Newer versions of Facter support structured facts which can be arrays or hashes.
These facts are available in Puppet 3.3+, but aren't enabled by default. You can
enable structured facts by setting the stringify_facts option to false in
puppet.conf for master/agent/standalone nodes.
Until structured facts are the default, facts like the FQDN of a node need to be retrieved through the legacy fact interface:
$::fqdn
The structured facts interface nests the FQDN inside the $::networking hash along
with other networking facts.
https://docs.puppet.com/facter/3.1/fact_overview.html#writing-structured-facts