static void tok_listComprehensions(L<S> tok) {

  if (!tok.contains("[")) ret;

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

    continue unless eq(tok.get(i), "[");

    int iOp = indexOfAny(tok, i+2, "?", ":", "in", "[", "]");

    if (iOp < 0) ret;

    if (!eqOneOf(tok.get(iOp), ":", "in")) continue; // not a list comprehension

    if (eqGet(tok, iOp+2, ".")) continue; // "in." (in is a variable name)

    Map<Int> bracketMap = getBracketMap(tok); // XXX - optimize

    S type = joinSubList(tok, i+2, iOp-3), id = tok.get(iOp-2);

    int j = scanOverExpression(tok, bracketMap, iOp+2, "|");

    S exp = join(subList(tok, iOp+2, j));

    j += 2;

    int k = scanOverExpression(tok, bracketMap, j, "]");

    S where = join(subList(tok, j, k));

    ++k;

    S code = "filter(" + exp + ", func(" + type + " " + id + ") -> Bool { " + where + " })";

    replaceTokens(tok, i, k, code);

    reTok(tok, i, k);

  } on fail {

    print("Was processing list comprehension: " + joinSubList(tok, i, i+30) + "...");

  }

}