RE: [xsl] How do I build a nodeset "programmatically" for passing to another template?

Subject: RE: [xsl] How do I build a nodeset "programmatically" for passing to another template?
From: "Zaleski, Matthew \(M.E.\)" <mzaleski@xxxxxxxx>
Date: Thu, 17 Aug 2006 17:15:53 -0400

Thanks for the background and the hint to look for "micropipelining".
I'm using Saxon 6.5.x which already supports automatic conversion from
RTF to nodeset (assuming I correctly read Michael Kay's excellent "XSLT
Programmer's Reference 2nd edition" book).  I'm assuming that for other
XSLT engines, the node-set() function would be needed in my output table
call...along the lines of <xsl:with-param name="entries"
select="xalan:node-set($speed_table_values)/*"/>.  Correct me if I'm not
understanding the proper extension usage for micropipelining.

To close the loop for the next poor sod trying to understand this
problem, I'm posting my working mini-demonstration of a stylesheet that
does what I want.  I make no claims as to having any skill whatsoever in
writing "good" XSL code.  Since the stylesheet only looks for a root
node, just feed it to itself to test it out.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.1"
	<xsl:strip-space elements="*"/>
	<xsl:output method="xml" indent="yes"/>

	<xsl:template match="/">
		<xsl:variable name="max_ay" select="0.600"/>
		<xsl:variable name="radii">
		<xsl:variable name="ay_90pct" select="format-number(0.9
* $max_ay, '#.##')"/>
		<xsl:variable name="speed_table_values">
			<xsl:call-template name="generate_speed_table">
				<xsl:with-param name="ay_target"
				<xsl:with-param name="radii"
		<!-- Show that the nodeset was built properly -->
		<!-- Now use the nodeset to generate our output table
			<xsl:call-template name="output_rows">
				<xsl:with-param name="entries"

	<xsl:template name="output_rows">
		<xsl:param name="entries"/>

		<xsl:if test="$entries">
			<xsl:call-template name="output_rows">
				<xsl:with-param name="entries"
select="$entries[position() != 1]"/>

	<xsl:template name="generate_speed_table">
		<xsl:param name="ay_target"/>  <!-- lateral acceleration
in g's -->
		<xsl:param name="radii"/> <!-- nodeset of <radius>
entries, in meters -->
		<xsl:param name="string_format">#.#</xsl:param> <!--
format to pass to string-format() -->
		<xsl:param name="result"></xsl:param>

			<xsl:when test="not($radii)">
				<xsl:copy-of select="$result"/>
				velocity = sqrt(radius * ay_target *
				speed_kmh = velocity * 3.6;
				speed_mph = velocity * 2.236936;

				<xsl:variable name="velocity">
					<xsl:call-template name="sqrt">
name="number" select="$radii[1] * $ay_target * 9.80665"/>
				<xsl:variable name="speed_kmh"
select="format-number($velocity * 3.6, $string_format)"/>
				<xsl:variable name="speed_mph"
select="format-number($velocity * 2.236936, $string_format)"/>
				<xsl:variable name="value">
select="format-number($velocity * 3.6, $string_format)"/>
select="format-number($velocity * 2.236936, $string_format)"/>
					<xsl:with-param name="ay_target"
					<xsl:with-param name="radii"
select="$radii[position() != 1]"></xsl:with-param>
name="string_format" select="$string_format"/>
name="result"><xsl:copy-of select="$result"/><xsl:copy-of

	<xsl:template name="sqrt"> <!-- copied from XSLT Cookbook
(O'Reilly) -->
		<!-- The number you want to find the square root of -->
		<xsl:param name="number" select="0"/>
		<!-- The current 'try'.  This is used internally. -->
		<xsl:param name="try" select="($number &lt; 100) +

($number >= 100 and $number &lt; 1000) * 10 +

($number >= 1000 and $number &lt; 10000) * 31 +

($number >= 10000) * 100"/>
		<!-- The current iteration, checked against maxiter to
limit loop count -->
		<xsl:param name="iter" select="1"/>
		<!-- Set this up to ensure against infinite loops -->
		<xsl:param name="maxiter" select="20"/>
		<!-- This template was written by Nate Austin using Sir
Isaac Newton's method of finding roots -->
			<xsl:when test="$try * $try = $number or $iter >
				<xsl:value-of select="$try"/>
				<xsl:call-template name="sqrt">
					<xsl:with-param name="number"
					<xsl:with-param name="try"
select="$try - (($try * $try - $number) div (2 * $try))"/>
					<xsl:with-param name="iter"
select="$iter + 1"/>
					<xsl:with-param name="maxiter"



