Subject: Re: Harmony - proxies | asynchronous

Dean Landolt dean at
Tue Sep 6 09:47:48 PDT 2011

On Tue, Sep 6, 2011 at 2:01 AM, Brendan Eich <brendan at> wrote:

> On Sep 5, 2011, at 9:36 PM, John J Barton wrote:
> On Sun, Sep 4, 2011 at 1:42 PM, Brendan Eich <brendan at> wrote:
>> On Sep 4, 2011, at 11:06 AM, John J Barton wrote:
>> As a reader I have to parse the function carefully to look for the
>> 'yield'. If I find one, then I know that this is not actually a function
>> after all. Then I need to mentally draw a line after the yield and label it
>> "entry-point #2".
>> This is addressed in ES6 by changing the head of the generator function as
>> follows:
>> spawn(function* () {
>>     try {
>>         var [foo, bar] = yield join(read("foo.json"),
>>                                     read("bar.json")).timeout(1000);
>>         render(foo);
>>         render(bar);
>>     } catch (e) {
>>         console.log("read failed: " + e);
>>     }
>> });
>>  (For others who have some trouble seeing the difference, here the
> function keyword is followed by the multiplication symbol).
> "generator() {}" would make a lot more since to me, it would more clearly
> alert the reader at no added cost for the writer, as well as helping new
> users of this feature separate it's effect from functions.
> We considered that, but generator is not reserved, and reserving it in ES6
> requires newline sensitivity at least. Consider an anonymous generator
> similar to the one you typed:
>   generator()
>   {...}
> where ... is actual code (and the {...} style may use multiple lines and
> indentation). This could be valid code in the field today, relyling on ASI
> to insert the semicolon after "generator()".
> What's more, the precedent in Python is not a negative or a trivial
> benefit. Besides reusing brain-print, we stand on field-tested design in a
> similar language. Python uses def for both functions and generators.

But isn't this just a design flaw in python (and js 1.7) -- remedied, no
less, by your disambiguating asterisk? Personally I'm fond of the asterisk,
and the symmetry of function* and yield*, but this is a distinct grammatical
construct from function, right? This argument doesn't strike me as very
winful against any other (syntactically safe) spelling.

> Next I have to read through the source of spawn() and track the lifetime-of
>> and references-to the object it received, seeking calls to send().
>> No, you can use spawn as a black box. It's an API entry point to the
>> taskjs library. You do not need to read the source to use an API.
> Hmm., the doc says:
>   Task spawn(generator function thunk)
> But as I understand it, the send() plays a role in the API to spawn
> correct?
> The value sent to yield expressions in your generator, yes. So? Again that
> does not mean you must read the inside of the black box. The API docs may be
> lacking, of course :-|.

What it's really lacking is a version with * syntax of harmony generators,
which fixes the locality of reference problems and makes it more clear when
you're working with a task. Any word on when they're intended to land in
spidermonkey? I see Dave Herman filed a bug back in June but there's no
status on it.

[snipped the rest]
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