;;                            S X M L   T o o l s               
; $Revision: 3.13 $ from $Date: 2003/07/12 07:08:07 $:
;
; This software is in Public Domain.
; IT IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND.
;
; Please send bug reports and comments to lisovsky@acm.org
;           Kirill Lisovsky
;
;   SXML normal form used for normalization-dependent functions:
; If attr-list is present it's always the second in SXML element.
; If aux-list is present - then list of attributes is always
; included, and aux-list is always the third.
;   Minimized form is just the same, but all the empty aux-lists are 
; absent, and empty attr-lists are present only in elements with aux-lists
; present. 

;==============================================================================
; Auxiliary functions.

; unlike filter-map from SRFI-1 this function uses separate predicate 
; and mapping functions. 
; Applies proc to  all the elements of source list that satisfy the predicate 
; and return the list of the results.
(define (filter-and-map pred proc lis)			
  (let rpt ((l lis))		
    (if (null? l)
      '()
      (if (pred (car l))
	(cons (proc (car l)) (rpt (cdr l)))
	(rpt (cdr l))))))
      
; Applies pred to every member of lst and yields #t if all the results
; are #t
(define (check-list pred lst) 
  (cond
    ((null? lst) #t)
    ((pred (car lst))
     (check-list pred (cdr lst)))
    (else #f)))

; Returns attr-list node for a given obj 
;   or #f if it is absent
(define (sxml:attr-list-node obj)
  (if (and (not (null? (cdr obj)))
	    (pair? (cadr obj)) 
	    (eq? '@ (caadr obj)))
	 (cadr obj)
	 #f))

; Returns attr-list wrapped in list
;   or '((@)) if it is absent and aux-list is present 
;   or '() if both lists are absent
(define (sxml:attr-as-list obj)
  (cond
    ((sxml:attr-list-node obj)
     => list)
    ((sxml:aux-list-node obj)
     '((@)))
    (else '())))

; Returns aux-list node for a given obj 
;   or #f if it is absent
(define (sxml:aux-list-node obj)
  (if
    (or (null? (cdr obj))
	(null? (cddr obj))
	(not (pair? (caddr obj)))
	(not (eq? (caaddr obj) '@@)))
    #f
    (caddr obj)))

; Returns aux-list wrapped in list 
;   or '() if it is absent
(define (sxml:aux-as-list obj)
  (cond 
    ((sxml:aux-list-node obj)
     => list)
    (else '())))

; optimized (string-rindex name #\:)
; returns position of a separator between namespace-id and LocalName
(define-macro (sxml:find-name-separator len)
  `(let rpt ((pos (-- ,len))) 
     (cond
       ((negative? pos) #f) 	
       ((char=? #\: (string-ref name pos)) pos)
       (else (rpt (-- pos))))))
  

; sxml error message
(define (sxml:error . messages)
  (cerr nl "SXML ERROR: ")
  (apply cerr messages)
  (cerr nl)
  (exit -1))

;==============================================================================
; Predicates

; Predicate which returns #t if given element <obj> is empty. 
; Empty element has no nested elements, text nodes, PIs, Comments or entities
; but it may contain attributes or namespace-id.
; It is a SXML counterpart of XML empty-element.
(define (sxml:empty-element? obj)
  (not 
    ((select-first-kid 
     (lambda(x)
       (or ((ntype-names?? '(*PI* *COMMENT* *ENTITY*)) x)
           ((ntype?? '*) x)
	   (string? x)))) obj)))

; Returns #t if the given <obj> is shallow-normalized SXML element.
; The element itself has to be normalised but its nested elements are not tested.
(define (sxml:shallow-normalized? obj)
  (or 
    (null? (cdr obj))
    (and (or 
	   (and 
	     (pair? (cadr obj)) 
	     (eq? (caadr obj) '@))
	   (not ((select-first-kid (ntype-names?? '(@ @@))) obj)))
	 (or (null? (cddr obj))
	     (and (pair? (caddr obj)) 
		  (eq? (caaddr obj) '@@))
	     (not ((select-first-kid (ntype?? '@@)) obj))))))

