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@typeonce/effect-machine

External home for the schema-first Machine API proposed in Effect PR #6429. During incubation this repository is the canonical implementation; the synchronization tool keeps the Effect PR mechanically aligned without a second logic implementation.

Early-release software: APIs may change, and releases are coupled to an exact Effect beta.

Installation

pnpm add @typeonce/effect-machine effect@4.0.0-beta.102

effect is an exact peer dependency, not a bundled runtime dependency. Consumers must install effect@4.0.0-beta.102. Upgrading this package may require upgrading Effect in lockstep; do not override the peer to another beta.

Entrypoints

import { Machine } from "@typeonce/effect-machine"
import { AtomMachine } from "@typeonce/effect-machine/reactivity"
import { ClusterMachine } from "@typeonce/effect-machine/cluster"

Each ESM entrypoint is independent and tree-shakeable. Importing the root does not load the reactivity or cluster adapters.

Basic machine

import { Effect, Schema } from "effect"
import { Machine } from "@typeonce/effect-machine"

class Idle extends Schema.TaggedClass("Idle")("Idle", {}) {}
class Running extends Schema.TaggedClass("Running")("Running", {}) {}
class Start extends Schema.TaggedClass("Start")("Start", {}) {}

const states = Machine.defineStates({ Idle, Running })

const Counter = Machine.make({
  id: "Counter",
  states: states.states,
  events: [Start],
  initial: states.initial.Idle(new Idle())
}).handle({
  Idle: {
    on: {
      Start: ({ target }) => Effect.succeed(target.full.Running(new Running()))
    }
  }
})

The exported namespaces preserve the API, type identifiers, service keys, semantics, and documentation of the Effect proposal.

Development and validation

Use pnpm 10 and Node.js 20 or newer:

pnpm install --frozen-lockfile
pnpm check

Individual commands are available for build, test, test:types, typecheck, format:check, test:consumer, test:sync, sync:check, and pack:check. Runtime tests use @effect/vitest; type tests use TSTyche and TypeScript 6.0.3.

Synchronizing Effect PR #6429

Make logic changes here first and run pnpm check. Then generate the mapped production files, runtime tests, and type tests into a writable Effect checkout:

pnpm sync:effect -- /path/to/effect

The explicit mapping covers only the eight production files and six test files. It rewrites package imports to Effect repository-relative .ts imports and restores Effect’s private PipeInspectableProto boundary. It never copies package metadata, documentation, release files, or changesets.

Check an existing checkout without writing:

pnpm sync:effect -- --check /path/to/effect

Check mode exits non-zero on any drift. pnpm test:sync exercises generation, a clean check, and drift detection in a disposable temporary directory. Never generate into a checkout with work you have not reviewed. After generation, inspect the Effect diff and run its targeted machine, reactivity, cluster, and type-test validations followed by pnpm check.

The current source reference is branch sandro/state-charts in the Effect repository. Exact dependency pins and the sync check are the proof boundary; vendoring the rest of Effect is intentionally unnecessary.

Examples

The Pokémon statechart example is a standalone React and Vite project that installs the published package from npm. Its dependency graph, lockfile, build, and CI job are isolated from this library package.

Releases

Add a changeset with pnpm changeset. CI validates frozen installation and the complete check suite. The release workflow opens version PRs and publishes with npm provenance through GitHub Actions.

Before the first release, create the typeonce-dev/effect-machine GitHub repository and configure npm trusted publishing for the repository and .github/workflows/release.yml environment. No npm token is intended.

When equivalent Machine modules ship in Effect, this package is intended to become a thin compatibility re-export package before eventual retirement.