is arity-based "polymorphism" safe to use in xsl 2.0

since the built-in position() function is awkward in some cases, i wrote
a little helper positionInContext($haystack, $needle) that will tell you
the position of $needle within $haystack.

<!-- this is the "internal" function: -->
<xsl:function name="r2c:positionInContext" as="xs:integer">
  <xsl:param name="haystack" as="node()*"/>
  <xsl:param name="needle" as="node()"/>
  <xsl:param name="position" as="xs:integer"/>
  <xsl:choose>
    <!-- found? -->
    <xsl:when test="$needle is $haystack[1]">
      <xsl:sequence select="$position"/>
    </xsl:when>
    <!-- haystack empty? -->
    <xsl:when test="not($haystack[2])">
      <xsl:sequence select="0"/>
    </xsl:when>
    <!-- try next node in haystack: -->
    <xsl:otherwise>
      <xsl:sequence select="
        r2c:positionInContext(
          $haystack[position() gt 1],
          $needle,
          $position + 1)"
      />
    </xsl:otherwise>
  </xsl:choose>
</xsl:function>

<!-- this is the "API" function: -->
<xsl:function name="r2c:positionInContext" as="xs:integer">
  <xsl:param name="haystack" as="node()*"/>
  <xsl:param name="needle" as="node()"/>
  <xsl:sequence select="r2c:positionInContext($haystack, $needle, 1)"/>
</xsl:function>

i know that xsl functions are not polymorphic as to datatypes, but the
spec says they are wrt number of arguments. i wonder: is this sort of
programming style ok, or am i stretching the spec? saxon processes it
just fine.

--
jC6rn nettingsmeier

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