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Computational expressions tail calls support, revived - #18804

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T-Gro merged 21 commits into
dotnet:mainfrom
majocha:tailcalls-ce
Aug 6, 2025
Merged

Computational expressions tail calls support, revived#18804
T-Gro merged 21 commits into
dotnet:mainfrom
majocha:tailcalls-ce

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@majocha

@majocha majocha commented Jul 31, 2025 •
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Revived #17018

Implements fsharp/fslang-suggestions#1006

TODO:

  • write some tests
  • decide how to deal with DoBang
  • RFC FS-1330
  • add example usage / implementations for some basic CEs to tests.
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github-actions Bot commented Jul 31, 2025 •
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❗ Release notes required

✅ Found changes and release notes in following paths:

Change path Release notes path Description
src/Compiler docs/release-notes/.FSharp.Compiler.Service/10.0.100.md
LanguageFeatures.fsi docs/release-notes/.Language/preview.md
@vzarytovskii

vzarytovskii commented Aug 1, 2025

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Nice
@majocha

majocha commented Aug 1, 2025

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So, some tests are up and running. I will fill them up with all imaginable tail call / non-tailcall combinations.

OTOH Applying this to TaskBuilder is very tricky and probably hopeless, given its type signature.
It returns just a running task and binds to awaitables that also may or may not be already running. I cannot come up with anything that wouldn't be horrendous (like for example communicating between TaskBuilder state machines via an AsyncLocal side channel to signal that we're executing in a recursive taill-call context).

It might be more useful for other computation expressions.
@majocha majocha mentioned this pull request Aug 1, 2025
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@majocha majocha changed the title WIP: Computational expressions tail calls support, revived Aug 1, 2025
@majocha
majocha marked this pull request as ready for review August 3, 2025 10:56
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majocha requested a review from a team as a code owner August 3, 2025 10:56
edgarfgp
edgarfgp reviewed Aug 3, 2025
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Comment thread src/Compiler/Facilities/LanguageFeatures.fs Resolved
majocha and others added 2 commits August 3, 2025 19:10
T-Gro
T-Gro reviewed Aug 4, 2025
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Comment thread docs/release-notes/.Language/preview.md Resolved
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edgarfgp requested a review from T-Gro August 6, 2025 09:17
@github-project-automation github-project-automation Bot moved this from New to In Progress in F# Compiler and Tooling Aug 6, 2025
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T-Gro enabled auto-merge (squash) August 6, 2025 14:08
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T-Gro merged commit 8a47c17 into dotnet:main Aug 6, 2025
@github-project-automation github-project-automation Bot moved this from In Progress to Done in F# Compiler and Tooling Aug 6, 2025
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majocha deleted the tailcalls-ce branch August 7, 2025 09:41
This was referenced Aug 19, 2025
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@dsyme

dsyme commented Oct 24, 2025

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@majocha Just to say a huge, huge thank you for getting this in. We should always have done tailcalls in computation expressions like this, and it's a relief to see it finally in place
@dsyme

dsyme commented Oct 24, 2025

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Thank you also to @T-Gro for your work in facilitating both the design repos and the implementation!
@brianrourkeboll brianrourkeboll mentioned this pull request Dec 3, 2025
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github-actions Bot pushed a commit to fsprojects/FSharp.Control.TaskSeq that referenced this pull request Mar 8, 2026
Repo Assist @github-actions
Add YieldFromFinal overloads for F# 10 compatibility (#62)
04a73dd 
- Add YieldFromFinal(IAsyncEnumerable<'T>) in MediumPriority (= YieldFrom)
- Add YieldFromFinal(seq<'T>) in MediumPriority (= YieldFrom)
- Add YieldFromFinal for generic unit-returning task-likes in LowPriority
- Add YieldFromFinal(Task<unit>) and YieldFromFinal(Async<unit>) in HighPriority
- Update TaskSeqBuilder.fsi with matching signatures
- Update release-notes.txt

The F# 10 compiler (dotnet/fsharp#18804) calls YieldFromFinal instead of
YieldFrom when yield! or do! appears in a tail-call position. These overloads
ensure taskSeq compiles without errors under F# 10.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actions github-actions Bot mentioned this pull request Mar 8, 2026
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@majocha @vzarytovskii @dsyme @edgarfgp @T-Gro