(defun foo (a) (+ a 1)) is a s-expression. For evaluation Lisp expands the DEFUN macro then and this returns a new s-expression. Which then is evaluated. > So

(defun foo (a) (+ a 1)) is a s-expression. For evaluation Lisp expands the DEFUN macro then and this returns a new s-expression. Which then is evaluated. > So are these "specials" being parsed by a grammar? Every special operator (and there are only a limited amount and this is not user extensible) needs to be implemented by a Lisp source interpreter or a Lisp compiler. Other tools like a code walker also need to know the syntax.