> The sbcl compiler (called python) even creates the typed methods by itself, so mostly the defgeneric line is enough.
Is this some new SBCL extension you are talking about? That `defgeneric` line is an error in CLOS.
Think of defgeneric as the function signature and defmethod as the template specialization. Not sure why you say this is an error in CLOS. Looks fine to me.
That said, most implementations try to auto-infer the generic function metaobject when you use defmethod without defgeneric. SBCL raises a warning.
Good reads on the topic:
http://www.gigamonkeys.com/book/object-reorientation-generic...
(defgeneric xplusone (x)
(:method (x) (+ 1 x)))