Effect 2.3 (Release)

Feb 10, 2024

Tim Smart

Founding Engineer

Michael Arnaldi

Chief Executive Officer

A new minor release of Effect has gone out, with some big changes we wanted to let you know about:

• Effect<R, E, A> has been changed to Effect<A, E = never, R = never>. This change makes for cleaner type signatures (Effect<void>) and ensures types are ordered by importance. The full list of types that got updated with the same change: Effect, Stream, STM, STMGen, Layer, Exit, Take, Fiber, FiberRuntime, Request, Resource, TExit, Deferred, TDeferred, Pool.

The following should be used:

import { Effect } from "effect"

interface Logger {
  print: (message: string) => Effect.Effect<void>
}

instead of:

import { Effect } from "effect"

interface Logger {
  print: (message: string) => Effect.Effect<never, never, void>
}

For this inhuman work we have to thank deeply Giulio Canti, who’s now officially known as <Canti, Giulio = never>!

• Context.Tag has been renamed to Context.GenericTag, string identifiers are now mandatory.

The following should be used:

import { Context } from "effect"

interface ServiceId {
  readonly _: unique symbol
}

interface Service {
  // ...
}

const Service = Context.GenericTag<ServiceId, Service>("@services/Service")

instead of:

import { Context } from "effect"

interface ServiceId {
  readonly _: unique symbol
}

interface Service {
  // ...
}

const Service = Context.Tag<ServiceId, Service>()

• A new Context.Tag base class has been added. The added class approach assists with creating unique tag identifiers, making use of the opaque type that you get for free using a class.

For example:

import { Context, Effect } from "effect"

class MyService extends Context.Tag("MyService")<
  MyService,
  { methodA: Effect.Effect<void> }
>() {}

const effect: Effect.Effect<void, never, MyService> =
  Effect.flatMap(MyService, _ => _.methodA)

For the changes above, a code-mod has been released to make migration as easy as possible.

You can run it by executing:

npx @effect/codemod minor-2.3 src/**/*

It might not be perfect - if you encounter issues, let us know! Also make sure you commit any changes before running it, in case you need to revert anything.

• @effect/platform has been refactored to remove re-exports from the base package.

You will now need to install both @effect/platform & the corresponding @effect/platform-* package to make use of platform specific implementations.

You can see an example at platform-node/examples/http-client.ts

Notice the imports:

import { runMain } from "@effect/platform-node/NodeRuntime"
import * as Http from "@effect/platform/HttpClient"

• A rewrite of the @effect/rpc package has been released, which simplifies the design and adds support for streaming responses.

You can see a small example of usage here: rpc-http/examples.

We start by defining our requests using S.TaggedRequest or Rpc.StreamingRequest:

import * as Rpc from "@effect/rpc/Rpc"
import * as S from "@effect/schema/Schema"
import { pipe } from "effect/Function"

export const UserId = pipe(S.number, S.int(), S.brand("UserId"))
export type UserId = S.Schema.To<typeof UserId>

export class User extends S.Class<User>()({
  id: UserId,
  name: S.string
}) {}

export class GetUserIds extends Rpc.StreamRequest<GetUserIds>()("GetUserIds", S.never, UserId, {}) {}
export class GetUser extends S.TaggedRequest<GetUser>()("GetUser", S.never, User, {
  id: UserId
}) {}

We then define our router:

import { NodeHttpServer, NodeRuntime } from "@effect/platform-node"
import * as Http from "@effect/platform/HttpServer"
import { Router, Rpc } from "@effect/rpc"
import { HttpRouter } from "@effect/rpc-http"
import { Effect, Layer, Array, Stream } from "effect"
import { createServer } from "http"
import { GetUser, GetUserIds, User, UserId } from "./schema.js"

// Implement the RPC server router
const router = Router.make(
  Rpc.stream(GetUserIds, () => Stream.fromIterable(Array.makeBy(1000, UserId))),
  Rpc.effect(GetUser, ({ id }) => Effect.succeed(new User({ id, name: "John Doe" })))
)

export type UserRouter = typeof router

// Create the http server
const HttpLive = Http.router.empty.pipe(
  Http.router.post("/rpc", HttpRouter.toHttpApp(router)),
  Http.server.serve(Http.middleware.logger),
  Http.server.withLogAddress,
  Layer.provide(NodeHttpServer.server.layer(createServer, { port: 3000 }))
)

Layer.launch(HttpLive).pipe(
  NodeRuntime.runMain
)

And finally the client:

import * as Http from "@effect/platform/HttpClient"
import { Resolver } from "@effect/rpc"
import { HttpResolver } from "@effect/rpc-http"
import { Console, Effect, Stream } from "effect"
import type { UserRouter } from "./router.js"
import { GetUser, GetUserIds } from "./schema.js"

// Create the client
const client = HttpResolver.make<UserRouter>(
  Http.client.fetchOk().pipe(
    Http.client.mapRequest(Http.request.prependUrl("http://localhost:3000/rpc"))
  )
).pipe(Resolver.toClient)

// Use the client
client(new GetUserIds()).pipe(
  Stream.runCollect,
  Effect.flatMap(Effect.forEach((id) => client(new GetUser({ id })), { batching: true })),
  Effect.tap(Console.log),
  Effect.runFork
)

• A new module called RateLimiter has been released to help you with rate limiting effects, an example of its usage:

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

class ApiLimiter extends Context.Tag("@services/ApiLimiter")<
  ApiLimiter,
  RateLimiter.RateLimiter
>() {
  static Live = RateLimiter.make(10, "2 seconds").pipe(
    Layer.scoped(ApiLimiter)
  )
}

const program = Effect.gen(function* () {
  const rateLimit = yield* ApiLimiter
  for (let n = 0; n < 100; n++) {
    yield* rateLimit(Effect.log("Calling RateLimited Effect"))
  }
})

program.pipe(
  Effect.provide(ApiLimiter.Live),
  Effect.runFork
)

There were several other smaller changes made, feel free to read through the changelog to see them all: Changelog.

Don’t forget to join our Discord Community to follow the last updates and discuss every tiny detail!

Tags:

• Releases
• Effect

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