hnix/README.md

# hnix

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Haskell parser, evaluator and type checker for the Nix language.

## Contents

<!-- TOC -->
- [Prerequisites](#prerequisites)
- [Getting Started](#getting-started)
- [Using the REPL](#using-the-repl)
- [Building with full debug info](#building-with-full-debug-info)
- [Building with benchmarks enabled](#building-with-benchmarks-enabled)
- [Building with profiling enabled](#building-with-profiling-enabled)
- [Using the Cachix binary cache](#using-the-cachix-binary-cache)
- [Contributing](#contributing)
  - [Evaluating Nixpkgs with HNix](#evaluating-nixpkgs-with-hnix)
<!-- /TOC -->

## Prerequisites
Until `hnix-store` is ready, `nix-store` is still used for interacting with the store paths, so Nix is still required installed and available through `$PATH`.

## Getting Started

```
git clone --recursive https://github.com/haskell-nix/hnix.git
cd hnix
nix-shell
cabal v2-configure --enable-tests
cabal v2-build
```

Run testing:
  * Default:
    ```
    cabal v2-test
    ```

  * All:
    ```
    env ALL_TESTS=yes cabal v2-test
    ```

  * Selected (list of tests is in `tests/Main.hs`):
    ```
    env NIXPKGS_TESTS=yes PRETTY_TESTS=1 cabal v2-test
    ```

Run built binary with Cabal (`--` is for separation between `cabal` & `hnix` args):
```
cabal v2-run hnix -- --help
```

## Using the REPL

Enter REPL:
```
hnix --repl
```

To evaluate an expression and make it available in the REPL as the `input` variable use:
```
hnix --eval -E '(import <nixpkgs> {}).pkgs.hello' --repl
```

Use the `:help` command for a list of all available REPL commands.

## Building with full debug info

To build `hnix` for debugging, and with full tracing output and stack traces, use:

```
nix-shell
cabal v2-configure --enable-tests --enable-profiling --flags=profiling --flags=tracing
cabal v2-build
cabal v2-run hnix -- -v5 --trace <args> +RTS -xc
```

Note that this will run quite slowly, but will give the most information as to what might potentially be going wrong during parsing or evaluation.

## Building with benchmarks enabled

To build `hnix` with benchmarks enabled:

```
nix-shell
cabal v2-configure --enable-tests --enable-benchmarks
cabal v2-build
cabal v2-bench
```

## Building with profiling enabled

To build `hnix` with profiling enabled:

```
nix-shell
cabal v2-configure --enable-tests --enable-profiling --flags=profiling
cabal v2-build
cabal v2-run hnix -- <args> +RTS -p
```

## Using the Cachix binary cache

If you're on macOS, you can use the binary cache at Cachix to avoid building the specific dependencies used by hnix. Just use these commands:

```
nix-env -iA cachix -f https://github.com/NixOS/nixpkgs/tarball/db557aab7b690f5e0e3348459f2e4dc8fd0d9298
cachix use hnix
```

## Contributing

1. If something in the [quests](https://github.com/haskell-nix/hnix/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22+no%3Aassignee) looks interesting, look through the thread and leave a comment taking it, to let others know you're working on it.

2. You are free to chat with everyone on [Gitter](https://gitter.im/haskell-nix/Lobby).

3. When pull request is ready to be submitted, to save time - please, test it with:

```
git submodule update --init --recursive
nix-shell --run "LANGUAGE_TESTS=yes cabal v2-test"
```

Please, check that all tests that were passing prior (most probably all tests mentioned in the command) are still passing for the PR, it is faster to chech that locally then through CI. It's OK if no new tests are passing.

### Evaluating Nixpkgs with HNix

Currently the main high-level goal is to be able to evaluate all of Nixpkgs. To run this yourself, first build `hnix` with `nix-build`, then run the following command:

```
./result/bin/hnix --eval -E "import <nixpkgs> {}" --find
```