sxml->xml writes directly to a port

* module/sxml/simple.scm: Remove "universal-sxslt-rules" -- it was a bad
  interface, and I couldn't find any users of it.
  (sxml->xml): Rewrite so that instead of generating another tree of
  data, we write the data directly to a port.

module/sxml/simple.scm

@@ -30,41 +30,146 @@
   #:use-module (sxml transform)
   #:use-module (ice-9 optargs)
   #:use-module (srfi srfi-13)
-  #:export (xml->sxml sxml->xml sxml->string universal-sxslt-rules))
+  #:export (xml->sxml sxml->xml sxml->string))
 
 (define* (xml->sxml #:optional (port (current-input-port)))
   "Use SSAX to parse an XML document into SXML. Takes one optional
 argument, @var{port}, which defaults to the current input port."
   (ssax:xml->sxml port '()))
 
-;; Universal transformation rules. Works for all XML.
-(define universal-sxslt-rules
-  #;
-  "A set of @code{pre-post-order} rules that transform any SXML tree
-into a form suitable for XML serialization by @code{(sxml transform)}'s
-@code{SRV:send-reply}. Used internally by @code{sxml->xml}."
-  `((@ 
-     ((*default* . ,(lambda (attr-key . value) ((enattr attr-key) value))))
-     . ,(lambda (trigger . value) (list '@ value)))
-    (*TOP*       . ,(lambda (tag . xml) xml))
-    (*ENTITY*    . ,(lambda (tag name) (list "&" name ";")))
-    (*PI*    . ,(lambda (pi tag str) (list "<?" tag " " str "?>")))
-    ;; Is this right for entities? I don't have a reference for
-    ;; public-id/system-id at the moment...
-    (*default*   . ,(lambda (tag . elems) (apply (entag tag) elems)))
-    (*text*      . ,(lambda (trigger str) 
-                      (if (string? str) (string->escaped-xml str) str)))))
+(define check-name
+  (let ((*good-cache* (make-hash-table)))
+    (lambda (name)
+      (if (not (hashq-ref *good-cache* name))
+          (let* ((str (symbol->string name))
+                 (i (string-index str #\:))
+                 (head (or (and i (substring str 0 i)) str))
+                 (tail (and i (substring str (1+ i)))))
+            (and i (string-index (substring str (1+ i)) #\:)
+                 (error "Invalid QName: more than one colon" name))
+            (for-each
+             (lambda (s)
+               (and s
+                    (or (char-alphabetic? (string-ref s 0))
+                        (eq? (string-ref s 0) #\_)
+                        (error "Invalid name starting character" s name))
+                    (string-for-each
+                     (lambda (c)
+                       (or (char-alphabetic? c) (string-index "0123456789.-_" c)
+                           (error "Invalid name character" c s name)))
+                     s)))
+             (list head tail))
+            (hashq-set! *good-cache* name #t))))))
+
+;; The following two functions serialize tags and attributes. They are
+;; being used in the node handlers for the post-order function, see
+;; below.
+
+(define (attribute-value->xml value port)
+  (cond
+   ((pair? value)
+    (attribute-value->xml (car value) port)
+    (attribute-value->xml (cdr value) port))
+   ((string? value)
+    (string->escaped-xml value port))
+   ((procedure? value)
+    (with-output-to-port port value))
+   (else
+    (string->escaped-xml
+     (call-with-output-string (lambda (port) (display value port)))
+     port))))
+
+(define (attribute->xml attr value port)
+  (check-name attr)
+  (display attr port)
+  (display "=\"" port)
+  (attribute-value->xml value port)
+  (display #\" port))
+
+(define (element->xml tag attrs body port)
+  (check-name tag)
+  (display #\< port)
+  (display tag port)
+  (if attrs
+      (let lp ((attrs attrs))
+        (if (pair? attrs)
+            (let ((attr (car attrs)))
+              (display #\space port)
+              (if (pair? attr)
+                  (attribute->xml (car attr) (cdr attr) port)
+                  (error "bad attribute" tag attr))
+              (lp (cdr attrs)))
+            (if (not (null? attrs))
+                (error "bad attributes" tag attrs)))))
+  (if (pair? body)
+      (begin
+        (display #\> port)
+        (let lp ((body body))
+          (cond
+           ((pair? body)
+            (sxml->xml (car body) port)
+            (lp (cdr body)))
+           ((null? body)
+            (display "</" port)
+            (display tag port)
+            (display ">" port))
+           (else
+            (error "bad element body" tag body)))))
+      (display " />" port)))
+
+;; FIXME: ensure name is valid
+(define (entity->xml name port)
+  (display #\& port)
+  (display name port)
+  (display #\; port))
+
+;; FIXME: ensure tag and str are valid
+(define (pi->xml tag str port)
+  (display "<?" port)
+  (display tag port)
+  (display #\space port)
+  (display str port)
+  (display "?>" port))
 
