Indices are a distraction

[domenic]

The narrative seems to be something like: "we have an existing iteration interface, { done, value }. This is missing index, so let's add it." But index never plays a role in any of the subsequent work and seems entirely useless; it's just an extra piece of information to be passed around. It definitely doesn't seem to be a fundamental part of the iteration interface on the same level as done and value.

[kriskowal]

Certainly is a distraction, not fundamental to anything so far written. I still need to write more about how index goes from being a position in space to a moment in time for signals and behaviors. Behaviors in particular benefit from being able to map a time to a value.

[domenic]

Right, that was the other thing. They appear as time in one signal example, but the time also seems redundant: you could just do Date.now(), since it is a signal, and there is no (or minimal) delay between the signal production and the callback being called.

[kriskowal]

For sensitive systems of behaviors, particularly in animation, every aspect of the system should be rendered based on a single snapshot of time. Consider an animation of an engine, piston, crankshaft, drive train.

[domenic]

OK, but in that case I would just bundle it into the value, and not make it a fundamental part of the protocol.

[kriskowal]

I am going to heed your words and minimize the discussion of index because it is a tangent. However, I do think it is worth embedding in the protocol itself. Another reason is that it is necessary to faithfully produce this equivalence:

array.forEach(function (value, index) {
    // ...
});
array.iterate().forEach(function (value, index) {
    // ...
})

[domenic]

I guess I don't really see that equivalence as very useful. If you move to iteration, you no longer get indices. Indices seem, at least intuitively, tied to the nature of arrays as random-access data structures; they don't make as much sense to me for iterables, even if in theory they could be added.

I wonder if any other languages' iterable/enumerable implementations include index in the protocol.

[kriskowal]

I wonder if any other languages' iterable/enumerable implementations include index in the protocol.

Not to my knowledge.