Question

I m tokenising a string with XSLT 1.0 and trying to prevent empty strings from being recognised as tokens. Here s the entire function, based on XSLT Cookbook:

<xsl:template name="tokenize">
    <xsl:param name="string" select="  " />
    <xsl:param name="delimiters" select=" ;# " />
    <xsl:param name="tokensplitter" select=" , " />
    <xsl:choose>
        <!-- Nothing to do if empty string -->
        <xsl:when test="not($string)" />

        <!-- No delimiters signals character level tokenization -->
        <xsl:when test="not($delimiters)">
            <xsl:call-template name="_tokenize-characters">
                <xsl:with-param name="string" select="$string" />
                <xsl:with-param name="tokensplitter" select="$tokensplitter" />
            </xsl:call-template>
        </xsl:when>
        <xsl:otherwise>
            <xsl:call-template name="_tokenize-delimiters">
                <xsl:with-param name="string" select="$string" />
                <xsl:with-param name="delimiters" select="$delimiters" />
                <xsl:with-param name="tokensplitter" select="$tokensplitter" />
            </xsl:call-template>
        </xsl:otherwise>
    </xsl:choose>
</xsl:template>

<xsl:template name="_tokenize-characters">
    <xsl:param name="string" />
    <xsl:param name="tokensplitter" />
    <xsl:if test="$string">
        <token><xsl:value-of select="substring($string, 1, 1)"/></token>
        <xsl:call-template name="_tokenize-characters">
            <xsl:with-param name="string" select="substring($string, 2)" />
        </xsl:call-template>
    </xsl:if>
</xsl:template>

<xsl:template name="_tokenize-delimiters">
    <xsl:param name="string" />
    <xsl:param name="delimiters" />
    <xsl:param name="tokensplitter" />

    <!-- Extract a delimiter -->
    <xsl:variable name="delimiter" select="substring($delimiters, 1, 1)"/>
    <xsl:choose>
        <!-- If the delimiter is empty we have a token -->
        <xsl:when test="not($delimiter) and $string !=   ">
            <xsl:text>£</xsl:text>
            <token><xsl:value-of select="$string"/></token>
            <xsl:text>$</xsl:text>
            <xsl:value-of select="$tokensplitter"/>
        </xsl:when>
        <!-- If the string contains at least one delimiter we must split it -->
        <xsl:when test="contains($string, $delimiter)">
            <!-- If it starts with the delimiter we don t need to handle the before part -->
            <xsl:if test="not(starts-with($string, $delimiter))">
                <!-- Handle the part that comes before the current delimiter with the next delimiter. -->
                <!-- If there is no next the first test in this template will detect the token. -->
                <xsl:call-template name="_tokenize-delimiters">
                    <xsl:with-param name="string" select="substring-before($string, $delimiter)" />
                    <xsl:with-param name="delimiters" select="substring($delimiters, 2)" />
                    <xsl:with-param name="tokensplitter" select="$tokensplitter" />
                </xsl:call-template>
            </xsl:if>
            <!-- Handle the part that comes after the delimiter using the current delimiter -->
            <xsl:call-template name="_tokenize-delimiters">
                <xsl:with-param name="string" select="substring-after($string, $delimiter)" />
                <xsl:with-param name="delimiters" select="$delimiters" />
                <xsl:with-param name="tokensplitter" select="$tokensplitter" />
            </xsl:call-template>
        </xsl:when>
        <xsl:otherwise>
            <!-- No occurrences of current delimiter so move on to next -->
            <xsl:call-template name="_tokenize-delimiters">
                <xsl:with-param name="string" select="$string" />
                <xsl:with-param name="delimiters" select="substring($delimiters, 2)" />
                <xsl:with-param name="tokensplitter" select="$tokensplitter" />
            </xsl:call-template>
        </xsl:otherwise>
    </xsl:choose>
</xsl:template>

Value for string that I m passing in is:

Europe;#6;#Global;#3;#Middle East, Africa and Caucasus;2;#Europe;#6;#Global;#3;#Middle East, Africa and Caucasus

(The £ and $ indicators are just there so I can see no empty strings are output. This is within SharePoint so is difficult to debug.)

This code hangs processing of the XSLT. The line causing the problem is <xsl:when test="not($delimiter) and $string != ">. As soon as I remove the second and test it works again. I ve also tried and string($string) without success.

Anyone know why this is happening and how to resolve it?

Answer 1

I believe my suspicion was correct: you re falling through to your <xsl:otherwise> clause when $string has a value, but $delimiter does not, causing an infinite loop, as you say.

Add the following new <xsl:when> clause after the first one:

    <xsl:when test="not($delimiter) and $string =   " />

That will prevent the execution from entering the <xsl:otherwise> block when it shouldn t.

A more elaborate explanation of what s going on and why it s looping:

There are three branches in the <xsl:choose> block.

    <xsl:when test="not($delimiter) and $string !=   ">
    <xsl:when test="contains($string, $delimiter)">
    <xsl:otherwise>

So, when neither $string nor $delimiter contain values, the first condition fails (because $string != is false). The second condition passes (because contains(nil,nil) always returns true (confirmed in Visual Studio)), which calls the template again with the same parameters (because the substring-before returns the empty string since it doesn t contain the empty delimiter). Ergo, an infinite loop.

The fix is to add a new, empty condition:

    <xsl:when test="not($delimiter) and $string !=   ">
    <xsl:when test="not($delimiter) and $string =   " />
    <xsl:when test="contains($string, $delimiter)">
    <xsl:otherwise>

EDIT: I ve poked around and I can t find a reference to the defined behaviour of contains when the second parameter is empty or nil. Tests have shown that Microsoft Visual Studio s XSLT engine returns true when the second parameter is either empty or nil. I m not sure if that s the defined behaviour or if it s up to the implementor to decide. Does anyone have a conclusive answer to this? Tomalak, I m looking at you.

Answer 2

Isn t string a reserved word? Can you try to replace that name for anything else?

EDIT: Supplied code ran without problem here: XSLT Tryit Editor v1.0 using:

<xsl:call-template name="tokenize">
   <xsl:with-param name="string">Europe;#6;#Global...</xsl:with-param>
</xsl:call-template>

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