Avoid double-raised exception in Ruby

gistfile1.rb

module NoDoubleRaise
  def raise(*args)
    if $! && args.first != $!
      warn "There is already one exception  #{caller.first} raised"
      exit! false
    else
      super
    end
  end
end

class Object
  include NoDoubleRaise
end

begin
  raise StandardError
rescue 
  raise RuntimeError
end