Provide Configuration to Your App via a Layer

Guideline

Transform your configuration schema into a Layer using Config.layer() and provide it to your main application Effect.

Rationale

Integrating configuration as a Layer plugs it directly into Effect's dependency injection system. This makes your configuration available anywhere in the program and dramatically simplifies testing by allowing you to substitute mock configuration.

Good Example

import { Effect, Layer } from "effect";

class ServerConfig extends Effect.Service<ServerConfig>()("ServerConfig", {
  sync: () => ({
    port: process.env.PORT ? parseInt(process.env.PORT) : 8080,
  }),
}) {}

const program = Effect.gen(function* () {
  const config = yield* ServerConfig;
  yield* Effect.log(`Starting application on port ${config.port}...`);
});

const programWithErrorHandling = Effect.provide(
  program,
  ServerConfig.Default
).pipe(
  Effect.catchAll((error) =>
    Effect.gen(function* () {
      yield* Effect.logError(`Program error: ${error}`);
      return null;
    })
  )
);

Effect.runPromise(programWithErrorHandling);

Explanation:
This approach makes configuration available contextually, supporting better testing and modularity.

Anti-Pattern

Manually reading environment variables deep inside business logic. This tightly couples that logic to the external environment, making it difficult to test and reuse.