Plain text in Ruby

plain_text.rb

class PlainText
  class << self
    def write(&block)
      return unless block_given?

      @previous_line = current_line
      @line = []
      @paragraph = []

      undefine_methods

      instance_eval(&block)
      (@paragraph << @line.join(' ')).join("\n").strip
    end

    def method_missing(name, *args, &block)
      if current_line == @previous_line
        @line.unshift(name)
      elsif current_line > @previous_line
        @paragraph << @line.join(' ')
        @line = [name.to_s]
        @previous_line = current_line
      else
        super
      end
    end

    private

    def current_line
      caller[1].split(':')[1].to_i
    end

    def undefine_methods
      untouchable_methods = [
        :object_id,
        :__send__,
        :instance_eval,
        :method_missing
      ]

      public_methods.each do |method|
        unless untouchable_methods.include?(method)
          instance_eval("undef :#{method}")
        end
      end
    end

  end
end

# Example plain text
text = PlainText.write do
  You can only use exclamation marks AND question marks as punctuation!
  Keywords that are used In Ruby have to be rewritten with uppercased letters like AND Or OR Or In!
  So you can shout a lot! Or you can ask a lot of questions?
  Even method names like public_methods Or send can be used In the text!
  Because we undefined them!
end

puts text