Install @lionlang/core

@lionlang/core is published to npm as an ESM-only package. This page covers how to install it with your preferred package manager, which peer dependencies you need, what the package exports, and the TypeScript configuration it requires.

Install the package

npm install @lionlang/core effect

yarn add @lionlang/core effect

pnpm add @lionlang/core effect

bun add @lionlang/core effect

If you are using Bun, run bun add @lionlang/core effect from your project root. Bun resolves and installs all transitive dependencies automatically without a separate bun install step after adding packages.

Peer dependencies

@lionlang/core has two peer dependencies that you must install alongside it:

Package	Role
`effect`	Provides the `Effect` type used by `run` and `evaluate`. All evaluation results are `Effect` values.
`typescript`	Required at build time. The package ships only TypeScript source types; there is no separate `@types` package.

TypeScript configuration

@lionlang/core is built with ESNext output and NodeNext module resolution. Your tsconfig.json must match these settings or the package’s subpath exports will not resolve correctly.

tsconfig.json

{
  "compilerOptions": {
    "target": "ESNext",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true
  }
}

Strict mode is required. The package uses exactOptionalPropertyTypes, noUncheckedIndexedAccess, and related strict flags internally. Disabling strict mode in your project may cause type errors when importing from @lionlang/core.

Package exports

@lionlang/core uses the Node.js exports field to expose fine-grained subpath entry points. Import directly from the path you need rather than the package root.

Core entry points

Import path	What it exports
`@lionlang/core/evaluation/evaluate`	`run` and `evaluate` — the top-level evaluation functions
`@lionlang/core/modules`	`stdlib` — the default environment with all built-in modules
`@lionlang/core/evaluation/environment`	`makeEnvironment` — creates a scoped `LionEnvironmentService`

Standard library modules

Each module is also importable individually if you want to compose a partial environment:

Import path	Module
`@lionlang/core/modules/number`	Arithmetic and comparison
`@lionlang/core/modules/string`	String operations
`@lionlang/core/modules/boolean`	Boolean logic
`@lionlang/core/modules/array`	Array construction and transformation
`@lionlang/core/modules/object`	Object access, method calls, and construction
`@lionlang/core/modules/func`	Function binding, partial application, and callbacks
`@lionlang/core/modules/value`	Type predicates and identity
`@lionlang/core/modules/console`	Logging utilities

Schemas and types

Import path	What it exports
`@lionlang/core/schemas/lion-expression`	`LionExpressionSchema` and `LionExpressionType`
`@lionlang/core/schemas/environment`	Environment schema
`@lionlang/core/schemas/evaluation`	Evaluation input/output schemas
`@lionlang/core/types/evaluation`	`EvaluateResult` and related TypeScript types

Special forms (individual imports)

Each special form is available at its own path if you need to compose a custom evaluator:

@lionlang/core/evaluation/special-forms/define
@lionlang/core/evaluation/special-forms/lambda
@lionlang/core/evaluation/special-forms/cond
@lionlang/core/evaluation/special-forms/match
@lionlang/core/evaluation/special-forms/begin
@lionlang/core/evaluation/special-forms/quote
@lionlang/core/evaluation/special-forms/eval

Verify the installation

After installing, run this snippet to confirm everything is wired up correctly:

import { Effect } from "effect";
import { run } from "@lionlang/core/evaluation/evaluate";
import { stdlib } from "@lionlang/core/modules";

const result = await Effect.runPromise(
  run(["number/add", 1, 2], stdlib)
);

console.log(result); // => 3

If you see 3 in the console, @lionlang/core is installed and working. See Quickstart for the next steps.

Get Started

Core Concepts

Standard Library

Guides

Install @lionlang/core

Install the package

Peer dependencies

TypeScript configuration

Package exports

Core entry points

Standard library modules

Schemas and types

Special forms (individual imports)

Verify the installation

​Install the package

​Peer dependencies

​TypeScript configuration

​Package exports

​Core entry points

​Standard library modules

​Schemas and types

​Special forms (individual imports)

​Verify the installation

Install the package

Peer dependencies

TypeScript configuration

Package exports

Core entry points

Standard library modules

Schemas and types

Special forms (individual imports)

Verify the installation