class IRB::SLex::Node

def search(chrs, opt = nil)
  return self if chrs.empty?
  ch = chrs.shift
  if node = @Tree[ch]
    node.search(chrs, opt)
  else
    if opt
      chrs.unshift ch
      self.create_subnode(chrs)
    else
      raise "node nothing"
    end
  end
end