<meta http-equiv="Context-Type" content="text/html; charset=iso-8859-1">
<?xml version="1.0" encoding="iso-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">
<html xmlns="http://www.w3.org/1999/xhtml" ><head><title>XSLT like transformations in Erlang </title><style type="text/css"> body {margin-left:10%; margin-right:5%;}
.logo{float:right;}
.toc UL {
list-style-type: none;
border: solid;
border-width: thin;
padding-left: 10px;
padding-right: 10px;
padding-top: 5px;
padding-bottom: 5px;
background: #f0f0f0;
letter-spacing: 2px;
line-height: 20px;
}
</style></head><body>
<h3 id="sect_4.2">Examples</h3>
<hr />
<h4>Example 1 Using xslapply</h4>
<p>original XSLT:</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
<xsl:template match="doc/title">
<h1>
<xsl:apply-templates/>
</h1>
</xsl:template>
</code></pre></td></tr></table>
<p>
becomes in Erlang:</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
template(E = #xmlElement{ parents=[{'doc',_}|_], name='title'}) ->
["<h1>",
xslapply(fun template/1, E),
"</h1>"];
</code></pre></td></tr></table>
<hr />
<hr />
<h4>Example 2 Using value_of and select</h4>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
<xsl:template match="title">
<div align="center"><h1><xsl:value-of select="." /></h1></div>
</xsl:template>
</code></pre></td></tr></table>
<p>
becomes:
</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
template(E = #xmlElement{name='title'}) ->
["<div align=\"center\"><h1>", value_of(select(".", E)), "</h1></div>"];
</code></pre></td></tr></table>
<hr />
<hr />
<h4>Example 3 Simple xsl stylesheet</h4>
<p>
A complete example with the XSLT sheet in the xmerl distribution.
</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
<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>
</code></pre></td></tr></table>
<hr />
<hr />
<h4>Example 4 Erlang version</h4>
<p>
Erlang transformation of previous example:
</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
-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).
</code></pre></td></tr></table>
<p>
It is important to end with a call to
<tt>xmerl_xs:built_in_rules/2</tt>
if you want any text to be written in "push" transforms.
That are the ones using a lot <tt>xslapply( fun
template/1, E )</tt> instead of
<tt>value_of(select("xpath",E))</tt>,
which is pull...
</p>
<hr />
<p>The largest example is the stylesheet to transform this document
from the Simplified Docbook XML format to xhtml. The source
file is <tt>sdocbook2xhtml.erl</tt>.
</p>
<h3 id="sect_4.3">Tips and tricks</h3>
<h4 id="sect_4.3.1">for-each</h4>
<p>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.
</p>
<h4 id="sect_4.3.2">position()</h4>
<p>The XSLT position() and #xmlElement.pos are not the
same. One has to make an own position in Erlang.</p>
<hr />
<h4>Example 5 Counting positions</h4>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
<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>
</code></pre></td></tr></table>
<p>Can be written as</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
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(_)->"".
</code></pre></td></tr></table>
<hr />
<h4 id="sect_4.3.3">Global tree awareness</h4>
<p>In XSLT you have "root" access to the top of the tree
with XPath, even though you are somewhere deep in your
tree.</p>
<p>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.</p>
<hr />
<h4>Example 6 Passing the root tree</h4>
<p>The following example piece will prepend the article
title to any section title</p>
<table border="1" cellspacing="0" cellpadding="5" width="100%"
bgcolor="#CCCCCC"><tr><td><pre><code>
template(E = #xmlElement{name='title'}, ETop ) ->
["<h3>", value_of(select("title", ETop))," - ",
xslapply( fun(A) -> template(A, ETop) end, E),
"</h3>"];
</code></pre></td></tr></table>
<hr />
</body></html>
