setting flag in XSLT to detect the first time through a loop - variables

Question

New to xslt. Using it in umbraco, so it's version 1.0.
Trying to insert separators between links in an inline footer list, so will put them before each link except the first one. This is a simple programming problem, where you set a flag to 0 outside the loop, then once in, you test if the flag is 1 and if it's not, you skip adding a separator before the link. As the last bit in the first pass through the loop, you set the flag to 1.
How can I accomplish this in xslt? I'm a bit flummoxed by the syntax and reading that once a variable value is set you can't change it. Anyone have a simple exmaple?

Answer 1

Here is a simple example:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:param name="pBase" select="'http://myBase.com/'"/>
<xsl:template match="num">
<xsl:if test="position() > 1">, </xsl:if>
<xsl:value-of select="."/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the following XML document:
<nums>
<num>01</num>
<num>02</num>
<num>03</num>
<num>04</num>
<num>05</num>
<num>06</num>
<num>07</num>
<num>08</num>
<num>09</num>
<num>10</num>
</nums>
the wanted, correct result is produced:
01, 02, 03, 04, 05, 06, 07, 08, 09, 10
and it is displayed in the browser as:
01, 02, 03, 04, 05, 06, 07, 08, 09, 10
Explanation:
XSLT is a functional language -- among other things this means that variables, once defined, cannot be changed.
The standard XPath position() function can be used to check if the position of the current node has a specific value.
The builtin XSLT templates are used and the one that matches an element has this body: <xsl:apply-templates/> . This is an abbreviation for: <xsl:apply-templates select="child::node()"/> and applies templates to all node children of the current node -- in document order.
Because we have specified <xsl:strip-space elements="*"/>, the whitespace-only children of any element has been stripped during the parsing of the XML document. This leaves only non-white-space children nodes of the top element nums and they are all num elements.
The value of the position() function inside a template is the position of the current node in the node-list formed when the <xsl:apply-templates> instruction is executed. This means that the value of the position() function inside the template matching num is 1 when the first num element is processed, 2 when the 2nd num element is processed, ..., 10 when the 10th num element is processed.
The generated output for all num elements where the value of position() is greater than 1 starts with the string ", " -- exactly as per the requirements of this question. For the first num element the string ", " isn't generated, because the value of position() in this case is 1.

Answer 2

There is no such thing as time in XSLT. You can't detect the "first time through a loop" because there is no concept of time, therefore no first time, in fact, it's not a loop in the traditional programming sense at all. All the items in the input list are conceptually processed in parallel. That's why you can't set variables for use in later iterations - there is no such thing as a "later iteration".
What you can do is to detect that you are processing the first item in the input sequence (or the first item in the input sequence after sorting, if you use xsl:sort). You do that with the test position() = 1.