(defn qsort-rs [[pivot & xs]]
  (when pivot
    (let [smaller #(< % pivot)]
      (lazy-cat (qsort (filter smaller xs))
                [pivot]
                (qsort (remove smaller xs))))))

http://rosettacode.org/wiki/Quicksort#Clojure

A Functional quick sort (Java imperative version seems to be quicker).

Functional quick sort

sort

Lisp