split-coll.cljs

(defn split-coll [elem coll]
   (loop [coll coll
          parts []
          part []]
     (if-let [e (first coll)]
       (if (= e elem)
         (recur (rest coll) (conj parts part) [])
         (recur (rest coll) parts (conj part e)))
       (if (seq part)
         (conj parts part)
         parts))))
       
(defn split-coll [elem coll]
   (loop [coll coll
          parts (transient [])
          part (transient [])]
     (if-let [e (first coll)]
       (if (= e elem)
         (recur (rest coll) (conj! parts (persistent! part)) (transient []))
         (recur (rest coll) parts (conj! part e)))
       (let [part (persistent! part)]
         (persistent!
          (if (seq part)
            (conj! parts part)
            parts))))))

(time (dotimes [n 1000]
         (split-coll :x (apply concat (repeat 100 [:a :b :c :x :x :d :x :e])))))