Re: [xsl] XPath 2.0 expression that detects a cycle of references?

["Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

>> Dimitre has an article on using two anonymous function together with "let",
to implement the recursion:
>>
>>
https://dnovatchev.wordpress.com/2012/10/15/recursion-with-anonymous-inline-f
unctions-in-xpath-3-0-2/
>
> Wow, 2012! And mentioning Roger Costellob&


There are two other places where this technique was presented:

[1] Balisage 2013, "Programming in XPath 3.1"

[2] The Evolution of XPath: Whatbs New in XPath 3.0 -- a video
training course at Pluralsight, 2013


Programming in pure XPath is a powerful way of producing valuable
modules that are completely portable and independent of any
vendor-specific XSLT or XQuery processors -- thus achieving maximum
spread and (re)usability regardless of platform or programming
language. This could be one reason why XSLT/XQuery vendors -- even
those who are aware of this --  rarely, if at all, mention XPath
programming... :)



Roger certainly knows about this technique, because he was de facto a
co-author of [1]. This is why he specifically asks about an XPath 2.0
solution.


The technique described in [1] and [2] was used (in a comprehensive
example) for implementing, instantiating and using a new,
custom-defined data-type in XPath 3.0 -- the Binary Search Tree
datatype.

While the Balisage paper was limited in time, the Pluralsight course
dedicates a single, 40-minutes module on XPath 3.0 programming,
preceded by another 17 minutes+  single clip on implementing recursion
using anonymous functions in XPath 3.0.


Links:

[1] Paper:
http://www.balisage.net/Proceedings/vol10/html/Novatchev01/BalisageVol10-Nova
tchev01.html
,
     Slides:
http://www.balisage.net/Proceedings/vol10/author-pkg/Novatchev01/BalisageVol1
0-Novatchev01.html

[2] Course: https://www.pluralsight.com/courses/xpath-3-0-whats-new



Cheers,
Dimitre

On Tue, Mar 29, 2016 at 4:19 AM, Michael MC<ller-Hillebrand
mmh@xxxxxxxxx <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>> Martin Honnen wrote:
>>
>>> I have no idea how one would have to handle this using XPath 3b& any
suggestions?
>>
>> Dimitre has an article on using two anonymous function together with "let",
to implement the recursion:
>>
>>
https://dnovatchev.wordpress.com/2012/10/15/recursion-with-anonymous-inline-f
unctions-in-xpath-3-0-2/
>
> Wow, 2012! And mentioning Roger Costellob&
>
> Assuming my original function worked correctly, this would be the XPath 3.0
version of it:
>
> let $f := function(
>   $this as element()+,
>   $visited as xs:string*,
>   $f1 as function(element(), xs:string*, function(*)) as xs:boolean
>   ) as xs:boolean
>   {
>   let $refId := $this/for-more-info/@idref,
>      $refTgt := $this/../item[@id = $refId]
>   return
>     if (not(exists($refTgt))) then false()
>       else if ($refId = $visited) then true()
>       else some $e in $refTgt satisfies $f1($e, ($visited, $refId), $f1)
>   }
> return $f(., (), $f)
>
> At least with Saxon 9.6.0.7 (in Oxygen) in gives the same results.
>
> Thanks a lot for hints, I learned quite a bit!
>
> - Michael
>
> Complete example:
>
> Input:
>
> <?xml version="1.0" encoding="UTF-8"?>
> <document>
>    <item id="HF">
>        <title>Huckleberry Finn</title>
>        <for-more-info idref="MT"/>
>    </item>
>    <item id="MT">
>        <name>Mark Twain</name>
>        <for-more-info idref="SP"/>
>        <for-more-info idref="ZP"/>
>    </item>
>    <item id="SP">
>        <publisher>Springer</publisher>
>        <for-more-info idref="HF"/>
>    </item>
>    <item id="XP">
>        <publisher>XPress</publisher>
>        <for-more-info idref="HF"/>
>    </item>
>    <item id="YP">
>        <publisher>YPress</publisher>
>        <for-more-info idref="ZP"/>
>    </item>
>    <item id="ZP">
>        <publisher>ZPress</publisher>
>    </item>
> </document>
>
> Stylesheet including both options as attributes cycle2 (XSLT function) and
cycle3 (Xpath 3.0):
>
> <?xml version="1.0" encoding="UTF-8"?>
> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
>   xmlns:xs="http://www.w3.org/2001/XMLSchema";
>   xmlns:my="my" exclude-result-prefixes="#all"
>   version="3.0">
>
>   <xsl:output indent="yes"/>
>
>   <xsl:template match="document">
>     <report>
>       <xsl:for-each select="item">
>         <xsl:copy>
>           <xsl:copy-of select="@id"/>
>           <xsl:attribute name="cycle2" select="my:CycleFound(., ())"/>
>           <xsl:attribute name="cycle3"
>             select="
>               let $f := function(
>                 $this as element()+,
>                 $visited as xs:string*,
>                 $f1 as function(element(), xs:string*, function(*)) as
xs:boolean
>                 ) as xs:boolean
>                 {
>                 let $refId := $this/for-more-info/@idref,
>                    $refTgt := $this/../item[@id = $refId]
>                 return
>                   if (not(exists($refTgt))) then false()
>                     else if ($refId = $visited) then true()
>                     else some $e in $refTgt satisfies $f1($e, ($visited,
$refId), $f1)
>                 }
>               return $f(., (), $f)
>                     "
>           />
>         </xsl:copy>
>       </xsl:for-each>
>     </report>
>   </xsl:template>
>
>   <xsl:function name="my:CycleFound" as="xs:boolean">
>     <xsl:param name="this" as="element()?"/>
>     <xsl:param name="visited" as="xs:string*"/>
>     <xsl:variable name="refId" select="$this/for-more-info/@idref"
as="xs:string*"/>
>     <xsl:variable name="refTgt" select="$this/../item[@id = $refId]"
as="element()*"/>
>
>     <xsl:sequence select="
>     if (not(exists($refTgt))) then false()
>     else if ($refId = $visited) then true()
>     else some $e in $refTgt satisfies my:CycleFound($e, ($visited, $e/@id))
>     "/>
>   </xsl:function>
>
> </xsl:stylesheet>
>
>



--
Cheers,
Dimitre Novatchev
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