Does anyone actually use CLOS? It's always held up as this great example of language extensibility, but my impression is that since it's not part of the core language Lisp folk tend to create their own abstractions instead.
Beat by a few minutes again, as piokuc says, it's in the standard. But even so, it may still be implemented as "just a library" in some CL implementations. That's the beauty of the language, it's so versatile you can extend it within itself, and it really feels like a language extension and not like you're accessing yet another API. If someone wanted a different object system, they could produce it within CL giving totally different OO semantics.
