effect-ts

const processUser = Effect.fn("processUser")(function* (userId: string) {
  yield* Effect.logInfo(`Processing user ${userId}`)
  const user = yield* getUser(userId)
  return yield* processData(user)
})
 
// Second argument for cross-cutting concerns (retry, timeout)
const fetchWithRetry = Effect.fn("fetchWithRetry")(
  function* (url: string) {
    const data = yield* fetchData(url)
    return yield* processData(data)
  },
  flow(
    Effect.retry(Schedule.recurs(3)),
    Effect.timeout("5 seconds")
  )
)

import { Effect, ServiceMap } from "effect"
 
class Database extends ServiceMap.Service<
  Database,
  {
    readonly query: (sql: string) => Effect.Effect<unknown[]>
    readonly execute: (sql: string) => Effect.Effect<void>
  }
>()("@app/Database") {}

import { Effect, Layer } from "effect"
 
class Users extends ServiceMap.Service<
  Users,
  {
    readonly findById: (id: UserId) => Effect.Effect<User, UserNotFoundError>
    readonly all: () => Effect.Effect<readonly User[]>
  }
>()("@app/Users") {
  static readonly layer = Layer.effect(
    Users,
    Effect.gen(function* () {
      const http = yield* HttpClient.HttpClient
      const findById = Effect.fn("Users.findById")(function* (id: UserId) {
        const response = yield* http.get(`/users/${id}`)
        return yield* HttpClientResponse.schemaBodyJson(User)(response)
      })
      const all = Effect.fn("Users.all")(function* () {
        const response = yield* http.get("/users")
        return yield* HttpClientResponse.schemaBodyJson(Schema.Array(User))(response)
      })
      return { findById, all }
    })
  )
}

import { Schema } from "effect"
 
const UserId = Schema.String.pipe(Schema.brand("UserId"))
type UserId = typeof UserId.Type
 
const Email = Schema.String.pipe(Schema.brand("Email"))
type Email = typeof Email.Type
 
class User extends Schema.Class("User")({
  id: UserId,
  name: Schema.String,
  email: Email,
  createdAt: Schema.Date,
}) {
  get displayName() { return `${this.name} (${this.email})` }
}
 
// Construct with makeUnsafe for brands
const userId = UserId.makeUnsafe("user-123")

import { Match, Schema } from "effect"
 
class Success extends Schema.TaggedClass("Success")("Success", {
  value: Schema.Number,
}) {}
class Failure extends Schema.TaggedClass("Failure")("Failure", {
  error: Schema.String,
}) {}
const Result = Schema.Union([Success, Failure])
type Result = typeof Result.Type
 
// Exhaustive pattern matching
const render = (r: Result) => Match.valueTags(r, {
  Success: ({ value }) => `Got: ${value}`,
  Failure: ({ error }) => `Error: ${error}`,
})

import { Schema } from "effect"
 
class UserNotFoundError extends Schema.TaggedErrorClass("UserNotFoundError")(
  "UserNotFoundError",
  { userId: UserId, message: Schema.String }
) {}
 
// Yieldable: yield directly in generators
const getUser = Effect.fn("getUser")(function* (id: UserId) {
  const user = yield* findUser(id)
  if (!user) yield* new UserNotFoundError({ userId: id, message: "Not found" })
  return user
})

// Single tag
const recovered = program.pipe(
  Effect.catchTag("UserNotFoundError", (e) =>
    Effect.succeed(`User ${e.userId} missing`)
  )
)
 
// Multiple tags
const recovered2 = program.pipe(
  Effect.catchTags({
    UserNotFoundError: (e) => Effect.succeed("not found"),
    ValidationError: (e) => Effect.succeed("invalid"),
  })
)

import { Effect, Layer } from "effect"
 
// Compose layers for the app
const appLayer = UserService.layer.pipe(
  Layer.provideMerge(DatabaseLayer),
  Layer.provideMerge(LoggerLayer),
  Layer.provideMerge(ConfigLayer),
)
 
// Provide once at the entry point
const main = program.pipe(Effect.provide(appLayer))
Effect.runPromise(main)

import { describe, expect, it } from "@effect/vitest"
import { Effect, Layer } from "effect"
 
it.effect("queries database", () =>
  Effect.gen(function* () {
    const db = yield* Database
    const results = yield* db.query("SELECT *")
    expect(results.length).toBe(2)
  }).pipe(Effect.provide(Database.testLayer))
)

const program = fetchData.pipe(
  Effect.timeout("5 seconds"),
  Effect.retry(Schedule.exponential("100 millis").pipe(
    Schedule.compose(Schedule.recurs(3))
  )),
  Effect.tap((data) => Effect.logInfo(`Fetched: ${data}`)),
  Effect.withSpan("fetchData"),
)