XSL Variables: Recursion 101

XSL is a very powerful tool. There really isn’t anything it can’t do when it comes to transforming XML documents. However, sometimes it’s necessary to operate on nodes in a way that isn’t possible without having variables to guide us. Here is a reminder (to myself) on XSL recursion.

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output omit-xml-declaration="yes"/>

    <!-- root template -->
    <xsl:template match="/root">
        <ul>
            <xsl:call-template name="pagebreak">
                <xsl:with-param name="childpos">0</xsl:with-param>
                <xsl:with-param name="curpos">0</xsl:with-param>
                <xsl:with-param name="maxpos">
                    <xsl:value-of select='count(*)'/>
                </xsl:with-param>
            </xsl:call-template>
        </ul>
    </xsl:template>

    <xsl:template name="pagebreak" >
        <xsl:param name="childpos"/>
        <xsl:param name="curpos"/>
        <xsl:param name="maxpos"/>
        <xsl:variable name="nodetitle" select='name(*[$childpos + 1])'/>

        <!-- Apply template based on node title -->
        <!-- OPERATE ON: /root/body -->
        <xsl:if test="$nodetitle = 'body' ">
            <!-- pass in the current "body" node of the / -->
            <xsl:apply-templates select='child::*[$childpos + 1]'> 

                <xsl:with-param name="lipos">
                    <xsl:choose>
                        <xsl:when test="$curpos=0">1</xsl:when>
                        <xsl:when test="$curpos=1">2</xsl:when>
                        <xsl:when test="$curpos=2">3</xsl:when>
                    </xsl:choose>
                </xsl:with-param>
            </xsl:apply-templates>
            <xsl:if test="$curpos = 2 and name(*[$childpos + 2]) != 'text_lines'">
            <!--     If we're at the third position of body,
                    and the next node isn't a text-line, print our ULs. -->
                <!-- TEMPLATE CONTENTS OMITTED -->
            </xsl:if>
        </xsl:if>

        <!-- OPERATE ON: /root/text_lines -->
        <xsl:if test="$nodetitle = 'text_lines' ">
            <xsl:text disable-output-escaping="yes">&lt;/ul&gt;</xsl:text>
                <div class='section_title'>
                    <p><xsl:value-of select='child::*[$childpos + 1]'/></p>
                </div>
            <xsl:text disable-output-escaping="yes">&lt;ul&gt;</xsl:text>
        </xsl:if>

        <!-- RECURSIVE(Set variables to operate each time through) -->
        <xsl:if test="$childpos &lt; ($maxpos - 1)">
            <xsl:call-template name="pagebreak">
                    <!-- Static Variable: Curront position within array of child nodes -->
                    <xsl:with-param name="childpos">
                        <xsl:value-of select='$childpos + 1'/>
                    </xsl:with-param>
                    <xsl:with-param name="curpos">
                        <xsl:choose>
                             <xsl:when test="$curpos=2 or $nodetitle = 'text_lines'">0</xsl:when>
                             <xsl:when test="$curpos != 2">
                                <xsl:value-of select="$curpos + 1"/>
                            </xsl:when>
                        </xsl:choose>
                    </xsl:with-param>
                    <!-- Static Variable: Max length of array of child nodes. -->
                    <xsl:with-param name="maxpos">
                        <xsl:value-of select='$maxpos + 0'/>
                    </xsl:with-param>
            </xsl:call-template>
        </xsl:if>

    </xsl:template>

    <!-- mybody template -->
    <xsl:template name="mybody" match='body'>
        <xsl:param name="lipos"/>

        <xsl:variable name="grid_counter" select="$lipos mod 3"/>

        <li class="grid_column_{$grid_counter}">
            <!-- TEMPLATE CONTENTS OMITTED -->
        </li>

    </xsl:template>

    <!-- OTHER TEMPLATES OMITTED -->

</xsl:stylesheet>