idiomatic alternative to choose -> test -> value-of (XSLT 1.0) - xslt

Question

In the work I do I seem to see a lot of code liek this..
<xsl:choose>
<xsl:when test="long_xpath_to_optional/#value1">
<xsl:value-of select="long_xpath_to_optional/#value"/>
</xsl:when>
<xsl:when test="another_long_xpath_to_optional/#value">
<xsl:value-of select="another_long_xpath_to_optional/#value"/>
</xsl:when>
<etc>
</etc>
<otherwise>
<xsl:value-of select="default_long_xpath_to_value"/>
</otherwise>
</xsl:choose>
its very long and very repetitive.
When I'm were working in some other (psuedo) language I would go
let values = concat(list(long_xpath_to_optional_value),list(another_long_xpath_to_optional_value))
let answer = tryhead(values,default_long_xpath_to_value)
i.e. create a list of values in priority order, and then take the head.
I only evaluate each path once
how would you do something similar in XSLT 1.0 (we can use node-sets).

Answer 1

I was wondering if you can create a node-set somehow
You can - but it's not going to be any shorter:
<xsl:variable name="values">
<xsl:apply-templates select="long_xpath_to_optional/#value" mode="values"/>
<xsl:apply-templates select="another_long_xpath_to_optional/#value" mode="values"/>
<xsl:apply-templates select="default_long_xpath_to_value/#value" mode="values"/>
</xsl:variable>
<xsl:value-of select="exsl:node-set($values)/value[1]" xmlns:exsl="http://exslt.org/common"/>
and then:
<xsl:template match="#value" mode="values">
<value>
<xsl:value-of select="."/>
</value>
</xsl:template>
But at least the repetition is eliminated.
Alternatively, you could do:
<xsl:template match="#value" mode="values">
<xsl:value-of select="."/>
<xsl:text>|</xsl:text>
</xsl:template>
and then:
<xsl:value-of select="substring-before($values, '|')"/>

Answer 2

To use variables you write
<xsl:variable name="value1" select="long_xpath_to_optional/#value1"/>
<xsl:variable name="value2" select="another_long_xpath_to_optional/#value"/>
<xsl:variable name="value3" select="default_long_xpath_to_value"/>
and then in XPath 2 or 3 all you would need is ($value1, $value2, $value3)[1] or head(($value1, $value2, $value3)) but in XSLT 1 with XPath 1 all you can write as a single expression is ($value1 | $value2 | $value3)[1] which sorts in document order so unless the document order is the same as your test order this wouldn't work to check the values; rather you would need to maintain the
<xsl:choose>
<xsl:when test="$value1">
<xsl:value-of select="$value1"/>
</xsl:when>
<xsl:when test="$value2">
<xsl:value-of select="$value2"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$value3"/>
</xsl:otherwise>
</xsl:choose>
Of course in XPath 2 you wouldn't really need the variables and could use (long_xpath_to_optional/#value1, another_long_xpath_to_optional/#value, default_long_xpath_to_value)[1] as well directly.