; Returns #t if the given <obj> is normalized SXML element.
;  The element itself and all its nested elements have to be normalised.
(define (sxml:normalized? obj)
    (and
      (sxml:shallow-normalized? obj)
    (check-list
      (lambda(x)
	(if
	   (sxml:element? x)
	   (sxml:normalized? x)
	   #t))
       (sxml:content obj))
    ))

; Returns #t if the given <obj> is shallow-minimized SXML element.
; The element itself has to be minimised but its nested elements are not tested.
(define (sxml:shallow-minimized? obj)
  (and
    (sxml:shallow-normalized? obj)
    (not (and (sxml:aux-list-node obj) 
	      (null? (sxml:aux-list obj))))
    (not (and (sxml:attr-list-node obj)
	      (null? (sxml:attr-list obj))
	      (not (sxml:aux-list-node obj))))))

; Returns #t if the given <obj> is minimized SXML element.
;  The element itself and all its nested elements have to be minimised.
(define (sxml:minimized? obj)
    (and
      (sxml:shallow-minimized? obj)
    (check-list
      (lambda(x)
	(if
	   (sxml:element? x)
	   (sxml:minimized? x)
	   #t))
       (sxml:content obj))
    ))

;==============================================================================
; Accessors  

; Returns a name of a given SXML node
; It is introduced for the sake of encapsulation.
(define sxml:name car)

; A version of sxml:name, which returns #f if the given <obj> is 
; not a SXML element.
; Otherwise returns its name.
(define (sxml:element-name obj)
  (and ((ntype?? '*) obj) 
       (car obj)))

; Safe version of sxml:name, which returns #f if the given <obj> is 
; not a SXML node.
; Otherwise returns its name.
(define (sxml:node-name obj)
  (and (pair? obj) 
       (symbol? (car obj))
    (car obj)))

; Returns Local Part of Qualified Name (Namespaces in XML production [6])
; for given obj, which is ":"-separated suffix of its Qualified Name
; If a name of a node given is NCName (Namespaces in XML production [4]), then 
; it is returned as is.
; Please note that while SXML name is a symbol this function returns a string.
(define (sxml:ncname obj)
  (let* ((name (symbol->string (car obj)))
	 (len (string-length name)))
    (cond
      ((sxml:find-name-separator len)
       => (lambda (pos) 
	    (substring name (+ pos 1) len)))
      (else name))))

; Returns namespace-id part of given name, or #f if it's LocalName
(define (sxml:name->ns-id sxml-name)
  (let* ((name (symbol->string sxml-name)))
    (cond
      ((sxml:find-name-separator (string-length name))
       => (lambda (pos) 
	    (substring name  0 pos)))
      (else #f))))
    

; Returns the content of given SXML element or nodeset (just text and element
; nodes) representing it as a list of strings and nested elements in document 
; order.  This list is empty if <obj> is empty element or empty list.
(define (sxml:content obj)
  (((if (nodeset? obj) 
      sxml:filter
      select-kids) 
    (lambda(x)
      (or
	(string? x)   ;  ((ntype?? '*text*) x)
       ((ntype?? '*) x)))) 
   obj))

;------------------------------------------------------------------------------
; Normalization-dependent accessors
;
;
; "Universal" accessors are less effective but may be used for non-normalized SXML
; Safe accessors are named with suffix '-u'
;
; "Fast" accessors are optimized for normalized SXML data.
; They are not applicable to arbitrary non-normalized SXML data
; Their names has no specific suffixes

; Returns all the content of normalized SXML element except attr-list and
; aux-list.
; Thus it includes PI, COMMENT and  ENTITY nodes as well as TEXT and ELEMENT nodes
; returned by sxml:content.
; Returns  a list of nodes in document order or empty list if <obj> is empty 
; element or empty list.
; This function is faster than sxml:content
(define (sxml:content-raw obj)
  ((if (and (not (null? (cdr obj))) 
	    (pair? (cadr obj)) (eq? (caadr obj) '@))
     (if (and (not (null? (cddr obj))) 
	      (pair? (caddr obj)) (eq? (caaddr obj) '@@))
       cdddr
       cddr)
     cdr) obj))


; Returns the list of attributes for given element or nodeset.
; Analog of ((sxpath '(@ *)) obj)
; Empty list is returned if there is no list of attributes.
(define (sxml:attr-list-u obj)
  (cond (((select-first-kid (ntype?? '@)) obj)
	 => cdr)
	(else '())))

