:PPP

convert.lisp

(defun convert (string)
  (let ((designators '(("0y" . 2)
                       ("0o" . 8)
                       ("0x" . 16))))
    (cond ((string= "" string) 0)
          ((every #'digit-char-p string)
           (parse-integer string))
          ((> (length string) 2)
           (parse-integer string
                          :start 2
                          :radix (cdr (assoc (subseq string 0 2)
                                             designators
                                             :test #'string=))))
          (t (error (format nil "Illegal base designation in ~a" string))))))