sunet/scheme/xml/reader.scm

;; Token ::= Contents | Start-tag | End-tag | Eof

(define read-comments (make-parameter #f))
(define collapse-whitespace (make-parameter #f))

;; read-xml : [Input-port] -> Document
(define (read-xml . maybe-port)
  (read-from-port (if (null? maybe-port) (current-input-port) (car maybe-port))))


;; read-from-port : Input-port -> Document
(define (read-from-port in)
  (let*-values (((in pos) (positionify in))
                ((misc0 start) (read-misc in pos)))
    (make-document (make-prolog misc0 #f)
                   (cond
                     ((start-tag? start) (read-element start in pos))
                     ((element? start) start)
                     (else (error 'read-xml "expected root element - received ~a" start)))
                   (let-values (((misc1 end-of-file) (read-misc in pos)))
                     (unless (eof-object? end-of-file)
                       (error 'read-xml "extra stuff at end of document ~a" end-of-file))
                     misc1))))

;; read-misc : Input-port (-> Location) -> (listof Misc) Token
(define (read-misc in pos)
  (let read-more ()
    (let ((x (lex in pos)))
      (cond
        ((or (pi? x) (comment? x))
         (let-values (((lst next) (read-more)))
           (values (cons x lst) next)))
        ((and (pcdata? x) (andmap char-whitespace? (string->list (pcdata-string x))))
         (read-more))
        (else (values null x))))))

;; read-element : Start-tag Input-port (-> Location) -> Element
(define (read-element start in pos)
  (let ((name (start-tag-name start))
        (a (source-start start))
        (b (source-stop start)))
    (make-element
     a b name (start-tag-attrs start)
     (let read-content ()
       (let ((x (lex in pos)))
         (cond
           ((eof-object? x)
            (error 'read-xml "unclosed ~a tag at [~a ~a]" name 
		   (format-source a)
		   (format-source b)))
           ((start-tag? x) (cons (read-element x in pos) (read-content)))
           ((end-tag? x)
            (unless (eq? name (end-tag-name x))
              (error 'read-xml "start tag ~a at [~a ~a] doesn't match end tag ~a at [~a ~a]"
		     name
		     (format-source a)
		     (format-source b)
		     (end-tag-name x)
		     (format-source (source-start x))
		     (format-source (source-stop x))))
            null)
           ((entity? x) (cons (expand-entity x) (read-content)))
           ((comment? x) (if (read-comments)
                             (cons x (read-content))
                             (read-content)))
           (else (cons x (read-content)))))))))

;; expand-entity : Entity -> (U Entity Pcdata)
;; more here - allow expansion of user defined entities
(define (expand-entity x)
  (let ((expanded (default-entity-table (entity-text x))))
    (if expanded
        (make-pcdata (source-start x) (source-stop x) expanded)
        x)))

;; default-entity-table : Symbol -> (U #f String)
(define (default-entity-table name)
  (case name
    ((amp) "&")
    ((lt) "<")
    ((gt) ">")
    ((quot) "\"")
    ((apos) "'")
    (else #f)))

;; lex : Input-port (-> Location) -> Token
(define (lex in pos)
  (let ((c (peek-char in)))
    (cond
      ((eof-object? c) c)
      ((eq? c #\&) (lex-entity in pos))
      ((eq? c #\<) (lex-tag-cdata-pi-comment in pos))
      (else (lex-pcdata in pos)))))

;; lex-entity : Input-port (-> Location) -> Entity
(define (lex-entity in pos)
  (let ((start (pos)))
    (read-char in)
    (let ((data (case (peek-char in)
                  ((#\#)
                   (read-char in)
                   (let ((n (case (peek-char in)
                              ((#\x) (read-char in)
                               (string->number (read-until #\; in pos) 16))
                              (else (string->number (read-until #\; in pos))))))
                     (unless (number? n)
                       (lex-error in pos "malformed numeric entity"))
                     n))
                  (else
                   (begin0
                     (lex-name in pos)
                     (unless (eq? (read-char in) #\;)
                       (lex-error in pos "expected ; at the end of an entity")))))))
      (make-entity start (pos) data))))

