Referencing hash values within module

nvidia_driver_install.pp

# https://groups.google.com/forum/#!topic/puppet-users/1ol4b1euTiE
class nvidia::driver_install (
  include stdlib 
  
  $model_hash = {
      009d => "$::nvidia::params::quadro_fx_4500_driver",
      06dc => "$::nvidia::params::quadro_6000_driver",
      06d9 => "$::nvidia::params::quadro_5000_driver",
      11ba => "$::nvidia::params::quadro_K5000_driver",
      17c2 => "$::nvidia::params::gtx_titanx_driver",
      17f0 =>  "$::nvidia::params::quadro_M6000_driver",
  }
  
) inherits nvidia::params {

  if ($::is_virtual == true) and ($::class == 'server') {
    notify { 'This is a virtual machine and the nvidia driver doesn\'t get intalled' : 
  }
    # only run nvidia installer if the machine is a workstation and the driver is not already installed
  } elsif ($::class == 'workstation') and ($::nvidia_installed == 'false') {
      if (!empty($model_hash[$::video_card_id])) {
        notify { "Installing driver for ($model_hash[key])" : }
        exec { 'kdm-stop' :
          command => '/usr/bin/service kdm stop' ,
          unless  => '/usr/bin/service kdm status | grep -i "stop" ' ,
          before  => Exec['nvidia-driver-install'] ,
        }
        # install nvidia driver
        exec { 'nvidia-driver-install' :
          command => "/usr/src/($model_hash[value]).run -s -X -N --force-tls=new --no-x-check --no-cc-version-check" ,
          require => File["/usr/src/($model_hash[value]).run"] ,
          notify  => Exec['reboot_after_nvidia'] ,
        }
        # reboot after nvidia install
        exec { 'reboot_after_nvidia' :
          command     => "/sbin/reboot" ,
          refreshonly => true ,
        }
      } else {
        warning("Could not lookup video_card_id (${::video_card_id}) to driver name")
      }
  }
}