Re: [xsl] XSLT 4 xsl:with

Subject: Re: [xsl] XSLT 4 xsl:with
From: "Pieter Masereeuw pieter@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 20 May 2020 07:32:40 -0000
Thanks everyone for your comments. It is great to be part of a community 
like this. You made me think better, and that's why I'd like share some 
other thoughts on this subject.

It seems that XSLT has enough power to facilitate anything that you want 
to do in processing XML (and other stuff). Also, as Gerrit pointed out, 
it already has facilities like *@context-item* that you may want to 
extend to other places as well, so no need for new words (Ockham's 
razor, more or less).

My main point was that I wanted to express my intentions in a more 
natural way. Therefore, I came up with <xsl:with> (I now like Graydon's 
<xsl:with-context> better). The additional effect of a cardinality check 
would also be very beneficial, because often, when I return to older 
code, I wonder if my comment really/still applies and whether or not the 
(implied) schema of the input may have changed in the meantime.

Now, of course, XSLT has an excellent facility for detecting such 
errors: the @as attribute. So instead of *<xsl:with-context 
select="foo">* I might write:

*<xsl:variable name="single-foo" as="element(foo)" select="foo"/>**
**<xsl:for-each select="$single-foo">*...

That would also have the benefit that it does not only specify the 
expected cardinality, but also other type aspects.

Using a variable may be a bit verbose (but I do it quite often), so 
instead of a new element like <xsl:with-context>, we might also extend 
the idea behind type-checking. Adding an @as attribute to constructions 
like xsl:for-each should be avoided (I think), because my intended 
semantics would be different from its normal use. But maybe some new 
attribute with the required checking effect, like for instance 

We then might have*<xsl:for-each select="foo" context-as="element(foo)">*.

The @context-as attribute could then also be allowed on other 
constructs, such as <xsl:apply-templates>, although I do see some 
difficulties in some situations.

I must confess that, in the end, @context-as feels somewhat clumsy to 
me, so I am still attracted to my initial idea of just writing 
<xsl:with-context select="foo">. But then, maybe the type-checking idea 
will trigger some new thoughts?


On 5/20/20 6:06 AM, Mukul Gandhi gandhi.mukul@xxxxxxxxx wrote:
> On Tue, May 19, 2020 at 2:23 PM Pieter Masereeuw pieter@xxxxxxxxxxxx 
> <mailto:pieter@xxxxxxxxxxxx> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx 
> <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote:
>     I would be very happy if I could make my intentions clearer by
>     using a real XSLT construct in this situation, such as *<xsl:with
>     select="...">.*
> I think that, this would be a useful instruction for XSLT, for setting 
> runtime context for other XSLT instructions. I also remember that, 
> sometimes I used to use xsl:for-each to establish runtime context for 
> other XSLT instructions, which is perhaps not good software engineering.
> -- 
> Regards,
> Mukul Gandhi
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