 (define* (sxml->xml tree #:optional (port (current-output-port)))
   "Serialize the sxml tree @var{tree} as XML. The output will be written
 to the current output port, unless the optional argument @var{port} is
 present."
-  (with-output-to-port port
-    (lambda ()
-      (SRV:send-reply
-       (post-order
-        tree
-        universal-sxslt-rules)))))
+  (cond
+   ((pair? tree)
+    (if (symbol? (car tree))
+        ;; An element.
+        (let ((tag (car tree)))
+          (case tag
+            ((*TOP*)
+             (sxml->xml (cdr tree) port))
+            ((*ENTITY*)
+             (if (and (list? (cdr tree)) (= (length (cdr tree)) 1))
+                 (entity->xml (cadr tree) port)
+                 (error "bad *ENTITY* args" (cdr tree))))
+            ((*PI*)
+             (if (and (list? (cdr tree)) (= (length (cdr tree)) 2))
+                 (pi->xml (cadr tree) (caddr tree) port)
+                 (error "bad *PI* args" (cdr tree))))
+            (else
+             (let* ((elems (cdr tree))
+                    (attrs (and (pair? elems) (pair? (car elems))
+                                (eq? '@ (caar elems))
+                                (cdar elems))))
+               (element->xml tag attrs (if attrs (cdr elems) elems) port)))))
+        ;; A nodelist.
+        (for-each (lambda (x) (sxml->xml x port)) tree)))
+   ((string? tree)
+    (string->escaped-xml tree port))
+   ((null? tree) *unspecified*)
+   ((not tree) *unspecified*)
+   ((eqv? tree #t) *unspecified*)
+   ((procedure? tree)
+    (with-output-to-port port tree))
+   (else
+    (string->escaped-xml
+     (call-with-output-string (lambda (port) (display tree port)))
+     port))))
 
 (define (sxml->string sxml)
   "Detag an sxml tree @var{sxml} into a string. Does not perform any
@@ -80,81 +185,34 @@ formatting."
     '()
     sxml)))
 
-;; The following two functions serialize tags and attributes. They are
-;; being used in the node handlers for the post-order function, see
-;; above.
-
-(define (check-name name)
-  (let* ((str (symbol->string name))
-         (i (string-index str #\:))
-         (head (or (and i (substring str 0 i)) str))
-         (tail (and i (substring str (1+ i)))))
-    (and i (string-index (substring str (1+ i)) #\:)
-         (error "Invalid QName: more than one colon" name))
-    (for-each
-     (lambda (s)
-       (and s
-            (or (char-alphabetic? (string-ref s 0))
-                (eq? (string-ref s 0) #\_)
-                (error "Invalid name starting character" s name))
-            (string-for-each
-             (lambda (c)
-               (or (char-alphabetic? c) (string-index "0123456789.-_" c)
-                   (error "Invalid name character" c s name)))
-             s)))
-     (list head tail))))
-
-(define (entag tag)
-  (check-name tag)
-  (lambda elems
-    (if (and (pair? elems) (pair? (car elems)) (eq? '@ (caar elems)))
-        (list #\< tag (cdar elems)
-              (if (pair? (cdr elems))
-                  (list #\> (cdr elems) "</" tag #\>)
-                  " />"))
-        (list #\< tag
-              (if (pair? elems)
-                  (list #\> elems "</" tag #\>)
-                  " />")))))
- 
-(define (enattr attr-key)
-  (check-name attr-key)
-  (let ((attr-str (symbol->string attr-key)))
-    (lambda (value)
-      (list #\space attr-str
-            "=\"" (and (not (null? value)) value) #\"))))
-
 (define (make-char-quotator char-encoding)
-  (let ((bad-chars (map car char-encoding)))
+  (let ((bad-chars (list->char-set (map car char-encoding))))
  
     ;; Check to see if str contains one of the characters in charset,
     ;; from the position i onward. If so, return that character's index.
     ;; otherwise, return #f
     (define (index-cset str i charset)
-      (let loop ((i i))
-        (and (< i (string-length str))
-             (if (memv (string-ref str i) charset) i
-                 (loop (+ 1 i))))))
- 
+      (string-index str charset i))
+    
     ;; The body of the function
-    (lambda (str)
+    (lambda (str port)
       (let ((bad-pos (index-cset str 0 bad-chars)))
-        (if (not bad-pos) str   ; str had all good chars
-            (string-concatenate-reverse
-             (let loop ((from 0) (to bad-pos) (out '()))
-               (cond
-                ((>= from (string-length str)) out)
-                ((not to)
-                 (cons (substring str from (string-length str)) out))
-                (else
-                 (let ((quoted-char
-                        (cdr (assv (string-ref str to) char-encoding)))
-                       (new-to
-                        (index-cset str (+ 1 to) bad-chars)))
-                   (loop (1+ to) new-to
-                         (if (< from to)
-                             (cons* quoted-char (substring str from to) out)
-                             (cons quoted-char out)))))))))))))
+        (if (not bad-pos)
+            (display str port)          ; str had all good chars
+            (let loop ((from 0) (to bad-pos))
+              (cond
+               ((>= from (string-length str)) *unspecified*)
+               ((not to)
+                (display (substring str from (string-length str)) port))
+               (else
+                (let ((quoted-char
+                       (cdr (assv (string-ref str to) char-encoding)))
+                      (new-to
+                       (index-cset str (+ 1 to) bad-chars)))
+                  (if (< from to)
+                      (display (substring str from to) port))
+                  (display quoted-char port)
+                  (loop (1+ to) new-to))))))))))
 
 ;; Given a string, check to make sure it does not contain characters
 ;; such as '<' or '&' that require encoding. Return either the original