anchor.diff:  
   (defun pass1-return-from (form env)
     (destructuring-bind (name &optional result) (cdr form)
  +    (check-type name symbol)
       (let ((tag (or (lookup-block-in-environment name env)
                      (error "RETURN-FROM refers to unknown block ~S." name))))
         (incf (lexical-variable-use-count tag))
  
positive.code: 
  (defun pass1-block (form env)
    (destructuring-bind (name &body forms) (cdr form)
      (let* ((var (make-instance 'block-information
                                 :name name
                                 :definition-point *current-lambda*))
  
negative.code: 
  (defun pass1-go (form env)
    (destructuring-bind (tag-name) (cdr form)
      (check-type tag-name (or symbol integer))
      (let ((tag (or (lookup-go-tag-in-environment tag-name env)
                     (error "GO refers to unknown tag ~S." tag-name))))
        (incf (go-tag-use-count tag))
  