creating-from-synchronous-and-callback-code

description: Use sync and async to create Effects from synchronous or callback-based computations, making them composable and type-safe. globs: "**/*.ts" alwaysApply: true

Creating from Synchronous and Callback Code

Rule: Use sync and async to create Effects from synchronous or callback-based computations, making them composable and type-safe.

Example

import { Effect } from "effect";

// Synchronous: Wrap a computation that is guaranteed not to throw
const effectSync = Effect.sync(() => Math.random()); // Effect<never, number, never>

// Callback-based: Wrap a Node.js-style callback API
function legacyReadFile(
  path: string,
  cb: (err: Error | null, data?: string) => void
) {
  setTimeout(() => cb(null, "file contents"), 10);
}

const effectAsync = Effect.async<string, Error>((resume) => {
  legacyReadFile("file.txt", (err, data) => {
    if (err) resume(Effect.fail(err));
    else resume(Effect.succeed(data!));
  });
}); // Effect<string, Error, never>

Explanation:

• Effect.sync is for synchronous computations that are guaranteed not to throw.
• Effect.async is for integrating callback-based APIs, converting them into Effects.

Explanation:
Many APIs are synchronous or use callbacks instead of Promises.
By lifting them into Effects, you gain access to all of Effect's combinators, error handling, and resource safety.