sS ai_groupUsingProductions(S s, AI_BottomUpParser1 p) {
  p.splitSplittables = false;
  p.parse(javaTokNPunctuation(s));
  for (AI_BottomUpParser1.Word g : p.groups()) {
    int i = g.wordFrom*2+1, j = g.wordTo*2-1;
    S pre = get(p.cnc, i-1), post = get(p.cnc, j+1);
    //print("pre=" + pre + ", post=" + post);
    if (endsWith(pre, "{") && startsWith(post, "}"))
      continue;
    tokPrepend(p.cnc, i, "{");
    tokAppend(p.cnc, j, "}");
  }
  ret join(p.cnc);
}

Began life as a copy of #1018198