Stream Extras

Description

This issue is to discuss potential additions and enhancements for mithril/stream.

This is a collection of helpers I've found useful working with Streams: https://github.com/spacejack/mithril-stream-extra
It's a bit TypeScript-heavy because I wanted to add a ReadonlyStream type, but otherwise I think it's also got useful helpers for plain JS.

(Revisiting it however, I found the ReadonlyStream type is now broken with the current Typescript compiler... I'm having trouble coming up with a Stream-compatible read-only type so that ReadonlyStream types are usable with all Stream functions. This might need to be done as a complete custom stream .d.ts or brought into core to work.)

In addition to the above, these functions are for getting promises from streams:

/**
 * Promise that resolves on stream's initial value
 * Credit to @isiahmeadows for eliminating the extra map
 */
export function one<T>(s: ReadonlyStream<T>): Promise<T> {
	return new Promise<T>(resolve => {
		let done = false
		let s1: Stream<T>
		s1 = s.map(v => {
			if (done) {
				return
			}
			done = true
			if (s1 != null) {
				s1.end(true)
			}
			resolve(v)
		})
		if (done) {
			s1.end(true)
		}
	})
}

/**
 * Promise that resolves on stream's next value
 */
export function nextOne<T>(s: ReadonlyStream<T>): Promise<T> {
	return one(dropInitial(s))
}

Why

Having used streams in various ways, this is a set of helpers I've found most useful. I'd also like to hear from others about what additional stream functions or patterns they're using. And any suggestions/critiques or antipattern warnings about the above are welcome as well.

Review the proposed helpers in the linked mithril-stream-extra repository and the TypeScript ReadonlyStream concerns described here. The issue does not define a selected scope or acceptance criteria; progress would require deciding which stream additions, typings, or promise helpers belong in core.