svoid tok_for_unpair(LS tok) {
  int i = -1;
  while ((i = jfind(tok, i+1, "for (<id> <id>, <id> <id> : unpair <id>")) >= 0) {
    S type1 = tok.get(i+4), type2 = tok.get(i+10);
    int iUnpair = indexOf(tok, "unpair", i);
    int iClosing = findEndOfBracketPart(tok, iUnpair)-1;
    if (!eqGet(tok, iClosing+2, "{"))
      fail("Use { with for unpair");
    S pairVar = makeVar();
    replaceTokens(tok, i+4, iUnpair+1, "Pair<" + type1 + ", " + type2 + "> " + pairVar + ":");
    tok.set(iClosing+2, "{ "
      + type1 + " " + tok.get(i+6) + " = pairA(" + pairVar + "); "
      + type2 + " " + tok.get(i+12) + " = pairB(" + pairVar + "); ");
    reTok(tok, i, iClosing+3);
  }
}