Re: [xsl] Sequential numbers in pure xslt, breaking the no-side-effect rule

["Andrew Welch" <andrew.j.welch@xxxxxxxxx>]

On 3/16/07, Abel Braaksma <abel.online@xxxxxxxxx> wrote:
> Hi XSLT'ers,
>
> AFAIK the answer to this is a simple, short "no, cannot be done". But I
> wanted to check it with the specialists to be sure ;)
>
> The request is simple: create a function that returns '1' on first call,
> and returns one higher each next call, without overlaps or jumps,
> without any input. Let's call it my:seq-number:
>
> <xsl:function name="my:seq-number" as="xs:integer">
>     <!-- some implementation -->
> </xsl:function>
>
> then the following line would return '1 2 3':
> <xsl:value-of select="my:seq-number(), my:seq-number(), my:seq-number()" />
>
> There are three scenarios to resolve this issue:
>
>   1. Use an extension function in the host language (java, .net)
>   2. Use an extension instruction like saxon:assign
>   3. Use 'hidden features' of generate-id().
>
> The first two are obvious. The last one is the best I good get with
> "pure xslt", but as I tested, does not work with AltovaXML (in fact, it
> is not even guaranteed to work on other or future versions of Saxon):
>
> <xsl:function name="my:seq:number" as="xs:integer">
>     <xsl:variable name="node"><xsl:comment /></xsl:variable>
>     <xsl:sequence select="xs:integer(substring(generate-id($node), 2) -
> 1" />
> </xsl:function>
>
> this will indeed return 1,2,3 etc, provided that, depending on the order
> of execution, the first node that is auto-created is this node, and that
> no other nodes are created meanwhile. (FYI, Saxon numbers document nodes
> as d1, d2 etc, where 'd1' is the input doc).
>
> Doing this with AltovaXML generates too much randomness, i.e., the
> output of generate-id is: idroot219951944 idroot219959376 etc (this is
> not a non-comformance bug. Not being able to deal with empty
> <xsl:comment /> is, however, but I am getting adrift...).
>
> Am I overlooking something, or is this about the best I can get? I know
> I am in violation and that requesting for functions/variables/templates
> that return different results with the same input is asking for breaking
> the rules.
>
> Thanks for any extra insights on an already overly discussed subject,

Really interesting point Abel, but aren't you effectively hacking a
feature of Saxon to get the results you want, and only then can you
get them if you call that function without calling others in between -
for example:

<xsl:stylesheet version="2.0"
xmlns:seq="seq"
xmlns:xs="http://www.w3.org/2001/XMLSchema";
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>

<xsl:function name="seq:number" as="xs:integer">
  <xsl:variable name="node"><xsl:comment /></xsl:variable>
  <xsl:sequence select="xs:integer(substring(generate-id($node), 2)) - 1" />
</xsl:function>

<xsl:function name="seq:number2" as="xs:integer?">
  <xsl:variable name="node"><xsl:comment /></xsl:variable>
  <xsl:message><xsl:copy-of select="$node"/></xsl:message>
  <xsl:sequence select="()"/>
</xsl:function>

<xsl:template match="/">
	<xsl:sequence select="for $x in (1 to 10) return
		if ($x mod 2 = 1) then
			seq:number()
		else
			seq:number2()"/>
</xsl:template>

</xsl:stylesheet>

This calls a different function in between calls to your function that
creates nodes which increment the number returned by generate-id() (it
uses xsl:message to force the variable to be evaluated) , which makes
the output:

1 4 7 10 13

cheers
andrew