A pattern enforcing compiler™ (PEC™) allows classes to be marked as having a given design pattern, e.g. Singleton. The PEC™ then checks that the marked class conforms to the pattern and issues an error message if it does not, thus the pattern checking is much like type checking. The PECs™ downloadable from this site require no new syntax and therefore they can be used with existing: editors, IDEs, pretty printers, etc. The downloadable PECs™ are extensible and therefore as well as using the supplied patterns a programmer can write their own patterns and have the PEC™ enforce these.