effect-ts-resources

Effect-TS Resource Management

Overview

Manage resource lifecycles using Scope and acquireRelease to guarantee cleanup. Cleanup always runs, even if the program fails, throws, or is interrupted.

When to Use

• Symptoms: Resource leaks (hanging connections), manual try/finally blocks, complex cleanup logic.
• Triggers: Opening files, connecting to databases, starting servers, acquiring locks.
• When NOT to use: For simple data transformations or values that don't require explicit closing/release.

Core Pattern

Manual try/finally is error-prone in Effect because it bypasses interruption handling.

Anti-Pattern (Manual)	Effect Pattern (Safe)
try { conn.open() } finally { conn.close() }	Effect.acquireRelease(open, close)

Quick Reference

Function	Purpose
Effect.acquireRelease	Define acquisition and guaranteed release logic.
Effect.scoped	Create a boundary where all resources in scope are released.
Effect.addFinalizer	Add a cleanup action to the current scope.

Implementation

1. acquireRelease pattern

Guarantees cleanup even on failure or interruption.

import { Effect } from 'effect';

const withDatabaseConnection = Effect.acquireRelease(
  Effect.tryPromise(() => pool.connect()), // Acquire
  (connection) => Effect.sync(() => connection.release()) // Release
);

const program = Effect.gen(function* () {
  const conn = yield* withDatabaseConnection;
  return yield* conn.query('SELECT * FROM users');
});

2. Scoped resources

Multiple resources share a lifecycle boundary. Resources are released in LIFO (Last-In, First-Out) order.

import { Effect, Scope } from 'effect';

const program = Effect.scoped(
  Effect.gen(function* () {
    const db = yield* managedConnection;
    const cache = yield* managedCache;
    // Both cleaned up when scope closes (cache first, then db)
    return yield* doWork(db, cache);
  })
);

3. File handling

const withFile = (path: string) => Effect.acquireRelease(
  Effect.tryPromise(() => fs.open(path, 'r')),
  (handle) => Effect.promise(() => handle.close())
);

Common Mistakes

• Using try/finally: Bypasses Effect's interruption model. Use acquireRelease.
• Forgetting Effect.scoped: Resources won't be released until the parent scope closes (often the app end).
• Wrong Order: Resources are released in reverse order of acquisition. Ensure dependencies are acquired first.

REQUIRED BACKGROUND: Use effect-ts-fundamentals for core generator patterns.