result.rb

module Result
  class << self
    def not_nil(value)
      if value.nil?
        None
      else
        Some.new(value)
      end
    end

    def some(value)
      Some.new(value)
    end

    def none
      None
    end
  end

  None = Object.new

  class << None
    def flat_map
      self
    end

    def map
      self
    end

    def or_else
      yield
    end

    def get_or_else
      yield
    end

    def for_each
    end
  end

  class Some
    def initialize(value)
      @value = value
    end

    def flat_map
      yield @value
    end

    def map
      Some.new(yield @value)
    end

    def or_else
      self
    end

    def get_or_else
      @value
    end

    def for_each(&block)
      flat_map(&block)
      nil
    end
  end

  private_constant :None, :Some
end