anchor.diff: -{stdenv, fetchurl, openssl, pkgconfig
  +{ stdenv, fetchurl, openssl, pkgconfig
   , withPerl ? false, perl
   , withPython ? false, python3
   , withTcl ? false, tcl
  
positive.code:     + optionalString withTcl "--enable-tcl --with-tcl=${tcl}/lib "
      + optionalString withCyrus "--enable-cyrus ";
  
    meta = {
      description = "Advanced IRC bouncer";
      homepage = http://wiki.znc.in/ZNC;
      maintainers = [ stdenv.lib.maintainers.viric ];
      license = "ASL2.0";
      platforms = stdenv.lib.platforms.unix;
    };
  }
  
negative.code: 
  with stdenv.lib;
  stdenv.mkDerivation rec {
    name = "znc-1.2";
  
    src = fetchurl {
      url = "http://znc.in/releases/${name}.tar.gz";
      sha256 = "07bh306wl5494sqsgz4a526wvyrylkc8vpnbr5pkxwjg90mcv8nr";
    };
  
    buildInputs = [ openssl pkgconfig ]
  