;; lex-tag-cdata-pi-comment : Input-port (-> Location) -> Start-tag | Element | End-tag | Pcdata | Pi | Comment
(define (lex-tag-cdata-pi-comment in pos)
  (let ((start (pos)))
    (read-char in)
    (case (non-eof peek-char in pos)
      ((#\!)
       (read-char in)
       (case (non-eof peek-char in pos)
         ((#\-) (read-char in)
          (unless (eq? (read-char in) #\-)
            (lex-error in pos "expected second - after <!-"))
          (let ((data (lex-comment-contents in pos)))
            (unless (eq? (read-char in) #\>)
              (lex-error in pos "expected > to end comment (\"--\" can't appear in comments)"))
            ;(make-comment start (pos) data)
            (make-comment data)))
         ((#\[) (read-char in)
          (unless (string=? (read-string 6 in) "CDATA[")
            (lex-error in pos "expected CDATA following <["))
          (let ((data (lex-cdata-contents in pos)))
            (make-pcdata start (pos) data)))
         (else (skip-dtd in pos)
               (skip-space in)
               (unless (eq? (peek-char in) #\<)
                 (lex-error in pos "expected pi, comment, or element after doctype"))
               (lex-tag-cdata-pi-comment in pos))))
      ((#\?) (read-char in)
       (let ((name (lex-name in pos)))
         (skip-space in)
         (let ((data (lex-pi-data in pos)))
           (make-pi start (pos) name data))))
      ((#\/) (read-char in)
       (let ((name (lex-name in pos)))
         (skip-space in)
         (unless (eq? (read-char in) #\>)
           (lex-error in pos "expected > to close ~a's end tag" name))
         (make-end-tag start (pos) name)))
      (else
       (let ((name (lex-name in pos))
             (attrs (lex-attributes in pos)))
         (skip-space in)
         (case (read-char in)
           ((#\/)
            (unless (eq? (read-char in) #\>)
              (lex-error in pos "expected > to close empty element ~a" name))
            (make-element start (pos) name attrs null))
           ((#\>) (make-start-tag start (pos) name attrs))
           (else (lex-error in pos "expected / or > to close tag `~a'" name))))))))

;; lex-attributes : Input-port (-> Location) -> (listof Attribute)
(define (lex-attributes in pos)
  (quicksort (let loop ()
               (skip-space in)
               (cond
                 ((name-start? (peek-char in))
                  (cons (lex-attribute in pos) (loop)))
                 (else null)))
             (lambda (a b)
               (let ((na (attribute-name a))
                     (nb (attribute-name b)))
                 (cond
                   ((eq? na nb) (lex-error in pos "duplicated attribute name ~a" na))
                   (else (string<? (symbol->string na) (symbol->string nb))))))))

;; lex-attribute : Input-port (-> Location) -> Attribute
(define (lex-attribute in pos)
  (let ((start (pos))
        (name (lex-name in pos)))
    (skip-space in)
    (unless (eq? (read-char in) #\=)
      (lex-error in pos "expected = in attribute ~a" name))
    (skip-space in)
    ;; more here - handle entites and disallow "<"
    (let* ((delimiter (read-char in))
           (value (case delimiter
                    ((#\' #\")
                     (list->string
                      (let read-more ()
                        (let ((c (non-eof peek-char in pos)))
                          (cond
                            ((eq? c delimiter) (read-char in) null)
                            ((eq? c #\&)
                             (let ((entity (expand-entity (lex-entity in pos))))
                               (if (pcdata? entity)
                                   (append (string->list (pcdata-string entity)) (read-more))
                                   ;; more here - do something with user defined entites
                                   (read-more))))
                            (else (read-char in) (cons c (read-more))))))))
                    (else (lex-error in pos "attribute values must be in ''s or in \"\"s")))))
      (make-attribute start (pos) name value))))

;; skip-space : Input-port -> Void
;; deviation - should sometimes insist on at least one space
(define (skip-space in)
  (let loop ()
    (let ((c (peek-char in)))
      (when (and (not (eof-object? c)) (char-whitespace? c))
        (read-char in)
        (loop)))))

;; lex-pcdata : Input-port (-> Location) -> Pcdata
;; deviation - disallow ]]> "for compatability" with SGML, sec 2.4 XML spec 
(define (lex-pcdata in pos)
  (let ((start (pos))
        (data (let loop ()
                (let ((next (peek-char in)))
                  (cond
                    ((or (eof-object? next) (eq? next #\&) (eq? next #\<))
                     null)
                    ((and (char-whitespace? next) (collapse-whitespace))
                     (skip-space in)
                     (cons #\space (loop)))
                    (else (cons (read-char in) (loop))))))))
    (make-pcdata start
                 (pos)
                 (list->string data))))

;; lex-name : Input-port (-> Location) -> Symbol
(define (lex-name in pos)
  (let ((c (read-char in)))
    (unless (name-start? c)
      (lex-error in pos "expected name, received ~a" c))
    (string->symbol
     (list->string
      (cons c (let lex-rest ()
                (cond
                  ((name-char? (peek-char in))
                   (cons (read-char in) (lex-rest)))
                  (else null))))))))

