anchor.diff:      [ ncurses which perl ]
       ++ optional headerCache  gdbm
       ++ optional sslSupport   openssl
  +    ++ optional gssSupport   kerberos
       ++ optional saslSupport  cyrus_sasl
       ++ optional gpgmeSupport gpgme;
   
  
positive.code:     # I set the value 'mailbox' because it is a default in the configure script
      "--with-homespool=mailbox"
    ] ++ optional sslSupport  "--with-ssl"
      ++ optional saslSupport "--with-sasl";
  
    meta = {
  
negative.code: , openssl ? null
  , cyrus_sasl ? null
  , gpgme ? null
  , kerberos ? null
  , headerCache  ? true
  , sslSupport   ? true
  , saslSupport  ? true
  , gpgmeSupport ? true
  , imapSupport  ? true
  , withSidebar  ? true
  , gssSupport   ? true
  }:
  
  assert headerCache  -> gdbm       != null;
  