Functions for working with `TaskSeq` and `Channel`?

[njlr]

Similar to fsprojects/FSharp.Control.AsyncSeq#170

TaskSeq.toChannel : ChannelWriter<'a> -> TaskSeq<'a> -> Task<unit>

TaskSeq.fromChannel : ChannelReader<'a> -> TaskSeq<'a>

TaskSeq.toChannel would be used to fill a ChannelWriter from a TaskSeq

TaskSeq.fromChannel would be used to empty a ChannelReader into a TaskSeq

[github-actions]

🤖 This is an automated response from Repo Assist.

Great suggestion! System.Threading.Channels is part of the .NET BCL and available on netstandard2.1 (this library's target), so this would require no new dependencies.

Here's a sketch of how both functions could be implemented using this library's own primitives:

/// Write all elements of a TaskSeq to a ChannelWriter, then mark it complete.
let toChannel (writer: ChannelWriter<'T>) (source: IAsyncEnumerable<'T>) : Task =
    task {
        try
            for item in source do
                do! writer.WriteAsync(item)
            writer.TryComplete() |> ignore
        with exn ->
            writer.TryComplete(exn) |> ignore
    }

/// Produce a TaskSeq that reads elements from a ChannelReader until it completes.
let fromChannel (reader: ChannelReader<'T>) : IAsyncEnumerable<'T> =
    taskSeq {
        while! reader.WaitToReadAsync() do
            let mutable item = Unchecked.defaultof<_>
            while reader.TryRead(&item) do
                yield item
    }

The while! reader.WaitToReadAsync() pattern maps cleanly onto channels' completion semantics — when the channel is complete and drained, WaitToReadAsync returns false and the sequence ends naturally.

A few design questions worth discussing with the maintainers:

1. Completion semantics: Should toChannel always call TryComplete() after finishing, or should there be a non-completing variant for multi-producer patterns?
2. Cancellation: Both WriteAsync and WaitToReadAsync accept a CancellationToken. These could be threaded through via a withCancellation-style overload.
3. Error propagation: writer.TryComplete(exn) propagates exceptions to channel readers, which seems correct for toChannel.

A PR implementing these would be a welcome contribution! The AGENTS.md has build/test instructions, and the existing TaskSeq module in src/FSharp.Control.TaskSeq/TaskSeq.fs would be the right place to add these.

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[github-actions]

🤖 This is an automated response from Repo Assist.

I've implemented TaskSeq.toChannelAsync and TaskSeq.ofChannel and submitted a draft PR — [Repo Assist] feat: add TaskSeq.toChannelAsync and TaskSeq.ofChannel for System.Threading.Channels integration.

What was implemented:

// Write all elements of a TaskSeq to a ChannelWriter, then mark it complete.
// Exceptions are propagated to the channel so downstream readers observe them.
TaskSeq.toChannelAsync : ChannelWriter<'T> -> TaskSeq<'T> -> Task

// Create a TaskSeq from a ChannelReader. Ends naturally when the channel
// is completed and fully drained.
TaskSeq.ofChannel : ChannelReader<'T> -> TaskSeq<'T>

Implementation notes:

• toChannelAsync uses while! e.MoveNextAsync() + writer.WriteAsync per element; calls writer.TryComplete() on success or writer.TryComplete(exn) on failure
• ofChannel uses the idiomatic while! reader.WaitToReadAsync() + inner while reader.TryRead(&item) drain loop
• One new dependency: System.Threading.Channels 8.0.0 (needed for netstandard2.1; built into net5.0+)
• 29 new tests; all 5280 tests pass

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