There is no need to CPS transform functions and there is no need for
deferred functions either. It can all be done with today's generators and a
little helper library.
With the C# async/await notation:
- The yield keyword is your "await" keyword.
- The little * in function* is your "async" keyword.
With this you can write:
function* asyncEach(array, fn) {
for (var i = 0; i < array.length; i++) yield fn(array[i], i);
}
and you can call it as:
function* myFunc(array) {
yield asyncEach(array, function*(elt, i) {
var foo = yield asyncBar(elt);
// more ...
})
}
Note that there is *no* helper API in all these async functions that call
other async functions; The helper API is only needed to interface this with
the classical callback world: at the very bottom of the stack when you call
low level callbacks-based I/O functions, and at the top of the stack when
the event loop runs one of your generator functions.
The trick is that you need a clever run function to do the little
yield/next dance with generator functions that call other generator
functions.
I've implemented this in
https://github.com/bjouhier/galaxy/blob/master/lib/galaxy.js (the run and
invoke functions)
The only thing I don't like about it is the awkward syntax:
- yield precedence does not work well
- yield is prefix, which does not chain well
- and yield is heavy anyway
In short, this is a hack to get going but I'm still waiting for the full
concurrency proposal and its awesome ! syntax.
Bruno
> Consider the following:
>
> function* yieldEach(array){
> array.forEach(n => {
> yield n;
> });
> }
>
> In order for this to work, not only does `yieldEach` have to be suspended
for the inner yield, but forEach does as well. That means CPS transforming
functions based on whether they call a yielding function.
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