tangus

    lst.lazy.grep(Array).flat_map(&:itself).sum

    lst = [[1, 2], :dud, [3, 4], [5, 6]]
    lst.grep(Array).flatten.sum
    => 21

  def partition (arr)
    yes = []
    no = []
    arr.each do |elt|
      if yield elt
        yes << elt
      else
        no << elt
      end
    end
    [yes, no]
  end