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(_at_)googlemail(_dot_)com]
Sent: Tuesday, April 17, 2012 11:51 PM
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
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(_at_)saxonica(_dot_)com>:
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 Malý 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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