Allow `let!` and `use!` binding with type annotation without parentheses. by edgarfgp · Pull Request #18508 · dotnet/fsharp · GitHub
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Allow let! and use! binding with type annotation without parentheses. - #18508

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T-Gro merged 38 commits into
dotnet:mainfrom
edgarfgp:fix-10697
May 16, 2025
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Allow let! and use! binding with type annotation without parentheses.#18508
T-Gro merged 38 commits into
dotnet:mainfrom
edgarfgp:fix-10697

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@edgarfgp

@edgarfgp edgarfgp commented Apr 26, 2025 •
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Description

Allow let! and use! binding with type annotation without parentheses.

Fixes #10697

BEFORE

let f =
    async {
        let! (a: int) = async { return 1 } // Valid
        let! b: int = async { return 1 } // Error
        use! (a: int) = ...  //Error
        use! b: int = ... //Error
        return a
    }

AFTER

let f =
    async {
        let! (a: int) = ... // Valid
        let! b: int = ... // Valid
        return a
    }

Once #18487 is merged

let f =
    async {
        use! (a: int) = ...  // Valid
        use! b: int = ... // Valid
        return a
    }

Checklist

  • Test cases added
  • Release notes entry updated

@github-actions

github-actions Bot commented Apr 26, 2025 •
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edgarfgp
edgarfgp commented Apr 30, 2025
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Comment thread src/Compiler/pars.fsy Outdated
edgarfgp
edgarfgp commented Apr 30, 2025
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Comment thread src/Compiler/pars.fsy Outdated
@edgarfgp
edgarfgp requested a review from auduchinok April 30, 2025 16:24
@edgarfgp

edgarfgp commented Apr 30, 2025 •
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It might be interesting in a follow up PR to add error recovery for cases where we have a headBindingPattern COLON error

let! x: 
use! stream: 
let x: 
use x:

Where we can use reportParseErrorAt mColon (FSComp.SR.parsExpectingType())

baronfel
baronfel approved these changes May 1, 2025
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Love the depth of test coverage here.

@edgarfgp edgarfgp closed this May 12, 2025
@edgarfgp edgarfgp reopened this May 12, 2025
T-Gro
T-Gro requested changes May 14, 2025
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This is really a nice addition @edgarfgp 👍 .

I think this is a change where we would be better with having a languageFeature guard with recovery.

Reason is, people might be having mismatched SDKs locally vs CI.

This change would allow code to pass locally, but then surprisingly fail parsing when ran on CI with a different SDK version.

LanguageVersion will cover for that scenario.

@edgarfgp
edgarfgp requested a review from T-Gro May 15, 2025 19:46
@edgarfgp

edgarfgp commented May 16, 2025

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@T-Gro
T-Gro merged commit 8b7bf60 into dotnet:main May 16, 2025
@edgarfgp edgarfgp mentioned this pull request Jun 11, 2025
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@edgarfgp edgarfgp mentioned this pull request Aug 26, 2025
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@github-actions github-actions Bot mentioned this pull request Mar 20, 2026
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@baronfel baronfel baronfel approved these changes
@T-Gro T-Gro T-Gro approved these changes
@auduchinok auduchinok Awaiting requested review from auduchinok
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@brianrourkeboll brianrourkeboll brianrourkeboll approved these changes
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Successfully merging this pull request may close these issues.

let! binding with type annotation without parentheses yields error FS0010: Unexpected symbol ':' in expression

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@edgarfgp @baronfel @brianrourkeboll @T-Gro