anchor.diff:    buildPhase = ":";
   
     installPhase = ''
  -    for api in api/GL{,ES{,2,3},SC{,2}}; do
  +    for api in GL{,ES{,2,3},SC{,2}}; do
         pushd $api
           while read header; do
             install -D -m644 -v $header $out/include/$(basename "$api")/$header
  
positive.code: { stdenv
  , fetchFromGitHub
  , lib
  }:
  
negative.code: stdenv.mkDerivation rec {
    name = "opengl-headers-${version}";
  
    src = fetchurl {
      url = "http://opengl-headers.tar.xz";
      multihash = "QmZvWAAPb4FAB4psCuvfKZW1N638AFG7ZTLX1Jr4kRE8UB";
      sha256 = "77172528da0549cebdaf4f5f129e020bfad722fdf9808f5e32d14766c2e81081";
    };
  
    configurePhase = ":";
  