We want design parity with FSharp.Control.TaskSeq

[dsyme]

/repo-assist We want design parity between FSharp.Control.AsyncSeq and FSharp.Control.TaskSeq.

https://github.com/fsprojects/FSharp.Control.TaskSeq

One difference is withCancellation is missing from FSharp.Control.AsyncSeq but more research about reaching design parity is needed.

[github-actions]

Pull request created: #278

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I've done a full API comparison between FSharp.Control.AsyncSeq and FSharp.Control.TaskSeq and raised a draft PR implementing withCancellation as a first step. Here's a summary of the findings.

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withCancellation

A draft PR has been opened: it adds AsyncSeq.withCancellation, which mirrors TaskSeq.withCancellation. It wraps an AsyncSeq<'T> so that the given CancellationToken is passed to GetAsyncEnumerator, overriding the token supplied by the caller — useful for EF Core and similar libraries.

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Full API gap analysis: TaskSeq → AsyncSeq

Functions in TaskSeq that are missing from AsyncSeq (ordered by likely priority):

Function	Description
partition / partitionAsync	Split into two arrays by predicate — no equivalent in AsyncSeq
compareWith / compareWithAsync	Lexicographic sequence comparison
tryTail	Safe tail — returns None on empty instead of raising
skipWhileInclusive / skipWhileInclusiveAsync	Like takeWhileInclusive but for skip
takeWhileInclusiveAsync	Async variant of existing takeWhileInclusive
appendSeq / prependSeq	Convenience for appending/prepending a seq<'T>
collectAsync	Async variant of collect (i.e., async bind/flatMap)
delay	Defers sequence creation to enumeration time
lengthBy / lengthByAsync	Count elements matching a predicate
lengthOrMax	Returns length, but stops at a maximum (avoids full enumeration)
insertManyAt / removeManyAt	Bulk insert/remove by index
exceptOfSeq	except that takes a seq instead of AsyncSeq
where / whereAsync	Aliases for filter/filterAsync
box / unbox / cast	Type-erasing/narrowing helpers

Full API gap analysis: AsyncSeq → TaskSeq

AsyncSeq has many capabilities not in TaskSeq — these appear intentional, reflecting AsyncSeq's broader use cases for reactive and event-driven pipelines:

• Observable support: ofObservable, ofObservableBuffered, toObservable
• Channel support: toChannel, fromChannel
• Parallel operations: mapAsyncParallel, mapAsyncUnorderedParallel, iterAsyncParallel, etc.
• Merge/interleave: merge, mergeAll, mergeChoice, interleave, interleaveMany, interleaveChoice
• Combine-latest: combineLatest, combineLatestWith, combineLatestWithAsync
• Temporal/buffering: bufferByCountAndTime, bufferByTime, intervalMs
• Reactive utilities: cache, zapp, zappAsync, allPairs
• Time-based gating: takeUntil, takeUntilSignal, skipUntil, skipUntilSignal
• Traversal: traverseOptionAsync, traverseChoiceAsync
• Source: AsyncSeqSrc<'T> (push-based source)

These are worth preserving as differentiators.

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Happy to continue implementing more of the missing functions above if that's the direction maintainers want to take.

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