values-from-bag function

Is there a standard XACML function for getting the attribute values from
a bag?

Say I want to add all the values of an attribute.  I can't do:

<Apply FunctionId="...integer-add">
  <AttributeDesignator AttributeId="foo" DataType="integer"/>
</Apply>

I need something like:

<Apply FunctionId="...integer-add">
  <Apply FunctionId="...integer-values-from-bag">
    <AttributeDesignator AttributeId="foo" DataType="integer"/>
  </Apply>
</Apply>

Regards,
--Paul