anchor.diff:    src = fetchurl {
       urls = tarballUrls version;
       hashOutput = false;
  -    sha256 = "7c2464ad6cb7b513b2c350a092d919327e1f63d12ff024836acbb504475da5c6";
  +    sha256 = "deec377b95aa72ec4e1a33fe2c938d2480749d740b5291a7cc1d77808d3710bf";
     };
   
     nativeBuildInputs = [
  
positive.code:   passthru = {
      srcVerification = fetchurl rec {
        failEarly = true;
        urls = tarballUrls "3.1";
        inherit (src) outputHashAlgo;
        outputHash = "7c2464ad6cb7b513b2c350a092d919327e1f63d12ff024836acbb504475da5c6";
        fullOpts = {
          pgpsigUrls = map (n: "${n}.sig") urls;
          pgpKeyFingerprint = "7DF8 4374 B1EE 1F97 64BB  E25D 0DDC AA32 78D5 264E";
  
negative.code:     "mirror://gnu/bison/bison-${version}.tar.xz"
    ];
  
    version = "3.2";
  in
  stdenv.mkDerivation rec {
    name = "bison-${version}";
  