maybe.rb

class None
  def map(&block)
    self
  end

  def flat_map(&block)
    self
  end

  def value
    raise "Value not present"
  end
end

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

  def map(&block)
    val = yield @value
    Some.new(val)
  end

  def flat_map(&block)
    yield @value
  end

  def value
    @value
  end
end

Some.new(2).flat_map{|x| Some.new(1).map {|y| x + y}} # => Some(3)

Some.new(2).flat_map{|x| None.map {|y| x + y}} # => None