> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lionlang.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Install @lionlang/core

> Add @lionlang/core to your TypeScript project with npm, yarn, pnpm, or bun. Covers peer dependencies, package exports, and tsconfig requirements.

`@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

<CodeGroup>
  ```bash npm theme={null}
  npm install @lionlang/core effect
  ```

  ```bash yarn theme={null}
  yarn add @lionlang/core effect
  ```

  ```bash pnpm theme={null}
  pnpm add @lionlang/core effect
  ```

  ```bash bun theme={null}
  bun add @lionlang/core effect
  ```
</CodeGroup>

<Tip>
  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.
</Tip>

## 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.

```json tsconfig.json theme={null}
{
  "compilerOptions": {
    "target": "ESNext",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true
  }
}
```

<Note>
  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`.
</Note>

## 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:

```typescript theme={null}
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](/quickstart) for the next steps.