(defvar *all-quiet* nil) =>  *ALL-QUIET*
(defvar *saved-warnings* '()) =>  *SAVED-WARNINGS*
(defun quiet-warning-handler (c)
  (when *all-quiet*
    (let ((r (find-restart 'muffle-warning c)))
      (when r 
        (push c *saved-warnings*)
        (invoke-restart r)))))
=>  CUSTOM-WARNING-HANDLER
(defmacro with-quiet-warnings (&body forms)
  `(let ((*all-quiet* t)
         (*saved-warnings* '()))
     (handler-bind ((warning #'quiet-warning-handler))
       ,@forms
       *saved-warnings*)))
=>  WITH-QUIET-WARNINGS
(setq saved
  (with-quiet-warnings
    (warn "Situation #1.")
    (let ((*all-quiet* nil))
      (warn "Situation #2."))
    (warn "Situation #3.")))
>>  Warning: Situation #2.
=>  (#<SIMPLE-WARNING 42744421> #<SIMPLE-WARNING 42744365>)
(dolist (s saved) (format t "~&~A~%" s))
>>  Situation #3.
>>  Situation #1.
=>  NIL