Async Iterators about fluture

[Avaq]

Ah. I realize I've misunderstood your original question. I'm glad you've found a solution. I can't really see a way to work around the problem of that trailing Future: You have to yield synchronously because Infinite only works with synchronous generators, and you only find out that the underlying async generator was done some ticks later, after having already yielded that Future.

[Avaq]

Hi @ftaiolivista. I answered a very similar question some time ago. It was in a GitHub issue, so not that easy to discover. I converted it to a Q&A Discussion. I think it might be what you need: #478

[ftaiolivista]

Thank you @Avaq for the quick reply. Looked ad #478. Looks clear how to wrap a standard generator with Lazy List but not clear to me on how to wrap an async iterator that yield promises.

[ftaiolivista]

@Avaq got it working this way. The problem is that I have one last future with undefined value because the Infinite loop cancellation happen after one last promise with undefined value

import { S, F } from './src/lib.js' // S = sanctuary F = Fluture
import { createReadStream, promises as FS } from 'fs'
import parse from 'csv-parse'
import Infinite from 'lazy-infinite'

const parsing = createReadStream('file.csv').pipe(parse())

const infinite = asynciterable =>
    Infinite.of(function * () {
        const i = asynciterable[Symbol.asyncIterator]()
        let goon = true
        do {
            yield F.attemptP(() =>
                i.next().then(({ done, value }) => {
                    goon = !done
                    return done ? undefined : value
                })
            )
        } while (goon)
    })

S.pipe([
    infinite,
    F.map(
        F.chain(v => {
            console.log('process', v)
            return F.after(2000)(v)
        })
    ),
    i => F.go(i.gen),
    F.fork(err => console.error('err', err))(console.log)
])(parsing)