final: prev: let
  haskellPackages = prev.haskellPackages.extend (self: super: {
    kassandra = self.callCabal2nix "kassandra" (prev.sources.kassandra + "/kassandra") {};
    standalone = self.callCabal2nix "standalone" (prev.sources.kassandra + "/standalone") {};
    taskwarrior = self.callHackageDirect {
      pkg = "taskwarrior";
      ver = "0.5.0.0";
      sha256 = "sha256-elDUtz0NSG4WHxkyCQ1CunYXWIVRj6EqkKSchPy+c3E=";
    } {};
  });
in {
  kassandra = haskellPackages.standalone;
}