The future parser is a feature in Puppet 3.8 designed to provide functionally identical to the Puppet language in Puppet 4.0.
You can use these options to enable the future parser for the "from" catalog, the "to" catalog, or both catalogs:
--parser-from futurewill enable the future parser for the "from" catalog--parser-to futurewill enable the future parser for the "to" catalog--parser futurewill enable the future parser for both the "from" catalog and the "to" catalog
Note that you can also enable the future parser by creating a file named environment.conf in the base directory of your Puppet checkout. When octocatalog-diff computes the catalog from this directory, Puppet will read this file and act upon it accordingly.