[GUI] Proposal for MacOS MenuBar

[Krasimir Angelov]

   I propose simple scheme for portable for menus
based on two simple ideas:
     1. We can define two separatate menu types. 
          - Common menu bar: this is a menu with
commands which are common for each toplevel window.
Usually native Windows applications has three common
sub-menus in the menu bar: the first menu is usualy
File, the second is Edit and the last is Help. If the
application supports View menu usually this is the
third menu. 
          - Document menu bar: each toplevel window
can have its own menu with its own commands. Under
Windows MFC based MDI applications supports different 
menus for each document types but usually for all of 
them exists the same File, Edit, View and Help menus. 

   I think that is good idea to express this fact 
more natural. The Haskell GUI library can define one 
common menu and the place, where the document menus 
to be placed. When any window becomes active its menu 
will be merged with common menu. When there aren't
active windows then the MDI frame will display just
default menu. 
   I hope that this can be suitable for MacOS. This
convention will encourage developers to define the
common menu and the document specific menus and then 
leave OS specific layer to build application menu in
natural way.

    2. We can explicitly define the document model 
which are most suitable for the application (MDI, SDI
 or NDI). The model must be specified at startup just 
like in the ObjectIO. The meanings of models are:    
       - SDI - Under Windows and GTK we have multiple 
top level windows and usually the application 
finishes when all windows are closed. Each window has
its own menu which are part of the window. Under acOS
the difference is that the application continues 
execution even if all top level windows are closed.
The menu is placed at desktop.
       - MDI - Under Windows we have one toplevel 
MDIFrame with many child frames and the application 
finishes when its MDIFrame is closed. Under GTK we
have one toplevel window with embeded GtkNoteBook 
widget. The child frames are expressed with pages in 
the notebook and the application finishes when the 
toplevel window is closed. Under both Windows and GTK,
the menu is placed on MDI frame and it is a
composition of the common menu and the current
document menu. Under MacOS MDI interface will have 
the same behavior as SDI.
       - NDI - simple interface with just one dialog
without MenuBar.

Krasimir

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