A lazy quick sort

LazyQsort.clj

(ns sort
  (:use clojure.test))

(defn qsort [xs]
  "Sorts the specified sequence using the quick sort algorithm"
  (if-let [[pivot & rest] (seq xs)]
    (let [smaller? #(< % pivot)]
      (lazy-cat (qsort (filter smaller? rest))
                [pivot]
                (qsort (remove smaller? rest))))))

(testing "qsort"
  (testing "with empty sequence"
    (is (= (qsort []) (seq []))))
  (testing "with unsorted sequence"
    (is (= (qsort [3, 2, 1, 4, 2]) [1, 2, 2, 3, 4]))))

LazyQsort.cs

public static IEnumerable<T> LazyQsort<T>(IEnumerable<T> seq, Func<T, T, bool> comp)
{
	if (seq.Any() == false) 
	{
		return new T[0];
	}

	var pivot = seq.First();
	var xs = seq.Skip(1);
	return LazyQsort(xs.Where(x => comp (x, pivot)), comp)
		   .Union(new[] { pivot })
		   .Union(LazyQsort(xs.Where(x => !comp (x, pivot)), comp));
}