class PDF::Reader::Explore

def ls (entry = nil)
  parts = @pwd.split('/')
  obj   = @root
  parts.shift if parts[0] == ""
  parts.push(entry) if entry
  parts.each do |p|
    case obj
    when Hash
      unless obj.has_key?(p)
        puts "invalid path at #{p}"
        return
      end
      obj = obj[p]
    when Array
      obj = obj[p.to_i]
    end
    obj = @xref.object(obj)
  end
  output_parent(obj)
  "#{@pwd}: #{obj.class}"
end