(defn fibs []
  ((fn rfib [a b]
     (lazy-seq (cons a (rfib b (+' a b)))))
   0 1))

(time (do (nth (fibs) 10000) nil))
"Elapsed time: 6.386237 msecs"
nil

;;;; A java version that takes approx. 30ms

public class NthFib {
	private static BigInteger nthFib(int n) {
		BigInteger a = BigInteger.ZERO;
		BigInteger b = BigInteger.ONE;
		BigInteger z;
		for (int i = 1; i < n; i++) {
			z = b;
			b = a.add(z);
			a = z;
		}
		return b;
	}

	public static void main(String[] args) {
		long s = System.currentTimeMillis();
		BigInteger f = nthFib(10000);
		long e = System.currentTimeMillis();
		System.out.println("Took " + (e - s) + "ms.");
		System.out.println(f);
	}
}