check if a variable has been declared.

iceandrews · June 10th, 2009, 03:39 PM

Is there a method that allows you to check to see if a variable/parameter has been declared before calling it? Obviously calling an undeclared variable/parameter results in an error.

Logically speaking I'm looking for something along these lines.

Code:

 
<xsl:choose>
     <xsl:when test="$Test"/>
     <xsl:otherwise/>
</xsl:choose>

A parallel function that I have in mind is the "doc-available ()" function. Using this I can continue processing even if the document URI doesn't resolve. I'd like a similar functionality but with a variable. (Or perhaps even a <xsl:call-template/>. Check if there is a named template that exists with that name before calling it.)

I'm using XSLT 2.0 & Saxon-9SA

Thank you much!

mhkay · June 10th, 2009, 03:46 PM

No, there's no such method. (Does any other language have such a thing? Perhaps some purely interpreted shell languages.) Whether or not a variable is declared is a compile-time condition entirely under the stylesheet author's control, which is a big difference from doc-available() which tests a run-time condition outside the stylesheet's control. (And different from function-available(), which tests a compile-time condition outside the programmer's control).

iceandrews · June 10th, 2009, 04:04 PM

That's what I figured.

The issue arose when using the <saxon:call-template name="{$tname}"/> instruction. We're dynamically creating a few templates on an external source, out of our control.

But not ALL the named templates are constructed dynamically. Occasionally there's an error when a template is called with no matching named pair. So it would've been a simple way to check for existence inside the stylesheet itself before deciding which templates to call. (Apart from examining the input documents)

Just to be clear, you can't use "element-available()" to check for a NAMED called template instruction rather than the generic one.

Thanks!

mhkay · June 10th, 2009, 04:09 PM

You might be better off creating match-templates dynamically rather than named templates. You can create them to match elements in some namespace that doesn't exist in your source, and then invoke them by apply-templates to some dummy element created for the purpose. There's then a clean fallback if no template rule matches.

samjudson · June 10th, 2009, 04:19 PM

You could load the external template using document() and then check if it contains the named template manually of course?

<xsl:if test="document('template.xsl')//xsl:template[@name=$Test]">
...