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