gistfile1.txt

(ns id-gen)

(def ids "abcdefghijklmnopqrstuvwxyz")

(defn create-generator []
  "returns a generator ref"
  (ref {:ids ids, :pos 0}))

(defn- inc-gen
  "increments generator counter
   must be called from within a transaction"
  [gen]
  (alter gen assoc :pos (inc (:pos @gen))))

(defn- get-chars
  "gets the next char(s) in the sequence"
  [s offset]
  (if (>= offset (count s))
    (let [div-val (dec (int (/ offset (count s))))
          mod-val (mod offset (count s))]
      (apply str (get-chars s div-val) (get-chars s mod-val)))
    (subs s offset (inc offset))))

(defn get-id [gen]
  (dosync
    (let [pos (:pos @gen)]
      (inc-gen gen)
      (get-chars (:ids @gen) pos))))

(def g (create-generator))
(println (pr-str (for [x (range 777)] (get-id g))))