es_ppoi.rb

class Array
  def +@
    false
  end
end

class TrueClass
  def +(o)
    to_s + o.join(',')
  end
end

class FalseClass
  def +(o)
    to_s + o.join(',')
  end
end

class String
  def +(o)
    [self, o.to_s].join
  end
end

p !+[] #=> true
p !+[]+[] #=> "true"
p !+[]+[]+![] #=> "truefalse"
p (!+[]+[]+![]).length #=> 9