anchor.diff:  
     src = fetchurl {
       url = "http://mercurial.selenic.com/release/${name}.tar.gz";
  -    sha256 = "0lwgncim4cy91ly8389h2bbhl4nbi8xjgp0kx37kgq8q2lx2nil6";
  +    sha256 = "1r6hdxka867lpsq2jq3vz662m3ywflg4yylayc9g0s9gmiww5pgi";
     };
   
     inherit python; # pass it so that the same version can be used in hg2git
  
positive.code:     '';
  
    meta = {
      description = "A fast, lightweight SCM system for very large distributed projects";
      homepage = "http://www.selenic.com/mercurial/";
      license = stdenv.lib.licenses.gpl2;
      maintainers = [ stdenv.lib.maintainers.eelco ];
    };
  
negative.code: , guiSupport ? false, tk ? null, curses }:
  
  let
    version = "3.1";
    name = "mercurial-${version}";
  in
  
  stdenv.mkDerivation {
  