Trying to detect os in vagrantfile

VagrantfileOSDetection

module OS
  def OS.windows?
        (/cygwin|mswin|mingw|bccwin|wince|emx/ =~ RUBY_PLATFORM) != nil
  end
  def OS.mac?
    (/darwin/ =~ RUBY_PLATFORM) != nil
  end
  def OS.unix?
    !OS.windows?
  end
  def OS.linux?
    OS.unix? and not OS.mac?
  end
end

$usenfssyncedfolders= OS.mac? true:false
$puppetsftype= OS.mac? 'nfs':'vboxsf'


==== ERror output ===
Line number: 50
Message: TypeError: OS is not a module