dyn:evaluate() inside <xsl:for-each> yields strange results - xslt

Question

Consider the following XSL transformation:
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:exsl="http://exslt.org/common"
xmlns:dyn="http://exslt.org/dynamic"
extension-element-prefixes="dyn">
<xsl:variable name="_raw">
<test>1</test>
<test>2</test>
</xsl:variable>
<xsl:variable name="list" select="exsl:node-set($_raw)"/>
<xsl:template match="/">
<result>
<xsl:for-each select="$list/test">
<loop>
<xsl:value-of select="dyn:evaluate('exsl:node-set($list)/test')"/>
</loop>
</xsl:for-each>
</result>
</xsl:template>
</xsl:transform>
Executing this on any input gives:
<?xml version="1.0" encoding="UTF-8"?>
<result xmlns:exsl="http://exslt.org/common">
<loop>1</loop>
<loop/>
</result>
What I don't understand is:
The esxl:note-set() inside dyn:evaluate() is necessary if I want to reference $list in the XPath string. Otherwise, the first <loop> is also empty. Why? $list is already a node set.
It's exactly the same code executed twice. Why does it yield no result the second time?
This works if I don't take the values from $list, but from the XML input instead. Where's the difference?
If I remove the <xsl:for-each>, dyn:evaluate() works without the exsl:node-set() in it. Why? There's no reference to the context in the expression that is evaluated, it shouldn't make a difference.
My XSLT processor is Xalan 2.7.2.

Answer 1

I believe what you want to do is:
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:exsl="http://exslt.org/common"
xmlns:dyn="http://exslt.org/dynamic"
extension-element-prefixes="exsl dyn">
<xsl:variable name="_raw">
<test>1</test>
<test>2</test>
</xsl:variable>
<xsl:variable name="list" select="exsl:node-set($_raw)"/>
<xsl:template match="/">
<result>
<xsl:for-each select="$list/test">
<loop>
<xsl:value-of select="dyn:evaluate(.)"/>
</loop>
</xsl:for-each>
</result>
</xsl:template>
</xsl:transform>
Which will result in:
<?xml version="1.0" encoding="UTF-8"?>
<result><loop>1</loop><loop>2</loop></result>
Edit:
I am still not sure what you are after here, but let me point out a few details:
It's exactly the same code executed twice. Why does it yield no result
the second time?
That may be a bug in Xalan. If you run your code with libxslt, the result will be:
<?xml version="1.0"?>
<result xmlns:exsl="http://exslt.org/common"><loop>1</loop><loop>1</loop></result>
The esxl:note-set() inside dyn:evaluate() is necessary if I want to
reference $list in the XPath string. Otherwise, the first is
also empty. Why? $list is already a node set.
I don't think it's necessary. Or perhaps I don't understand what it's necessary for. In any case, changing this:
<loop>
<xsl:value-of select="dyn:evaluate('exsl:node-set($list)/test')"/>
</loop>
to:
<loop>
<xsl:value-of select="dyn:evaluate('$list/test')"/>
</loop>
will result in:
<?xml version="1.0" encoding="UTF-8"?>
<result xmlns:exsl="http://exslt.org/common"><loop>1</loop><loop>1</loop></result>
and this time the result is same for both Xalan and libxslt.