Re: having a template remember not to call itself agai

Hi everyone,

I have a stylesheet with many templates that must all chain together and play nice with each other. So I write them in the following form:

B <xsl:template match="CONDITION1_HERE">

B B B <!-- apply this template's processing first -->

B B B <xsl:variable name="result" as="element()">

B B B B B ...PROCESSING1_HERE...

B B B </xsl:variable>

B B B <!-- apply subsequent self-or-children templates last -->

B B B <xsl:apply-templates select="$result"/>

B </xsl:template>

When a template applies its processing first then calls other templates last, I will call it btail-callb template chaining (although I donbt know the correct term).

For btail-callb chaining to work, PROCESSING1_HERE must transform the content so that CONDITION1_HERE is not met again (or at least not met in a way that loops infinitely).

But, what if PROCESSING1_HERE is very complex (nested moded templates, recursion, etc.) and sometimes CONDITION1_HERE will match after this template was previously applied, and there is no practical way to embed the complexity of predetermining PROCESSING1_HEREbs failure to remove the condition into CONDITION1_HEREbs match expression?

This could be avoided by using bhead-callb chaining:

B <xsl:template match="CONDITION2_HERE">

B B B <!-- apply subsequent self-or-children templates first -->

B B B <xsl:variable name="result" as="node()*">

B B B B B <xsl:next-match/>

B B B </xsl:variable>

B B B <!-- apply this template's processing last -->

B B B ...PROCESSING2_HERE...

B </xsl:template>

But now, all bets are off on what PROCESSING2_HERE will encounter. Maybe the result will have multiple elements, or be filtered out to zero elements, or might have text() nodes interspersed due to reformatting and styling templates. Maybe <xsl:next-match/> modified the content such that CONDITION2_HERE isnbt even matched any more. PROCESSING2_HERE must handle a much wider range of possible input, and the more templates that exist in the stylesheet, the more varied the input from <xsl:next-match/> might be. (I actually had all my templates written as bhead-callb chaining, and I am converting them to btail-callb chaining due to such issues.)

So now Ibm back to btail-callb chaining, and figuring out how to get a template to not call itself when it fails to remove the condition triggering the match. I tried setting a tunnelling variable that would give a heads-up to the template not calling itself again:

B <xsl:template match="CONDITION1_HERE[not($CONDITION1_CALLED)]">

B B B <xsl:param name="CONDITION1_CALLED" as="xs:boolean" select="false()" tunnel="yes"/>

B B B <!-- apply this template's processing -->

B B B <xsl:variable name="result" as="element()">

B B B B B b&PROCESSING1_HEREb&

B B B </xsl:variable>

B B B <!-- apply subsequent self-or-children templates -->

B B B <xsl:apply-templates select="$result">

B B B B B <xsl:with-param name="CONDITION1_CALLED" as="xs:boolean" select="true()" tunnel="yes"/>

B B B </xsl:apply-templates>

B </xsl:template>

but the templatebs $CONDITION1_CALLED parameter is out-of-scope in its match expression.

So now the only solution I can think of is to put some kind of temporary marker attribute in the matching element, then have a final document-down cleanup pass to remove the markers. And if multiple templates need markers, Ibll need to clean them all up. Icky.

Is there a more elegant way to handle this that am missing?

Thanks as always for your collective wisdom, and thanks for making it this far!

* Chris

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Chris Papademetrious

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