We want design parity with FSharp.Control.AsyncSeq

[dsyme]

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

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

One difference is withCancellation is missing from FSharp.Control.AsyncSeq but more research about reaching design parity is needed. Look into what's needed for TaskSeq here.

[github-actions]

🤖 This is an automated response from Repo Assist.

Great research topic! Here is a systematic gap analysis comparing FSharp.Control.AsyncSeq (commit 7c774fe) against the current FSharp.Control.TaskSeq 1.0.0.

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Functions in AsyncSeq but NOT in TaskSeq

Group 1 — Pure sequence operations (natural fits for TaskSeq)

AsyncSeq function	Notes
chunkBy / chunkByAsync	Groups consecutive elements by a key, yielding (key * 'T list) pairs. Complements the existing chunkBySize.
distinctUntilChangedWith / distinctUntilChangedWithAsync	Custom equality predicate for the existing distinctUntilChanged. Straightforward addition.
firstOrDefault default	Convenience over tryHead >> Option.defaultValue. AsyncSeq also has lastOrDefault.
lastOrDefault default	Same as above for the last element.
splitAt count	Returns (firstN array * remaining TaskSeq) — single-pass; unlike take+skip which require two separate enumerations.
zipWith mapping / zipWithAsync mapping	zip then map as a single pass; avoids an intermediate tuple allocation. Also zipWith3/zipWithAsync3.
replicateInfinite value	Convenience over initInfinite (fun _ -> value).
replicateInfiniteAsync computation	Same for async computations.
replicateUntilNoneAsync computation	Emits elements until the async computation returns None.
threadStateAsync folder state	Stateful async map: ('State -> 'T -> Task<'U * 'State>) -> 'State -> TaskSeq<'T> -> TaskSeq<'U>. Useful for carrying accumulated state through a stream.

Group 2 — Materialise-and-sort / reverse (design question)

AsyncSeq has rev, sort, sortBy, sortByDescending, sortWith, sortDescending.
These were proposed for TaskSeq in PR #309 / PR #316 and the decision was not to add them. Noting here for completeness.
AsyncSeq returns array<'T> (not AsyncSeq<'T>) from these — a notable design difference from Seq.

Group 3 — Reactive / concurrent / streaming

These exist in AsyncSeq but require concurrent scheduling, making them substantially heavier to implement reliably:

Function	What it does
merge / mergeAll / mergeChoice	Concurrent stream merging
interleave / interleaveChoice / interleaveMany	Round-robin interleaving
combineLatest / combineLatestWith / combineLatestWithAsync	Latest-value combination (reactive style)
bufferByCount / bufferByCountAndTime / bufferByTime	Time-window buffering
intervalMs	Timer-based element emission
takeUntil / takeWhileAsync / skipUntil	Async signal-based control
mapAsyncParallel / mapAsyncUnorderedParallel / …	Parallel map variants (related to #143)
iterAsyncParallel / iterAsyncParallelThrottled	Parallel iter variants
zipParallel / zipWithParallel / zipWithAsyncParallel	Parallel zip

Group 4 — Not applicable to TaskSeq

AsyncSeq function	Reason not applicable
asyncSeq builder	Replaced by taskSeq
toBlockingSeq / toArraySynchronously / toListSynchronously	TaskSeq already has synchronous toArray / toList
toAsyncEnum / ofAsyncEnum	TaskSeq is IAsyncEnumerable<'T> natively
toAsyncSeq / ofSeqAsync	Cross-library concern
ofObservable / ofObservableBuffered / toObservable	Requires System.Reactive or similar dependency
fromChannel / toChannel / put	System.Threading.Channels specific
zapp / zappAsync	Applicative-style, very niche
cache	Tricky with IAsyncEnumerable reset semantics — needs discussion
getIterator / close / create / error	AsyncSeq implementation internals

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Functions in TaskSeq but NOT in AsyncSeq (TaskSeq advantages)

TaskSeq 1.0.0 has several combinators that AsyncSeq lacks — these represent places where TaskSeq already exceeds AsyncSeq:

TaskSeq function	Notes
withCancellation	Just added in 1.0.0! Explicitly passes a CancellationToken to GetAsyncEnumerator. AsyncSeq handles this via the Async ambient token.
partition / partitionAsync	Single-pass split into two arrays; no AsyncSeq equivalent.
appendSeq / prependSeq	Interop with regular seq<'T>; AsyncSeq has concatSeq but not separate prepend.
skipWhileInclusive / takeWhileInclusive + async	Inclusive predicate scanning; AsyncSeq lacks these.
compareWith / compareWithAsync	Lexicographic comparison returning int.
tryTail	Optional tail; AsyncSeq has tail (throws on empty).
box / unbox / cast	Type coercions.
lengthOrMax / lengthBy / lengthByAsync	Bounded and predicated length.
drop	Non-throwing skip alias (explicit no-throw semantics).
exceptOfSeq	Except against a regular seq<'T>.
collectSeq / collectSeqAsync	Collect/flatMap against a seq<'T> projection.
insertManyAt / removeManyAt	Multi-element positional ops.
Rich ofArray / ofList / ofResizeArray / ofTaskSeq / ofTaskList / ofTaskArray / ofAsyncSeq / ofAsyncList / ofAsyncArray	AsyncSeq has fewer conversion sources.
toIListAsync / toResizeArrayAsync	Additional materialisation targets.

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Summary

The most tractable items for design parity (in order of ease and value) are in Group 1 above: chunkBy, distinctUntilChangedWith, zipWith, firstOrDefault/lastOrDefault, splitAt, replicateInfinite/replicateUntilNoneAsync, and threadStateAsync. These are all pure sequential operations with clear semantics.

The reactive/concurrent group (Group 3) would be a larger design investment and may or may not be in scope — that seems worth a separate discussion.

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[dsyme]

/repo-assist work on group 1

[github-actions]

Pull request created: #349

Generated by Repo Assist

[github-actions]

Pull request created: #350

Generated by Repo Assist

[github-actions]

🤖 This is an automated response from Repo Assist.

As requested, I've implemented all Group 1 functions from the AsyncSeq design-parity gap analysis. Draft PR created: [Repo Assist] feat: add Group 1 AsyncSeq design-parity functions (branch: repo-assist/fix-issue-345-group1-20260317).

Functions added

Function	Description
replicateInfinite	Infinite sequence repeating a constant value
replicateInfiniteAsync	Infinite sequence from an async thunk
replicateUntilNoneAsync	Sequence from async thunk, stops on None
firstOrDefault	First matching element or default
lastOrDefault	Last matching element or default
splitAt	Split prefix of N elements from remainder
zipWith / zipWithAsync	Zip two sequences with a mapping function
zipWith3 / zipWithAsync3	Zip three sequences with a mapping function
chunkBy / chunkByAsync	Chunk consecutive elements with equal keys
threadState / threadStateAsync	Stateful map threading state through sequence

Note: distinctUntilChangedWith/distinctUntilChangedWithAsync are in separate PR #346.

Test status

✅ Build: 0 warnings, 0 errors
✅ Format: clean
✅ Tests: 4,942 passed, 2 skipped (infrastructure), 0 failed
326 new tests across 6 new test files

Generated by Repo Assist for issue #345 · ◷

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