selfsym.nix

let
  overlay = self: super: {
    haskellPackages = with self.haskell.lib; super.haskellPackages.override (old: {
      overrides = self.lib.composeExtensions (old.overrides or (_: _: {})) (hself: hsuper: {
        hello = overrideCabal hsuper.hello (olddrv: {
          enableExecutableProfiling = true;
        });
      });
    });
  };
  pkgs = import <nixpkgs> { overlays = [overlay]; config = {}; };
in
  pkgs.haskellPackages.hello