anchor.diff:  
   (defvar *in-let*)
   (defvar *orig-form*)
  -(defvar *symbol-macros*)
   
   (defmacro nonlocal (&body body)
     `(progn ,@body))
  
positive.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)
                   (removef *symbol-macros* name :key #'car))
                 (expansion-done (form)
                   (setf form (wrap-symbol-macros form))
                   (push form exprs)
  
negative.code: The `local' macro is loosely based on Racket's support for internal
  definitions."
    (multiple-value-bind (body decls) (parse-body orig-body)
      (let (vars hoisted-vars labels *in-let* *orig-form* exprs symbol-macros)
        (labels ((in-subenv? ()
                   "Are we within a binding form?"
                   (or *in-let* symbol-macros))
                 (at-beginning? ()
                   "Return non-nil if this is the first form in the `local'."
                   (not (or vars hoisted-vars labels (in-subenv?))))
  