Memoized version of 4clojure problem 101

joly-4clojure-solution101.clj

(def levdist
  (let [lev (atom nil)
        impl
        (fn [s t]
          (let [lev @lev]
            (cond
             (empty? s) (count t)
             (empty? t) (count s)
             :else (let [ns (rest s)
                         nt (rest t)]
                     (if (= (first s) (first t))
                       (lev ns nt)
                       (inc (min (lev s nt)
                                 (lev ns t)
                                 (lev ns nt))))))))]
    (reset! lev (memoize impl))
    impl ;; or @lev, either one works!
    ))