Using EXSLT

iceandrews · February 15th, 2011, 02:48 PM

We have a situation where we'd like to use dyn:evaluate() from the EXSLT extention function library, but we can't seem to get anything to work. We are using Saxon 8.9 in house, but in order to remain processor agnostic and portable, we wanted didn't want to use the saxon:evaluate() function.

We've reviewed all the documentation on the exslt.org website surround th dyn:evaluate() function, but there's no third party implementations of this function to use. (plus some of the zip packages are corrupt in the dynamic area of the EXSLT website.)

As a last resort, we can use saxon:evaluate(), but that will cause additional work for us down the road. We planned on using this transformation as part of a stand alone application that's being built on .NET as well, and obviously if we can make processor independent, it would integrate seamlessly there.

Any suggestions on how to get dyn:evaluate to work, or is there another alternative that would need those basics needs.

Thanks!

samjudson · February 15th, 2011, 04:24 PM

There are various things in XSLT which might help, but none is a easy solution.

Firstly, Saxon is available in .Net as well as Java, so you might consider restricting your targets to Saxon only. This would also give you the ability to use XSLT 2.0, which is a big improvement over XSLT 1.0 If this really isn't an option then you will need to code against this.

One way would be to write your own extension method in .Net, and then write some simple XSLT, using the function-available() function to determine if one of the three options is available.

Code:

<xsl:choose>
<xsl:when test="function-available('saxon:evaluate')">
  <xsl:value-of select="saxon:evaluate($xpath)"/>
</xsl:when>
<xsl:when test="function-available('dyn:evaluate')">
  <xsl:value-of select="dyn:evaluate($xpath)"/>
</xsl:when>
<xsl:when test="function-available('myext:evaluate')">
  <xsl:value-of select="dyn:evaluate($xpath)"/>
</xsl:when>
<xsl:otherwise>
  <xsl:message terminate="yes">Unsupported XSLT processor.</xsl:message>
</xsl:otherwise>
</xsl:when>

Basic implementations of evaluate in C# can be found here: http://stackoverflow.com/questions/2...piledtransform. Others may exist, I didn't look for long.

Another final option is to explain how you want to use the evaluate() function, and maybe there is actually a way to do this without using evaluate() at all.

mhkay · February 15th, 2011, 05:01 PM

The reason Saxon doesn't implement dyn:evaluate is its insistence on making the variables from the expression context available for use within the expression - this means that it's impossible to optimize variables at compile time because you don't know statically where all the references are; this was too high a price to pay. So saxon:evaluate has a mechanism for explicit passing of parameters instead.

If you're not using variables or dependent on other parts of the context, then it's easy to write an xsl:function called dyn:evaluate that wraps a call on saxon:evaluate; or you can write code that calls either saxon:evaluate() or dyn:evaluate() based on the result of function-available().