; Returns the list of auxiliary nodes for given element or nodeset.
; Analog of ((sxpath '(@@ *)) obj)
; Empty list is returned if a list of auxiliary nodes is absent.
(define (sxml:aux-list obj)
  (if
    (or (null? (cdr obj))
	(null? (cddr obj))
	(not (pair? (caddr obj)))
	(not (eq? (caaddr obj) '@@)))
    '()
    (cdaddr obj)))  

; Returns the list of auxiliary nodes for given element or nodeset.
; Analog of ((sxpath '(@@ *)) obj)
; Empty list is returned if a list of auxiliary nodes is absent.
(define (sxml:aux-list-u obj)
  (cond (((select-first-kid (ntype?? '@@)) obj)
	 => cdr)
	(else '())))

; Return the first aux-node with <aux-name> given in SXML element <obj> 
; or #f is such a node is absent.
; NOTE: it returns just the FIRST node found even if multiple nodes are
; present, so it's mostly intended for nodes with unique names 
(define (sxml:aux-node obj aux-name)
  (cond 
    ((assq aux-name (sxml:aux-list obj)))
    (else #f))) 

; Return a list of aux-node with <aux-name> given in SXML element <obj> 
; or '() if such a node is absent.
(define (sxml:aux-nodes obj aux-name)
  (filter 
    (lambda(x) (eq? aux-name (car x)))
    (sxml:aux-list obj)))

; Accessor for an attribute <attr-name> of given SXML element <obj> which 
; It returns: 
;    the value of the attribute if the attribute is present
;    #f if there is no such an attribute in the given element
(define (sxml:attr obj attr-name)
  (cond 
    ((assq attr-name (sxml:attr-list obj))
     => cadr)
    (else #f)))


; Accessor for a numerical attribute <attr-name> of given SXML element <obj> 
; which It returns: 
;    a value of the attribute as the attribute as a number if the attribute 
;    is present and its value may be converted to number using string->number
;    #f if there is no such an attribute in the given element or
;    its value can't be converted to a number
(define (sxml:num-attr obj attr-name)
  (cond 
    ((assq attr-name (sxml:attr-list obj))
     => (lambda(x) (string->number (cadr x))))
    (else #f)))

; Accessor for an attribute <attr-name> of given SXML element <obj> which 
; may also be an attributes-list or nodeset (usually content of SXML element)
;
; It returns: 
;    the value of the attribute if the attribute is present
;    #f if there is no such an attribute in the given element
(define (sxml:attr-u obj attr-name)
  (cond 
    ((assq attr-name
	   ; the list of attributes is computed below
	   (cond
	     ((and (not (null? (cdr obj))) 
		   (pair? (cadr obj))
		   (eq? '@ (caadr obj)))
	      (cdadr obj))   ; fast track for normalized elements 
	     ((eq? '@ (car obj))
	      (cdr obj))     ; if applied to attr-list
	     (else (sxml:attr-list-u obj))))
     => cadr)
    (else #f)))

; Returns the list of namespaces for given element.
; Analog of ((sxpath '(@@ *NAMESPACES* *)) obj)
; Empty list is returned if there is no list of namespaces.
(define (sxml:ns-list obj)
  (cond ((assv '*NAMESPACES* (sxml:aux-list obj))
	 => cdr)
	(else '())))

; Returns the list of namespace-assoc's for given namespace-id in 
; SXML element <obj>.
; Analog of ((sxpath '(@@ *NAMESPACES* namespace-id)) obj)
; Empty list is returned if there is no namespace-assoc with namespace-id
; given.
(define (sxml:ns-id->nodes obj namespace-id)
  (filter 
    (lambda(x)
      (eq? (car x) namespace-id))
    (sxml:ns-list obj)))

; It returns: 
;    A  URI's for namespace-id given 
;    #f if there is no namespace-assoc with namespace-id given
(define (sxml:ns-id->uri obj namespace-id)
  (cond 
    ((assq namespace-id (sxml:ns-list obj))
     => cadr)
    (else #f)))

