(define (extractor v p)
 (if (null? v) #f (p v)))

; (cadar-of <procedure of n arguments>)
(define-syntax extract
 (ir-macro-transformer
  (lambda (expr inject compare)
   (assert (pair? expr))
   (let* ((extractor (second expr))
	  (proc (third expr))
	 )
   ;(list 'quote
    `(lambda x
     (->* x
      (,proc)
      (extractor ,extractor)))
   ;)
  ))))




; Procedures to get the EntitiesDescriptor attributes
;  - the metadata about the metadata
; *TOP* -> EntitiesDescriptor -> @ -> ...
(define meta-meta
 (sxpath '(EntitiesDescriptor @)))

(define meta-meta/validUntil
  (extract cadar
	   (sxpath '(validUntil))))

(define idp-entites
  ;(sxpath '("EntitiesDescriptor/EntityDescriptor[IDPSSODescriptor]")))
  (sxpath '(EntitiesDescriptor (EntityDescriptor(IDPSSODescriptor)))))