class Test
  def initialize(@step : Hash(Symbol, String) | Nil, @tree : String)
  end

  def initialize
    @step = {} of Symbol => String
    @tree = ""
  end

  YAML.mapping({
    :step => {
      type: Hash(Symbol, String),
      nilable: true
    },
    :tree => String
  })

  def to_yaml(yaml : YAML::Generator)
    hash = {
    {% for key, value in @type.instance_variables %}
      {{key}}: %var{key},
    {% end %} # expecting token "=>" not "NEWLINE"
    } of String => YAML::Any
  end
end