gtk:application-add-window (application window)

application -- a gtk:application instance
window -- a gtk:window widget

Adds a window to the application. This call can only happen after the application has started. Typically, you should add new application windows in response to the emission of the "GApplication::activate" signal. This call is equivalent to setting the application property of the given window to the given application, that is:

(gtk:application-add-window application window)
== (setf (gtk:window-application window) application)  

Normally, the connection between the application and the window will remain until the window is destroyed, but you can explicitly remove it with the gtk:application-remove-window function. GTK will keep the application running as long as it has any windows.