; Returns a list of namespace-assocs nodes for NS URI given 
(define (sxml:ns-uri->nodes obj URI)
  (filter
    (lambda (ns-assoc) 
      (string=? (cadr ns-assoc) URI))
    (sxml:ns-list obj)))

; Returns a namespace-id for NS URI given 
(define (sxml:ns-uri->id obj URI)
  (let rpt ((ns-assocs (sxml:ns-list obj)))
  (cond
      ((null? ns-assocs) #f)
      ((string=? (cadar ns-assocs) URI)
       (caar ns-assocs))
      (else (rpt (cdr ns-assocs)))
    )))

; Returns namespace-id for given namespace-assoc list
(define sxml:ns-id car)

; Returns URI for given namespace-assoc list
(define sxml:ns-uri cadr)

; It returns namespace prefix for given namespace-assoc list
;  Original (as in XML document) prefix for namespace-id given 
; has to be strored as the third element in namespace-assoc list 
; if it is different from namespace-id.
;    If original prefix is omitted in namespace-assoc then
;      namespace-id is used instead
(define (sxml:ns-prefix ns-assoc)
      (if (> (length ns-assoc) 2)
	(caddr ns-assoc)
	(car ns-assoc))) 

;==============================================================================
; Data modification functions
; Constructors and mutators for normalized SXML data
; 
; This functions are optimized for normalized SXML data.
; They are not applicable to arbitrary non-normalized SXML data
; 
; Most of the functions are provided in two variants: 
; 1. side-effect intended functions for linear update of given elements.
;   Their names are ended with exclamation mark.
;   An example: 
;      sxml:change-content! 
; 2. pure functions without side-effects which return modified elements.
;   An example: 
;      sxml:change-content
 
; Change the content of given SXML element to <new-content>
; If <new-content> is an empty list then the <obj> is transformed 
; The resulting SXML element is normalized
; Former name sxml:content!
(define (sxml:change-content! obj new-content)
  (set-cdr! obj 
	    `(
              ,@(sxml:attr-as-list obj)
              ,@(sxml:aux-as-list obj)
	      ,@new-content)))

; Change the content of given SXML element to <new-content>
; If <new-content> is an empty list then the <obj> is transformed 
; to an empty element
; The resulting SXML element is normalized
(define (sxml:change-content obj new-content)
  `(,(sxml:name obj) 
              ,@(sxml:attr-as-list obj)
              ,@(sxml:aux-as-list obj)
	,@new-content))

; The resulting SXML element is normalized, if <new-attrlist> is empty,
; the cadr of <obj> is (@)
(define (sxml:change-attrlist obj new-attrlist)
  `(,(sxml:name obj) 
     ,@(cond 
	 (new-attrlist
	  `((@ ,@new-attrlist)))
	 ((sxml:aux-list-node obj)
	   '((@)))
	 (else `()))
     ,@(sxml:aux-as-list obj)
     ,@(sxml:content obj)))

; The resulting SXML element is normalized, if <new-attrlist> is empty,
; the cadr of <obj> is (@)
; Former name sxml:attrlist!
(define (sxml:change-attrlist! obj new-attrlist)
  (set-cdr! obj 
	`(
	  ,@(cond 
	      (new-attrlist
		`((@ ,@new-attrlist)))
	      ((sxml:aux-list-node obj)
	       '((@)))
	      (else `()))
	  ,@(sxml:aux-as-list obj)
	  ,@(sxml:content obj))))
      
; Change a name of SXML element destructively
; Former name was 'sxml:name!'
(define (sxml:change-name! obj new-name)
  (set-car! obj new-name))

; Returns SXML element with its name changed 
(define (sxml:change-name obj new-name)
  (cons new-name (cdr obj)))

; Returns SXML element <obj> with attribute <attr> added or #f
; if the attribute with given name already exists, 
; <attr> is (<attr-name> <attr-value>)
; Pure functional counterpart to sxml:add-attr!
(define (sxml:add-attr obj attr)
  (let ((attr-list (sxml:attr-list obj)))
    (if (assq (car attr) attr-list) 
      #f
      `(,(sxml:name obj)
	(@ ,@(cons attr attr-list))
	,@(sxml:aux-as-list obj)
	,@(sxml:content obj)))))

