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+;;; Haunt --- Static site generator for GNU Guile
+;;; Copyright © 2015 David Thompson <davet@gnu.org>
+;;;
+;;; This file is part of Haunt.
+;;;
+;;; Haunt is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Haunt is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Haunt.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; SXML to HTML conversion.
+;;
+;;; Code:
+
+(define-module (haunt html)
+  #:use-module (sxml simple)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
+  #:use-module (ice-9 hash-table)
+  #:export (sxml->html
+            sxml->html-string))
+
+(define %void-elements
+  '(area
+    base
+    br
+    col
+    command
+    embed
+    hr
+    img
+    input
+    keygen
+    link
+    meta
+    param
+    source
+    track
+    wbr))
+
+(define (void-element? tag)
+  "Return #t if TAG is a void element."
+  (pair? (memq tag %void-elements)))
+
+(define %escape-chars
+  (alist->hash-table
+   '((#\" . "quot")
+     (#\& . "amp")
+     (#\' . "apos")
+     (#\< . "lt")
+     (#\> . "gt"))))
+
+(define (string->escaped-html s port)
+  "Write the HTML escaped form of S to PORT."
+  (define (escape c)
+    (let ((escaped (hash-ref %escape-chars c)))
+      (if escaped
+          (format port "&~a;" escaped)
+          (display c port))))
+  (string-for-each escape s))
+
+(define (object->escaped-html obj port)
+  "Write the HTML escaped form of OBJ to PORT."
+  (string->escaped-html
+   (call-with-output-string (cut display obj <>))
+   port))
+
+(define (attribute-value->html value port)
+  "Write the HTML escaped form of VALUE to PORT."
+  (if (string? value)
+      (string->escaped-html value port)
+      (object->escaped-html value port)))
+
+(define (attribute->html attr value port)
+  "Write ATTR and VALUE to PORT."
+  (format port "~a=\"" attr)
+  (attribute-value->html value port)
+  (display #\" port))
+
+(define (element->html tag attrs body port)
+  "Write the HTML TAG to PORT, where TAG has the attributes in the
+list ATTRS and the child nodes in BODY."
+  (format port "<~a" tag)
+  (for-each (match-lambda
+             ((attr value)
+              (display #\space port)
+              (attribute->html attr value port)))
+            attrs)
+  (if (and (null? body) (void-element? tag))
+      (display " />" port)
+      (begin
+        (display #\> port)
+        (for-each (cut sxml->html <> port) body)
+        (format port "</~a>" tag))))
+
+(define (doctype->html doctype port)
+  (format port "<!DOCTYPE ~a>" doctype))
+
+(define* (sxml->html tree #:optional (port (current-output-port)))
+  "Write the serialized HTML form of TREE to PORT."
+  (match tree
+    (() *unspecified*)
+    (('doctype type)
+     (doctype->html type port))
+    ;; Unescaped, raw HTML output.
+    (('raw html)
+     (display html port))
+    (((? symbol? tag) ('@ attrs ...) body ...)
+     (element->html tag attrs body port))
+    (((? symbol? tag) body ...)
+     (element->html tag '() body port))
+    ((nodes ...)
+     (for-each (cut sxml->html <> port) nodes))
+    ((? string? text)
+     (string->escaped-html text port))
+    ;; Render arbitrary Scheme objects, too.
+    (obj (object->escaped-html obj port))))
+
+(define (sxml->html-string sxml)
+  "Render SXML as an HTML string."
+  (call-with-output-string
+   (lambda (port)
+     (sxml->html sxml port))))