static MapSO listToWordTree(LS l) {
  ret listToWordTree(l, "x"); // any old value that is not a map
}

static MapSO listToWordTree(LS l, S value) {
  MapSO tree = wordTree();
  for (S s : unnull(l))
    wordTreeAdd(tree, javaTokC(s), value);
  ret simplifyWordTree(tree);
}