Module helpers 

Glue between Swan promises and the host’s async runtime.

The engine runs imports as background tasks. It does not depend on any runtime: the host passes a SpawnFn that starts a Task on its own executor. Without one, tasks go onto a thread-local queue that the host drains with run_pending.

promise_async is also useful to hosts: it turns a Rust future into a Swan promise, so a host function can do asynchronous work.

Examples

A host function that returns a promise:

use swan_core::value::{BuiltinFn, Value};
use texl_core::{Engine, helpers::promise_async};

let engine = Engine::new(None);
engine.add_builtin("fetch_answer", Value::Builtin(BuiltinFn::new("fetch_answer", |_| {
    promise_async(None, async { Value::Numb(42.0) })
})));
assert_eq!(block_on(engine.render("<% fetch_answer() %>")), "42");

Functions

promise_async

Wraps an async operation in a background task that resolves a Swan Promise.

run_pending

Polls queued fallback tasks until no further progress is possible.

spawn

Runs task with spawner, or queues it with spawn_default if spawner is None.

spawn_default

Fallback spawner: queues the task on a thread-local queue.

spawner_fn

Builds a SpawnFn from a plain closure.

Type Aliases

SpawnFn

A host-provided function that runs a background task to completion.

Task

A background task, as handed to a spawner. It is not Send: tasks run on the thread that created them.