nix library

default.nix

{ lib ? import ./nix/lib.nix { depsPath = ./nix/deps; } }:

let

  pkgs = lib.fetchDep "nixpkgs";

  shell = pkgs.mkShell {
    buildInputs = [
      pkgs.haskellPackages.ghc
      (lib.addDep pkgs)
    ];
  };
  
in {
  inherit pkgs shell;
}

lib.nix

{ depsPath }:

rec {

  githubTarball = {owner, repo, rev, sha256}:
    builtins.fetchTarball { url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz"; inherit sha256; };

  fetchDep = dep: import (githubTarball (builtins.fromJSON (builtins.readFile (depsPath + "/${dep}.json")))) {};

  addDep = nixpkgs: (nixpkgs.writeScriptBin "add-dep" ''
    ${nixpkgs.nix-prefetch-github}/bin/nix-prefetch-github --no-prefetch $@ > ${depsPath}/$2.json
  '');
}

shell session

[user@laptop:~/Code/skeleton-nix]$ nix-shell
these derivations will be built:
  /nix/store/vyv3iznl81zcqkl68gp133smvi3jmnpz-add-dep.drv
building '/nix/store/vyv3iznl81zcqkl68gp133smvi3jmnpz-add-dep.drv'...

[nix-shell:~/Code/skeleton-nix]$ add-dep nikita-volkov hasql
/nix/store/8c7azl6f1fxgh6g2p8nxmfv2jm8j84m3-add-dep/bin/add-dep: ligne 1: /nix/store/xr9xwwz6b1zqihci28g02qghp3vvwqan-deps/hasql.json: Read-only file system