class bootstrap {

class yum {

package { [ "yum-priorities", "yum-fastestmirror"]:
ensure => installed,
before => File["/etc/yum/yum.conf"];
}

file { "/etc/yum/":
ensure => directory,
owner => "root",
group => "root",
purge => true,
mode => 755,
}

(...)

}

class packages inherits yum {

package {[
"net-snmp",
"net-snmp-utils",
(...)