Re: [xsl] The philosophical implications of an XSLT processor implemented in XSLT

["Roger L Costello costello@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Dimitre wrote:

> So, here is a true challenge,  XPath in XPath, then XSLT in XPath

Wow!

Mind-blowing stuff Dimitre!

/Roger

From: Dimitre Novatchev dnovatchev@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Sent: Friday, May 22, 2020 11:26 AM
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Subject: Re: [xsl] The philosophical implications of an XSLT processor
implemented in XSLT

>B  It was believed that XML languages such as XSLT were not sufficient in
speed and/or language facilities ...

While having an XSLT processor written completely in XSLT is a great
achievement and a stepping stone in our progress, we need to be careful when
saying that XSLT is an "XML language".

Yes, an XSLT stylesheet is an XML document, but it is much more than that.
XSLT is based on two independent languages: XML and XPath, each of which
doesn't know about XSLT, and has scope of problem coverage, where XSLT is not
involved. And XSLT has some concepts, that have nothing to do with it being an
XML language, but that have parallels in other programming languages.

Actually, it is the latest developments in XPath 3 (maps) that made it
possible to produce an XSLT processor written in XSLT, which is claimed to
have a practically feasible performance.

And, if I read well Dr. Kay's message, it is exactly the XPath parsing that
**is not** implemented in XSLT, instead it is implemented in Javascript.

For me the philosophicalB implications of the forthcoming XSLT processor
"written in XSLT" is that this helps us better understand the relative
importance and actual role of every language that is used in XSLT. Simply that
this can be done is not something new at all. What is new is why it was not
done until now and why/how it has been finally done.

If we can implement an XPath processor (or shall we say "engine") written
entirely in XPath, -- and I believe we can -- then we surely can implement an
XSLT processor written entirely in XPath. Then an XSLT processor in XSLT
becomes as trivial as:

<xsl:sequence select="my:XsltProcessorInXpath(whateverparams)"/>

Now, one can argue that the huge set of XPath functions and operators cannot
(or are not feasible to) be implemented in XPath.

To this my answer is: I believe these functions and operators **can** be
implemented by a core subset of XPath.

So, here is a true challenge,B  XPath in XPath, then XSLT in XPath:B 
1. B A "core XPath subset", and
2. B Then using this subset, implement an XPath engine built with XPath, and
3. Then implement an XSLT processor built in XPath.
What is the main benefit in any such exercise? Not the mere fact of the
achievement, but the new knowledge and ideas that we acquire while doing this.
B 
Cheers,
Dimitre


On Thu, May 21, 2020 at 9:18 AM Roger L Costello mailto:costello@xxxxxxxxx
<mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi Folks,

Michael Kay reports that, within a few weeks, Saxonica will be releasing an
XSLT processor implemented in XSLT.

That will be a key event.

Here is one philosophical implication of that event.

Philosophical Implication #1

Up to this period in time, it has been believed that "system" applications --
such as XSLT processors -- which process XML documents must be written in a
non-XML language such as Java, C#, C++, C, or some other imperative language.
It was believed that XML languages such as XSLT were not sufficient in speed
and/or language facilities to handle the complex processing that is required
of a compiler or other system-level application. Those were false beliefs.
Saxonica has created a proof by counterexample that they are false beliefs.

That changes the world.

So ... it's time to do this:

- implement an XML Schema validator using XSLT
- implement an RDF ontology tool using XSLT
- implement a DFDL processor using XSLT
- and many others.

What are the other philosophical implications of an XSLT processor implemented
in XSLT?

/Roger



--
Cheers,
Dimitre Novatchev
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Truly great madness cannot be achieved without significant intelligence.
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To invent, you need a good imagination and a pile of junk
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Never fight an inanimate object
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To avoid situations in which you might make mistakes may be the
biggest mistake of all
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Quality means doing it right when no one is looking.
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I finally figured out the only reason to be alive is to enjoy it.
B 
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