XSLT like transformations in Erlang

From 84adefa331c4159d432d22840663c38f155cd4c1 Mon Sep 17 00:00:00 2001 From: Erlang/OTP Date: Fri, 20 Nov 2009 14:54:40 +0000 Subject: The R13B03 release. --- lib/xmerl/doc/src/xmerl_xs_examples.html | 291 +++++++++++++++++++++++++++++++ 1 file changed, 291 insertions(+) create mode 100644 lib/xmerl/doc/src/xmerl_xs_examples.html (limited to 'lib/xmerl/doc/src/xmerl_xs_examples.html') diff --git a/lib/xmerl/doc/src/xmerl_xs_examples.html b/lib/xmerl/doc/src/xmerl_xs_examples.html new file mode 100644 index 0000000000..aaa3bc5033 --- /dev/null +++ b/lib/xmerl/doc/src/xmerl_xs_examples.html @@ -0,0 +1,291 @@ + + + +XSLT like transformations in Erlang +

Examples

Example 1 Using xslapply

original XSLT:


+
+  <xsl:template match="doc/title">
+      <h1>
+        <xsl:apply-templates/>
+      </h1>
+  </xsl:template>
+  
+

+ becomes in Erlang:


+
+  template(E = #xmlElement{ parents=[{'doc',_}|_], name='title'}) ->
+      ["<h1>",
+           xslapply(fun template/1, E),
+       "</h1>"];
+  
+

+ +

Example 2 Using value_of and select


+
+  <xsl:template match="title">
+    <div align="center"><h1><xsl:value-of select="." /></h1></div>
+  </xsl:template>
+  
+

+ becomes: +


+
+template(E = #xmlElement{name='title'}) ->
+    ["<div align=\"center\"><h1>", value_of(select(".", E)), "</h1></div>"];
+  
+

Example 3 Simple xsl stylesheet

+ A complete example with the XSLT sheet in the xmerl distribution. +


+
+
+<xsl:stylesheet version="1.0"
+		xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+		xmlns="http://www.w3.org/TR/xhtml1/strict">
+
+  <xsl:strip-space elements="doc chapter section"/>
+  <xsl:output
+	method="xml"
+	indent="yes"
+	encoding="iso-8859-1"
+  />
+
+  <xsl:template match="doc">
+    <html>
+      <head>
+        <title>
+          <xsl:value-of select="title"/>
+        </title>
+      </head>
+      <body>
+        <xsl:apply-templates/>
+      </body>
+    </html>
+  </xsl:template>
+
+  <xsl:template match="doc/title">
+    <h1>
+      <xsl:apply-templates/>
+    </h1>
+  </xsl:template>
+
+  <xsl:template match="chapter/title">
+    <h2>
+      <xsl:apply-templates/>
+    </h2>
+  </xsl:template>
+
+  <xsl:template match="section/title">
+    <h3>
+      <xsl:apply-templates/>
+    </h3>
+  </xsl:template>
+
+  <xsl:template match="para">
+    <p>
+      <xsl:apply-templates/>
+    </p>
+  </xsl:template>
+
+  <xsl:template match="note">
+    <p class="note">
+      <b>NOTE: </b>
+      <xsl:apply-templates/>
+    </p>
+  </xsl:template>
+
+  <xsl:template match="emph">
+    <em>
+      <xsl:apply-templates/>
+    </em>
+  </xsl:template>
+
+</xsl:stylesheet>
+ 
+

Example 4 Erlang version

+ Erlang transformation of previous example: +


+
+
+-include("xmerl.hrl").
+
+-import(xmerl_xs, 
+	[ xslapply/2, value_of/1, select/2, built_in_rules/2 ]).
+
+doctype()->
+    "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\"\
+ \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd \">".
+
+process_xml(Doc)->
+	template(Doc).
+
+template(E = #xmlElement{name='doc'})->
+    [ "<\?xml version=\"1.0\" encoding=\"iso-8859-1\"\?>",
+      doctype(),
+      "<html xmlns=\"http://www.w3.org/1999/xhtml\" >"
+      "<head>"
+      "<title>", value_of(select("title",E)), "</title>"
+      "</head>"
+      "<body>",
+      xslapply( fun template/1, E),
+      "</body>"
+      "</html>" ];
+
+
+template(E = #xmlElement{ parents=[{'doc',_}|_], name='title'}) ->
+    ["<h1>", 
+     xslapply( fun template/1, E), 
+     "</h1>"];
+
+template(E = #xmlElement{ parents=[{'chapter',_}|_], name='title'}) ->
+    ["<h2>", 
+     xslapply( fun template/1, E),
+     "</h2>"];
+
+template(E = #xmlElement{ parents=[{'section',_}|_], name='title'}) ->
+    ["<h3>", 
+     xslapply( fun template/1, E),
+     "</h3>"];
+
+template(E = #xmlElement{ name='para'}) ->
+    ["<p>", xslapply( fun template/1, E), "</p>"];
+
+template(E = #xmlElement{ name='note'}) ->
+    ["<p class=\"note\">"
+     "<b>NOTE: </b>",
+     xslapply( fun template/1, E),
+     "</p>"];
+
+template(E = #xmlElement{ name='emph'}) ->
+    ["<em>", xslapply( fun template/1, E), "</em>"];
+
+template(E)->
+    built_in_rules( fun template/1, E).
+ 
+

+ It is important to end with a call to + xmerl_xs:built_in_rules/2 + if you want any text to be written in "push" transforms. + That are the ones using a lot xslapply( fun + template/1, E ) instead of + value_of(select("xpath",E)), + which is pull... +

The largest example is the stylesheet to transform this document + from the Simplified Docbook XML format to xhtml. The source + file is sdocbook2xhtml.erl. +

+ + +

Tips and tricks

+ +

for-each

The function for-each is quite common in XSLT stylesheets. + It can often be rewritten and replaced by select/1. Since + select/1 returns a list of #xmlElements and xslapply/2 + traverses them it is more or less the same as to loop over all + the elements. +

+ + +

position()

The XSLT position() and #xmlElement.pos are not the + same. One has to make an own position in Erlang.

Example 5 Counting positions


+
+<xsl:template match="stanza">
+  <p><xsl:apply-templates select="line" /></p>
+</xsl:template>
+
+<xsl:template match="line">
+  <xsl:if test="position() mod 2 = 0">&#160;&#160;</xsl:if>
+  <xsl:value-of select="." /><br />
+</xsl:template>
+ 
+

Can be written as


+
+template(E = #xmlElement{name='stanza'}) ->
+    {Lines,LineNo} = lists:mapfoldl(fun template_pos/2, 1, select("line", E)),
+    ["<p>", Lines, "</p>"].
+
+template_pos(E = #xmlElement{name='line'}, P) ->
+    {[indent_line(P rem 2), value_of(E#xmlElement.content), "<br />"], P + 1 }.
+
+indent_line(0)->"&#160;&#160;";
+indent_line(_)->"".
+ 
+

+ + +

Global tree awareness

In XSLT you have "root" access to the top of the tree + with XPath, even though you are somewhere deep in your + tree.

The xslapply/2 function only carries back the child part + of the tree to the template fun. But it is quite easy to write + template funs that handles both the child and top tree.

Example 6 Passing the root tree

The following example piece will prepend the article + title to any section title


+
+template(E = #xmlElement{name='title'}, ETop ) ->
+    ["<h3>", value_of(select("title", ETop))," - ",
+     xslapply( fun(A) -> template(A, ETop) end, E),
+     "</h3>"];
+ 
+

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