Levenshtein distance in lisp (Recursive/slow)

leven.lisp

(defun leven-distance (string1 string2)
  (if (= (length string1) 0)
    (length string2)

  (if (= (length string2) 0)
    (length string1)

  (min (+ (leven-distance (subseq string1 0 (- (length string1) 1))
                          string2)
          1)

       (+ (leven-distance string1
                          (subseq string2 0 (- (length string2) 1)))
          1)

       (+ (leven-distance (subseq string1 0 (- (length string1) 1))
                          (subseq string2 0 (- (length string2) 1)))
          (if (equal (subseq string1 (- (length string1) 1))
                     (subseq string2 (- (length string2) 1)))
          0 1))))))


(defun get-string (prompt)
  (format T prompt)
  (read-line *query-io*))

(defun main ()
  (format T "The diff is: ~a"
    (leven-distance
      (get-string "string1: ")
      (get-string "string2: ")))

  (quit))

(main)