exslt func problem

[Andy Chambers]

I think I'm being stupid here so I'd be grateful if someone were to help me out.

I'm trying to write the simplest function that could possibly work,
and it doesn't. When I run this, against any input, I get
"javax.xml.transform.TransformerException:
javax.xml.transform.TransformerException: Instance method call to
method func requires an Object instance as first argument".

Here's the stylesheet...

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                xmlns:my="http://formedix.com/functions";
                xmlns:ex="http://exslt.org/common";
                xmlns:func="http://exslt.org/func";
                xmlns:dyn="http://exslt.org/dynamic";
                extension-element-prefixes="ex func dyn">

  <func:function name="my:func">
    <func:result select="'hi'"/>
  </func:function>

  <xsl:template match="/">
    <test-output>
      before
      <xsl:value-of select="my:func()"/>
      after
    </test-output>
  </xsl:template>

</xsl:stylesheet>               

--
Andy