Effect

The @effect/vitest package provides an enhanced it function that extends standard Vitest functionality with support for Effect-specific testing needs. The main entry point is import { it } from "@effect/vitest".

Key features include:

• it.effect: Runs a scoped test with test services like TestClock and TestConsole.
• it.live: Runs a scoped test using the live Effect environment (e.g., real system clock, real console).
• it.layer: Shares a Layer between multiple tests.
• it.prop: Runs property tests using Effect Schema values or FastCheck arbitraries.
• it.flakyTest: Retries an Effect that might fail until it succeeds or hits a timeout.

The @effect/ai-anthropic package is an Anthropic provider designed for the Effect AI ecosystem. It provides:

• A typed Anthropic API client.
• Language model layers.
• Tooling support.
• Telemetry helpers for monitoring AI interactions.

The @effect/opentelemetry package provides an integration for OpenTelemetry within the Effect ecosystem. It allows you to export Effect tracing, metrics, and logs through the OpenTelemetry SDK. It provides specialized layers for different environments:

• NodeSdk: For Node.js environments.
• WebSdk: For browser-based environments.

Effect's AI modules offer a provider-agnostic interface for interacting with various language models. This abstraction allows you to switch between different AI providers without changing your core business logic. Key capabilities include:

• Text Generation: Generating raw text responses from a model.
• Structured Decoding: Using Schema to decode model responses into typed, structured objects.
• Streaming: Handling partial responses via streaming interfaces.

The typeperf harness measures deterministic TypeScript diagnostics (instantiations, materialized types, and symbols) for specific fixtures. It is used as a regression gate to ensure that type-level optimizations do not negatively impact performance.

Each suite has a shared baseline. The cost of a fixture is calculated as the delta between the fixture's metric and the suite's baseline metric:

metric delta = fixture metric - suite baseline metric.

Threshold files store the maximum allowed deltas for instantiations and types. Symbol deltas are informational and do not affect command status.

The @effect/openapi-generator tool automates the creation of TypeScript code based on OpenAPI specifications. It generates:

• Effect Schema types
• HTTP clients
• HttpApi modules

Effect Schema is a TypeScript-first library used for defining data shapes, validating unknown input, and transforming values. It operates on two primary directions:

• Decoding: Converting unknown external data (like API responses or config files) into typed, validated values.
• Encoding: Converting typed values back into serializable formats (like JSON or FormData).

Key use cases include defining types that provide both TypeScript types and runtime validators, validating input with clear error messages, and transforming values between domain types and serialization formats.

The @example JSDoc tag allows you to provide usage examples for your source code.

Key features:

• Type Checking: All examples are automatically type-checked using tsc to ensure they are valid.
• Execution: Examples are run using tsx.
• Testing: You can use the Node.js assert module within your examples to perform on-the-fly testing of the code snippets.

There are two primary patterns for executing configuration lookups:

1. Yield in Effect.gen: This is the standard way. It automatically uses the ConfigProvider currently available in the service map (via Layers or provideService).
2. Call .parse(provider) directly: This is useful for testing or when you want to use a specific provider instance regardless of the current environment context. The .parse method accepts only the provider.

// 1. Yielding in a generator
const program = Effect.gen(function*() {
  const host = yield* Config.string("HOST")
})

// 2. Direct parsing with a specific provider
const host = Config.string("HOST")
const result = Effect.runSync(host.parse(provider))