Intuitive Clojure

I just downloaded and tried Clojure for the first time. With a little help from clojure dot org, I managed to write the following snippet that demonstrates the use of tail calls, Java interoperation, exceptions and a bit of I/O. Of course, as is typical for lisps, it just worked the first time.

The program simplifies div expressions. The input is given in format <numerator> <denominator>, for example, 4/2, is given as 4 2.

 1 (defn gcd [a b]
 2     (if (= a b)
 3         a
 4         (if (> a b)
 5            (recur (- a b) b)
 6            (recur a (- b a)))))
 7
 8 (defn run []
 9     (let [line (read-line)
10           args (.split line " ")
11           len (alength args)]
12         (if (< len 2)
13            (println "Expected two arguments.")
14            (try (let [a (Integer/parseInt (aget args 0))
15                       b (Integer/parseInt (aget args 1))
16                       gcd (gcd a b)]
17                    (println a "/" b "=" (/ a gcd) "/" (/ b gcd)))
18                (catch NumberFormatException
19                    ex
20                    (println "Expected natural numbers."))))))
21 (run)