Re: [xsl] [xslt 2.0] Difference betwen functions and templates

["Mukul Gandhi" <gandhi.mukul@xxxxxxxxx>]

Hi Justin,
 I agree with you, that "xsl:template match= ..." is the essence of
XSLT. Without it, XSLT cannot work.

I feel, it's interesting to discuss the differences between
"xsl:template name= ..." and xsl:function. Both are callable
components, and are sort of subroutines (they, actually are). Are both
of these needed in XSLT 2.0, or we can just have xsl:function or
xsl:template name= ...

As we have already discussed, xsl:function (a user-defined function)
can be called only from within a XPath expression (something like,
/abc/pqr[xx = ns:func()]/uvw

(this is a new thing in XSLT/XPath 2.0, and is a very useful innovation).

But, xsl:template name= ... *cannot* be called from a XPath
expression. Now the questions is, is xsl:template name= ... able to do
something, which xsl:function cannot do? Yes, xsl:template name= has
some features, which xsl:function doesn't have.

Please consider the below example:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xx="http://dummy-ns";
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; version="2.0">

<xsl:output method="xml" indent="yes" />

<xsl:template match="/">
  <result>
    <xsl:call-template name="dummy-template" />
  </result>
</xsl:template>

<xsl:function name="xx:dummy-func" as="node()+">
  <dummy-content/>
</xsl:function>

<xsl:template name="dummy-template">
  <dummy-content/>
</xsl:template>

</xsl:stylesheet>

I am calling a named template, using xsl:call-template. The output of
this stylesheet is:

<?xml version="1.0" encoding="UTF-8"?>
<result xmlns:xx="http://dummy-ns";>
 <dummy-content/>
</result>

Can we do a similar thing using xsl:function? We cannot..

For example, will this work?

[1]
<xsl:template match="/">
 <result>
   xx:dummy-func()
 </result>
</xsl:template>

or, will this work?

[2]
<xsl:template match="/">
 <result>
   <xsl:value-of select="xx:dummy-func()" />
 </result>
</xsl:template>

(xsl:value-of constructs a text node, so this won't work)

I would have considered xsl:function and xsl:template name= ... to be
equivalent, if [1] produced the same output as, xsl:call-template.

My conclusion therefore is, xsl:function and xsl:template name= are
very different, and both are required in XSLT 2.0.

On 7/19/07, Justin Johansson <procode@xxxxxxxxxx> wrote:
> Mukul,
>
> Thanks for your contribution to this lively discussion.
>
> >I feel, having xsl:template in XSLT 2.0 is very important, for XSLT
> >2.0 to be backward compatible with XSLT 1.0.
>
> It is not a question of backward compatibilty.
>
> xsl:template is the very essence of XSLT as opposed to XQuery.
>
> Take away xsl:template's from XSLT and you essentiallly have
> XQuery availalble to you in a lesser XML-based syntax.
>
> The whole model of XSLT is to present to the programmer
> a series of nodes which can be matched to a path-match
> expression and then have automatic invocation of a rule to
> prepare (return) a result (nodal) series (aka sequence) upon
> recursive descent of the input XML tree.
>
> This is important in anyone's undertanding of XSLT :-
>
> What the XSLT processor does for you, and saves you the
> trouble of, is to do a recursive descent of the source XML
> tree and match rules, which you declare via xsl:template,
> to be fired (much like callbacks in C/C++) whenever
> the recursive descent of the source tree encounters
> an XML node which matches the pattern you declared via
> xsl:template match=
>
> XQuery has no facility to do this.  XQuery is dumbed down XSLT,
> though has some facilities which are important when dealing
> with larger databases.
>
> XQuery, exists soley for the reason of an attempt to by-pass an
> XML-based programming language syntax for the processing XML.
>
> I am sure that Michael Kay would reply in a more concise manner than myself.
>
>
>
>
>
> The bottom line is that named templates and functions are essentially
> >> the same thing and it would have been possible for XSLT 2.0 to do
> >> away with either xsl:call-template or xsl:function.
>
> >They probably look similar, but IMHO both are useful members of XSLT
> >2.0. As you also said, xsl:function can be called from within an XPath
> >expression (and, this is a very important difference) while
> >xsl:template cannot be.
>
> >I feel, having xsl:template in XSLT 2.0 is very important, for XSLT
> >2.0 to be backward compatible with XSLT 1.0.
>
> >And of course, xsl:function is really beneficial, as also stated by
> >others in this thread.
> >
> >--
> >Regards,
> >Mukul Gandhi
>
> Justin Johansson
> Schema-aware XSLT evangelist


--
Regards,
Mukul Gandhi