Thanks for sharing the example.  I further tested the program as following:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
	        xmlns:x="http://xsl/stack"
                        version="2.0">

 <xsl:output method="text" />

 <xsl:template match="/">
   <!-- 1. --> <xsl:variable name="stack" select="()" />
   <!-- 2. --> <xsl:variable name="stack" select="x:push($stack, 1)" />
   <!-- 3. --> <xsl:value-of select="x:top($stack)" />
   <!-- 4. --> <xsl:variable name="stack" select="x:push($stack, 2)" />
   <!-- 5. --> <xsl:value-of select="x:top($stack)" />
   <!-- 6. --> <xsl:value-of select="x:top(x:pop($stack))" />
 </xsl:template>

 <xsl:function name="x:push" as="item()+">
   <xsl:param name="stack" as="item()*"/>
   <xsl:param name="item"  as="item()"/>
   <xsl:sequence select="$item, $stack"/>
 </xsl:function>

 <xsl:function name="x:pop" as="item()*">
   <xsl:param name="stack" as="item()*"/>
   <xsl:sequence select="remove($stack, 1)"/>
 </xsl:function>

 <xsl:function name="x:top" as="item()?">
   <xsl:param name="stack" as="item()*"/>
   <xsl:sequence select="$stack[1]"/>
 </xsl:function>

</xsl:stylesheet>

I get the output:
121

I am happy with this; but have following questions:

1) On this line <!-- 2. --> , I create a variable 'stack'. This is a
new *variable* and not the old one (on line <!-- 1. -->; because we
cannot modify variables in XSLT). This doesn't make me quite happy :)

2) On line <!-- 6. -->, I do x:top(x:pop($stack)). This modifies a
transient stack, and doesn't modify the variable $stack. I would like
the variable $stack to be modified. But that's not possible, we know
:)

I guess, these limitations will prohibit some stack specific programs
to be built.

Can we think of some strategies to overcome these limitations.


On Wed, Feb 20, 2008 at 9:19 PM, Florent Georges <lists@xxxxxxxxxxxx> wrote:
>    <xsl:function name="x:push" as="item()+">
>       <xsl:param name="stack" as="item()*"/>
>       <xsl:param name="item"  as="item()"/>
>       <xsl:sequence select="$item, $stack"/>
>    </xsl:function>
>
>    <xsl:function name="x:pop" as="item()*">
>       <xsl:param name="stack" as="item()*"/>
>       <xsl:sequence select="remove($stack, 1)"/>
>    </xsl:function>
>
>    <xsl:function name="x:top" as="item()?">
>       <xsl:param name="stack" as="item()*"/>
>       <xsl:sequence select="$stack[1]"/>
>    </xsl:function>
>
>  :-)
>
>  That's just an idea, you might want to control more
> precisely errors (what if one pops an empty stack?, etc.)



-- 
Regards,
Mukul Gandhi