static Producer<S> javaTokC_iterator(S s) {
  ret new Producer<S>() {
    final int l = strL(s);
    int i = 0;
    
    public S next() {
      if (i >= l) ret null;
      
      int j = i;
      char c, d;
      
      // scan for whitespace
      while (j < l) {
        c = s.charAt(j);
        d = j+1 >= l ? '\0' : s.charAt(j+1);
        if (c == ' ' || c == '\t' || c == '\r' || c == '\n')
          ++j;
        else if (c == '/' && d == '*') {
          do ++j; while (j < l && !s.substring(j, Math.min(j+2, l)).equals("*/"));
          j = Math.min(j+2, l);
        } else if (c == '/' && d == '/') {
          do ++j; while (j < l && "\r\n".indexOf(s.charAt(j)) < 0);
        } else
          break;
      }
      
      i = j;
      if (i >= l) ret null;
      c = s.charAt(i);
      d = i+1 >= l ? '\0' : s.charAt(i+1);
  
      // scan for non-whitespace
      if (c == '\'' || c == '"') {
        char opener = c;
        ++j;
        while (j < l) {
          if (s.charAt(j) == opener || s.charAt(j) == '\n') { // end at \n to not propagate unclosed string literal errors
            ++j;
            break;
          } else if (s.charAt(j) == '\\' && j+1 < l)
            j += 2;
          else
            ++j;
        }
      } else if (Character.isJavaIdentifierStart(c))
        do ++j; while (j < l && (Character.isJavaIdentifierPart(s.charAt(j)) || "'".indexOf(s.charAt(j)) >= 0)); // for stuff like "don't"
      else if (Character.isDigit(c)) {
        do ++j; while (j < l && Character.isDigit(s.charAt(j)));
        if (j < l && s.charAt(j) == 'L') ++j; // Long constants like 1L
      } else if (c == '[' && d == '[') {
        do ++j; while (j+1 < l && !s.substring(j, j+2).equals("]]"));
        j = Math.min(j+2, l);
      } else if (c == '[' && d == '=' && i+2 < l && s.charAt(i+2) == '[') {
        do ++j; while (j+2 < l && !s.substring(j, j+3).equals("]=]"));
        j = Math.min(j+3, l);
      } else
        ++j;
        
      S t = quickSubstring(s, i, j);
      i = j;
      ret t;
    }
  };
}

Began life as a copy of #1004582