anchor.diff:  ;;;; MOVING ARGUMENTS
   
   (defun expex-filter-and-move-args (x)
  +  (expex-import-variables x)
     (with ((moved new-expr) (assoc-splice (filter #'expex-move (expex-guest-filter-arguments x))))
       (values (apply #'+ moved) new-expr)))
   
  
positive.code:     (values moved `((%%go-nil ,.x. ,@new-expr)))))
  
  (defun expex-expr-%=-0 (place val)
    (expex-import-variables place val)
    (with ((moved new-expr) (expex-move-args (list val)))
      (values moved (expex-make-%= place new-expr.))))
  
  
negative.code:   (!? (expex-variable-name x)
        (add-wanted-variable !)))
  
  (defun expex-import-variables (val)
    (& *expex-import?*
       (import-variables?)
       (adolist (.val)
         (expex-import-variable !))))
  
  
  ;;;; GUEST CALLBACKS
  