anchor.diff:    accept(ConstantVisitor visitor) => visitor.visitString(this);
   
     String toString() {
  -    return 'StringConstant(${Error.safeToString(value.slowToString())})';
  +    return 'StringConstant("${value.slowToString()}")';
     }
   }
   
  
positive.code: 
    accept(ConstantVisitor visitor) => visitor.visitType(this);
  
    String toString() => 'TypeConstant(${Error.safeToString(representedType)})';
  }
  
  class ListConstant extends ObjectConstant {
  
negative.code:     sb.write('MapConstant({');
      for (int i = 0 ; i < keys.entries.length ; i++) {
        if (i > 0) sb.write(',');
        sb.write(keys.entries[i]);
        sb.write(':');
        sb.write(values[i]);
      }
      sb.write('})');
      return sb.toString();
  