Create and return an enum-prompting hbox and button. hbox is the gtk container widget, selected-proc?? is a proc that when invoked returns #t or #f depending on the state of the boolean displayed in hbox. The returned value is a list: (hbox getter). PROMPT is the prompt to display, CHOICES is an a-list of symbols and strings. INITVAL is a symbol in the CHOICES a-list. See also prompt-enum.