nix-bindings-haskell

Haskell bindings to the Nix C API.

Packages

Package	Description
nix-bindings	Safe, ergonomic Haskell API with a Nix monad, type-checked accessors, and automatic resource management (import Nix.C)
nix-bindings-sys	Raw FFI bindings, auto-generated by hs-bindgen

Quick start

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeApplications #-}
import Data.Int (Int64)
import Nix.C

main :: IO ()
main = do
  initNix
  result <- runNix $
    withStore "daemon" $ \store ->
      withEvalState store $ \state ->
        evalAs @Int64 state "{ a = { b = 42; }; }.a.b"
  print result -- Right 42

Building

nix develop
cabal build all
cabal test all

Flake outputs

Package	Description
nix-bindings (default)	High-level library built from committed bindings
nix-bindings-sys	Low-level FFI bindings built from committed source
nix-bindings-regenerated	High-level library built from regenerated bindings
nix-bindings-sys-regenerated	Low-level FFI bindings regenerated from Nix C API headers at build time

The -regenerated variants use hs-bindgen to regenerate bindings from Nix C API headers at build time. Override the nix flake input to generate bindings for a different Nix version:

nix build .#nix-bindings-regenerated --override-input nix github:NixOS/nix/3.34.4

Regenerating FFI bindings

The raw bindings in nix-bindings-sys are generated from Nix C API headers and committed to the repository. To regenerate manually:

nix develop
cd nix-bindings-sys
rm -rf src/Generated binding-specs
mkdir -p binding-specs
./generate-bindings

The Nix C API headers come from the nix flake input (NixOS/nix).