[User23]

Very interesting comment!

To clarify, as you know CLOS isn’t the CL type system. I was particularly thinking about things like fixnum arithmetic.

The CMUCL and SBCL manual sections on code generation discuss this and it can be verified with DISASSEMBLE.

[aidenn0]

Missed your reply when it happened. Note that you cannot specialize a method on "fixnum" since it's not a class (though you can on "number" or "integer" since they are classes).