Loop-recur TCO for self-referencing

factorial.clj

;;;; Partial Tail Call Optimization in Clojure
;; See this for why no full implicit TCO: https://groups.google.com/forum/#!msg/clojure/4bSdsbperNE/tXdcmbiv4g0J

; Naive non-optimized tail-recursive factorial function
(defn naive-factorial
  ([n] (naive-factorial n 1))
  ([n acc]
    (if (zero? n)
        acc
        (naive-factorial (- n 1) (* acc n)))))

; Optimized factorial function using the loop-recur special form
(def factorial
  (fn [n]
    (loop [cnt n acc 1]
       (if (zero? cnt)
           acc
           (recur (dec cnt) (* acc cnt))))))