anchor.diff:          (target) => target is Collection ? new List$(target) : null, 
           (target) => target is Map ? new Map$(target) : null,
           (target) => target is String ? new String$(target) : null,
  +        (target) => target is num ? new Num$(target) : null,
           (target) => new Mixin(target),
         ];
       }
  
positive.code:         
    void each(f(x)) {
      if (e == null) return;
      e.forEach(f);
    }
    void forEach(f(x)) => each(f);
    
  
negative.code:   }  
      
    String toDebugString() => String$.debugString(e);
  }
  
  class Num$ extends Mixin {
    num target;
    Num$(target) : super(target) {
      this.target = target;
    }
  
    times(iterator(int n)) {
      for (int i = 0; i < e; i++) iterator(i);
    }    
  }
  
  class String$ extends Mixin {
  