Re: [xsl] having a template remember not to call itself again

["Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

My instinct when writing a pipeline with multiple steps is to use different
modes in each step.

I wouldn't characterise fn:transform() as a replacement for modes. I would use
it only where one transformation needs to invoke another dynamically.

Michael Kay
Saxonica

> On 5 Mar 2023, at 16:20, Chris Papademetrious
christopher.papademetrious@xxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> 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:
>
>   <xsl:template match="CONDITION1_HERE">
>
>     <!-- apply this template's processing first -->
>     <xsl:variable name="result" as="element()">
>       ...PROCESSING1_HERE...
>     </xsl:variable>
>
>     <!-- apply subsequent self-or-children templates last -->
>     <xsl:apply-templates select="$result"/>
>   </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:
>
>   <xsl:template match="CONDITION2_HERE">
>
>     <!-- apply subsequent self-or-children templates first -->
>     <xsl:variable name="result" as="node()*">
>       <xsl:next-match/>
>     </xsl:variable>
>
>     <!-- apply this template's processing last -->
>     ...PROCESSING2_HERE...
>   </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:
>
>   <xsl:template match="CONDITION1_HERE[not($CONDITION1_CALLED)]">
>     <xsl:param name="CONDITION1_CALLED" as="xs:boolean" select="false()"
tunnel="yes"/>
>
>     <!-- apply this template's processing -->
>     <xsl:variable name="result" as="element()">
>       b&PROCESSING1_HEREb&
>     </xsl:variable>
>
>     <!-- apply subsequent self-or-children templates -->
>     <xsl:apply-templates select="$result">
>       <xsl:with-param name="CONDITION1_CALLED" as="xs:boolean"
select="true()" tunnel="yes"/>
>     </xsl:apply-templates>
>   </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
>
> -----
> Chris Papademetrious
> Tech Writer, Implementation Group
> (610) 628-9718 home office
> (570) 460-6078 cell
>
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