anchor.diff: -{ stdenv, fetchurl, cmake, doxygen
  +{ stdenv, fetchurl, cmake, doxygen, darwin
   , zlib }:
   
   let
  
positive.code:       homepage = "http://icculus.org/physfs/";
        description = "Library to provide abstract access to various archives";
        license = licenses.free;
        platforms = platforms.linux;
      };
    };
  
  
negative.code: 
      nativeBuildInputs = [ cmake doxygen ];
  
      buildInputs = [ zlib ]
        ++ stdenv.lib.optionals stdenv.isDarwin [ darwin.apple_sdk.frameworks.Foundation ];
  
      enableParallelBuilding = true;
  
  