// map: index of opening bracket -> index of closing bracket
static Map<Int> getBracketMapC(L tok) {
  new TreeMap<Int, Int> map;
  new L<int> stack;
  int n = l(tok);
  for i to n: {
    if (getBracketMapC_opening.contains(tok.get(i)))
      stack.add(i);
    else if (getBracketMapC_closing.contains(tok.get(i))) {
      if (!empty(stack))
        map.put(liftLast(stack), i);
    }
  }
  ret map;
}

static L<S> getBracketMapC_opening = ll("{", "(");
static L<S> getBracketMapC_closing = ll("}", ")");

Began life as a copy of #1002118