get-setf-expansion place &optional environment
=> vars, vals, store-vars, writer-form, reader-form
Arguments and Values:
environment---an environment object.
vars, vals, store-vars, writer-form, reader-form---a setf expansion.
Determines five values constituting the setf expansion for place in environment; see Section 18.104.22.168 (Setf Expansions).
If environment is not supplied or nil, the environment is the null lexical environment.
(get-setf-expansion 'x) => NIL, NIL, (#:G0001), (SETQ X #:G0001), X
;;; This macro is like POP (defmacro xpop (place &environment env) (multiple-value-bind (dummies vals new setter getter) (get-setf-expansion place env) `(let* (,@(mapcar #'list dummies vals) (,(car new) ,getter)) (if (cdr new) (error "Can't expand this.")) (prog1 (car ,(car new)) (setq ,(car new) (cdr ,(car new))) ,setter)))) (defsetf frob (x) (value) `(setf (car ,x) ,value)) => FROB ;;; The following is an error; an error might be signaled at macro expansion time (flet ((frob (x) (cdr x))) ;Invalid (xpop (frob z)))
Affected By: None.
Exceptional Situations: None.
defsetf, define-setf-expander, setf
Any compound form is a valid place, since any compound form whose operator f has no setf expander are expanded into a call to (setf f).