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Async / Await

Arden has first-class support for asynchronous programming.

Async Functions

Define an async function using async. It returns a Task<T>.

async function fetchData(): Task<String> {
    return "Data";
}

Await

Use await to resolve a Task<T> into T.

async function loadMessage(): Task<String> {
    data: String = await fetchData();
    return data;
}

Tasks

Task<T> is runtime-scheduled:

  • Creating a task (async function call or async { ... }) immediately spawns a runtime worker thread.
  • The task body runs concurrently in that worker.
  • Subsequent await calls return the cached result.

Current runtime behavior is thread-backed: Unix-like platforms use the pthread runtime, while Windows uses Win32 thread primitives. Multiple tasks can run in parallel, and await joins the task if it is not finished yet.

Task Methods

  • task.is_done(): Boolean
  • task.cancel(): None
  • task.await_timeout(ms: Integer): Option<T>

Reference examples:

  • examples/14_async.arden
  • examples/28_async_runtime_control.arden

Async Blocks

async { ... } creates a Task<T> expression.

task: Task<Integer> = async {
    return 21 * 2;
};

value: Integer = await task; // value == 42

Expression-bodied async blocks also infer the tail expression type directly, so builtin/static calls, lambdas, ranges, and assertion-style expressions work without an explicit return.

import std.string.*;

task: Task<String> = async { Str.upper("arden") };
f: Task<(Integer) -> Integer> = async { (x: Integer) => x + 1 };
r: Task<Range<Integer>> = async { range(0, 3) };
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