class REXML::XPathParser

def evaluate_predicate(expression, nodesets)
  enter(:predicate, expression, nodesets) if @debug
  new_nodeset_count = 0
  new_nodesets = nodesets.collect do |nodeset|
    new_nodeset = []
    subcontext = { :size => nodeset.size }
    nodeset.each_with_index do |node, index|
      if node.is_a?(XPathNode)
        subcontext[:node] = node.raw_node
        subcontext[:index] = node.position
      else
        subcontext[:node] = node
        subcontext[:index] = index + 1
      end
      result = expr(expression.dclone, [node], subcontext)
      trace(:predicate_evaluate, expression, node, subcontext, result) if @debug
      result = result[0] if result.kind_of? Array and result.length == 1
      if result.kind_of? Numeric
        if result == node.position
          new_nodeset_count += 1
          new_nodeset << XPathNode.new(node, position: new_nodeset_count)
        end
      elsif result.instance_of? Array
        if result.size > 0 and result.inject(false) {|k,s| s or k}
          if result.size > 0
            new_nodeset_count += 1
            new_nodeset << XPathNode.new(node, position: new_nodeset_count)
          end
        end
      else
        if result
          new_nodeset_count += 1
          new_nodeset << XPathNode.new(node, position: new_nodeset_count)
        end
      end
    end
    new_nodeset
  end
  new_nodesets
ensure
  leave(:predicate, new_nodesets) if @debug
end