Effect.ts: Absence as First-Class

Resources • Lesson 22 of 51

// Start two operations concurrently
const fiber1 = Effect.fork(fetchFromAPI1());
const fiber2 = Effect.fork(fetchFromAPI2());

// Fibers run in background (values being resolved)
// We have handles to potentially-absent values!

const program = Effect.gen(function* () {
  // Do other work while they run...
  yield* doOtherStuff();

  // Join: wait for absent values to arrive
  const result1 = yield* Fiber.join(fiber1);
  const result2 = yield* Fiber.join(fiber2);

  return combineResults(result1, result2);
});

// Or interrupt if we don't need them anymore:
fiber1.interrupt();  // Stop waiting for that value

const { Fiber } = await import('effect');
const task1 = Effect.gen(function* () {
      yield* Effect.sleep('50 millis');
      return 'Task 1 done';
});
const task2 = Effect.gen(function* () {
      yield* Effect.sleep('30 millis');
      return 'Task 2 done';
});
const start = Date.now();
const fiber1 = Effect.runFork(task1);
const fiber2 = Effect.runFork(task2);
const result1 = await Effect.runPromise(Fiber.join(fiber1));
const result2 = await Effect.runPromise(Fiber.join(fiber2));
const elapsed = Date.now() - start;
return `Fibers!

Task 1: ${result1} (50ms)
Task 2: ${result2} (30ms)
Total time: ${elapsed}ms

Concurrent execution!`;