(defn accumulate-iter [comb null-val term next a b]
  (defn iter [a result]
    (if (> a b)
      result
      (iter (next a) (comb (term a) result))))
  (iter a null-val))

(defn accumulate-recur [comb null-val term next a b]
  (if (> a b)
    null-val
    (comb (term a)
          (accumulate-recur comb null-val term next (next a) b))))

(defn add [a b]
  (+ a b))

(defn mult [a b]
  (* a b))

(defn id [n] n)
(defn inc [n] (+ n 1))

(defn sum [a b]
  (accumulate-recur add 0 id inc a b))

(defn factorial [a b]
  (accumulate-recur mult 1 id inc a b))

(var x 1)
(while (< x 10)
  (printf "n=%d, sum 1-n: %d, factorial 1-n: %d" x (sum 1 x) (factorial 1 x))
  (set x (+ x 1)))