anchor.diff:  abstract class bool extends Object {
     external const factory bool.fromEnvironment(String name,
         {bool defaultValue: false});
  +
     bool operator &(bool other);
     bool operator |(bool other);
     bool operator ^(bool other);
  
positive.code: abstract class Iterable<E> {
    E get first;
    bool get isEmpty;
    Iterator<E> get iterator;
    int get length;
  
    Iterable<T> expand<T>(Iterable<T> f(E element));
  
    R fold<R>(R initialValue, R combine(R previousValue, E element)) => null;
  
  
negative.code:   double roundToDouble();
    int truncate();
    double truncateToDouble();
  
    external static double parse(String source, [double onError(String source)]);
  }
  
  class Duration implements Comparable<Duration> {}
  
  class Error {
    Error();
    static String safeToString(Object object) => '';
    external StackTrace get stackTrace;
  }
  
  class Exception {
    factory Exception([var message]) => null;
  