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Subject: Re: [xsl] XPath 3.0: Is it possible to do recursion in an anonymous function? From: Dimitre Novatchev <dnovatchev@xxxxxxxxx> Date: Sun, 14 Oct 2012 06:48:37 -0700 |
On Sun, Oct 14, 2012 at 1:03 AM, Michael Kay <mike@xxxxxxxxxxxx> wrote: > 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? It (using a named function) is simpler if one writes in XSLT or XQuery. It is impossible, if one doesn't. Cheers, Dimitre > > 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. > -- 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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