(defun add-suffix (number)
  (let* ((suffixes #10("th"  "st"  "nd"  "rd"  "th"))
         (last2 (mod number 100))
         (last-digit (mod number 10))
         (suffix (if (< 10 last2 20)
                   "th"
                   (svref suffixes last-digit))))
    (format nil "~a~a" number suffix)))