LET GUI_Widget

###
LET GUI_Widget

            GUI (Graphic-User-Interface) input mode:

        If command GUI\PANEL has been issued before,  the  LET  command  defines
        widgets  in the master window defined by GUI\PANEL. The widget is a sim-
        ple prompt when option /PROMPT is set, a  slider  if  option  /RANGE  is
        present,  a  list of choices if option /CHOICE or /INDEX is given, and a
        selection of files with the specified filter when option /FILE is speci-
        fied.  If  neither of these options is present, the LET command works in
        the usual way.

        The widgets are created and activated by command GUI\GO. Standard  input
        can  be  used,  and  pressing button GO will define all the variables as
        specified. If button ABORT is pressed instead, none of the variables are
        modified and an error is returned. Error handling is available.

        Options  related  to the GUI Widget mode are: /CHOICE,  /FILE, /FORMULA,
        /INDEX, /PROMPT and /RANGE