Support empty-bodied computation expressions

[brianrourkeboll]

Description

• Add support for empty-bodied computation expressions.
  • Language suggestion: https://github.com/fsharp/fslang-suggestions/issues/1232
  • RFC FS-1144: https://github.com/fsharp/fslang-design/pull/774 (which see for more explanation of why this specific approach was taken)
  • RFC discussion: https://github.com/fsharp/fslang-design/discussions/775

Examples

builder { }

seq { }

Checklist

• [x] Test cases added.
• [x] Release notes entry updated.

[!IMPORTANT] Shoutout to @edgarfgp @fabulous-dev for sponsoring my work on this.

[github-actions[bot]]

:heavy_exclamation_mark: Release notes required

---

:white_check_mark: Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
LanguageFeatures.fsi	docs/release-notes/.Language/preview.md

[vzarytovskii]

Haven't reviewed it yet, but thinking out loud:

How would this play with resumable state machines. I assume it should be fine since it's just a transformation essentially.

And second, orthogonal comment - this feature will encourage more CE use, which my itself is not bad, but might lead to more nested CEs, which will involve more checking = being slower. We really need to do something with it. I made an attempt or two in the past, but change surface was bigger than I anticipated.

[brianrourkeboll]

How would this play with resumable state machines. I assume it should be fine since it's just a transformation essentially.

That's a good call-out. I'll add some tests to make sure.

[psfinaki]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 2 pipeline(s).

[psfinaki]

Cool stuff! Hope to give it a review soon. Can be a nice and intuitive addition to the language.