fn main() -> anyhow::Result<()> {
    let peripherals = Peripherals::take()?;
    let mut led = PinDriver::output(
                      peripherals.pins.gpio4)?;
    let mut button = PinDriver::input(
                      peripherals.pins.gpio9)?;

    loop {
        blink_led_on_button_press(&mut button,
            &mut led).expect(
            "Error in blink_led_on_button_press");
    }
}
