effect-ts

Effect-TS 专家指南

Effect-TS 是一个函数式 TypeScript 库，提供带类型的效果、结构化并发和强大的运行时。本技能介绍正确的使用模式，并纠正大模型生成内容中的常见误解。

快速参考

import { Effect, Layer, Context, Fiber, Schedule, Cache, Scope } from "effect";
import { Schema, JSONSchema } from "@effect/schema";

核心类型签名：

Effect<Success, Error, Requirements>
//      ↑        ↑       ↑
//      |        |       └── Dependencies (provided via Layers)
//      |        └── Expected errors (typed, must be handled)
//      └── Success value

---

常见误解

大模型的输出常常包含错误的 API。 请使用此表进行纠正：

错误写法（AI 输出中常见）	正确写法
Effect.cachedWithTTL(...)	Cache.make({ timeToLive: Duration })
Effect.cachedInvalidateWithTTL(...)	cache.invalidate(key) / cache.invalidateAll()
Effect.match(...)	Effect.either + Either.match，或 Effect.catchTag
“线程本地存储”	通过 FiberRef 实现的“纤程本地存储”
JSON Schema Draft 2020-12	@effect/schema 生成 Draft-07
纤程被“取消”	纤程被“终止”或“中断”
所有队列都有背压	只有有界队列有背压；滑动队列和丢弃队列没有
--only=production	--omit=dev（npm 7+）

---

错误处理：两种错误类型

Effect 区分：

1. 预期错误（失败） - 在 E 通道中带有类型，必须处理
2. 意外错误（缺陷） - 运行时错误，会被捕获，但不带类型

// Expected error - typed
const fetchUser = (id: string): Effect.Effect<User, UserNotFoundError | NetworkError> => ...

// Handle expected errors
const handled = pipe(
  fetchUser("123"),
  Effect.catchTag("UserNotFoundError", (e) => Effect.succeed(defaultUser)),
  Effect.catchTag("NetworkError", (e) => Effect.retry(schedule))
);

// Unexpected errors (defects) - captured by runtime
Effect.catchAllDefect(program, (defect) =>
  Console.error("Unexpected error", defect)
);

---

纤程与取消（对 MCP 至关重要）

纤程是轻量级虚拟线程，支持原生中断：

// Fork a fiber
const fiber = yield* Effect.fork(longRunningTask);

// Interrupt it (e.g., when MCP client disconnects)
yield* Fiber.interrupt(fiber);

// Structured concurrency: child fibers auto-terminate with parent
const parent = Effect.gen(function* () {
  yield* Effect.fork(backgroundTask);  // Auto-interrupted when parent ends
  yield* mainTask;
});

// Daemon fibers outlive their parent
yield* Effect.forkDaemon(longLivedBackgroundTask);

---

并发原语

Effect.race - 先完成者胜出，其余任务会被中断

// First to succeed wins; other is automatically interrupted
const result = yield* Effect.race(
  fetchFromCache,
  fetchFromDatabase
);

带并发控制的 Effect.all

// Process 50 documents with max 5 concurrent
const results = yield* Effect.all(documents.map(processDoc), {
  concurrency: 5  // NOT a "worker pool" - limits concurrent tasks
});

队列类型

// Bounded - applies back-pressure (offer suspends when full)
const bounded = yield* Queue.bounded<string>(100);

// Dropping - discards new items when full (no back-pressure)
const dropping = yield* Queue.dropping<string>(100);

// Sliding - discards oldest items when full (no back-pressure)
const sliding = yield* Queue.sliding<string>(100);

---

用于依赖注入的 Layer

Layer 用于构造服务，而不会泄漏依赖：

// Define a service
class Database extends Context.Tag("Database")<
  Database,
  { query: (sql: string) => Effect.Effect<Result> }
>() {}

// Create layer (dependencies handled at construction)
const DatabaseLive = Layer.effect(
  Database,
  Effect.gen(function* () {
    const config = yield* Config;  // Dependency injected here
    return {
      query: (sql) => Effect.tryPromise(() => runQuery(sql, config))
    };
  })
);

// Provide to program
const runnable = program.pipe(Effect.provide(DatabaseLive));

