Provides some Design Patterns. Design Patterns were introduced mainly by the Gang of Four in their great book: Design Patterns -- Elements of Reusable Object-Oriented Software (E. Gamma et al.) We also use the book Design Patterns and Contracts (J.-M. Ézéquiel et al.)

The currently available Design Patterns are:

• Abstract Factory
  reified by FACTORY;
• Chain Of Responsibility
  reified by two classes: CHAIN_OF_RESPONSIBILITY the Chain itself, and CHAIN_HANDLER that can handle a request from the Chain;
• Command
  reified by COMMAND. Two useful subclasses are also provided that add extra features: MACRO_COMMAND that allows the execution of multiple commands at once, and UNDOABLE_COMMAND that can undo a command;
• Observer
  reified by OBSERVER that can observe an OBSERVABLE (in the lib/abilities cluster);
• Visitor
  reified by VISITOR that can visit a VISITABLE (in the lib/abilities cluster).