haskell.nix/docs/user-guide-stack.md

User Guide (stack project)

Here we will look into how to generate the pkgs.nix file for a stack.yaml project. For the full integration please see the User Guide

Using stack-to-nix

With nix-tools in PATH, we can simply run the following command on a stack project:

stack-to-nix -o nix stack.yaml > nix/.stack-pkgs.nix

This will produce a nix/.stack-pkgs.nix file that looks like the following:

{
  resolver = "lts-12.17";
  overlay = hackage:
    {
      packages = {
        "o-clock" = hackage.o-clock."0.1.1".revisions.default;
        ...
      } // {
        my-package = ./.stack.nix/my-package.nix;
        ...
      };
    };
}

This file contains the stackage resolver, as well as an overlay of packages. The overlay specifies which extra-deps (here: o-clock-0.1.1) we wanted to overlay over the stackage snapshot, and what local packages we want (here: my-package).

We will then create the following nix/pkgs.nix file:

let stack-pkgs = import ./.stack-pkgs.nix; in
{ stackage, ... }:
{ pkg-def = stackage.${stack-pkgs.resolver};
  inherit (stack-pkgs) overlay;
}

If you came here from the User Guide, go back and complete the setup.