sclass LineBuffer {
  VF1<S> onLine;
  S currentLine = "";
  
  *() {}
  *(VF1<S> *onLine) {}
  
  void append(S s) {
    currentLine += s;
    int i = 0, j;
    while ((j = indexOf(currentLine, i, '\n')) >= 0) {
      S line = dropTrailingBackslashR(substring(currentLine, i, j));
      callF(onLine, line);
      i = j+1;
    }
    currentLine = substring(currentLine, i);
  }
}