get-choices-from-user in Dialogs

• (get-choices-from-user title message choices parent init-choices style) -> list of exact non-negative integers or #f
   title : string
     message : string or #f
   choices : list of strings
     parent = #f : frame% or dialog% object or #f
   init-choices = null : list of exact non-negative integers
     style = '(single) : list of symbols in '(single multiple extended)

  Gets a list box selection from the user via a modal dialog, using parent as the parent window if it is specified. The dialog's title is title. The dialog's list box is labelled with message and initialized by selecting the items in init-choices.

  The style must contain exactly one of 'single, 'multiple, or 'extended. The styles have the same meaning as for creating a list-box% object. (For the single-selection style, only the last selection in init-choices matters.)

  The result is #f if the user cancels the dialog, the list of selections otherwise.