Subject: Re: [xsl] Sequential numbers in pure xslt, breaking the no-side-effect rule From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx> Date: Fri, 16 Mar 2007 14:35:40 -0400 |
It is possible to do whatver in XSLT.
Cheers, Wendell
Here is an example how to write any XSLT transformation (the function f:transform) that will have the ability to get the next "tick" (next consecutive sequence number) at any time.
The transformation will only need (this can be done almost entirely in a wrapper) to surround its oun output with two "coventional outputs" -- the new tick count and the stop condition for the transformation.
Every "tick" corresponds to a single iteration as carried out by f:iterUntil().
f:iterUntil() (yes, that same FXSL function) iterates whatever function is passed as its second argument until the stop condition (the predicate passed as its first argument) evaluates to true().
This is a very generic approach. *Any* transformation can be substituted for the body of f:transform().
The only discipline is the layout of the results and to start a new iteration (for example whenever it thinks something significant has happened that needs to increment the tick counter) by returning with a false() stop condition.
or stopping iself by returning a true() stop condition.
Here's a small demo:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:f="http://fxsl.sf.net/" exclude-result-prefixes="f xs">
<xsl:import href="../f/func-iter.xsl"/>
<!-- To be applied on any xml file, or with initial template named "initial" -->
<xsl:output omit-xml-declaration="yes"/>
<xsl:variable name="vExecutionLimit" as="xs:integer" select="100"/> <xsl:variable name="vNL" select="'
'"/>
<xsl:template name="initial" match="/">
<xsl:variable name="vRawResults" select= "f:iterUntil(f:last(), f:transform(), (0,false()))"/>
Results:
Last tick: <xsl:sequence select="$vRawResults[1]"/> Stop condition: <xsl:sequence select="$vRawResults[last()]"/>
Transform output: <xsl:text/> <xsl:sequence select= "for $i in 2 to count($vRawResults) -1 return $vRawResults[$i]" />
</xsl:template>
<xsl:function name="f:transform" as="item()+"> <xsl:param name="pWorld" as="item()+"/>
<xsl:variable name="vnewTick" select="$pWorld[1]+1"/>
<xsl:variable name="vmyResults" as="item()*"> <!-- Do whatever processing is needed here --> <!-- and produce our "useful" results -->
<xsl:sequence select= " remove(remove($pWorld, count($pWorld)),1), $vnewTick, ' ', 3*$vnewTick, $vNL"/>
<!-- Set the stop condition in the last item --> <xsl:sequence select= "if($vnewTick gt $vExecutionLimit) then true() else false() "/> </xsl:variable>
<!-- Produce the results --> <!-- The "tick" is always the 1st item returned -->
<xsl:sequence select="$vnewTick, $vmyResults"/> </xsl:function>
<xsl:function name="f:transform" as="element()"> <f:transform/> </xsl:function>
<xsl:template match="f:transform" as="item()+" mode="f:FXSL"> <xsl:param name="arg1" as="item()+"/>
<xsl:sequence select="f:transform($arg1)"/> </xsl:template>
<xsl:function name="f:last" as="xs:boolean"> <xsl:param name="arg1" as="item()*"/>
<xsl:sequence select="xs:boolean($arg1[last()])"/> </xsl:function>
<xsl:function name="f:last" as="element()"> <f:last/> </xsl:function>
<xsl:template match="f:last" as="xs:boolean" mode="f:FXSL"> <xsl:param name="arg1" as="item()*"/>
<xsl:sequence select="f:last($arg1)"/> </xsl:template> </xsl:stylesheet>
In this case I show a transformation, which can use the tick count at any point. To illustrate doing some useful work, it produces the tick count multiplied by 3.
The stop condition is: exceeding 100 iterations.
The final output produced is:
Results:
Last tick: 101 Stop condition: true
Transform output: 1 3 2 6 3 9 4 12 5 15 6 18 7 21 8 24 9 27 10 30 11 33 12 36 13 39 14 42 15 45 16 48 17 51 18 54 19 57 20 60 21 63 22 66 23 69 24 72 25 75 26 78 27 81 28 84 29 87 30 90 31 93 32 96 33 99 34 102 35 105 36 108 37 111 38 114 39 117 40 120 41 123 42 126 43 129 44 132 45 135 46 138 47 141 48 144 49 147 50 150 51 153 52 156 53 159 54 162 55 165 56 168 57 171 58 174 59 177 60 180 61 183 62 186 63 189 64 192 65 195 66 198 67 201 68 204 69 207 70 210 71 213 72 216 73 219 74 222 75 225 76 228 77 231 78 234 79 237 80 240 81 243 82 246 83 249 84 252 85 255 86 258 87 261 88 264 89 267 90 270 91 273 92 276 93 279 94 282 95 285 96 288 97 291 98 294 99 297 100 300 101 303
Conclusion:
This is trivial (and actually quite boring) to achieve in a functional language. To quote Simon Peyton-Jones, "Haskell is the finest imperative language" :o)
====================================================================== Wendell Piez mailto:wapiez@xxxxxxxxxxxxxxxx Mulberry Technologies, Inc. http://www.mulberrytech.com 17 West Jefferson Street Direct Phone: 301/315-9635 Suite 207 Phone: 301/315-9631 Rockville, MD 20850 Fax: 301/315-8285 ---------------------------------------------------------------------- Mulberry Technologies: A Consultancy Specializing in SGML and XML ======================================================================
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