Re: [xsl] XPath 3.0: Is it possible to do recursion in an anonymous function?

[Dimitre Novatchev <dnovatchev@xxxxxxxxx>]

> Using Dimitre's technique, I implemented the "until" function:
>
> <?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";
>                             version="3.0">
>
>     <xsl:output method="text"/>
>
>     <xsl:variable name="isNegative" select="function($x as xs:integer) {$x lt 0}" />
>     <xsl:variable name="decrement" select="function($x as xs:integer) {$x - 1}" />
>     <xsl:variable name="_until" select="
>                   function(
>                                     $p as function(item()*) as xs:boolean,
>                                     $f as function(item()*) as item()*,
>                                     $x as item()*,
>                                     $_until as function(function(), function(), item()*, function()) as item()*
>                                  ) as item()*
>                      {if ($p($x)) then $x else $_until($p, $f, $f($x), $_until)}
>         " />
>
>     <xsl:variable name="until" select="
>                   function(
>                                      $p as function(item()*) as xs:boolean,
>                                      $f as function(item()*) as item()*,
>                                      $x as item()*
>                                   ) as item()*
>                       {$_until($p, $f, $x, $_until)}
>           " />
>
>     <xsl:template match="/">
>         <xsl:value-of select="$until($isNegative, $decrement, 3)" />
>     </xsl:template>
>
> </xsl:stylesheet>
>
> /Roger
>
>

Nice, Roger,

The naming of the last argument makes the code *look* like ordinary recursion.

And this could deceive some people! :)  Also, the name of this
argument will have to change for a new function to match the function
name.


I would personally prefer a more standard and unchangeable name, such
as "_step".

To go further, the type of the  "_step" argument could be specified as
function()+ .

This could be used to implement "non-deterministic" functions, where
at each step, the next processing step is randomly determined from the
available choices ($_step functions).

I feel overwhelmed at what can be accomplished with pure XPath 3.0
anonymous functions.

-- 
Cheers,
Dimitre Novatchev
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