anchor.diff:    (expex-guest-filter-setter `(%= ,p ,(? (%=? v)
                                            (%=-place v)
                                            v))))
  +
  +(define-gensym-generator expex-sym e)
   
   (defun expex-add-var ()
     (funinfo-var-add *funinfo* (expex-sym)))
  
positive.code: 
  (defun expex-move-args (x)
    (with ((moved new-expr) (assoc-splice (@ #'expex-move (expex-guest-filter-arguments x))))
      (values (apply #'append moved) new-expr)))
  
  
  ;;;; EXPRESSION EXPANSION
  
negative.code: 
  (defvar *expex* nil)
  
  
  ;;;; SHARED SETTER FILTER
  
  (defun %=-make-call-to-local-function (x)
    (with-%= place value x
      (expex-body (apply #'+ (frontend `((%= ,place (apply ,value. ,(compiled-list .value)))))))))
  
  (defun expex-compiled-funcall (x)
    (alet (%=-value x)
      (? (& (cons? !)
            (| (function-expr? !.)
               (funinfo-find *funinfo* !.)))
         (%=-make-call-to-local-function x)
         (list x))))
  
  
  ;;;; GUEST CALLBACKS
  