CL-USER> (set-dispatch-macro-character #\# #\x 'hex-read)
 T
 CL-USER> (defun hex-read (stream char arg &optional (recursive-p nil))
            (declare (ignore char arg))
            (let ((*read-base* 16))             
              (read stream t nil t)))
 HEX-READ
 CL-USER> #xaa
 170
 CL-USER> #x#(aa)
 #(170)
 CL-USER> #x#(aa bb cc)
 #(170 187 204)
 CL-USER>