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Re: [xsl] For-each adds whitespace per iteration: why?


Subject: Re: [xsl] For-each adds whitespace per iteration: why?
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Fri, 10 Jan 2014 17:27:06 +0000

On 10 Jan 2014, at 17:05, Eliot Kimber <ekimber@xxxxxxxxxx> wrote:

> In the context of writing an XSLT to generate DTD syntax from RNGs (for
> DITA 1.3) I discovered that for-each results in whitespace being emitted
> for each iteration. This came as a surprise. Reading the spec it says,
> under clause 7, Repetition:
>
> "For each item in the input sequence, evaluating the sequence constructor
> <http://www.w3.org/TR/xslt20/#dt-sequence-constructor> produces a sequence
> of items (see 5.7 Sequence Constructors
> <http://www.w3.org/TR/xslt20/#sequence-constructors>). These output
> sequences are concatenated; ...
>
> I understand "These output sequences are concatenatedb to mean that
string
> concatenation rules are applied, which explains the white space.

No, this is a concatenation of two or more sequences to produce a single
sequence. No whitespace is added at this point.

>
> My question: why is for-each defined in this way?

It isn't.
>
>
> I tested this with this little XSLT transform:
>
> <?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:xd="http://www.oxygenxml.com/ns/doc/xsl"
>  exclude-result-prefixes="xs xd"
>  version="2.0">
>
>  <xsl:output method="text"/>
>
>  <xsl:template name="test-for-each">
>    <xsl:variable name="strings" select="('one', 'two', 'three', 'four')"/>
> value-of $strings=<xsl:value-of select="$strings"/>
> for $str in $strings return concat('/', $str, '/')=<xsl:sequence
> select="for $str in $strings return concat('/', $str, '/')"/>
> string-join($strings, '')=<xsl:sequence select="string-join($strings,
> '')"/>
> for-each over strings: "<xsl:for-each select="$strings">
>  <xsl:sequence select="concat('/',.,'/')"/>
> </xsl:for-each>"
>  </xsl:template>
>
> </xsl:stylesheet>
>
>
>
> Which produces this output using Saxon 9.5.1.2:
>
> value-of $strings=one two three four
> for $str in $strings return concat('/', $str, '/')=/one/ /two/ /three/
> /four/
> string-join($strings, '')=onetwothreefour
> for-each over strings: "/one/ /two/ /three/ /four/"
>
The whitespace is being added as part of the process of constructing your
final result tree from a sequence of strings. The result tree is constructed
as a document node, following the rules of 5.7.1 Constructing Complex Content

http://www.w3.org/TR/2009/PER-xslt20-20090421/#constructing-complex-content

or equivalently the rules applied by the Serializer

http://www.w3.org/TR/xslt-xquery-serialization/#serdm

The simplest way to avoid the space separation is to construct text nodes
rather than strings, which happens if you replace xsl;sequence by xsl:value-of
in

> <xsl:sequence select="concat('/',.,'/')"/>

Michael Kay
Saxonica

>
> I see that the for-each result is consistent with the flowr expression.
>
> Is my analysis correct that the only way to construct a string with no
> extra whitespace using a loop is to use string-join() as in my test case?
>
> For my DTD-generation application that would mean using the for-each loop
> to construct a sequence of strings and then using string-join on the
> sequence to avoid additional whitespace. Of course I can simply account
> for the space inserted by the concatenation and get the correct indention
> and keep my code a bit simpler.
>
> Cheers,
>
> Eliot
>
> --
> Eliot Kimber
> Senior Solutions Architect
> "Bringing Strategy, Content, and Technology Together"
> Main: 512.554.9368
> www.reallysi.com
> www.rsuitecms.com
>
>
>
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