static L<Symbol> allToSymbol(Collection<? extends CharSequence> l) {
  ifdef SymbolAsString
  ret allToString(l);
  endifdef
  ifndef SymbolAsString
  L<Symbol> out = emptyList(l);
  for (CharSequence s : l)
    out.add(toSymbol(s));
  ret out;
  endifndef
}