anchor.diff:        (let ((stack (list 0)) symbol value)
           (flet ((next-symbol ()
                    (multiple-value-bind (s v) (funcall lexer)
  -                   (setq symbol (or s 'eof) value v))))
  +                   (setq symbol (or s 'yacc-eof-symbol) value v))))
             (next-symbol)
             (loop
              (let* ((state (car stack))
  
positive.code: (defpackage #:yacc
    (:use #:common-lisp)
    (:export #:make-production #:make-grammar #:make-parser #:parse-with-lexer
             #:define-grammar #:define-parser
             #:yacc-parse-error #:yacc-parse-error-terminal
             #:yacc-parse-error-value #:yacc-parse-error-expected-terminals)
    #+CMU
  
negative.code: (defun compute-all-lookaheads (kernels grammar)
    "Compute the LR(1) lookaheads for all the collections in KERNELS."
    (declare (list kernels) (type grammar grammar))
    (setf (item-lookaheads (kernel-item (car kernels))) (list 'yacc-eof-symbol))
    (let ((previously-changed kernels) (changed '())
          (propagate-only nil))
      (declare (optimize (speed 3) (space 0)))
  