static void tok_listComprehensions(L<S> tok) {
  if (!tok.contains("[")) ret;
  for (int i = 1; i < l(tok); i += 2) {
    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
    
    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(tok.subList(iOp+2, j));
    j += 2;
    int k = scanOverExpression(tok, bracketMap, j, "]");
    S where = join(tok.subList(j, k));
    ++k;
      
    S code = "filter(" + exp + ", func(" + type + " " + id + ") -> Bool { " + where + " })";
    replaceTokens(tok, i, k, code);
    reTok(tok, i, k);
  }
}