file {"/tmp/b": 
    ensure => directory, checksum => mtime,
    recurse => true, purge => true, force => true,
    source => "/tmp/empty",
    mode => 0755, owner => root, group => root;
    "/tmp/empty": 
    ensure => directory,
    before => File["/tmp/b"];
    "/tmp/b/b": 
    ensure => file,
    content => "bla",
}