anchor.diff:      binary = self.binary_0_7_2_2;       # core package in ghc >= 7.2.2
       caseInsensitive = super.caseInsensitive; # undo the override from ghc 7.2.2
       HsSyck = self.HsSyck_0_51;
  -    jailbreakCabal = super.jailbreakCabal.override { Cabal = self.Cabal_1_16_0_3; };
       random = null;                      # core package in ghc <= 7.0.x
     };
   
  
positive.code:   ghc783Prefs = self : super : ghcHEADPrefs self super // {
      cabalInstall_1_20_0_4 = super.cabalInstall_1_20_0_4.override { Cabal = self.Cabal_1_20_0_2; };
      codex = super.codex.override { hackageDb = super.hackageDb.override { Cabal = self.Cabal_1_20_0_2; }; };
      MonadRandom = self.MonadRandom_0_2_0_1; # newer versions require transformers >= 0.4.x
      mtl = self.mtl_2_1_3_1;
    };
  
negative.code:     deepseq = self.deepseq_1_2_0_1;
      dlist = super.dlist.override { cabal = self.cabal.override { Cabal = self.Cabal_1_16_0_3; }; };
      exceptions = null;                  # none of our versions compile
      jailbreakCabal = super.jailbreakCabal.override { Cabal = self.Cabal_1_16_0_3; };
      logict = super.logict.override { cabal = self.cabal.override { Cabal = self.Cabal_1_16_0_3; }; };
      monadPar = self.monadPar_0_1_0_3;
      nats = null;                        # none of our versions compile
  