Partition contiguous groups of integers

contiguous-xf.clj

(ns xf.contiguous
  (:require [clojure.data.int-map :as i]))

(defn partition-contiguous
  ([]
   (let [buffer (volatile! (i/dense-int-set))]
     (fn [xf]
       (fn
         ([] (xf))
         ([result]
          (xf (let [rest @buffer]
                (if (empty? rest)
                  result
                  (unreduced (xf result rest))))))
         ([result item]
          (let [contiguous @buffer
                previous   (last contiguous)]
            (if (or (nil? previous) (== item (inc previous)))
              (do (vswap! buffer conj item)
                  result)
              (do (vreset! buffer (into (i/dense-int-set) [item]))
                  (if (empty? contiguous)
                    result
                    (xf result contiguous))))))))))
  ([coll]
   (sequence (partition-contiguous) coll)))