sclass LineBuffer {
  VF1<S> onLine;
  new StringBuilder currentLine;

  *() {}
  *(VF1<S> *onLine) {}
  
  void append(S s) {
    append(s, onLine);
  }
  
  void append(S s, VF1<S> onLine) {
    currentLine.append(s);
    if (contains(s, '\n')) {
      int i = 0, j;
      s = str(currentLine);
      while ((j = indexOf(s, i, '\n')) >= 0) {
        S line = dropTrailingBackslashR(substring(s, i, j));
        callF(onLine, line);
        i = j+1;
      }
      currentLine = new StringBuilder(substring(s, i));
    }
  }
  
  int size() { ret l(currentLine); }
}

Began life as a copy of #1007086