[plt-scheme] SXML Experience?

Thanks for you answer, In between, i've build this.
It's not very good, but functional. It transforms and has
(not intended) side effects.

(define (xml-get xml xpath default)
  (let ((v ((sxpath xpath) xml)))
    (if (null? v)
    default
    (cadr v))))

(define (xml-set xml xpath value)

  (define (create-branch xml xpath element)
    (if (and (null? (cdr xpath)) (eq? (car xpath) '//))
    (if (null? ((sxpath xpath) xml))
        '(*TOP* (*PI* xml "version=\"1.0\" encoding=\"UTF-8\"") (element 
'nil))
        xml)
    (let ((v ((sxpath xpath) xml)))
      (if (null? v)
          (let* ((rxpath (reverse xpath))
             (nelem  (car rxpath))
             (nxpath (reverse (cdr rxpath))))
        (let ((nxml (create-branch xml nxpath nelem)))
          (create-branch nxml xpath element)))
          (let ((nv (car v)))
        (if (eq? (car (cdr nv)) 'sxml-nil)
            (set-cdr! nv (list (list (string->symbol element) 'sxml-nil)))
            (set-cdr! nv (cons (list (string->symbol element) 'sxml-nil)
                       (cdr nv))))
        xml)))))

  (let ((v ((sxpath xpath) xml)))
    (if (null? v)
    (let* ((rxpath (reverse xpath))
           (nelem (car rxpath))
           (nxpath (reverse (cdr rxpath))))
      (let ((nxml (create-branch xml nxpath nelem)))
        (xml-set nxml xpath value)))
    (begin
      (set-car! (cdar v) value)
      xml))))