Given an array of TaskEither, what's the best way to run them all in parallel and collect all Left and Right?

[evelant]

Let's say I have an array of TaskEither but I want to run all of them regardless of failure. What's the best way to achieve that with fp-ts?

I came up with the following:

pipe(
    nonCriticalFns,
     A.sequence(T.ApplicativePar),
     T.map(A.separate)
)

This gets me the desired T.Task<Separated<Errors[], Results[]>> but I'm not sure if there's a better or more concise way to express this. Thoughts?

[0x706b]

You could use wilt from the Witherable typeclass (basically an effectful partitionMap):

import { pipe, identity } from 'fp-ts/function'
import * as T from 'fp-ts/Task'
import * as TE from 'fp-ts/TaskEither'
import * as RA from 'fp-ts/ReadonlyArray'

declare const effects: ReadonlyArray<TE.TaskEither<Error, string>>

pipe(
  effects,
  RA.wilt(T.ApplicativePar)(identity),
)

[evelant]

Thanks! This is a situation where I wish for more documentation as someone still learning FP concepts. I don't think there's any way I could have deduced the purpose of A.wilt based on the docs.

The entirety of the docs for it are "export declare const wilt: PipeableWilt1<'Array'>". and following that to the Witherable docs only gives a single sentence "Witherable represents data structures which can be partitioned with effects in some Applicative functor.". Going to the section on Wilt from there it's practically impossible to figure out the purpose of Wilt from just the very complex type presented.

From my perspective trying to learn these things the docs aren't much help. They tell me that Witherable exists but assume that I already understand its purpose and how to use it. Without an example like you just gave it's more or less hopeless for me to have figured out I could use wilt.

It would likely be super helpful if there were a 1-2 sentence "plain english" description of each typeclass including "what is this useful for" with a small practical example for each function like you just provided.