effect-module-layermap

name	effect-module-layermap
description	Guidance for `effect/LayerMap` focused on APIs like make, Layers, and Service. Load after `effect-skill-router` when this module is the primary owner.

Effect Module LayerMap

Owned scope

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

What it is for

• Module-specific APIs and usage patterns for Effect programs.

API quick reference

• make
• Layers
• Service
• LayerMap
• Services
• fromRecord
• Key
• Error
• Success
• TagClass
• 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.
• Use the reference docs to select the smallest API surface that solves your task.
• Validate behavior against existing tests before introducing new usage patterns.

Starter example

import { Effect, Layer, LayerMap, Context } from "effect"

// Define a service key
const DatabaseService = Context.Service<{
  readonly query: (sql: string) => Effect.Effect<string>
}>("Database")

// Create a LayerMap that provides different database configurations
const createDatabaseLayerMap = LayerMap.make((env: string) =>
  Layer.succeed(DatabaseService)({
    query: (sql) => Effect.succeed(`${env}: ${sql}`)
  })
)

// Use the LayerMap
const program = Effect.gen(function*() {
  const layerMap = yield* createDatabaseLayerMap

  // Get a layer for a specific environment
  const devLayer = layerMap.get("development")

  // Get services directly
  const services = yield* layerMap.services("production")

Common pitfalls

• Prefer explicit, typed combinators over ad-hoc casting or unchecked assumptions.

Not covered here

• Adjacent modules in effect/* and effect/unstable/* are out of scope for this owner.

Escalate to

• effect-skill-router for routing and ownership checks.

Reference anchors

• Module source: packages/effect/src/LayerMap.ts
• Representative tests: inspect nearby modules in packages/effect/test.
• API details: references/api-reference.md
• Usage notes: references/usage-reference.md
• Ownership mapping: references/owner.md