{stdenv, fetchurl, yacc}:

assert yacc != null;

stdenv.mkDerivation {
  name = "flex-2.5.4a";
  src = fetchurl {
    url = ftp://ftp.nluug.nl/pub/gnu/non-gnu/flex/flex-2.5.4a.tar.gz;
    md5 = "bd8753d0b22e1f4ec87a553a73021adf";
  };
  buildInputs = [yacc];
}