XPath/XQuery fold-right function

Processes the supplied sequence from right to left, applying the supplied function repeatedly to each item in turn, together with an accumulated result value.

The effect of the function is equivalent to the following implementation in XQuery:

declare function fn:fold-right(
        $seq as item()*, 
        $zero as item()*, 
        $f as function(item(), item()*) as item()*) 
        as item()* {
  if (fn:empty($seq))
  then $zero
  else $f(fn:head($seq), fn:fold-right(fn:tail($seq), $zero, $f))
};

or its equivalent in XSLT:

<xsl:function name="fn:fold-right" as="item()*">
  <xsl:param name="seq" as="item()*"/>
  <xsl:param name="zero" as="item()*"/>
  <xsl:param name="f" as="function(item(), item()*) as item()*"/>
  <xsl:choose>
    <xsl:when test="fn:empty($seq)">
      <xsl:sequence select="$zero"/>
    </xsl:when>
    <xsl:otherwise>
      <xsl:sequence select="$f(fn:head($seq), fn:fold-right(fn:tail($seq), $zero, $f))"/>
    </xsl:otherwise>
  </xsl:choose>
</xsl:function>