This is just a repository of an Advanced Calculator application written in Eiffel that does not support Floats, Power, and Trigonometry but supports Set operations through multiple software design patterns (e.g., Singleton, Composite, Command, Observer, Lazy Initialization, and Visitor).
Furthermore, since a fully general expression tree has been designed and implemented, the application can support other notations (i.e., infix and postfix) with minimal change.