Port TaskSeq.takeWhileInclusive

[bartelink]

I'd like to see takeWhileInclusive (it has uses in Equinox) be ported from AsyncSeq.

Will post a PR to add it to the TODO list (and then one to implement it) in due course unless someone beats me to it, or there are objections to adding it...

[bartelink]

Spike impl:

let TaskSeq_takeWhileInclusive predicate (source: taskSeq<_>) = taskSeq {
    use e = source.GetAsyncEnumerator(CancellationToken())
    let! step = e.MoveNextAsync()
    let mutable go = step
    while go do
        let value = e.Current
        yield value
        if predicate value then
            let! more = e.MoveNextAsync()
            go <- more
        else
            go <- false
}

(derived from Internal.tryPick + base impl )

In context: https://github.com/jet/equinox/blob/master/src/Equinox.Core/Internal.fs#L15-L45

[abelbraaksma]

Thanks for your suggestion @bartelink! So this is like “get next, yield that, test predicate on that one, if true, repeat”. That is, return element first, before testing predicate.

Interesting function. I was about to add a whole section (just like I did for seq) listing all functions that I’ll implement and which (likely) not.

Your proposal looks good, as does the code, feel free to issue a PR, it’ll need to have matching tests (I’m a little more rigorous than the AsyncSeq team in that regard and need notable corner cases), but I can help you with that.

[abelbraaksma]

Btw, it should probably be added together with takeWhile and both should be paired with an async version for the predicate function. I’m happy to help with that.

[bartelink]

Thanks! Yes, I had noted that there was going to be no skimping on test coverage based on poking around ;)

But that's also why I confidently spent time converting Equinox and Propulsion over.

Won't get to the PR immediately but I'll get to it...

[abelbraaksma]

Does it make sense to also add a skipWhileInclusive(Async)? In a separate PR, of course. What do you think? It is not in AsyncSeq.

[bartelink]

That does seem to make sense (although I'm struggling to think of a time I've ever had the use case), but arguably you'd call it skipUntil ?
Of course, that would call the name of takeWhileInclusive into question, but it makes less sense there.
On balance the Inclusive-based name both on the skip and the take sides is probably best overall considering someone scanning intellisense to find the right tool for a job?

[abelbraaksma]

but arguably you'd call it skipUntil ?

Seq has Seq.skipWhile and I like to stick with its naming conventions. They are each others opposites w.r.t. the predicate, so in the end I guess it is a matter of taste ;). See #130.

[abelbraaksma]

This issue was implemented in #126 and will be published in the next version of NuGet (be it 0.4.0 or 0.3.x). 💯 @bartelink

[bartelink]

Seq has Seq.skipWhile and I like to stick with its naming conventions

On reflection, my suggestion doesn't make as much sense as it did in my head as I typed it. I was suggesting to replace the usage of the term WhileInclusive with Until, on the basis that it would naturally imply the Inclusive aspect. But I wasn't considering the fact that Until does mean inverting the predicate. Either way I was definitely not suggesting not providing a takeWhile, or having two functions that only differ by the fact that the predicate's meaning is inverted (I suffer enough mental anguish there being a filter and a where as it is!)

130 would be the better for removing any reference to Until (but commenting here to keep the noise down!)