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RE: [xsl] XPath 2.0: Problems with the two boolean constants true and false


Subject: RE: [xsl] XPath 2.0: Problems with the two boolean constants true and false
From: "Michael Kay" <mhk@xxxxxxxxx>
Date: Mon, 6 Oct 2003 15:16:32 +0100

Yes, this is a bug (or at any rate, it's a XSLT 2.0 feature that I
haven't implemented yet but that isn't on my published list of features
that I haven't implemented yet - there are probably quite a few of
these, and for the time being I am treating them as bugs in the
documentation rather than bugs in the code).

What's actually happening is that no type checking or conversion of
parameters is being done on the apply-templates call, but the code that
references the parameters is assuming they are of the declared type. The
net result is that the "A and B" is taking the effective boolean value
of the value actually passed in the parameters, and the effective
boolean value of the string 'false' is true.

Michael Kay 

> -----Original Message-----
> From: owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx 
> [mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Dimitre Novatchev
> Sent: 06 October 2003 11:15
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: RE: [xsl] XPath 2.0: Problems with the two boolean 
> constants true and false 
> 
> 
> > >  
> > >  I see two problems with the boolean constants true and false:
> > >  
> > >    1. They cannot be used in an XPath expression -- cannot be
> > >  distinguished from child::true and child::false
> > 
> > There are no constants "true" and "false". As in XPath 1.0, 
> the truth 
> > values are represented by the function calls true() and false(). No 
> > change here from 1.0.
> > >  
> > >    2. boolean('false') is true.  This is especially confusing
> > >  and may be the source of many programmers' headaches.
> > 
> > Again, no change here from 1.0. I haven't seen this cause 
> much problem 
> > in practice, though the introduction of xs:boolean alongside 
> > [fn:]boolean may be confusing. xs:boolean() uses the schema 
> rules: '0' 
> > and 'false' give false, '1' and 'true' give true, any other 
> string is 
> > an error.
> > >  
> > >  Because of these I chose in my code to use functions
> > >  returning xs:integer (0 and 1) and for templates to write 
> > >  code like the following:
> > >  
> > >    <xsl:template name="And" 
> match="*[namespace-uri()='allTrue-And']">
> > >      <xsl:param name="arg1"/>
> > >      <xsl:param name="arg2"/>
> > >           <xsl:value-of select="number(number($arg1) and
> > >  number($arg2))"/>
> > >    </xsl:template>
> > >  
> > >  Am I wrong? Is there a way to overcome the above problems?
> > >  
> > 
> > It seems odd to me to use numbers instead of booleans because you 
> > don't like the string-to-boolean conversions. If you don't like the 
> > string-to-boolean conversions just don't use them; you can 
> still use 
> > booleans!
> 
> My confusion is due to the following:
> 
> This transformation:
> 
> <xsl:stylesheet version="2.0" 
> xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
> xmlns:xs="http://www.w3.org/2001/XMLSchema"
> xmlns:f="http://fxsl.sf.net/"
> xmlns:test="my:test"
>   exclude-result-prefixes="f xs test"
> >
>   <xsl:output omit-xml-declaration="yes"/>
>   
>   <xsl:template match="/">
>    <xsl:apply-templates select="document('')/*/test:*[1]">
>      <xsl:with-param name="arg1" select="'false'"/>
>      <xsl:with-param name="arg2" select="1"/>
>    </xsl:apply-templates>
>   </xsl:template>
>   
>   <test:test/>
>   <xsl:template name="And" match="test:*">
>     <xsl:param name="arg1" as="xs:boolean"/>
>     <xsl:param name="arg2"  as="xs:boolean"/>
>          <xsl:value-of 
>          select="xs:boolean(xs:boolean($arg1) and 
> xs:boolean($arg2))"/>
>   </xsl:template>
> 
> </xsl:stylesheet>
> 
> Produces:
> 
>   true
> 
> 
> But 
> 
>       <xsl:value-of 
>          select="xs:boolean(xs:boolean('false') and xs:boolean(1))"/>
> 
> produces:
> 
>    false
> 
> 
> Is this a bug in Saxon 7.7?
> 
> 
> 
> 
> 
> 
> =====
> Cheers,
> 
> Dimitre Novatchev.
> http://fxsl.sourceforge.net/ -- the home of FXSL
> 
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