gui.begin(cfg);
	Group(`main`)
		.grabKeyboardFocus()
		.addHandler((KeyboardEvent e) {
			if (e.sinking && e.down) {
				if (e.unicode >= '0' && e.unicode <= '9') {
					onDigit(e.unicode - '0');
				} else if (KeySym.Return == e.keySym) {
					evalOp();
				} else switch (e.unicode) {
					case '/':
						onOp((long a, long b) { return b == 0 ? 0 : a / b; });
						break;
					case '*':
						onOp((long a, long b) { return a * b; });
						break;
					case '+':
						onOp((long a, long b) { return a + b; });
						break;
					case '-':
						onOp((long a, long b) { return a - b; });
						break;
					case '=':
						evalOp();
						break;
					default: break;
				}
			}
			return EventHandling.Continue;
		});
gui.end();