; Add an attribute <attr> for an element <obj>
; Returns #f if the attribute with given name already exists. 
; The resulting SXML node is normalized.
; Linear update counterpart to sxml:add-attr
(define (sxml:add-attr! obj attr)
  (let ((attr-list (sxml:attr-list obj)))
    (if (assq (car attr) attr-list) 
      #f
      (begin
      (set-cdr! obj 
	`(
	(@ ,@(cons attr attr-list))
	,@(sxml:aux-as-list obj)
	,@(sxml:content obj)))
      obj))))


; Returns SXML element <obj> with changed value of attribute <attr> or #f
; if where is no attribute with given name. 
; <attr> is (<attr-name> <attr-value>)
(define (sxml:change-attr obj attr)
  (let ((attr-list (sxml:attr-list obj)))
    (if (null? attr-list)
      #f
      (cond 
	((assv (car attr) attr-list) 
	 => (lambda (y)
	      `(,(sxml:name obj)
		 (@ ,@(map
			(lambda(at)
			  (if
			    (eq? at y)
			    attr
			    at))
			attr-list))
		 ,@(sxml:aux-as-list obj)
		 ,@(sxml:content obj)
		 )))
	(else #f)))))
    
; Change value of the attribute for element <obj> 
; <attr> is (<attr-name> <attr-value>)
; Returns #f if where is no such attribute
(define (sxml:change-attr! obj attr)
  (let ((x (sxml:attr-list obj)))
     (if (null? x)
       #f
       (cond 
	 ((assv (car attr) x) => (lambda (y)
				  (set-cdr! y (cdr attr)) obj))
	 (else #f)))))

; Set attribute <attr> of element <obj> 
; If there is no such attribute the new one is added
(define (sxml:set-attr obj attr)
  (let ((attr-list (sxml:attr-list obj)))
    (cond 
      ((assv (car attr) attr-list) 
       => (lambda (y)
	    `(,(sxml:name obj)
	       (@ ,@(map
		      (lambda(at)
			(if
			  (eq? at y)
			  attr
			  at))
		      attr-list))
	       ,@(sxml:aux-as-list obj)
	       ,@(sxml:content obj)
	       )))
      (else 
	`(,(sxml:name obj)
	   (@ ,@(cons attr attr-list)) 
	   ,@(sxml:aux-as-list obj)
	   ,@(sxml:content obj))))
    ))

; Set attribute <attr> of element <obj> 
; If there is no such attribute the new one is added
(define (sxml:set-attr! obj attr)
  (let ((attr-list (sxml:attr-list obj)))
     (cond 
       ((assv (car attr) attr-list) 
	=> (lambda (x) (set-cdr! x (cdr attr))))
       (else (set-cdr! obj
		       `((@ ,@(cons attr attr-list)) 
			 ,@(sxml:aux-as-list obj)
			 ,@(sxml:content obj))))
   )))

; Returns SXML element <obj> with an auxiliary node <aux-node> added 
(define (sxml:add-aux obj aux-node)
      `(,(sxml:name obj)
	(@ ,@(sxml:attr-list obj))
	(@@ ,@(cons aux-node (sxml:aux-list obj)))
	,@(sxml:content obj)))

; Add an auxiliary node <aux-node> for an element <obj>
(define (sxml:add-aux! obj aux-node)
      (set-cdr! obj 
	`(
	(@ ,@(sxml:attr-list obj))
	(@@ ,@(cons aux-node (sxml:aux-list obj)))
	,@(sxml:content obj)))
      obj)

; Eliminates empty lists of attributes and aux-lists for given SXML element 
; <obj> and its descendants ("minimize" it)
; Returns: minimized and normalized SXML element
(define (sxml:squeeze! obj)
   (set-cdr! obj 
  `(,@(cond 
	((sxml:attr-list-node obj)
	 => (lambda (atl) 
	      (if (and (null? (cdr atl)) 
		       (null? (sxml:aux-list obj)))
		 '()
	         (list atl))))	
	(else '()))
    ,@(cond ((sxml:aux-list-node obj)
	     => (lambda (axl) 
	      (if (null? (cdr axl))
		'()
	         (list axl))))
	(else '()))
    ,@(map
	(lambda(x)
	  (cond 
	    (((ntype?? '*) x)
	     (sxml:squeeze! x)
	     x)
	    (else x)))
       (sxml:content obj))
    ))
   )

