svoid tok_for_unpair(LS tok) {
  int i = -1;
  while (i = jfind(tok, "for (<id> <id>, <id> <id> : unpair <id>", i+1))) {
    S type1 = tok.get(i+2), type2 = tok.get(i+10);
    int j = indexOf(tok, "unpair", i);
    int k = indexOf(tok, "{", j);
    S pairVar = makeVar();
    replaceTokens(tok, i+4, j+1, "Pair<" + type1 + ", " + type2 + "> " + pairVar + ":");
    tok.set(k, "{ " + type1 + " " + tok.get(i+4) + " = pairA(" + pairVar + "); "
      + type2 + " " + tok.get(i+12) + " = pairB(" + pairVar + "); ");
    reTok(tok, i, k+1);
  }
}