On 11/02/2023 11:34, Chris Papademetrious
christopher.papademetrious@xxxxxxxxxxxx wrote:

The approach is limited by its use of template matches and regular
expressions. For some reason, I donbt feel inclined to write an XPath
grammar parser in XSLT. But still, some low-hanging fruit can be
obtained.

Have a look at Gunther Rademacher's REx Parser Generator
https://www.bottlecaps.de/rex/

It can be used to generate an XSLT parser for XPath 2. (I've used it
extensively in the past for analysing XPath 3 expressions.)

An alternative, if your XSLT platform supports it, is to use an
InvisibleXML parser https://invisiblexml.org/
There is an iXML grammar forB  XPath3.1 available
(https://github.com/invisibleXML/ixml/tree/master/samples/XPath) which
will also parse XPath2. You may be able to experiment with this using
Martin Honnen's XSLT3 Fiddle
(https://martin-honnen.github.io/xslt3fiddle/) which supports
invisibleXML parsing functions.

Note that the entry page to the XSLT 3 fiddle with support for Invisible
XML through John's library is not
https://martin-honnen.github.io/xslt3fiddle/ but
https://martin-honnen.github.io/xslt3fiddle/index-iXML.html. There you
could then make use of the XPath 3.1 grammar with code like e.g.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
B  version="3.0"
B  xmlns:xs="http://www.w3.org/2001/XMLSchema"
B  xmlns:jwL="https://github.com/johnlumley"
B  exclude-result-prefixes="#all"
B  expand-text="yes">

B  <xsl:include
href="https://martin-honnen.github.io/xslt3fiddle/xslt/jwiXML.processor.xsl"/

B  <xsl:param name="xpath31-grammar-uri"
as="xs:string">https://raw.githubusercontent.com/invisibleXML/ixml/master/sam
ples/XPath/XPath.reducedTree.ixml</xsl:param>

B  <xsl:variable name="parsed-xpath31-grammar"
select="jwL:compileGrammar(unparsed-text($xpath31-grammar-uri))"/>

B  <xsl:template match="xpath">
B B B  <xsl:copy>
B B B B B  <input>{.}</input>
B B B B B  <parsed-tree>{jwL:parse($parsed-xpath31-grammar, .)?tree =>
serialize(map{'method':'xml','indent':true()})}</parsed-tree>
B B B  </xsl:copy>
B  </xsl:template>

<root>
B  <examples>
B B B  <xpath>random-number-generator()?permute(1 to 5)</xpath>
B  </examples>
</root>

<root>
B  <examples>
B B B  <xpath><input>random-number-generator()?permute(1 to
5)</input><parsed-tree><![CDATA[<XPath>
B B  <PostfixExpr>
B B B B B  <FunctionCall>
B B B B B B B B  <UnprefixedName LocalPart="random-number-generator"/>
B B B B B B B B  <ArgumentList/>
B B B B B  </FunctionCall>
B B B B B  <Lookup>
B B B B B B B B  <KeySpecifier Name="permute"/>
B B B B B  </Lookup>
B B B B B  <ArgumentList>
B B B B B B B B  <RangeExpr>
B B B B B B B B B B B  <IntegerLiteral>1</IntegerLiteral>
B B B B B B B B B B B  <IntegerLiteral>5</IntegerLiteral>
B B B B B B B B  </RangeExpr>
B B B B B  </ArgumentList>
B B  </PostfixExpr>
</XPath>]]></parsed-tree></xpath>
B  </examples>
</root>