(require (lib "xml.ss" "xml"))

(define (load-xml-file file-name)
  (xml->xexpr
   (document-element
    (with-input-from-file file-name read-xml))))

(define (save-band-xml-file xexpr file-name)
  (let ((port (open-output-file file-name)))
    (write-xml
     (make-xml-document 'band "band.dtd" #f xexpr) port)
    (close-output-port port)))

(define (add-tony xexpr)
  `(band 
    ,@(append (cdr xexpr)
	      '((member
		 (name "Tony Iommi")
		 (instrument "guitar"))))))

;;; main program
(save-band-xml-file 
 (add-tony (load-xml-file "band.xml"))
 "band-neu.xml")