character vector giving the menu choices to be presented to the user.
OPTIONAL ARGUMENTS:
graphics:
logical flag: if TRUE, a graphics menu
(for example, a pop-up menu) will be used if
the current graphics device supports one.
title:
character string to be used as the title of the menu.
VALUE:
the number
corresponding to the selected item.
If no selection is made, 0 is returned.
NOTE:
For non-graphics menus, the user must respond with either 0 or a number
between 1 and length(choices) or a character string matching one of
the menu items.
DETAILS:
This is a generic function; currently there are no methods written for it.
This function can only be used in interactive mode, see interactive
for details on the exact conditions.