| *WITH-FORMAT-IF-EXISTS* keyword symbol |
| Establishes the default for the :if-exists format-slot of the base-format. If you want to change this default behavior, you can override this parameter globally or bind it dynamically. Alternatively you can specify a different value for :if-exists in the call to with-format. Valid keywords are the same as for Common Lisp open or with-open-file. Default is :supersede. |
(let ((*with-format-if-exists* :error))
(with-format (x3d "/tmp/box.x3d")
(write-the-object (make-instance 'box :length 100 :width 100 :height 100) cad-output)))
(with-format (x3d "/tmp/box.x3d" :if-exists :error)
(write-the-object (make-instance 'box :length 100 :width 100 :height 100) cad-output)