Re: [xsl] Avoiding dummy xsl:if with apply-templates

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2005-02-13 03:53 +0000, Frans Englich wrote:
> I find myself struggling with a construct I often need: conditionally, 
> "else",
> do something radically different depending on input.
>
> For example:
>
>            <xsl:variable name="el" select="elements" />
>             <xsl:if test="count($el)">

But you don't need a variable above, test="location-path" will return false 
if the return is an empty node-set.

>                 <ul>
>                     <xsl:apply-templates select="$el" />
>                 </ul>
>             </xsl:if>
>
> Here, the if statement and variable declaration exists solely to avoid an
> empty ul element; the special condition which occurs when the select misses.
>
> Producing xhtml tables is a similar case. I find these common situations in
> XSLT programming.
>
> These examples can be solved with usual conditional tests, as above, but I
> want to push the conditionalis upon the engine and write with templates; the
> clean, XSLT-like way. AFAICT, this made-up syntax would solve the problem:
>
> <xsl:apply-templates select="elements">
>         <ul>
>                 <xsl:apply/>
>         </ul>
> </xsl:apply-templates>

That isn't any more lines than:

 <xsl:if test="elements">
   <ul>
     <xsl:apply-templates select="elements"/>
   </ul>
 </xsl:if>

> Hence, when the select clause fails, the apply-templates body is not entered,
> and the conditionalis is not needed to be manually written and comes
> naturally, even.

But on what are you trying to economize?  It would seem you are overloading 
the <xsl:apply-templates> instruction, and it would be unclear where 
<xsl:with-param> and <xsl:sort> would sit, though I assume the <xsl:sort> 
would be a first child and the <xsl:with-param> would be a child of your 
suggested <xsl:apply/>.  If you are economizing on source-node-tree 
accesses in order to do multiple <xsl:apply/>, that can be done with 
node-set variables as in your original starting point ... it isn't so very 
much more verbose or "unnatural".  Also, what would be the current node 
list and current node for the <ul> in your above?  So far in XSLT, every 
select="location-path" in an element always sets a new current node list 
for the duration of the element ... what if someone used an attribute value 
template in an attribute of the <ul> element ... to which node would that 
refer?

> What is the proper way of doing what I want?

I think I've just written it above.  It doesn't overload any of the 
existing XSLT semantics, doesn't change the effect of select= and the 
current node list, and is consistent with the need to build an unordered 
list only if there are elements with which it is to be built.  A processor 
need not obtain all elements referred to in the test as it knows the 
semantics of the test= attribute and can return "true" at the first 
encounter of a return node.

I hope this is considered helpful.

...................... Ken


--
World-wide on-site corporate, govt. & user group XML/XSL training.
G. Ken Holman                 mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
Crane Softwrights Ltd.          http://www.CraneSoftwrights.com/s/
Box 266, Kars, Ontario CANADA K0A-2E0    +1(613)489-0999 (F:-0995)
Male Breast Cancer Awareness  http://www.CraneSoftwrights.com/s/bc
Legal business disclaimers:  http://www.CraneSoftwrights.com/legal