sclass LinesBuffer {
  new L<S> completeLines;
  S currentLine = "";
  
  void append(S s) {
    currentLine += s;
    int i;
    while ((i = currentLine.indexOf('\n')) >= 0) {
      // inefficient
      completeLines.add(dropTrailingBackslashR(substring(currentLine, 0, i)));
      currentLine = substring(currentLine, i+1);
    }
  }
  
  L<S> getAndClearCompleteLines() { ret cloneAndClearList(completeLines); }
}

Began life as a copy of #1007086