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


Subject: Re: [xsl] XPath 3.0: Is it possible to do recursion in an anonymous function?
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Sun, 14 Oct 2012 09:03:46 +0100

It's nice to know that this can be done, but I do wonder if it isn't simpler to use a named function instead?

Michael Kay
Saxonica

On 14/10/2012 00:01, Dimitre Novatchev wrote:
Finally, it is possible to hide the use of the second argument -- like this:


<xsl:stylesheet version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs"> <xsl:output method="text"/>

   <xsl:template match="/">
      <xsl:sequence select=
        "let $f := function($n as xs:integer,
                                          $f1 as function(xs:integer,
function()) as xs:integer
                                        ) as xs:integer
                         {if($n eq 0)
                             then 1
                             else $n * $f1($n -1, $f1)
                         },
                $F := function($n as xs:integer) as xs:integer
                           {$f($n, $f)}
          return
             $F(5)
        "/>
    </xsl:template>
  </xsl:stylesheet>


Cheers, Dimitre

On Sat, Oct 13, 2012 at 12:51 PM, Dimitre Novatchev
<dnovatchev@xxxxxxxxx> wrote:
Boh my previous answers had a slight issue (that didn't prevent Saxon
from executing them and producing the correct result) with the typing
of the "mock" function parameter $f1.

Here is this corrected:

<xsl:stylesheet  version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   exclude-result-prefixes="xs">
   <xsl:output method="text"/>

   <xsl:template match="/">
      <xsl:sequence select=
        "let $f := function($n as xs:integer,
                                    $f1 as function(xs:integer,
function()) as xs:integer
                                    ) as xs:integer
                         {if($n eq 0)
                             then 1
                             else $n * $f1($n -1, $f1)
                         }
          return
             $f(5, $f)
        "/>
    </xsl:template>
  </xsl:stylesheet>


Cheers, Dimitre

On Sat, Oct 13, 2012 at 12:47 PM, Dimitre Novatchev
<dnovatchev@xxxxxxxxx> wrote:
Here is an equivalent XSLT-based solution -- i both cases there is no
literal function defined -- just an inline one:

<xsl:stylesheet  version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   exclude-result-prefixes="xs">
   <xsl:output method="text"/>

   <xsl:template match="/">
      <xsl:sequence select=
        "let $f := function($n as xs:integer,
        $f1 as function(xs:integer) as xs:integer
        ) as xs:integer
        {if($n eq 0)
        then 1
        else $n * $f1($n -1, $f1)
        }
        return
        $f(5, $f)
        "/>
    </xsl:template>
  </xsl:stylesheet>

Again, the correct result is produced:

120


Cheers, Dimitre

On Sat, Oct 13, 2012 at 12:37 PM, Dimitre Novatchev
<dnovatchev@xxxxxxxxx> wrote:
You are right, but there is an easy workaround.

Here is an example with an in-line factorial function:


declare option saxon:output "omit-xml-declaration=yes"; let $f := function($n as xs:integer, $f1 as function(xs:integer) as xs:integer ) as xs:integer {if($n eq 0) then 1 else $n * $f1($n -1, $f1) } return $f(5, $f)

The result we get is correct:

120


Cheers, Dimitre

On Sat, Oct 13, 2012 at 12:03 PM, Costello, Roger L. <costello@xxxxxxxxx> wrote:
Hi Folks,

Is it possible to do recursion in an anonymous function?

Example: I would like to implement an "until" function. It has three arguments:

1. p is a boolean function
2. f is a function on x
3. x is the value being processed

Read the following function call as: decrement 3 until it is negative
       $until ($isNegative, $decrement, 3)

where
       $isNegative := function($x as xs:integer) {$x lt 0}
       $decrement := function($x as xs:integer) {$x - 1}

Here's how I attempted to implement function until:

$until := function(
                                      $p as function(item()*) as xs:boolean,
                                      $f as function(item()*) as item()*,
                                      $x as item()*
                                 ) as item()*
                          {
                              if ($p($x)) then
                                    $x
                              else
                                    $until($p, $f, $f($x))  <-- RECURSE ...THIS IS NOT ALLOWED, I THINK
                            }

Is there a way to implement function until in XPath 3.0? (I know how to implement it in XSLT 3.0)

/Roger



--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.


--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.


--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.


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