	     
; Eliminates empty lists of attributes and aux-lists for given SXML element 
; <obj> and its descendants ("minimize" it)
; Returns: minimized and normalized SXML element
(define (sxml:squeeze obj)
  `(,(sxml:name obj)
   ,@(cond 
	((sxml:attr-list-node obj)
	 => (lambda (atl) 
	      (if (and (null? (cdr atl)) 
		       (null? (sxml:aux-list obj)))
		 '()
	         (list atl))))	
	(else '()))
    ,@(cond ((sxml:aux-list-node obj)
	     => (lambda (axl) 
	      (if (null? (cdr axl))
		'()
	         (list axl))))
	(else '()))
    ,@(map
	(lambda(x)
	  (cond 
	    (((ntype?? '*) x)
	     (sxml:squeeze x))
	    (else x)))
       (sxml:content obj))))

; Eliminates empty lists of attributes and ALL aux-lists for given SXML element 
; <obj> and its descendants
; Returns: minimized and normalized SXML element
(define (sxml:clean obj)
  `(,(sxml:name obj)
   ,@(cond 
	((sxml:attr-list-node obj)
	 => (lambda (atl) 
	      (if (null? (cdr atl)) 
		 '()
	         (list atl))))	
	(else '()))
    ,@(map
	(lambda(x)
	  (cond 
	    (((ntype?? '*) x)
	     (sxml:clean x))
	    (else x)))
       (sxml:content obj))))
;==============================================================================
; SXPath-related 

;------------------------------------------------------------------------------
; Extensions

; select-first-kid:: Pred -> Node -> Node
; Given a Node, return its first child that satisfy
; the test-pred?
; Returns #f if there is no such a child
; select-first-kid:: Pred -> Nodeset -> Node
; The same as above, but select among children of all the nodes in
; the Nodeset
(define (select-first-kid test-pred?)
 (lambda(obj)
  (let rpt ((lst (if (symbol? (car obj)) 
		  (cdr obj)
		  obj)))
    (cond 
      ((null? lst) #f)
      ((and (pair? (car lst))
	    (test-pred? (car lst)))
	(car lst))
      (else (rpt (cdr lst)))) 
    )))

;------------------------------------------------------------------------------
; Fast node-parent 

; Returns a function of one argument - SXML element - which returns its parent
; node using *PARENT* pointer in aux-list
; '*TOP-PTR* may be used as a pointer to root node
; It return an empty list when applyed to root node
(define (sxml:node-parent rootnode)
  (lambda(obj)
  (cond 
    ((sxml:aux-node obj '*PARENT*)
     => (lambda(x)
 	  (if 
 	    (eq? '*TOP-PTR* (cadr x))
	  rootnode
	  ((cadr x)))))
    ((and (pair? obj)
          (eq? (car obj) '*TOP* ))
     '())           
     (else (sxml:error nl "PARENT pointer is absent in: " obj nl)
	   ))))

(define (sxml:add-parents obj . top-ptr)
  (let rpt 
    ((elt obj)
     (p '*TOP*)
     (at-aux (if (eq? (sxml:name obj) '*TOP*)
		(list (cons '@@ (sxml:aux-list-u obj)))
		(list
		  (cons '@ (sxml:attr-list obj))
		  (cons '@@ (cons `(*PARENT* ,(lambda() (car top-ptr))) 
						 (sxml:aux-list obj))))))
     ) ; *TOP* is a parent for top-level element
    (let* ((h (list (sxml:name elt)))
	   (b  (append 
		 at-aux
		 (map
		     (lambda(x)
		       (cond 
			 (((ntype?? '*) x)
			  (rpt x h
			       (list
				 (cons '@ (sxml:attr-list x))
				 (cons '@@ (cons `(*PARENT* ,(lambda() h)) 
						 (sxml:aux-list x))))
			       ))
			 (else x)))
		     (sxml:content elt)))))
      (set-cdr! h b)
      h)))


; Lookup an element using its ID 
(define (sxml:lookup id index)
    (cond
      ((assoc id index) 
       => cdr)
      (else #f)))

;==============================================================================
; Markup generation

