cabal-pack

A tool that helps you to turn in one command a Rust crate into a Haskell Cabal library!

To generate bindings, you need to annotate the Rust function you want to expose with hs-bindgen macro.

Getting started

Here a little screencast demonstrating how it works (commands walkthrough are just pasted below):

asciinema

N.B. You need in your $PATH a working Rust and Haskell environment, if you use Nix you can just enter: nix-shell -p cabal-install ghc cargo rustc

Welcome in this little cabal-pack / hs-bindgen demo 🙂

Let's start by creating a dumb Rust library!

``text $ cargo new --lib greetings Created librarygreetings` package

$ tree greetings greetings ├── Cargo.toml └── src └── lib.rs

1 directory, 2 files

$ cd greetings ```

Add hs-bindgen to the dependencies list:

text $ cargo add hs-bindgen Updating crates.io index Adding hs-bindgen v0.4.0 to dependencies.

And use it to decorate the function we want to expose:

```rust use hsbindgen::hsbindgen;

[hs_bindgen]

fn hello(name: &str) { println!("Hello, {name}!"); } ```

``text $ cargo build Compiling proc-macro2 v1.0.46 Compiling unicode-ident v1.0.4 Compiling quote v1.0.21 Compiling syn v1.0.101 Compiling serde_derive v1.0.145 Compiling serde v1.0.145 Compiling semver v1.0.14 Compiling toml v0.5.9 Compiling hs-bindgen v0.4.0 Compiling greetings v0.1.0 (/Users/yvan/demo/greetings) error: custom attribute panicked --> src/lib.rs:3:1 | 3 | #[hs_bindgen] | ^^^^^^^^^^^^^ | = help: message: fail to read content of.hsbindgenconfiguration file n.b. you have to run the commandcabal-pack` to generate it: Os { code: 2, kind: NotFound, message: "No such file or directory" }

error: could not compile greetings due to previous error ```

So, we will use cabal-pack to check our setup and generate Cabal files:

``text $ cargo install cabal-pack Updating crates.io index Ignored packagecabal-pack v0.4.0` is already installed, use --force to override

$ cabal-pack Error: Your Cargo.toml file should contain a [lib] section with a crate-type field that contains staticlib value:

[lib] crate-type = ["staticlib"] ```

N.B. if you're a Nix user, rather than rely on impure cargo install fell free to just nix run github:yvan-sraka/cabal-pack

Right, we edit the Cargo.toml accordingly:

```toml [package] name = "greetings" version = "0.1.0" edition = "2021"

See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies] hs-bindgen = "0.4.0"

[lib] crate-type = ["staticlib"] ```

```text $ cabal-pack Cabal files generated!

You should now be able to compile your library with cabal build and should add hs-bindgen to your crate dependencies list and decorate the Rust function you want to expose with #[hs_bindgen] attribute macro.

$ ls Cargo.lock Cargo.toml Setup.lhs greetings.cabal src target ```

```text $ cargo build Compiling hs-bindgen v0.4.0 Compiling greetings v0.1.0 (/Users/yvan/demo/greetings) Finished dev [unoptimized + debuginfo] target(s) in 0.55s

$ cabal build Build profile: -w ghc-9.0.2 -O1 In order, the following will be built (use -v for more details): - greetings-0.1.0 (lib:greetings) (first run) Preprocessing library for greetings-0.1.0.. Building library for greetings-0.1.0.. [1 of 1] Compiling Greetings ( src/Greetings.hs, /Users/yvan/demo/greetings/dist-newstyle/build/aarch64-osx/ghc-9.0.2/greetings-0.1.0/build/Greetings.o, /Users/yvan/demo/greetings/dist-newstyle/build/aarch64-osx/ghc-9.0.2/greetings-0.1.0/build/Greetings.dyn_o ) ```

It works! And so cargo build too if you just want to use the library in a Rust project!

Now let's try to use our freshly generated library in an Haskell app 😉

```text $ cd .. $ cabal init --non-interactive test [Log] Guessing dependencies... [Log] Using cabal specification: 3.8 [Warning] unknown license type, you must put a copy in LICENSE yourself. [Log] Creating fresh file CHANGELOG.md... [Log] Creating fresh directory ./app... [Log] Creating fresh file app/Main.hs... [Log] Creating fresh file test.cabal... [Warning] No synopsis given. You should edit the .cabal file and add one. [Info] You may want to edit the .cabal file and add a Description field.

$ tree test test ├── app │   └── Main.hs ├── CHANGELOG.md └── test.cabal

1 directory, 3 files ```

We create a cabal.project (equivalent to cargo workspace) to perform a local test without having to upload greetings on hackage:

cabal packages: ./greetings ./test

We edit test.cabal to make it depends on greetings library:

cabal executable test -- Other library packages from which modules are imported. build-depends: base, greetings

We write a minimalist main function that will make call hello from Greetings module

```haskell module Main where

import Foreign.C.String import Greetings

main :: IO () main = hello =<< newCString "Rust" ```

Let's check if everything works as expected:

text $ cabal run test Build profile: -w ghc-9.0.2 -O1 In order, the following will be built (use -v for more details): - test-0.1.0.0 (exe:test) (first run) Configuring executable 'test' for test-0.1.0.0.. Preprocessing executable 'test' for test-0.1.0.0.. Building executable 'test' for test-0.1.0.0.. [1 of 1] Compiling Main ( app/Main.hs, /Users/yvan/demo/dist-newstyle/build/aarch64-osx/ghc-9.0.2/test-0.1.0.0/x/test/build/test/test-tmp/Main.o ) Linking /Users/yvan/demo/dist-newstyle/build/aarch64-osx/ghc-9.0.2/test-0.1.0.0/x/test/build/test/test ... Hello, Rust!

That's all folks! Happy hacking 🙂

Nix support

The --enable-nix CLI arg makes cabal-pack generate a haskell.nix / naersk based flake.nix rather than the Setup.lhs.

N.B. when first working with hs-bindgen and Nix flakes, checking if Cargo.lock isn't in .gitignore and running cargo build and git add --all before nix build, will save you a lot of pain 😉

Acknowledgments

⚠️ This is still a working experiment, not yet production ready.

cabal-pack was heavily inspired by other interoperability initiatives, as wasm-pack and Maturin.

This project was part of a work assignment as an IOG contractor.