Forwards-compatible syntax proposal

[Steven Mascaro]

Ian Hickson wrote:
>> Another reaction is that there are ES4 source fragments that
>> /can/ be parsed by ES3 compilers, but whose meaning will silently
>> be something completely different in the two versions of the
>> language.  Here are some:
>> 
>>   // a generator expression in ES4, a loop calling a function
>>   // in ES3
>> 
>>   function f(x) {
>>       for ( i=0 ; i < 10 ; i++ )
>>           yield (f(), i)
>>   }
>> 
>>   // (artificial) three statements in ES3, two in ES4
>> 
>>   x = this function 
>>   f(x)
>>   {  x++ }
> 
> I think this is very dangerous, and unwise, in the context of the Web. I 
> strongly believe that if we want to have success in expanding the Web 
> platform, backwards-compatibility is critical. But that's another issue.

I agree. Lars, surely this is unacceptable by your very own reasoning 
--- because there will be ES3 code that will run in ES4, but with 
silently different behaviour.