class puphpet_drush (
  $drush,
  $php,
  $hhvm
) {

  $version  = $drush['version'] != undef
  $engine   = (array_true($php, 'install') or array_true($hhvm, 'install'))
  $composer = (array_true($php, 'composer') or array_true($hhvm, 'composer'))

  # Requires either PHP or HHVM, and Composer
  if $version and $engine and $composer {
    class { 'puphpet::php::drush':
      version => $drush['version']
    }
  }

}