anchor.diff:  
   (defvar *in-let*)
   (defvar *orig-form*)
  -(defvar *symbol-macros*)
   
   (defmacro nonlocal (&body body)
     `(progn ,@body))
  
positive.code:                          (unless exp?
                             (return (values form exps?))))))
                 (wrap-symbol-macros (form)
                   (if (null *symbol-macros*) form
                       `(symbol-macrolet ,*symbol-macros*
                          ,form)))
                 (step-expansion (form)
                   (multiple-value-bind (exp exp?)
  
negative.code:                  "Shorthand for recursing on an implicit `progn'."
                   `(progn ,@(mapcar #'expand-partially body)))
                 (symbol-macro (name exp)
                   (push (list name exp) symbol-macros))
                 (shadow-symbol-macro (name)
                   ;; Note that this removed /all/ instances.
                   (removef symbol-macros name :key #'car))
                 (expansion-done (form)
                   (setf form (wrap-symbol-macros form))
                   (push form exprs)
  