ClojureFactorialAndFoldl.clj

;; simple
(defn factorial [n]
  (if (zero? n)
    1
    (* n (factorial (dec n)))))

;; tail recursion
(defn factorial
  ([n] (factorial n 1))
  ([n sum]
     (if (zero? n)
       sum
       (recur (dec n) (* sum n)))))


(defn foldl [init folding-fn seq]
  (if (empty? seq)
    init
    (recur (folding-fn init (first seq)) folding-fn (rest seq))))