windowp

Arguments: object

Returns true if object is a window or a menu that is open (and therefore still usable), and otherwise returns nil. This may useful for determining whether the owner or parent of a window is a window rather the screen, for example, or whether a known window or menu is still open.

Specifically, true is returned if the object is a cg-stream of the basic-pane class or the menu class, and the stream has not been closed (due to close being called on it), and the process that created it has not been killed.

If an open window or menu's creation-process is killed, then the window is no longer usable, but Common Graphics may not realize that and will continue to regard the window as being an open stream. windowp will catch this situation, though, and will return nil after calling close on the stream so that it is properly closed.

See also screenp.

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Created 2015.5.21.