc n))))

(require '[clojure.string :as s])

(defn- fn-name [f]
  (-> f
      class
      (.getName)
      (s/split #"\$")
      last))

(doseq [fac [how-not-to-factorial just-factorial]]
  (let [n 65 bench-cycles 10000]
    (println (s/join [(fn-name fac) "(" n ")"]))
    (println (s/join (repeat 25 "=")))

    (print "Single run: ")
    (time (fac n))

    (print " Benchmark: ")
    (time (dotimes [_ bench-cycles] (fac n)))

    (print "    Result: ")
    (println (fac n))
    
    (println)))

Executable version of (updated) code available at https://replit.com/@dexterous/simplicate-dont-complify