Re: boolean(string(false())) is true - always?

The difference in return value between fn:boolean('false') and 
xs:boolean('false') must be in the top ten of XPath "gotcha's" -- I usually 
forget that despite having worked with XPath for more than a decade.

David

On Thu, 2 Mar 2017, Martin Honnen martin.honnen@xxxxxx wrote:

> On 02.03.2017 16:00, Michael MC<ller-Hillebrand mmh@xxxxxxxxx wrote:
>
>> <xsl:function name="dy:isFoo" as="xs:boolean">
>>     <xsl:param name="node" as="node()"/>
>>     <xsl:choose>
>>       <xsl:when test="$node[self::bar/@foo = 'x']">
>>             <xsl:value-of select="true()"/>
>>         </xsl:when>
>>         <xsl:otherwise>
>>             <xsl:value-of select="false()"/>
>>         </xsl:otherwise>
>>     </xsl:choose>
>> </xsl:function>
>> 
>> and changed that to the more elegant:
>> 
>> <xsl:function name="dy:isFoo" as="xs:boolean">
>>     <xsl:param name="node" as="node()"/>
>>     <xsl:sequence select="exists($node[self::bar/@foo = 'x'])"/>
>> </xsl:function>
>> 
>> BUT then I looked at my old code and said to myself: This could never have 
>> worked?!
>> 
>> Isn't xsl:value-of creating a text node, so in xsl:otherwise it creates 
>> 'false'. And if this is cast to boolean as the function requires, we should 
>> get true(), because the string is not empty?
>
> I think the rules lay out that the text node with 'true' or 'false' is 
> atomized to xs:untypedAtomic 'true' or 'false' and then the conversion to 
> xs:boolean is defined as a cast based on the XSD schema spec which treats 
> 'true' as the boolean value true and false as the boolean value false. So 
> what happens in language terms would be
>   'true' cast as xs:boolean
> which gives the boolean value true respectively
>   'false' cast as xs:boolean
> which gives the boolean value false and not
>   boolean('false')
> which would give the boolean value true.
>
>
> 
>

-- 
David Sewell
Manager of Digital Initiatives
The University of Virginia Press
Email: dsewell@xxxxxxxxxxxx   Tel: +1 434 924 9973
Web: http://www.upress.virginia.edu/rotunda