Re: [xml-dev] XPath as a stand-alone programming language

[Jim Melton <jim.melton@oracle.com>]

Dimitre,

Thanks for showing us your work on this.  Very interesting, I thought.

You suggested some new post-3.0 XPath features in 
your message.  A preferred way to let the XSLT 
and XML Query Working Groups know of such 
proposed new requirements would be to post them 
on W3C's public Bugzilla instance, using Product 
= "XPath / XQuery / XSLT" and Component = "XQuery 
3.1 Requirements and Use Cases".  (Note that 
there is no assurance that there will ever be 
another version of XPath, XQuery, or XSLT after 
the current 3.0 versions under development, nor 
that any such future version will be designated "3.1".)

You can locate that Bugzilla instance at 
https://www.w3.org/Bugs/Public/enter_bug.cgi

Hope this helps,
    Jim


At 10/24/2012 07:32 AM, Dimitre Novatchev wrote:
>A few months ago I had the pleasure to do "all XPath programming".
>
>I developed the Binary tree data type and the Set data type
>essentially completely in XPath 3.0.
>
>These can be found in my blog, respectively at:
>
> 
>http://dnovatchev.wordpress.com/2012/01/09/the-binary-search-tree-data-structurehaving-fun-with-xpath-3-0/
>
>and
>
> 
>http://dnovatchev.wordpress.com/2012/01/12/the-set-datatype-implemented-in-xpath-3-0/
>
>At the time this happened accidentally. I don't like to work with
>XQuery, but at that time Saxon's XSLT 3.0 processor didn't fully
>implement higher order functions. Saxon's  XQuery 3.0 did, so I
>reluctantly used XQuery 3.0 in my work. Doing so, I planned to move my
>whole code to XSLT 3.0 --whenever Saxon's XSLT 3.0 processor was ready
>for this (and now, in version 9.4 it is). Therefore I essentially
>coded everything as much in pure XPath 3.0 as possible.
>
>This experience clearly showed to me that it is possible to use XPath
>3.0 as a stand-alone programming language. This has many benefits, and
>one of them is that XPath-only code is fully transferrable between
>XSLT and XQuery.
>
>At the end of my latest blog post "Recursion with anonymous (inline)
>functions in XPath 3.0", I list a number of nice features we still
>need in XPath as a programming language, that could be added in a
>future, post-3.0 version:
>
>  1. Stand-alone XPath processors.
>
>  2. Import/include directives for XPath-only files (expression-files).
>
>  3. Separate packaging/compilation of XPath-only programs.
>
>  4. New data structures such as tuples.
>
>  5. Generics – parametric data types.
>
>
>Cheers,
>
>Dimitre
>
>
>
>
>On Wed, Oct 24, 2012 at 4:55 AM, Costello, Roger 
>L. <costello@mitre.org> wrote:
> > Thanks a lot Michael for the explanation. Fantastic!
> >
> > Below is a summary of my question plus 
> Michael's answer (slightly expanded).
> >
> > The XPath 3.0 specification says this:
> >
> >       XPath 3.0 is a composable language
> >
> > What does that mean?
> >
> > It means that every operator and language 
> construct allows any XPath expression to appear 
> as its operand (subject only to operator 
> precedence and data typing constraints).
> >
> > For example, take this expression:
> >
> > 3 + ____
> >
> > The plus (+) operator has a left-operand, 3. 
> What can the right-operand be? Answer: any 
> XPath expression! Let's use the max() function as the right-operand:
> >
> > 3 + max(___)
> >
> > Now, what can the argument to the max() 
> function be? Answer: any XPath expression! 
> Let's use a for-loop as its argument:
> >
> > 3 + max(for $i in 1 to 10 return ___)
> >
> > Now, what can the return value of the 
> for-loop be? Answer: any XPath expression! Let's use an if-statement:
> >
> > 3 + max(for $i in 1 to 10 return (if ($i gt 5) then $i*3 else $i*2)))
> >
> > The fact that XPath is a composable language 
> is very cool and very powerful.
> >
> > Contrast this with XSLT, which is not fully 
> composable: XPath expressions can be used as 
> operands to XSLT instructions, but not the 
> other way around. Similarly Java has constructs called statements that
> > cannot be nested inside expressions.
> >
> > /Roger
> >
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>
>
>
>--
>Cheers,
>Dimitre Novatchev
>---------------------------------------
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Jim Melton --- Editor of ISO/IEC 9075-* (SQL)     Phone: +1.801.942.0144
   Chair, ISO/IEC JTC1/SC32 and W3C XML Query WG    Fax : +1.801.942.3345
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