Promises

Async programming in Lazy is made to be simple and easy:

import "std/http" as Http

main {
    const res = await? Http::get("https://google.com");
    print(res.body);
}

Creating promises

let prom = Promise::spawn(fn() -> Result<i32, none> Result::Ok(1 + 1));
let res = await? prom; // 2

Promises return a Result, which is a special enum with two possible variants - T, the actual return value of the promise, or an Error:

Promise::spawn(fn() -> Result<none, str> {
    Result::Error("This promise always returns an error :x");
});

A question mark (?) can be put after the await keyword to short-circuit the execution context if the promise returns an Error.

Under the hood, Promises are handled by the tokio runtime.

let counter = 0;
Promise::interval(fn() {
    print(counter);
    counter += 1;
}, 1m);

Promise::timeout(fn() {
    print("This will be executed in 5 seconds!");
}, 5s);

await Promise::block(5m);