anchor.diff:  (defun parse-var-expression ()
     (get-next-token)
     (unless (eql *current-token* 'tok-identifier)
  -    (error "expected identifier after var"))
  +    (error 'kaleidoscope-error :message "expected identifier after var"))
     (let ((var-names (loop
                        for name = *identifier-string*
                        for init = nil
  
positive.code:                            collecting arg
                             until (eql *current-token* #\))
                             do (or (eql *current-token* #\,)
                                    (error
                                     "Expected ')' or ',' in argument list"))
                             do (get-next-token))))
          (get-next-token)) ; eat the ')'.
        (make-instance 'variable-expression :name id-name))))
  
negative.code: (defun parse-for-expression ()
    (get-next-token) ; eat the for.
    (unless (eql *current-token* 'tok-identifier)
      (error 'kaleidoscope-error :message "expected identifier after for"))
    (let ((id-name *identifier-string*))
      (get-next-token) ; eat identifier.
      (unless (eql *current-token* #\=)
        (error 'kaleidoscope-error :message "expected '=' after for"))
      (get-next-token)
      (let ((start (parse-expression)))
        (when start
          (unless (eql *current-token* #\,)
            (error 'kaleidoscope-error :message "expected ',' after for start value"))
          (get-next-token)
          (let ((end (parse-expression)))
            (when end
  