coin.rb

def Coin █ Coin.new █ end

class Coin
  def initialize &block
    toss &block if block_given?
  end
  
  def toss &block
    @toss = rand.round.zero?
    yield
  end
  
  on :heads {|string| puts string } if @toss
  on :tails {|string| puts string } unless @toss
end