`cargo-cabal`

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 cargo-cabal / 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 --features full Updating crates.io index Adding hs-bindgen v0.7.1 to dependencies. Features: + antlion + full + std

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

src/lib.rs:

```rust use hs_bindgen::*;

[hs_bindgen]

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

``text $ cargo build Compiling proc-macro2 v1.0.47 Compiling quote v1.0.21 Compiling unicode-ident v1.0.5 Compiling syn v1.0.105 Compiling serde_derive v1.0.149 Compiling semver-parser v0.7.0 Compiling serde v1.0.149 Compiling thiserror v1.0.37 Compiling antlion v0.3.1 Compiling semver v0.9.0 Compiling semver v1.0.14 Compiling lazy_static v1.4.0 Compiling hs-bindgen-traits v0.7.1 Compiling rustc_version v0.2.3 Compiling hs-bindgen-attribute v0.7.2 Compiling thiserror-impl v1.0.37 Compiling displaydoc v0.2.3 Compiling hs-bindgen-types v0.7.1 Compiling toml v0.5.9 Compiling hs-bindgen v0.7.1 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 ofhsbindgen.tomlconfiguration file n.b. you have to run the commandcargo-cabal` 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 cargo-cabal to check our setup and generate Cabal files:

``text $ cargo install cargo-cabal Updating crates.io index Ignored packagecargo-cabal v0.7.0` is already installed, use --force to override

$ cargo cabal init Error: Your Cargo.toml file should contain a [lib] section with a crate-type field that contains either staticlib or cdylib value, e.g.:

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

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

Right, we edit the Cargo.toml accordingly:

Cargo.toml:

```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 = { version = "0.7.1", features = ["full"] }

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

```text $ cargo cabal init 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 greetings v0.1.0 (/Users/yvan/demo/greetings) Finished dev [unoptimized + debuginfo] target(s) in 1.06s

$ 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) [1 of 1] Compiling Main ( omitted ... ) Linking /Users/yvan/demo/dist-newstyle/build/aarch64-osx/ghc-9.0.2/greetings-0.1.0/setup/setup ... Configuring greetings-0.1.0... Preprocessing library for greetings-0.1.0.. Building library for greetings-0.1.0.. [1 of 1] Compiling Greetings ( src/Greetings.hs, omitted ... ) ```

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.project:

cabal packages: ./greetings ./test

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

test/test.cabal (content partially omitted):

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

test/app/Main.hs:

```haskell module Main where

import Foreign.C.String import Greetings

main :: IO () main = withCString "Rust 🦀" hello ```

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, omitted ... ) 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 cargo-cabal 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.

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

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

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.