class Psych::Visitors::YAMLTree

def visit_Hash o
  if o.class == ::Hash
    register(o, @emitter.start_mapping(nil, nil, true, Psych::Nodes::Mapping::BLOCK))
    o.each do |k,v|
      accept k
      accept v
    end
    @emitter.end_mapping
  else
    visit_hash_subclass o
  end
end