Generator issue: exceptions while initializing arguments

[Brendan Eich]

Sorry to over-reply. This *does* work in SpiderMonkey:

js> function f(a = g) { function g(){}; yield a; }
js> var it = f()
js> it.next()
function g(){}

/be

Brendan Eich wrote:
> SpiderMonkey (Firefox 15 and newer has default parameters):
>
> js> function f(a = g) { function g(){}; return a; }
> js> f()
> function g(){}
>
> So function g is hoisted and a defaults to it, as expected.
>
> The trivial generator variant, i.e., what you get by putting a * after 
> function and before f, above:
>
> js> function* f(a = g) { function g() {}; return a; }
> js> var it = f();
> js> it.next();
> function g(){}
>
> (note well, not yet implemented in SpiderMonkey) should behave the 
> same, or crazypants.
>
> /be
>
> Brendan Eich wrote:
>> Brendan Eich wrote:
>>>>  However, the semantics of parameter default value initialization 
>>>> can result in exceptions and more closely links argument 
>>>> instantiations with the actual activation of the generator 
>>>> function. You can't really build the parameter bindings without 
>>>> performing declaration instantiation for the function.
>>>
>>> Agreed, that's absolutely true (no "really" about it -- or rather, 
>>> "for real" ;-). 
>>
>> And (I should have written), if your point was that we must bind all 
>> var and top level function/let/const declarations before the implicit 
>> yield; inserted "after the opening brace", I don't see a problem. 
>> Hoisted functions with usable initial values, hoisted vars with 
>> undefined initial values, and temporal dead zones for the let and 
>> const declarations that are at top (generator body) level. Right?
>>
>> /be
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