OOP has problems adding existing functionality to new types. Interfaces are a go at the problem but they fall short for several reasons. Clojure's protocols are

OOP has problems adding existing functionality to new types. Interfaces are a go at the problem but they fall short for several reasons. Clojure's protocols are a better solution (as far as I can tell). Clojure also provides multi-methods and hierarchies for more sophisticated function dispatch. Their use and the reasoning behind their design is well documented on Clojure's website.