MENU -- Menu Boxes


	1) Usage

	| OBJECT mnu[MENU];

	A MENU instance has no state, but all information required for
	creating menu is passed to it using arguments. There is only
	one singe method called SELECT. When a SELECT message is sent
	to an instance of MENU, the menu described in the argument list
	will be displayed on the screen. The terminal will be put into
	raw mode while the menu is displayed. The user can then select
	an item from the menu or close the menu without chosing an
	item. When closed, the menu will not be removed from the
	screen.

	The MENU class uses color set and frame set structures
	described in the 'common data structures' section.


	2) Methods


	2.1 SELECT

	| MNU.SELECT(x, y, default, cs, fs, items)
	| ! Num,Num,Num,Bvec,Bvec,Vec => Num

	MNU.SELECT() draws the menu described in the ITEMS argument at
	the position specified in the X and Y arguments on the terminal
	screen. The DEFAULT argument specifies the position of the menu
	item which will be selected when the menu is created. The
	assertion

	| 0 <= DEFAULT < number of items

	must hold. CS is a CSET structure holding the color set and FS
	is a FSET structure holding the frame drawing character set.
	They are described in the section 'common data structures'.

	Colors are used as follows:

	C_BACKGROUND	menu background
	C_FRAME		menu frame
	C_TEXT		menu text
	C_SELECT	selection bar

	The menu description passed to SELECT in the ITEMS argument is
	a table containing two-element structures of the form

	[ hotkey, "item text" ]

	where HOTKEY is a character and the item text is a string. The
	last item must be zero.

	For example, the following menu description would create a
	simple Yes/No choice:

	| [
	|   [ 'y', " Yes " ],
	|   [ 'n', " No"  ],
	|   0 
	| ]

	When using the frame set "++++-|", the menu would look like
	this:

	| +-------+
	| | _Yes_ |
	| | _No__ |
	| +-------+

	The following keys may be used in menues (^X denotes
	[control]+[X], K_X denotes ttyctl.K_X):

	Key	Alt.	Description
	---	----	-----------
	K_DOWN	^N	move to next item
	K_UP	^P	move to previous item
	K_RIGHT	ENTER	select item under menu bar
	K_LEFT	ESC	cancel selection

	When a hotkey (as defined in the ITEMS vector) is pressed, this
	is equal to moving the menu bar over the respective item and
	pressing ENTER.

	When an item has been selected, its position in the item list
	will be returned. When canceling a selection, -1 will be
	returned.


	2.2 SCRSELECT

	| MNU.SCRSELECT(x, y, default, size, cs, fs, items)
	| ! Num,Num,Num,Num,Bvec,Bvec,Vec => Num

	MNU.SCRSELECT is equal to MNU.SELECT except for the additional
	SIZE parameter. This parameter may be set to a maximum vertical
	size of the menu. Only up to SIZE items will be displayed. When
	more items are specified, the content of the menu will be
	scrolled if necessary.

	When SIZE=0, SCRSELECT is equal to SELECT.


	3) Common Data Structures


	3.1 CSET -- Color Sets

	The color set structure CSET, which is implemented in the
	FILEBOX, FORM, MENU, and PROMPT classes, has the following
	members:

	Member		Used for...
	C_BACKGROUND	box backgrounds
	C_FRAME		drawing box frames
	C_TEXT		writing text
	C_SOTEXT	writing higlighted text
	C_SELECT	drawing the selection bar

	For the exact usage of this structure, see the description of
	the classes which use it. The CSET structure has the same
	layout in all classes. Therefore, one and the same color set
	may be used in file boxes, forms, menues, and prompt boxes.


	3.2 FSET -- Frame Character Sets

	The frame character set structure FSET, which is implemented in
	the FILEBOX, FORM, and MENU classes, has the following members:

	F_UL	upper left corner
	F_UR	upper right corner
	F_LL	lower left corner
	F_LR	lower right corner
	F_HL	horizontal lines
	F_VL	vertical lines

	NOTICE: FSET is a packed structure. To define one, use

	var fs::FSET;

	and to access its members, use fs::F_UL, fs::F_UR, etc.

	EXAMPLE: Using the FSET structure PACKED"1234-|" would result
	in a box of the form

	| 1----------2
	| |          |
	| |          |
	| 3----------4

	The FSET structure has the same layout in all classes.
	Therefore, one and the same frame character set may be used in
	file boxes, forms, and menues.