anchor.diff:  abstract class EntityValidator {
   
     static Stream<String> validateFileStringContent(File entity,
  -      String targetContent) =>
  -          validateFileContentSha(entity, _getStringSha1(targetContent));
  +      String targetContent) {
  +    return validateFileContentSha(entity, _getStringSha1(targetContent));
  +  }
   
     static Stream<String> validateFileContentSha(File entity, String targetSha) {
       if(entity is! File) {
  
positive.code:   }
  }
  
  Stream expandStream(Stream source, Stream convert(input), {Stream onDone()}) {
    final controller = new StreamController();
  
  
negative.code:   return completer.future;
  }
  
  // TODO: move to bot?
  Stream _streamFromIterableFuture(Future<Iterable> future) {
    final controller = new StreamController();
  
  