effect-module-effect

name	effect-module-effect
description	Guidance for `effect/Effect` focused on APIs like gen, map, and fail. Load after `effect-skill-router` when this module is the primary owner.

Effect Module Effect

Owned scope

• Owns only effect/Effect.
• Source of truth: packages/effect/src/Effect.ts.

What it is for

• The Effect module is the core of the Effect library, providing a powerful and expressive way to model and compose asynchronous, concurrent, and effectful computations.

API quick reference

• gen
• map
• fail
• filter
• flatMap
• mapBoth
• provide
• runFork
• runSync
• service
• succeed
• failSync
• makeSpan
• mapEager
• mapError
• services
• Services
• failCause
• Full API list: references/api-reference.md

How to use it

• Start with constructor-style APIs to build values/services before composing operations.
• Prefer pipe-based composition to keep transformations explicit and testable.
• Keep runtime/execute APIs at edges; compose pure transformations before execution.

Starter example

import { Console, Effect } from "effect";

// Creating a simple effect
const hello = Effect.succeed("Hello, World!");

// Composing effects
const program = Effect.gen(function* () {
  const message = yield* hello;
  yield* Console.log(message);
  return message.length;
});

// Running the effect
Effect.runPromise(program).then(console.log); // 13

Common pitfalls

• Unsafe APIs bypass checks; prefer safe variants unless you control invariants explicitly.
• Scoped resources require deterministic lifecycle management to avoid leaks.
• Concurrency helpers can hide ordering/cancellation behavior; test interruption and race paths.

Not covered here

• Deep module subsets are owned by these facet skills:
  • effect-facet-effect-composition (effect/Effect#composition)
  • effect-facet-effect-concurrency (effect/Effect#concurrency)
  • effect-facet-effect-constructors (effect/Effect#constructors)
  • effect-facet-effect-context-di (effect/Effect#context-di)
  • effect-facet-effect-error-handling (effect/Effect#error-handling)
  • effect-facet-effect-execution (effect/Effect#execution)
  • effect-facet-effect-resource-scope (effect/Effect#resource-scope)

Escalate to

• effect-skill-router for routing and ownership checks.
• First facet entrypoint: effect-facet-effect-composition.

Reference anchors

• Module source: packages/effect/src/Effect.ts
• Representative tests: packages/effect/test/Effect.test.ts
• Representative tests: packages/effect/test/Channel.test.ts
• Representative tests: packages/effect/test/Deferred.test.ts
• Representative tests: packages/effect/test/Layer.test.ts
• Representative tests: packages/effect/test/Logger.test.ts
• Representative tests: packages/effect/test/LogLevel.test.ts
• API details: references/api-reference.md
• Usage notes: references/usage-reference.md
• Ownership mapping: references/owner.md