anchor.diff:  , fetchurl
   , cmake
   , google-gflags ? null
  -, glog ? null
  +, glog
   , runTests ? false
   }:
   
  
positive.code:     sha256 = "20bb5db05c3e3e14a4062e2cf2b0742d2653359549ecded3e0653104ef3deb17";
    };
  
    buildInputs = [ cmake ]
      ++ stdenv.lib.optional useGlog glog
      ++ stdenv.lib.optional (google-gflags != null) google-gflags;
  
    inherit eigen;
  
negative.code: 
    cmakeFlags = "
      -DEIGEN_INCLUDE_DIR=${eigen}/include/eigen3
    ";
  
    meta = with stdenv.lib; {
  