include "popup.m";
popup := load Popup Popup->PATH;

init:         fn();
mkbutton:     fn(win: ref Tk->Toplevel, name: string,
                 items: array of string, n: int): chan of string;
changebutton: fn(win: ref Tk->Toplevel, name: string,
                 items: array of string, n: int);
event:        fn(win: ref Tk->Toplevel, e: string,
                 items: array of string): int;
add:          fn(items: array of string, s: string):
                 (array of string, int);

Init must be called once to initialise the module.

Mkbutton creates a new button name, in Tk toplevel win. It returns a channel on which it delivers events (see event, below). Once created, name can be packed like any other Tk widget. When the button is pressed with button 1, a menu pops up offering a choice from the given items. The value n is the index in items of the button's initial value. The current choice is always displayed in the button. If items is nil or an empty array, the string `-----' is displayed instead.

Having created a popup button, the application must receive values on the channel returned by mkbutton and pass each value it receives to event (as parameter e). (Typically the application will receive on the channel in an alt statement that watches other channels too.) Event returns the result of a selection, or -1 if no selection was made. In either case, the text of the button name will reflect the currently active selection (the application can fetch it using `cget -text'). The items parameter must match that given to mkbutton (or most recently given to changebutton).

Changebutton changes the list of items in an existing popup button name, and sets its initial selection to the item with index n.

Add adds string s to the array items, if it is not already there, and in either case returns the resulting new array and the index of s therein. It is useful for calculating a list of items dynamically.