effection-typed-context

Type-aware context helpers for Effection.

effection-typed-context wraps Effection's context utilities so yielded operations keep track of which context values are required and which providers satisfy them.

Install

pnpm add effection-typed-context effection

Usage

effection-typed-context supports two integration styles:

1. Import from effection-typed-context as a drop-in replacement for the relevant Effection APIs.
2. Keep importing from effection and add the effection-typed-context ambient type augmentation.

Drop-in replacement

Import the typed APIs directly from effection-typed-context:

import { type Effect } from "effection";
import {
  createContext,
  provide,
  run,
  strip,
  type Provider,
  type Requirement,
} from "effection-typed-context";

const APIBaseUrl = createContext<string>("apiBaseUrl");

function* program() {
  return yield* APIBaseUrl.expect();
}

// Before requirements are provided:
// Generator<Effect<unknown> | Requirement<string>, string, unknown>

const providedProgram = provide(program, function* () {
  yield* APIBaseUrl.set("https://example.com");
});

// After requirements are provided:
// Generator<Effect<unknown> | Provider<string>, string, unknown>

const rootProgram = strip(() => providedProgram);

// At the root, strip removes all Provider types once context has been provided:
// Generator<Effect<unknown>, string, unknown>

const value = await run(() => rootProgram);

Effection augmentation

If you want to keep existing imports from effection, add the ambient types in your project:

/// <reference types="effection-typed-context/types" />

This is typically added in a project-level .d.ts file such as env.d.ts. After that, the typed signatures are available from effection directly:

import { createContext, run } from "effection";
import { provide } from "effection-typed-context";

const apiBaseUrl = createContext<string>("apiBaseUrl");

function* program() {
  return yield* apiBaseUrl.expect();
}

const value = await run(() =>
  provide(program, function* () {
    yield* apiBaseUrl.set("https://example.com");
  }),
);

When you use the module augmentation, run() and main() accept the typed operations directly, so you typically do not need strip() at the root.

API

• createContext(name, defaultValue?)
• provide(operation, provider)
• spawn(operation)
• resource(operation) With Effection alone, this is often written as resource<Type>(function* (provide) {}). With typed-context, prefer putting the type on provide instead: resource(function* (provide: Provide<Type>) {}).
• run(operation)
• main(operation)
• all(operations)
• strip(operation) Removes all Provider types from an operation. Use it at the root after all required context has been provided. This is mainly useful when importing the drop-in API from effection-typed-context; with the effection module augmentation, run() and main() can consume the typed operation directly.