ar2.clj

(defmacro areduce2 [f init xs]
  `(let [xs# ~xs]
     (loop [idx# 0 ret# ~init]
       (if (< idx# (alength xs#))
         (recur (unchecked-inc idx#) (~f ret# (aget xs# idx#)))
         ret#))))
(areduce2 + 0 (int-array (range 100)))

areduce.clj

(defn areduce1 [f init xs]
  (loop [idx 0 ret init]
    (if (< idx (alength xs))
      (recur (unchecked-inc idx) (f init (aget xs idx)))
      ret)))
(areduce1 + 0 (int-array (range 100)))

areduce.macro.clj

(defmacro areduce
"Reduces an expression across an array a, using an index named idx, and return value named ret, initialized to init, setting ret to the evaluation of expr at each step, returning ret."
{:added "1.0"}
[a idx ret init expr]
`(let [a# ~a]
(loop [~idx 0 ~ret ~init] (if (< ~idx (alength a#))
(recur (unchecked-inc ~idx) ~expr) ~ret))))

(areduce1 + 0 (int-array (range 100)))
=> 99