[lispm]

since around the early 80s it was common to write large Lisp software using class-oriented or even class-based OOP (a few used also prototype-based OOP). For example Flavors for the MIT Lisp Machine was class-based: multiple-inheritance, mixins, message sending with single dispatch, ... CLOS (the Common Lisp Object System) then changed OOP such that it better fits into Lisp: generic functions with multiple dispatch, classes, multiple-inheritance, meta object protocol, ... One of the drawbacks of those systems is that the code gets assembled at runtime (though cached) and thus to read and understand code one might need support from class/function browsers.