hs-bindgen

Handy macro to generate C-FFI bindings from Rust to Haskell.

This library intended to work best in a project configured by cabal-pack.

Examples

A minimal example would be to have a function annotated like this:

use hs_bindgen::*;

/// Haskell type signature are auto-magically inferred from Rust function
/// type! This feature could slow down compilation and be disabled with:
/// `hs-bindgen = { ..., default-features = false }`
#[hs_bindgen]
fn greetings(name: &str) {
    println!("Hello, {name}!");
}

This will be expanded to (you can try yourself with cargo expand):

use hs_bindgen::*;

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

#[no_mangle] // Mangling randomize symbols
extern "C" fn __c_greetings(__0: *const std::os::raw::c_char) {
    greetings(traits::ReprC::from(__0))
}

A more complete example, when we now try to pass a custom type to our interface:

use hs_bindgen::{traits::ReprC, *};

/// A custom Rust data-type
struct User {
    name: String,
}

/// Declare targeted Haskell signature
#[hs_bindgen(hello :: CString -> IO ())]
fn hello(user: User) {
    println!("Hello, {}!", user.name);
}

/// Implementation of the helper trait required by `hs_bindgen`
impl ReprC<*const i8> for User {
    fn from(ptr: *const i8) -> Self {
        User {
            name: <String as ReprC<*const i8>>::from(ptr),
        }
    }
}

Acknowledgments

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

hs-bindgen was heavily inspired by other interoperability initiatives, as wasm-bindgen and PyO3.

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