nyan.rb

# coding: utf-8

module Nyanrize
  refine String do
    def to_s
      "にゃ〜ん！"
    end
  end
end

class Nyan
  using Nyanrize

  def nyan
    "nyan".to_s
  end

  def context
    Proc.new { "nyan".to_s }
  end

  def eval(&block)
    instance_eval &block
  end
end

nyan = Nyan.new

puts "nyan".to_s
#=> nyan

puts nyan.nyan
#=> にゃ〜ん！

puts nyan.context.()
#=> にゃ〜ん！

puts nyan.eval { "nyan".to_s }
#=> nyan