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Re: [xsl] XPath 3.0: Is it possible to do recursion in an anonymous function?
2012-10-14 03:04:00
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(_at_)gmail(_dot_)com> 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(_at_)gmail(_dot_)com> 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(_at_)gmail(_dot_)com> 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(_at_)mitre(_dot_)org> 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
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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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