[T-R]

I think his point is that there's usually a very strict ordering to the events on an HTTP server - you parse and sanitize your input, make some database calls, and generate a response - at best, letting something else do the sequencing and composition for you doesn't gain you much, as it might in a reactive GUI. At worst it leaves room for subtle bugs or code that's less clear (arising from the statefulness of the Promse object itself).

Using a Promises, as opposed to reducing a list of computations async-style, also limits you to the Promise object's interface, so you lose (or at least add cruft to) the flexibility and composability of using native lists. By sequencing computations with lists, if I want some insight into what's happening, I just List.map(apply compose, logFunc). With promises, I have some work to do.

Promises have their uses, but it's definitely a tradeoff, and for most HTTP servers, I'd argue that their utility does seem a bit limited. I'd similarly say that making a point of using FRP to build a server would probably be a bit overkill for the task.

[TheZenPsycho]

What kind of object is in your list of async operations? promises. (though probably your own ad hoc, hand rolled and poorly specified version of them)

[T-R]

Just plain-old native functions - that's the whole point.

[TheZenPsycho]

when you put "plain old native functions" in an array, with the intent of executing them in sequence, with the output of i being fed into the input of i+1, congratulations, the functions are now implicitly promises.

Because, in the end, what, semantically, is the difference between:

runqueue([func1,func2,func3,func4]); and func1().then(func2).then(func3).then(func4);

No significant difference at all, really. except the promises permit you much more flexibility and options.

[T-R]

The difference is that the first works with all of the native list functions, as well as all of those in e.g., underscore, without any extra work. The latter doesn't. Now, the latter certainly offers some other features, but my point was that, in specifically building an HTTP server, it's been my experience that those features aren't of as much use as being able to use the native list functions to, say, map a log function onto the list of functions, or reduce while halting execution under particular conditions.