stacklock2nix

2022-12-15

For a while now I've wanted a way to use Nix to build a Haskell package that has a stack.yaml file. The go-to method in the Haskell community is to use haskell.nix, but haskell.nix has a few downsides1:

  • Evaluation can take quite a while, and building your project without using the IOHK cache can take a very long time.
  • haskell.nix is quite complicated. It can be hard to figure out problems and fix bugs.
  • It is completely separate from the Haskell infrastructure in Nixpkgs.

I decided to write a Nix library called stacklock2nix. It generates a Nixpkgs-compatible Haskell overlay from a stack.yaml and stack.yaml.lock file. This allows you to easily build a Haskell project with Nix (as long as you have a stack.yaml and stack.yaml.lock file). It allows you to use your stack.yaml file as a single-source-of-truth for Haskell dependency versions2.

You can find usage instructions, as well as two example projects in the README.

I've decided to do a series of blog posts where I use stacklock2nix to package various Haskell projects. Check out each one for a realistic example of using stacklock2nix:

  1. PureScript

    This post introduces an easy way to build a straight-forward Haskell project with stacklock2nix. This is good for beginners.

  2. Dhall

    This post introduces an advanced way to build a Haskell project with multiple packages. This is good for developers who need ultimate flexibility.

  3. Pandoc

    This post is similar to the post about building the PureScript compiler, but it sets up Pandoc to be statically linked. This would be a good example to follow for people that want to distribute fully statically-linked Haskell binaries.

Footnotes

  1. haskell.nix of course has a bunch of good points as well.↩︎

  2. As opposed to manually keeping dependency versions in sync between stack.yaml and your Nix code.↩︎

tags: haskell, nixos