elm2nix

Turn your Elm project into buildable Nix project

https://github.com/cachix/elm2nix#readme

LTS Haskell 24.9:0.4.0
Stackage Nightly 2025-09-10:0.5.0
Latest on Hackage:0.5.0

See all snapshots elm2nix appears in

BSD-3-Clause licensed by Domen Kozar
Maintained by [email protected]
This version can be pinned in stack with:elm2nix-0.5.0@sha256:80b4a8683c0cdfef290c1ea3b314cec528546e469f87e0e562d70b3414305034,1705

Module documentation for 0.5.0

Used by 1 package in nightly-2025-09-10(full list with versions):
elm2nix

elm2nix

Build status Hackage

Convert an Elm project into Nix expressions.

It consists of multiple commands:

  • elm2nix convert: Given elm.json in current directory, all dependencies are parsed and their sha256sum calculated
  • elm2nix snapshot: Reads packages from elm.json and writes them to binary cache file registry.dat used by elm-compiler.
  • elm2nix init: Generates default.nix that glues everything together

Assumptions

Supports Elm 0.19.1

Installation

It’s already included in devenv when using Elm:

{
  langauges.elm.enable = true;

  tasks = {
    "frontend:elm2nix" = {
      exec = "cd frontend && elm2nix convert > elm-srcs.nix && elm2nix snapshot";
      execIfModified = [ "frontend/elm.json" ];
      before = [ "devenv:enterShell" ];
    };
  };

}

Running tests (as per CI)

$ ./scripts/tests.sh

FAQ

Why is mkDerivation inlined into default.nix?

As it’s considered experimental, it’s generated for now. Might change in the future.

How do I use elm2nix with ParcelJS and Yarn?

Instead of running elm2nix init, create a default.nix with the following derivation:

https://github.com/cachix/elm2nix/issues/49#issuecomment-1696082884

Changes

Changelog for elm2nix

Unreleased

0.5.0 (2025-09-09)

  • Fix inconsistent indentation in generated elm-srcs.nix, now compatible with nixfmt-rfc-style (@sander)
  • Format the default.nix generated by elm2nix init, now compatible with nixfmt-rfc-style (@sander)

0.4.0 (2024-09-23)

  • snapshot creates a minimal registry.dat from elm.json without network access (@bmillwood)

0.3.0 (2022-09-06)

  • Prevent duplicates between src and test dependencies (@gpampara)
  • #48 Aeson 2 support (@gpampara)

0.2.1 (2020-11-22)

  • #40 Fix compatibility with newer versions of uglify.js (@turboMaCk)
  • #39 Switch to unversioned collection nodePackages for npm dependencies in default.nix (@ShrykeWindgrace)

0.2 (2019-12-28)

  • #35 Elm 0.19.1 support (@gpampara)

0.1.2 (2019-10-29)

  • #33 Minification of JS output (@turboMaCk)
  • #32 Make it possible to target JS output (@turboMaCk)
  • #31 Fetch test-dependencies (@prasmussen)

0.1.1 (2019-02-19)

Changes

  • #22 Support req-0.1.0.0 (@domenkozar)

0.1.0 (2018-12-28)

  • Initial release (@domenkozar)