anchor.diff:  
     setupCommand = if isGhcjs then "${ghc.nodejs}/bin/node ./Setup.jsexe/all.js" else "./Setup";
     ghcCommand = if isGhcjs then "ghcjs" else "ghc";
  +  ghcCommandCaps = toUpper ghcCommand;
   
   in
   stdenv.mkDerivation ({
  
positive.code:       LANG = "en_US.UTF-8";
        LOCALE_ARCHIVE = optionalString stdenv.isLinux "${glibcLocales}/lib/locale/locale-archive";
        shellHook = ''
          export NIX_GHC="${ghcEnv}/bin/${ghcCommand}"
          export NIX_GHCPKG="${ghcEnv}/bin/${ghcCommand}-pkg"
          export NIX_GHC_DOCDIR="${ghcEnv}/share/doc/ghc/html"
          export NIX_GHC_LIBDIR="${ghcEnv}/lib/${ghcEnv.name}"
        '';
      };
  
  
negative.code: let
  
    inherit (stdenv.lib) optional optionals optionalString versionOlder
                         concatStringsSep enableFeature optionalAttrs toUpper;
  
    isGhcjs = ghc.isGhcjs or false;
  
  