Lykn

Promise Combinators

When you need to coordinate multiple async operations.

Promise:all — All Must Succeed

(bind results (await (Promise:all #a(
  (fetch-user "alice")
  (fetch-user "bob")
  (fetch-user "carol")))))

const results = await Promise.all([
  fetchUser("alice"), fetchUser("bob"), fetchUser("carol")]);

If any promise rejects, the whole thing rejects. Use when all operations must succeed for the result to be meaningful.

Promise:all-settled — Wait for All, Success or Failure

(bind outcomes (await (Promise:all-settled #a(
  (fetch-user "alice")
  (fetch-user "bob")))))

Each outcome is { status: "fulfilled", value: ... } or { status: "rejected", reason: ... }. Use when you want results from all operations regardless of individual failures.

Note the camelCase conversion: all-settled → allSettled.

Promise:race — First to Settle Wins

(bind first (await (Promise:race #a(
  (fetch-from-primary)
  (fetch-from-backup)))))

The first promise to settle (fulfilled or rejected) determines the result. Use for timeouts or redundant requests.

Promise:any — First to Succeed Wins

(bind result (await (Promise:any #a(
  (try-server-a)
  (try-server-b)
  (try-server-c)))))

The first fulfilled promise wins. If all reject, throws AggregateError. Use for fallback chains where any success is acceptable.