case.pp

case $facts['os']['family'] {
  'debian': {
    $x11_pkg = 'xorg'
    $ssh_pkg = 'ssh'
  }
  'solaris': {
    $x11_pkg = 'x11/server/xorg'
    $ssh_pkg = 'network/ssh'
  }
  'windows': {
    $x11_pkg = 'xming'
    $ssh_pkg = 'putty'
  }
  'redhat': {
    $x11_pkg = 'xorg-x11-server-Xorg'
    $ssh_pkg = ['openssh', 'openssh-clients', 'openssh-server']
  }
  default: {
      fail("Operating system family ${::osfamily} is not supported.")
  }
}

new_facts.pp

class foo {

  file { '/tmp/ipaddr':
    ensure => file,
    content => "The IP is: ${facts['networking']['interfaces']['eth0']['ip']}",
  }
}

refs.pp

$packages = ['foo-util', 'rsyslog']

package { $packages:
  ensure => installed,
}  

service { 'syslog':
  ensure  => running,
  enable  => true,
  require => [ File['/etc/rsyslog.conf'], Package[$packages], User['tom','services-user'] ],
}

$arr = [1, 2, [3 ,4, [5, 6]]]