anchor.diff:    '';
   
     buildInputs = [
  -    openal curl libogg libvorbis SDL2 SDL2_image zlib
  +    openal curl libogg libvorbis libtheora SDL2 SDL2_image zlib clang
     ];
   
     NIX_CFLAGS_COMPILE = [
  
positive.code: { lib, stdenv, fetchFromGitHub, requireFile
  , openal, curl, libogg, libvorbis
  , SDL2, SDL2_image, zlib
  , unfree_assets ? false }:
  
  stdenv.mkDerivation rec {
    pname = "keeperrl";
    version = "alpha28";
  
    free-src = fetchFromGitHub {
      owner = "miki151";
      repo = "keeperrl";
      rev = version;
      sha256 = "0isj8ijn5a89m2r5cxk4lcsq0cydx7c0h87vgr8v5cndm3rd27cy";
    };
  
    assets = if unfree_assets then requireFile rec {
  
negative.code: 
        "nix-prefetch-url file://\$PWD/${name}".
      '';
      sha256 = "0115pxdzdyma2vicxgr0j21pp82gxdyrlj090s8ihp0b50f0nlll";
    } else null;
  
    sourceRoot = "source";
  