"David Carlisle" <david-news@d...> wrote in message 
news:46608917.2000608@d......
> Andy Fish wrote:
>> hi,
>>
>> i'm porting some xsl code from .net 1.1 to 2.0 and I have come across a 
>> transform which works in .net 1.1 and works in mxsml but does not work in 
>> .net 2.0. the stylesheet is this:
>>
>> <?xml version="1.0" encoding="UTF-8"?>
>> <xsl:stylesheet version="1.0" 
>> xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
>>  <xsl:template match="foo">
>>   <xsl:param name="param1"/>
>>   <xsl:value-of select="$param1/*"/>
>>   <xsl:apply-templates/>
>>  </xsl:template>
>> </xsl:stylesheet>
>>
>> and the input file is simply
>>
>> <foo />
>>
>> so $param1 has no value (empty string? empty node set? I'm not sure)
>>
>> with .net 2.0 I get an error message Unhandled Exception: 
>> System.Xml.XPath.XPathException: Expression must evaluate to a node-set. 
>> I'm guessing this is because the default parameter value is an empty 
>> string.
>>
>> in the real stylesheet, the parameter (if it is passed in) will be a node 
>> set. so to make sure I don't evaluate an illegal expression, I need to be 
>> able to tell whether the parameter value is an empty string (i.e. 
>> default) or a node set. how can I achieve this?
>>
>> Andy
>>
>>
>
>
> rather than have it default to an empty string, and then having to test 
> for that to avoid using the variable in path expressions, it's usually 
> simpler just to make it default to an empty node set, add
> <xsl:param name="param1" select="/.."/>
>
> David
>
>
> -- 
> http://dpcarlisle.blogspot.com

Thanks david, that's pretty much what I ended up doing

unfortunately there were quite a lot of templates with this optional 
parameter, although only one of them actually used the parameter. they are 
calling each other like this:

<xsl:template match="...">
   <xsl:param name="param1"/>
...
   <xsl:apply-templates>
      <xsl: with-param name="param1" select="$param1">  </xsl:template>
   </xsl:apply-templates/>
</xsl:template >

now, if any one of them gets called without a parameter, it passes in the 
blank parameter into the ones it calls (rather than not passing in a 
parameter - hence the default value does not apply), so this meant I had to 
put the default parameter into every one of the templates, not just the one 
that needed it.

so as well as some way of telling whether a variable contains a node set, 
string or RTF, I would also like to have an option on <xsl:call-template> 
and <xsl:apply template> that said:

if this parameter was passed in to me, pass the parameter into the next 
template,. otherwise don't pass in the parameter into the next template

Andy