funky-partition-by.clj

;;; do NOT try to print seqs partitioned by the following...
;;; example usage follows code

(defn partition-by* [f r]
  (let [igen (fn igen [l s]
               (lazy-seq
                (if-let [current (first s)]
                  (if (= l (f current))
                    (do (swap! r next)
                        (cons (first s)
                              (igen l (next s))))))))]
    (lazy-seq
     (cons
      (igen (f (first @r)) @r)
      (partition-by* f r)))))

(defn funky-partition-by [f coll]
  (partition-by* f (atom (seq coll))))

;;; from my REPL:

(comment

user> (let [foo (partition-by* even? (atom (range 10)))]
        (dorun (first foo))
        (second foo))
(1)
user> (let [foo (partition-by* even? (atom (range 10)))]
        (dorun (first foo))
        (dorun (second foo))
        (nth foo 2))
(2)
user> (let [foo (funky-parition-by even? (range 10))]
        (dorun (first foo))
        (dorun (second foo))
        (nth foo 2))
(2)
user> (funky-parition-by even? (range 10))
; Evaluation aborted.
user> (let [foo (funky-parition-by even? (range 10))]
        (doseq [i (range 9)]
          (dorun (nth foo i)))
        (nth foo 10))
(9)

)