\begin{verbatim}
load ('def.lefty');
definit ();
#
# initialize window data
#
canvas = defcanvas;
wrect = [0 = ['x' = 0; 'y' = 0;]; 1 = ['x' = 400; 'y' = 500;];];
setwidgetattr (canvas, ['window' = wrect;]);
#
# data structures
#
objarray = [];
objnum = 0;
#
# misc functions
#
min = function (a, b) {
    if (a <= b)
        return a;
    return b;
};
max = function (a, b) {
    if (b <= a)
        return a;
    return b;
};
rectof = function (p1, p2) {
    return [
        0 = ['x' = min (p1.x, p2.x); 'y' = min (p1.y, p2.y);];
        1 = ['x' = max (p1.x, p2.x); 'y' = max (p1.y, p2.y);];
    ];
};
pointadd = function (p1, p2) {
    return ['x' = p2.x + p1.x; 'y' = p2.y + p1.y;];
};
pointsub = function (p1, p2) {
    return ['x' = p2.x - p1.x; 'y' = p2.y - p1.y;];
};
#
# rendering functions
#
drawbox = function (obj, color) {
    box (canvas, obj, obj.rect, ['color' = color;]);
};
redrawboxes = function () {
    local i;
    clear (canvas);
    for (i = 0; i < objnum; i = i + 1)
        drawbox (objarray[i], 1);
};
redraw = function (canvas) {
    redrawboxes ();
};
#
# editing functions
#
new = function (rect) {
    objarray[objnum] = [
        'rect' = rect;
        'id' = objnum;
    ];
    objnum = objnum + 1;
    return objarray[objnum - 1];
};
reshape = function (obj, rect) {
    obj.rect = rect;
    return obj;
};
move = function (obj, p) {
    obj.rect[0] = pointadd (obj.rect[0], p);
    obj.rect[1] = pointadd (obj.rect[1], p);
    return obj;
};
delete = function (obj) {
    if (obj.id ~= objnum - 1) {
        objarray[obj.id] = objarray[objnum - 1];
        objarray[obj.id].id = obj.id;
    }
    remove (objnum - 1, objarray);
    objnum = objnum - 1;
};
#
# user interface functions
#
# left mouse button creates new box
# middle button moves a box
# right button deletes a box
#
leftdown = function (data) {
    if (data.obj ~= null)
        return;
    leftbox = new (rectof (data.pos, data.pos));
    drawbox (leftbox, 1);
    setgfxattr (canvas, ['mode' = 'xor';]);
};
leftmove = function (data) {
    if (~leftbox)
        return;
    drawbox (leftbox, 1);
    clearpick (canvas, leftbox);
    reshape (leftbox, rectof (data.ppos, data.pos));
    drawbox (leftbox, 1);
};
leftup = function (data) {
    if (~leftbox)
        return;
    drawbox (leftbox, 1);
    clearpick (canvas, leftbox);
    reshape (leftbox, rectof (data.ppos, data.pos));
    setgfxattr (canvas, ['mode' = 'src';]);
    drawbox (leftbox, 1);
    remove ('leftbox');
};
middledown = function (data) {
    if (data.obj == null)
        return;
    middlebox = data.obj;
    middlepos = data.pos;
    setgfxattr (canvas, ['mode' = 'xor';]);
};
middlemove = function (data) {
    if (~middlebox)
        return;
    drawbox (middlebox, 1);
    clearpick (canvas, middlebox);
    move (middlebox, pointsub (middlepos, data.pos));
    middlepos = data.pos;
    drawbox (middlebox, 1);
};
middleup = function (data) {
    if (~middlebox)
        return;
    drawbox (middlebox, 1);
    clearpick (canvas, middlebox);
    move (middlebox, pointsub (middlepos, data.pos));
    setgfxattr (canvas, ['mode' = 'src';]);
    drawbox (middlebox, 1);
    remove ('middlepos');
    remove ('middlebox');
};
rightup = function (data) {
    if (data.pobj == null)
        return;
    drawbox (data.obj, 0);
    clearpick (canvas, data.obj);
    delete (data.obj);
};
dops = function () {
    local s;

    s = ['x' = 8 * 300; 'y' = 10.5 * 300;];
    canvas = createwidget (-1, ['type' = 'ps'; 'size' = s;]);
    setwidgetattr (canvas, ['window' = wrect;]);
    redraw (canvas);
    destroywidget (canvas);
    canvas = defcanvas;
};
\end{verbatim}
