uniffi-haskell

Haskell bindings for UniFFI 0.32.

The Rust crate must build both a shared library, used to read UniFFI metadata, and a static library, used when linking Haskell:

[lib]
crate-type = ["cdylib", "staticlib"]

[dependencies]
uniffi = "=0.32.0"

This library is largely "vibecoded" under careful human review.

Nix flake

This is the most straightforward and foolproof way to use this in a polyglot project, if you are already using Nix.

How

Add this repository as a flake input, then generate a Cabal package with:

bindings = uniffi-haskell.lib.mkUniffiHaskellCabalPackage {
  inherit pkgs;
  crate = myRustCrate;
  libraryName = "my_crate";
  packageName = "my-crate-bindings";
  license = "MPL-2.0";
};

Cabal package

We support manually building a Cabal package for easy consumption in a typical Haskell project. Integrating this into a CI pipeline is left as an exercise for the reader.

How

Create cabal-header.txt:

cabal-version: 3.0
name: my-crate-bindings
version: 0.1.0
build-type: Simple

Generate the package:

cargo run -p uniffi-bindgen-haskell --bin uniffi-bindgen-haskell -- \
  --library target/release/libmy_crate.dylib \
  --out-dir generated \
  --cabal-file my-crate-bindings.cabal \
  --cabal-header cabal-header.txt \
  --cabal-native-library my_crate \
  --cabal-extra-lib-dir /absolute/path/to/generated/native-static

mkdir -p generated/native-static
cp target/release/libmy_crate.a generated/native-static/

Add both packages to cabal.project:

packages:
  haskell/uniffi-runtime
  generated

Then run cabal build all.

Raw Haskell source

If you want to integrate this into a non-Cabal build system, that is also feasible. This offers straightforward generation of just the Haskell source files and C shims.

How

Build the Rust crate, then run:

cargo run -p uniffi-bindgen-haskell --bin uniffi-bindgen-haskell -- \
  --library target/release/libmy_crate.dylib \
  --out-dir generated

Use libmy_crate.so on Linux. The output contains Haskell sources under generated/haskell, C sources under generated/cbits, and generated/manifest.json. Compile the Haskell and C sources, depend on haskell/uniffi-runtime, and link libmy_crate.a.

myRustCrate must expose lib/libmy_crate.dylib or .so and lib/libmy_crate.a. Use metadataLibrary and staticLibrary to override those paths. The result is a generated Cabal source package containing the bindings and static library.