static LS tok_moveImportsUp(L<S> tok) {

  new StringBuilder buf;

  //print("tok_moveImportsUp n=" + l(tok));

  //print("Source begins: " + quote(shorten(join(tok), 200)));

  // scan imports on top

  int i;

  new Set<S> have;

  for (i = 1; i < l(tok); i += 2)

    if (eq(tok.get(i), 'import)) {

      int j = indexOf(tok, i+2, ";");

      if (j < 0) break;

      S s = joinSubList(tok, i, j+1);

      have.add(s);

      i = j;

    } else break;

  //print("tok_moveImportsUp have " + l(have) + " after " + i);

  new L<IntRange> reToks;

  // scan imports in text

  for (int i2 : cloneList(indicesOf(tok, "import")))

    if (i2 >= i) {

      int j = indexOf(tok, i2+2, ";");

      if (j < 0) continue; // huh?

      S s = joinSubList(tok, i2, j+1);

      //print("Found import at " + i2 + ": " + s);

      if (!have.contains(s)) {

        buf.append(s).append("\n");

        have.add(s);

      }

      replaceTokens(tok, i, j+1, "");

      ifndef tok_moveImportsUp_skipMostReToks

        reToks.add(intRange(i2, j+1));

      endifndef

    }

  if (nempty(buf)) {

    if (l(tok) == 1) addAll(tok, "", "");

    tok.set(1, str(buf)+"\n"+tok.get(1));

    reToks.add(intRange(1, 2));

  }

  ret reTok_multi(tok, reToks);

}