static L<S> ctxActions(S body) {
  L<S> lines = lines(body);
  int i = 0;
  new L<S> out;
  while (i < l(lines)) {
    Pair<S, Int> p = ctxAction(lines, i);
    if (p == null) break;
    out.add(p.a);
    i = p.b+1;
  }
  ret out;
}