anchor.diff: -{ lib, fetchurl, fetchpatch, stdenv, gnutls, glib, pkg-config, check, libotr, python2
  +{ lib, fetchurl, fetchpatch, stdenv, gnutls, glib, pkg-config, check, libotr, python3
   , enableLibPurple ? false, pidgin ? null
   , enablePam ? false, pam ? null
   }:
  
positive.code:     homepage = "https://www.bitlbee.org/";
      license = licenses.gpl2Plus;
  
      maintainers = with maintainers; [ pSub ];
      platforms = platforms.gnu ++ platforms.linux;  # arbitrary choice
    };
  }
  
negative.code: 
    nativeBuildInputs = [ pkg-config ] ++ optional doCheck check;
  
    buildInputs = [ gnutls libotr python3 ]
      ++ optional enableLibPurple pidgin
      ++ optional enablePam pam;
  
  