Re: [xsl] RE: syntax sugar for call-template

Subject: Re: [xsl] RE: syntax sugar for call-template
From: Uche Ogbuji <uche.ogbuji@xxxxxxxxxxxxxxx>
Date: Fri, 16 Feb 2001 09:32:43 -0700
> David Carlisle wrote:
> > Howver This is still an element and so still not usable in XPath
> > expressions, so I'd rather have
> >
> > ... something...
> >
> > and then have 
> > select="my:func(xpath)"
> >  essentially doing something equivalent to
> > <xsl:variable name="x"><xf:func one="xpath" /></xsl:variable> ...
> > select="$x"
> Couldn't agree more strongly.  Thinking about Uche's comments on
> run-time dynamism and introspection yesterday (I don't know what that
> means but it sure sounds good) another option would be single new XSLT
> function:

introspection is in short the ability to query an object for its metadata.  
For example.  An example of metadata of a named template might be the 
parameters it expects.  Metadata on a stylesheet might be the templates it 

I do like yours and David's ideas in this area.

>   call-template('my:func', 'one', xpath,
>                            'two', $rtf)
> I don't know whether this would be more or less acceptable than a
> means of defining XSLT user extension functions?  The one big
> limitation is that you wouldn't be able to return node sets (aside
> from those constructed as an RTF) so there would be limitations on
> this.

This is pretty much meta-programming: building up the construct on the fly.  
It requires dynamicism, and in many cases, introspection.

Imagine being able to automatically assign items in a node-set to the 
corresponding positional parameters in a template (with position being 
determined by the document order of the with-param elements in the template).

> Even without a general call-template() function, if we're going for
> XSLT user extension functions there's still the issue of how the
> parameters are passed.  In saxon:function, they're passed by position.
> Another alternative would be, as above, if they were passed by name
> using something like:
>   my:func('one', xpath, 'two', $rtf)
> rather than:
>   my:func(xpath, $rtf)
> I like being able to set parameters by name.  It also might lead to
> interesting situations if you dynamically alter the names of the
> parameters (they're just strings, after all) [if we had a
> call-template() function then you could dynamically alter the name of
> the template too!)

Yes.  This allows such useful techniques as delegation,  where, say a named 
template could dynamically find and dispatch to another template specialized 
to handle the needed function.

Uche Ogbuji                               Principal Consultant
uche.ogbuji@xxxxxxxxxxxxxxx               +1 303 583 9900 x 101
Fourthought, Inc.                
4735 East Walnut St, Ste. C, Boulder, CO 80301-2537, USA
Software-engineering, knowledge-management, XML, CORBA, Linux, Python

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