anchor.diff:            sha256 = sha256;
           };
   
  +      # Return null if x == null otherwise return the argument
  +      nullable = x: ret: if x == null then null else ret;
  +
         #
         # Applications
         #
  
positive.code: 
        f2c = callPackage ./f2c { };
  
        tests = {
          cfour = callPackage ./tests/cfour { };
          cp2k = callPackage ./tests/cp2k { };
          bagel = callPackage ./tests/bagel { };
  
negative.code:         dalton = callPackage ./tests/dalton { };
          hpcg = callPackage ./tests/hpcg { };
          hpl = callPackage ./tests/hpl { };
          mesa-qc = nullable mesa-qc (callPackage ./tests/mesa { });
          molcas = callPackage ./tests/molcas { };
          #molcasUnstable = callPackage ./tests/molcas { molcas=self.molcasUnstable; };
          mrcc = nullable mrcc (callPackage ./tests/mrcc { });
          nwchem = callPackage ./tests/nwchem { };
          psi4 = callPackage ./tests/psi4 { };
          qdng = nullable qdng (callPackage ./tests/qdng { });
          dgemm = callPackage ./tests/dgemm { };
          stream = callPackage ./tests/stream { };
          turbomole = nullable turbomole (callPackage ./tests/turbomole { });
          xtb = callPackage ./tests/xtb { };
        }  // lib.optionalAttrs (cfg.licMolpro != null) {
          molpro = callPackage ./tests/molpro { };
  