hnix/README.md

# hnix

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

## Prerequisites

Nix is installed and in your `$PATH`. This is so that `nix-store` can be used
for interacting with store paths, until `hnix-store` is ready.

## Getting Started

```
$ git clone --recursive https://github.com/haskell-nix/hnix.git
...
$ cd hnix
$ nix-shell
$ cabal v2-configure --enable-tests
$ cabal v2-build
$ cabal v2-test
# To run all of the tests, which takes up to a minute:
$ env ALL_TESTS=yes cabal v2-test
# To run only specific tests (see `tests/Main.hs` for a list)
$ env NIXPKGS_TESTS=yes PRETTY_TESTS=1 cabal v2-test
$ ./dist/build/hnix/hnix --help
```

## Using the REPL

To enter the `hnix` REPL use

```
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
$ ./dist/build/hnix/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 --arg doBenchmarks true
$ 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
$ ./dist/build/hnix/hnix <args> +RTS -p
```

## Building with GHCJS

From the project root directory, run:

```
$ NIX_CONF_DIR=$PWD/ghcjs nix-build ghcjs
```

This will build an `hnix` library that can be linked to your GHCJS
application.

## 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
```

## How you can help

### Issue Tracker Backlog

If you're looking for a way to help out, try taking a look
[here](https://github.com/haskell-nix/hnix/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22+no%3Aassignee).
When you find an issue that looks interesting to you, comment on the ticket to
let others know you're working on it; look for others who might have done the
same. You can talk with everyone live on
[Gitter](https://gitter.im/haskell-nix/Lobby).

When you're ready to submit a pull request, test it with:

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

Make sure that all the tests that were passing prior to your PR are still
passing afterwards; 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
```