Your First Program

The simplest useful Flint program on current hardware support is an RP2040 LED blink.

This version uses the HAL-facing modules instead of raw register writes:

use micro/gpio
use time/delay

fn main() {
    let builtin_led = gpio.builtin_led()
    if builtin_led.is_none() {
        return
    }

    if let Option.Some(led) = builtin_led {
        loop {
            led.toggle()
            delay.millis(500)
        }
    }
}

What To Notice

• use imports modules with explicit paths.
• fn main() is a normal function. There is no hidden runtime wrapper in the language syntax.
• let is immutable by default.
• is_none() makes the missing-hardware guard obvious up front.
• loop is the simplest infinite loop form.
• Method calls such as led.toggle() are ordinary Flint syntax, not macros.

About builtin_led()

Flint also exposes gpio.builtin_led() as a convenience API, but it returns Option<gpio.OutputPin> because not every board has a direct GPIO-backed onboard LED.

Use it when you want a helper and are prepared to handle the missing case:

let builtin_led = gpio.builtin_led()
if builtin_led.is_none() {
    return
}

if let Option.Some(led) = builtin_led {
    led.toggle()
}

This keeps the missing-hardware case explicit in the source without pushing the main path deeper to the right.

A Slightly Lower-Level Version

Flint can also target the hardware more directly when needed. The repository includes examples that use unsafe and volatile_write to configure GPIO on the RP2040 without going through a higher-level HAL abstraction.

That is an important part of Flint’s design: higher-level APIs should exist, but they should not block you from reaching the machine when necessary.