;; skip-dtd : Input-port (-> Location) -> Void
(define (skip-dtd in pos)
  (let skip ()
    (case (non-eof read-char in pos)
      ((#\') (read-until #\' in pos) (skip))
      ((#\") (read-until #\" in pos) (skip))
      ((#\<)
       (case (non-eof read-char in pos)
         ((#\!) (case (non-eof read-char in pos)
                  ((#\-) (read-char in) (lex-comment-contents in pos) (read-char in) (skip))
                  (else (skip) (skip))))
         ((#\?) (lex-pi-data in pos) (skip))
         (else (skip) (skip))))
      ((#\>) (void))
      (else (skip)))))

;; name-start? : Char -> Bool
(define (name-start? ch)
  (or (char-alphabetic? ch) 
      (eq? ch #\_)
      (eq? ch #\:)))

;; name-char? : Char -> Bool
(define (name-char? ch)
  (or (name-start? ch)
      (char-numeric? ch)
      (eq? ch #\.)
      (eq? ch #\-)))

;; read-until : Char Input-port (-> Location) -> String
;; discards the stop character, too
(define (read-until char in pos)
  (list->string
   (let read-more ()
     (let ((c (non-eof read-char in pos)))
       (cond
         ((eq? c char) null)
         (else (cons c (read-more))))))))

;; non-eof : (Input-port -> (U Char Eof)) Input-port (-> Location) -> Char
(define (non-eof f in pos)
  (let ((c (f in)))
    (cond
      ((eof-object? c) (lex-error in pos "unexpected eof"))
      (else c))))

;; gen-read-until-string : String -> Input-port (-> Location) -> String
;; uses Knuth-Morris-Pratt from
;; Introduction to Algorithms, Cormen, Leiserson, and Rivest, pages 869-876
;; discards stop from input
(define (gen-read-until-string stop)
  (let* ((len (string-length stop))
         (prefix (make-vector len 0))
         (fall-back
          (lambda (k c)
            (let ((k (let loop ((k k))
                       (cond
                         ((and (> k 0) (not (eq? (string-ref stop k) c)))
                          (loop (vector-ref prefix (sub1 k))))
                         (else k)))))
              (if (eq? (string-ref stop k) c)
                  (add1 k)
                  k)))))
    (let init ((k 0) (q 1))
      (when (< q len)
        (let ((k (fall-back k (string-ref stop q))))
          (vector-set! prefix q k)
          (init k (add1 q)))))
    ;; (vector-ref prefix x) = the longest suffix that matches a prefix of stop
    (lambda (in pos)
      (list->string
       (let/ec out
         (let loop ((matched 0) (out out))
           (let* ((c (non-eof read-char in pos))
                  (matched (fall-back matched c)))
             (cond
               ((= matched len) (out null))
               ((zero? matched) (cons c (let/ec out (loop matched out))))
               (else (cons c (loop matched out)))))))))))

;; "-->" makes more sense, but "--" follows the spec.
(define lex-comment-contents (gen-read-until-string "--"))
(define lex-pi-data (gen-read-until-string "?>"))
(define lex-cdata-contents (gen-read-until-string "]]>"))

;; positionify : Input-port -> Input-port (-> Location)

;; Well, this really depends on scsh-0.6 and should be replace by
;; big-scheme's more-port
;; For S48 you probably need to do something completely different

(define (positionify in)
  (let ((line 1)
	(char 0)
	(offset 0)
	(old-handler (port-handler in)))
    (set-port-buffering in bufpol/block 1)
    (let ((handler (make-buffered-input-port-handler
		    (port-handler-discloser old-handler)
		    (port-handler-close old-handler)
		    (lambda (data buffer start needed)
		      (let ((res 
			     ((port-handler-buffer-proc old-handler) 
			      data buffer start needed)))
			(if (number? res)
			    (begin
			      (set! char (add1 char))
			      (set! offset (add1 offset))
			      (let ((c (byte-vector-ref buffer 0)))
				(when (= c 10)
				      (set! line (+ line 1))
				      (set! char -1)))))
			res))
		    (port-handler-ready? old-handler)
		    (port-handler-steal old-handler))))
      (set-port-handler! in handler)
      (values in
	      (lambda ()
		(make-location line char offset))))))
;		(- n (- (port-limit in) (port-index in))))))))

;; lex-error : Input-port String (-> Location) TST* -> alpha
(define (lex-error in pos str . rest)
  (error 'lex-error " at position:" (format-source (pos)) str rest))

;; format-source : Location -> string
;; to format the source location for an error message
(define (format-source loc)
  (if (location? loc)
      (format #f "~a.~a/~a" (location-line loc) (location-char loc) (location-offset loc))
      (format #f "~a" loc)))