Conditional sorting by QueryString values

gistfile1.xml

<xsl:variable name="sortByDate" select="umbraco.library:RequestQueryString('sort') = 'date'" />
<xsl:variable name="sortByName" select="umbraco.library:RequestQueryString('sort') = 'name'" />

<xsl:for-each select="$allTheNodesToShow">
	<xsl:sort select="@nodeName[$sortByName]" data-type="text" order="ascending" />
	<xsl:sort select="@createDate[$sortByDate]" data-type="text" order="descending" />
	
	<p>
		<xsl:value-of select="@nodeName" />, created: <xsl:value-of select="@createDate" />
	</p>
	
</xsl:for-each>