RE: Boolean Short Curcuit

Well, this could happen because ancestor::page:error/@name exists, but
doesn't match the name of any document($form-uri)/form/field...

The XPath 2.0 spec says that with an expression (A and B), you've got no
guarantee that B won't be called if A is false. That's different from 1.0,
and it's designed to allow optimization of joins. In fact Saxon will
generally evaluate A first, except in some join predicates: for example

for $i in 1 to 10
for $j in 1 to 10
where ($j gt 5 and $i gt 3)
return x

might be rewritten as

for $i in 1 to 10[. gt 3]
for $j in 1 to 10[. gt 5]
return x

So the message is: you shouldn't be relying on order of evaluation; but in
this case, I don't think that's likely to be the cause of the problem.

The way to avoid reliance on order of evaluation is to rewrite (A and B) as
(if (A) then B else false()). 

Michael Kay
http://www.saxonica.com/

> -----Original Message-----
> From: Alan [mailto:alan-xsl-list@xxxxxxxxx] 
> Sent: 23 September 2005 09:51
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject:  Boolean Short Curcuit
> 
> In Saxon 8.(4|5).
> 
> I'm calling this function.
> 
> <xsl:function name="page:field" as="element()">
>   <xsl:param name="name" as="xs:string"/>
>   <xsl:sequence select="document($form-uri)/form/field[name = 
> $name][1]"/>
> </xsl:function>
> 
> During this template match. Note that I'm performing a test to see
> if the parameter exists. I expect that when it doesn't exist, the
> function part of the test will not be called.
> 
> <xsl:template
>     match="page:message[ancestor::page:error[@name]
>         and page:field(ancestor::page:error/@name)/error]"
>     mode="page:page">
> <page:message><xsl:value-of
>     
> select="page:field(ancestor::page:error/@name)/error"/></page:message>
> </xsl:template>
> 
> But it appears to be getting called.
> 
> Recoverable error of :
>   XPTY0004: An error occurred matching pattern
>   {page:message[ancestor::page:error[@name] and
>         page:field(ancestor::page:error/@name)/error]}
>   : An empty sequence is not allowed as the result of 
> function page:field()
> 
> I can provide more context if necessary. I tried if/else statements
> in the call to page:field, but that still produced the error.
> 
> Thanks.
> 
> --
> Alan Gutierrez - alan@xxxxxxxxx
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