Re: [xsl] making dynamic evaluation via xsl:evaluate more dynamic

[Michael Kay <mike@xxxxxxxxxxxx>]

By all means raise this feedback with the XSL WG. The best way to do so 
is via the W3C bugzilla system - that's the way the WGs manage their agenda.

I think the answer is that no-one has previously suggested a need for 
this feature. It strikes me as raising a lot of questions. In your use 
case, how do you find out what external variables the XPath expression 
uses, so that you can bind the right names? If you don't know the names 
statically, you presumably need some way to discover them dynamically. 
But then, knowing the names of the parameters isn't much use if you 
don't know their semantics; where does this knowledge come from?

Michael Kay
Saxonica

On 17/04/2012 18:53, Jakub Mal} wrote:
> Hello,
> the new instruction evaluate allows for dynamic evaluation of expressions in
> stylesheets.
> This:
> <xsl:evaluate xpath="'1 + 1'">
> </xsl:evaluate>
> Returns 2
>
> All variables in the evaluated expression must be bound using with-param,
> like in
> <xsl:evaluate xpath="'$p1 + $p2'">
>    <xsl:with-param name="p1" select="1" />
>    <xsl:with-param name="p2" select="2" />
> </xsl:evaluate>
> Which returns 3.
>
> The syntactic rules for with-param are I think the same as in the case of
> call-template. Aren't those unnecessarily restrictive in this case?
> I suppose (please correct me, if I am wrong) the cost of dynamic evaluation
> would not change much, if attribute value template was allowed for the
> attribute name of with-param in evaluate, such e.g.:
> <xsl:evaluate xpath="'$p1 + $p2'">
>    <xsl:with-param name="{'p' || '1'}" select="1" />
>    <xsl:with-param name="{'p' || '2'}" select="2" />
> </xsl:evaluate>
>
> Did this question arise when semantics of evaluate was discussed?
> I have encountered an application where this would come in handy (well, it
> would provide an alternative solution to a problem which I solved
> differently), so maybe those applications that require dynamic evaluation
> would appreciate it as well. I was a bit surprised that it is not possible,
> because it feels appropriate to me. When dealing with dynamic evaluation,
> why not let the names of variables to by dynamic as well?
>
> Jakub Maly.
> http://www.xrg.cz