A menu-bar% object is created for a particular
frame% object. A frame can have at most one menu bar;
an exn:fail:contract exception is raised when a new menu bar is created for a frame that
already has a menu bar.
Creates a menu bar in the specified frame. The menu bar is initially
empty. If 'root is supplied as parent, the
menu bar becomes active only when no other frames are shown. A
'root parent is allowed only when
current-eventspace-has-menu-root? returns #t, and
only if no such menu bar has been created before, otherwise
an exn:fail:contract exception is raised.
The demand-callback procedure is called by the default
on-demand method with the object itself.
Enables or disables the menu bar (i.e., all of its menus). Each
menu’s is-enabled? method returns
#f only if the menu is specifically disabled (in addition to
the menu bar).
Returns the menu bar’s frame.
Returns #t if the menu bar is enabled, #f otherwise.