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

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What you suggest, Phil, seems like a nice workaround.

As for the previous post:
There is some static analysis going on in when xsl:evaluate is used?
I thought it works somehow like this:
When xsl:evaluate is encountered, the value passed to xpath attribute is
passed to the XPath parser together with the names of free variables used in
the expression (collected from the with-param instructions). The expression
is parsed, variables are bound to the values provided by with-param and
evaluated. I thought the whole process would not have to change very much,
only the attribute name of each with-param will now be evaluated similarly
as in e.g. xsl:element name="...", allowing attribute value template.

> -----Original Message-----
> From: Philip Fearon [mailto:pgfearo@xxxxxxxxxxxxxx]
> Sent: Tuesday, April 17, 2012 11:51 PM
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [xsl] making dynamic evaluation via xsl:evaluate more dynamic
>
> Just a thought - now XPath 3.0 has the Let Expression, wouldn't it be
possible
> to safely wrap the XPath string with a Let Expression that declares the
> dynamic variables - before passing this as a parameter to xsl:evaluate?
>
> Phil
>
> 2012/4/17 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

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