; Filter the 'fragments'
; The fragments are a list of strings, characters,
; numbers, thunks, #f -- and other fragments.
; The function traverses the tree depth-first, and returns a list
; of strings, characters and executed thunks, and ignores #f and '().
;
; If all the meaningful fragments are strings, then
;  (apply string-append ... )
; to a result of this function will return its string-value 
;
; It may be considered as a variant of Oleg Kiselyov's SRV:send-reply:
; While SRV:send-reply displays fragments, this function returns the list 
; of meaningful fragments and filter out the garbage.
(define (sxml:clean-feed . fragments)
  (reverse
  (let loop ((fragments fragments) (result '()))
    (cond
      ((null? fragments) result)
      ((not (car fragments)) (loop (cdr fragments) result))
      ((null? (car fragments)) (loop (cdr fragments) result))
      ((pair? (car fragments))
        (loop (cdr fragments) 
	      (loop (car fragments) result)))
      (else
        (loop (cdr fragments) 
	      (cons (car fragments) result)))))))

;------------------------------------------------------------------------------
; XML

; Creates the XML markup for attributes.
(define (sxml:attr->xml attr)
   (list " " (sxml:ncname attr)
	 "='" (cadr attr) "'"))

; Return a string or a list of strings where all the occurences of 
; characters < > & " ' in a given string are replaced by corresponding 
; character entity references. See also:  sxml:string->html
(define sxml:string->xml
  (make-char-quotator
   '((#\< . "&lt;") (#\> . "&gt;") (#\& . "&amp;") 
		    (#\" . "&quot;") (#\' . "&apos;"))))

; A version of dispatch-node specialized and optimized for SXML->XML
; transformation.
(define (sxml:sxml->xml tree)
  (cond
    ((nodeset? tree)
     (map (lambda (a-tree) 
	    (sxml:sxml->xml a-tree)) 
	  tree))
    ((pair? tree)
     (let* ((name (sxml:name tree))   ; NS (URI-prefixed) not supported
	    (nm (symbol->string name))
	    (content (sxml:content-raw tree)))
	 `("<" ,nm ,@(map sxml:attr->xml (sxml:attr-list tree))
	   ,@(if (null? content) '("/>")
	       `(">" ,@(sxml:sxml->xml content) "</" ,nm ">")))))
    ((string? tree) (sxml:string->xml tree)) ; *text*
    (else (sxml:error "sxml->html - unexpected type of node: " tree))))


;------------------------------------------------------------------------------
; HTML

; Creates the HTML markup for attributes.
(define (sxml:attr->html attr)
	 (if (equal? "" (cadr attr))
             (list " " (sxml:ncname attr))
             (list " " (sxml:ncname attr) "='" (cadr attr) "'")))

; Given a string, check to make sure it does not contain characters
; < > & " that require encoding. Return either the original
; string, or a list of string fragments with special characters
; replaced by appropriate character entities.
; Borrowed from Oleg Kiselyov's XML-to-HTML.scm (where its name is
; string->goodHTML)
(define sxml:string->html
  (make-char-quotator
   '((#\< . "&lt;") (#\> . "&gt;") (#\& . "&amp;") (#\" . "&quot;"))))


; This predicate yields #t for "non-terminated" HTML 4.0 tags
(define (sxml:non-terminated-html-tag? tag) 
  (memq tag 
     '(area base basefont br col frame hr img input isindex link meta param)))


; A version of dispatch-node specialized and optimized for SXML->HTML
; transformation.
(define (sxml:sxml->html tree)
  (cond
    ((nodeset? tree)
     (map (lambda (a-tree) 
	    (sxml:sxml->html a-tree)) 
	  tree))
    ((pair? tree)
     (let* ((name (sxml:name tree))
	    (nm (symbol->string name))
	    (content (sxml:content-raw tree)))
	 `("<" ,nm ,@(map sxml:attr->html (sxml:attr-list tree))
	   ,@(if (null? content)
	       (if (sxml:non-terminated-html-tag? name) '(">") '("/>"))
	       `(">" ,@(sxml:sxml->html content) "</" ,nm ">")))))
    ((string? tree) (sxml:string->html tree)) ; *text*
    (else (sxml:error "sxml->html - unexpected type of node: " tree))))