async/await improvements

[Jeff Morrison]

On 11/12/14, 4:10 PM, Kevin Smith wrote:
>
>     The only thing they couldn't do (under this proposal) is expose
>     the promise being used to userland (to eliminate the chance for
>     userland to hold on to the promise and expect to be able to add an
>     error handler at any time).
>
>
> And lose the ability to combine the results of async functions with 
> "all", "race", and any other promise combinator?  That's a core 
> strength of the current design.
A very good point.

Crazy, half-baked idea: Move the "forwards" vs "throws/logs" distinction 
to the callsite (in sync contexts only?) rather than the definition 
context as was described at the beginning of this thread.

The thought-process running along the lines of making the default 
behavior to log/report, but with an escape hatch when logging is *not* 
what you want.
It's easier to notice an undesired log (and suppress it if necessary) 
than it is to notice that a log is *missing* in exceptional circumstances.

```javascript
async function asyncLibrary(data) {
   // ...
}

function doStuff() {
   // Becomes sugar for something like
   // asyncLibrary(badData).catch(err => {
   //   console.error(err);
   //   throw err;
   // });
   //
   // This makes logging-to-console the default
   var toplevelResult = asyncLibrary(badData);

   // No additional .catch() -- just pushes new syntax to discourage
   // swallowed-by-default. When you want this "storing" behavior, you 
simply
   // opt-in to it via syntax (or a stdlib?) rather than opting out
   var storedResult = ^asyncLibrary(badData);

   // For combinators, you get something like:
   Promise.all([
     ^asyncLibrary(data1),
     ^asyncLibrary(data2)
   ]);
}

async function doOtherAsyncStuff() {
   // This stays status quo
   try {
     asyncLibrary(badData);
   } catch (e) {
     // caught!
   }
}
```

(Frankly the `^` syntax I used here seems a bit arcane to me -- but 
maybe someone can see through it and can think of a more expressive syntax?)

-Jeff

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