> -----Original Message-----
> From: Wendell Piez [mailto:wapiez@xxxxxxxxxxxxxxxx]
> Sent: Thursday, August 17, 2006 11:48 AM
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [xsl] How do I build a nodeset
> "programmatically" for passing to another template?
> Matthew,
> What you're trying to do is a useful and very powerful
> technique, only unfortunately disallowed by a restriction in
> classical XSLT 1.0, which defines a variable bound
> dynamically in such a way as a result tree fragment (RTF),
> which by definition may not be processed further. (An RTF may
> only be copied to the result tree or converted to a string,
> which is somewhat useful but not as much as one would like.)
> Because this restriction was considered by some to be rather
> artificial, and the technique so useful, it was removed in
> XSLT 2.0, where what you are doing will work transparently.
> In a conformant XSLT 1.0 processor, you will get an error
> when you try this, typically along the lines of "cannot
> process Result Tree Fragment". To get around this, many XSLT
> 1.0 processors provide an extension function. For example, a
> function node-set() is available, in many processors, in the
> EXSLT namespace (see, which you could use, as
> in node-set($speed_table_values), to get up and running.
> I believe the node-set() extension function may also be
> available natively in an XSLT 1.1 processor, but since the
> 1.1 specification was shelved before making Recommendation
> status, YYMV.
> FWIW, some of us are calling this technique
> "micropipelining", as it entails creating a tree fragment and
> then processing it. Not only is it very powerful, it's very
> much in the XSLT 2.0 spirit of things, and at the core of any
> number of advanced methodologies such as
> (pre-eminently) FXSL.
> Cheers,
> Wendell
> At 11:34 AM 8/17/2006, you wrote:
> >I'm using Saxon 6.5.x (and XSL 1.1).
> >
> >Searches on the web and this list's archives give me
> tantalizing hints
> >that what I want to do is theoretically possible.  All of
> the examples
> >I find seem to be "reducers" (e.g. sum a set of numbers spread
> >throughout a nodeset, or combine nodes into a single string), rather
> >than "builders".
> >
> >My stylesheets are pull style that build XSL-FO output for further
> >processing by Apache-FOP.  What I'm trying to do is build a
> nodeset in
> >a variable so that I can rely on some generic fo:table templates to
> >produce the output rather than custom templates for each occurrence.
> >Due to limits of what is currently in the XML input files,
> I'm forced
> >to do some calculation/nodeset building to supplement the structure
> >already in the XML file.
> >
> >Is it possible for a chunk of XSL like:
> ><xsl:variable name="max_ay"
> >select="/vdt:report/vdt:run_metrics/*[normalize-space(text()) = 'Avg
> >Ay']/vdt:statistics/vdt:statistic[@stat_name='Average']"/>
> ><xsl:variable name="ay_90pct" select="format-number(0.9 * $max_ay,
> >'#.##')"/> <xsl:variable name="speed_table_values">
> >         <xsl:call-template name="ml_generate_speed_table">
> >                 <xsl:with-param name="ay_target"
> select="$ay_90pct"/>
> >                 <xsl:with-param name="radii">
> >                         <radius>30</radius>
> >                         <radius>60</radius>
> >                         <radius>61</radius>
> >                         <radius>100</radius>
> >                 </xsl:with-param>
> >                 <xsl:with-param
> >name="string_format">#.#</xsl:with-param>
> >         </xsl:call-template>
> ></xsl:variable>
> >
> >
> >To result in the variable $speed_table_values looking
> something like ?:
> ><entry>
> >         <radius>30</radius>
> >         <speed_km_h>60.9</speed_km_h>
> >         <speed_mph>50.1</speed_mph>
> ></entry>
> ><entry>
> >         <radius>60</radius>
> >         <speed_km_h>72.9</speed_km_h>
> >         <speed_mph>60.1</speed_mph>
> ></entry>
> ><entry>
> >         <radius>61</radius>
> >         <speed_km_h>81.9</speed_km_h>
> >         <speed_mph>70.4</speed_mph>
> ></entry>
> ><entry>
> >         <radius>100</radius>
> >         <speed_km_h>99.9</speed_km_h>
> >         <speed_mph>75.1</speed_mph>
> ></entry>
> >
> >(The numbers in the table are bogus but the nodeset
> structure is what
> >I'm interested in.)
> >
> >I would then have a later <xsl:call-template> that contained
> ><xsl:with-param select="$speed_table_values">
> >
> >As you can see, this particular problem is mostly interating
> over nodes
> >provided within the XSL sheet itself rather than the source
> XML.  Only
> >the first line of my example is grabbing a value/node from
> the source
> >tree.  I need to accomplish this in a single pass (not
> multiple calls
> >to an XSLT transformer).  Assuming what I want to do is
> possible in XSL
> >1.1, any links to similar examples would be much appreciated.

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