// For testing - swap implementation
const DatabaseTest = Layer.succeed(Database, {
  query: () => Effect.succeed(mockResult)
});

---

资源管理

Effect.ensuring - 始终运行终结器

const program = pipe(
  Effect.tryPromise(() => openConnection()),
  Effect.ensuring(Console.log("Cleanup"))  // Runs on success, failure, OR interrupt
);

acquireUseRelease 模式

const withConnection = Effect.acquireUseRelease(
  Effect.tryPromise(() => db.connect()),     // Acquire
  (conn) => Effect.tryPromise(() => conn.query("SELECT *")),  // Use
  (conn) => Effect.promise(() => conn.close())  // Release (always runs)
);

用于资源生命周期管理的 Scope

Effect.scoped(
  Effect.gen(function* () {
    const file = yield* openFile("data.txt");  // Acquired
    const data = yield* file.read();
    return data;
  })  // File automatically released when scope closes
);

---

缓存

不存在 Effect.cachedWithTTL。 请使用 Cache 模块：

import { Cache } from "effect";

const cache = yield* Cache.make({
  capacity: 100,
  timeToLive: Duration.minutes(5),
  lookup: (key: string) => fetchExpensiveData(key)
});

// Use the cache
const value = yield* cache.get("my-key");

// Invalidate
yield* cache.invalidate("my-key");
yield* cache.invalidateAll();

---

使用 Schedule 重试

import { Schedule } from "effect";

// Retry 3 times with exponential backoff
const policy = Schedule.exponential("100 millis").pipe(
  Schedule.intersect(Schedule.recurs(3))
);

const robust = Effect.retry(unstableOperation, policy);

// Retry until condition
const untilSuccess = Effect.retry(operation, {
  until: (err) => err.code === "RATE_LIMITED"
});

---

Schema 与 JSON Schema

@effect/schema 生成 JSON Schema Draft-07（而不是 2020-12）：

import { Schema, JSONSchema } from "@effect/schema";

const User = Schema.Struct({
  id: Schema.String,
  age: Schema.Number.pipe(Schema.positive())
});

// Generate JSON Schema (Draft-07)
const jsonSchema = JSONSchema.make(User);
// { "$schema": "http://json-schema.org/draft-07/schema#", ... }

// Decode (parse)
const user = Schema.decodeUnknownSync(User)(rawData);

// Encode
const json = Schema.encodeSync(User)(user);

---

可观测性与 OpenTelemetry

Effect 原生集成了 OpenTelemetry：

import { NodeSdk } from "@effect/opentelemetry";
import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http";

// Add tracing to any effect
const traced = Effect.withSpan("processRequest")(myEffect);

// Logging with context
yield* Effect.log("Processing request");
yield* Effect.annotateLogs("requestId", "abc-123");

// FiberRef for fiber-local context propagation
const RequestId = FiberRef.unsafeMake<string>("");
yield* FiberRef.set(RequestId, "req-456");

---

不适合使用 Effect 的场景

场景	建议
简单的 MCP 工具（< 100 LOC）	使用 FastMCP 或原生 SDK
团队不熟悉 FP	学习曲线陡峭；可考虑 NestJS
包体积至关重要	Effect 至少会增加 15-25kb 的 gzip 压缩体积
现有 NestJS/TypeORM 代码库	与基于类的 DI 不兼容

---

MCP 服务模式

带类型错误的工具处理程序

const searchTool = Effect.gen(function* () {
  const args = yield* parseArgs(input);
  const db = yield* Database;
  const results = yield* db.query(args.query);
  return formatResults(results);
}).pipe(
  Effect.catchTag("ParseError", () =>
    Effect.fail({ code: -32602, message: "Invalid params" })
  ),
  Effect.catchTag("DatabaseError", () =>
    Effect.fail({ code: -32603, message: "Internal error" })
  )
);

请求作用域

// Each MCP request gets its own scope
const handleRequest = (request: MCPRequest) =>
  Effect.scoped(
    Effect.gen(function* () {
      // Resources acquired here auto-release when request completes
      const tempFile = yield* createTempFile();
      const result = yield* processRequest(request, tempFile);
      return result;
    })
  );

---

资源

• Effect 文档
• Effect GitHub
• @effect/schema JSON Schema
• @effect/opentelemetry