For the record, I proposed this feature before, and it wasn't seen as a good
idea, for some reason:
https://esdiscuss.org/topic/function-is-not-mandatory#content-47
Given how close ES6 is to ship, I think it's too late to make such changes to
the spec, we will have to live with it. Use Traceur to generate state machines
from your "yield functions" and use that as a basis in your code.
Best regards,
François
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As pretty everyone already seen, generators are usually used in composition
with promises to yield (pun intended) a plain simple linear code. This solution
looks very much like monads from Haskell, yet in a better syntax: every a <- b
in Haskell is a = yield b in JS, and that aids to get rid of several useless
lines of code.
Actually, one could easily implement other monads over Haskell, changing the
structure of the data passed to `yield`. Generators + promises are almost a
Cont monad (continuations). But here's an issue.
Let's take a look at the List monad (nondeterminism), specifically how we would
use one in JS:
function* doesntMatter() {
var a = yield [1, 2, 3];
var b = yield [1, 2, 3];
return a + b;
}
Now, when we run(doesntMatter)(), we should get [2, 3, 4, 3, 4, 5, 4, 5, 6].
But there's a problem with implementation: we would like to run the rest of the
computation for every item in an array passed to `yield`, but we can't! There's
no way one could copy the current state of an iterator.
The same happens to our original generator + promise usage. We could use the
same syntax to work with events (i.e. repetitive callback calls), not just
series of nested callbacks, but we don't have that vital iter.copy() method.
Obviously, mentioning Haskell in this message was overkill, and that could be a
reason for someone to diasgree that we really need such feature. But, as I
previously described, it's quite a natural thing that is missing, and it
doesn't have too much in common with Haskell.
What is the right way to put this thing into discussion/standardization
process? What do you think about it?
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