class Raabro::Tree

def lookup_error(stack=[])
nt "le(): "; Raabro.pp(self, colors: true)
  return nil if @result != 0
  return [ self, stack ] if @children.empty?
  @children.each { |c|
    es = c.lookup_error(stack.dup.push(self.name))
    return es if es }
  nil
end