Example Haskell Packages Override from GitHub - Nix

haskell-override-git.nix

{ callPackage, haskell, lib, pkgs, ...}:
let

  fetchCabal = { cabal2nix, fetchgit, fetchzip, haskellPackages, runCommand, ... }:
    let
      srcPackage = src: folder:
        runCommand "src-package"
          {
            inherit src;
            buildInputs = [ cabal2nix ];
          }
          ''
            mkdir -p $out
            cp -r $src/${folder}/* $out
            cd $out
            cabal2nix . > package.nix
          '';
      fetch = src: folder: haskellPackages.callPackage "${srcPackage src folder}/package.nix" {};
    in {
      inherit fetch;
      fromGit = url: rev: sha256: fetch (fetchgit {
        inherit url rev sha256;
      });
      fromZip = url: sha256: fetch (fetchzip {
        inherit url sha256;
      });
    };

  fast = p: haskell.lib.dontHaddock (haskell.lib.dontCheck p);

  haskellPackagesOverridden = pkgs.haskellPackages.override {
    overrides = self: super: let
        fetchCabal' = callPackage fetchCabal { haskellPackages = self; };
      in {
        drifter-postgresql = # drifter-postgresql (latest on GitHub)
          fast (fetchCabal'.fromZip
            "https://github.com/MichaelXavier/drifter-postgresql/archive/b6281b10724665bb8a68e4a9bca48e061431ef4e.zip"
            "0p6pgj5kpmacljljys64lr4r2bysbc8rxl4ha0ijrskqg66irfkh"
            "");
      };
    };
in mkDerivation {...}