> (consp x) being true does not rule out (functionp x), which it should Exactly. That's what "punning lists" means. > It's okay if car and cdr like it. Tha

> (consp x) being true does not rule out (functionp x), which it should Exactly. That's what "punning lists" means. > It's okay if car and cdr like it. That's arguable. But the real problem is if XAR and XDR accept it. Functions, however they are implemented, should not be mutable. That way lies madness.