anchor.diff:         (add-flags nix:o-rdonly)
          (check-type if-exists (member nil :error-if-symlink))
          (check-type if-does-not-exist (member nil :error))
  -       (unless if-does-not-exist (setf if-does-not-exist :error)))
  +       (when (eql :default if-does-not-exist) (setf if-does-not-exist :error)))
         (:output
          (add-flags nix:o-wronly)
          (check-type if-exists file-if-exists)
          (check-type if-does-not-exist file-if-does-not-exist)
  -       (unless if-exists (setf if-exists :overwrite))
  -       (unless if-does-not-exist (setf if-does-not-exist :create)))
  +       (when (eql :default if-exists) (setf if-exists :overwrite))
  +       (when (eql :default if-does-not-exist) (setf if-does-not-exist :create)))
         (:io
          (add-flags nix:o-rdwr)
          (check-type if-exists file-if-exists)
          (check-type if-does-not-exist file-if-does-not-exist)
  -       (unless if-exists (setf if-exists :overwrite))
  -       (unless if-does-not-exist (setf if-does-not-exist :create))))
  +       (when (eql :default if-exists) (setf if-exists :overwrite))
  +       (when (eql :default if-does-not-exist) (setf if-does-not-exist :create))))
       (values flags if-exists if-does-not-exist)))
   
   (defun process-file-flags (direction flags if-exists if-does-not-exist
  
positive.code:   (nix:stat-size (nix:fstat (input-handle-of device))))
  
  (defun open-file (filename &key (direction :input)
                    (if-exists nil if-exists-p)
                    (if-does-not-exist nil if-does-not-exist-p)
                    truncate append nonblocking (extra-flags 0) (mode #o666))
    (handler-case
        (make-instance 'file-device
                       :filename (namestring filename)
                       :direction direction
                       :if-exists (if (and if-exists-p (null if-exists))
                                      :error if-exists)
                       :if-does-not-exist (if (and if-does-not-exist
                                                   (null if-does-not-exist-p))
                                              :error if-does-not-exist)
                       :truncate truncate
                       :append append
                       :nonblocking nonblocking
  
negative.code: (defmethod device-position ((device file-device))
    (position-of device))
  
  (defmethod (setf device-position) (offset (device file-device) &key (from :start))
    (ecase from
      (:start
       (nix:lseek (input-handle-of device) offset nix:seek-set)
       (setf (position-of device) offset))
  