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feat: Higher-Kinded Types prototype (parser + RFC) - #63390

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Sai Asish Y (SAY-5) wants to merge 1 commit into
microsoft:mainfrom
SAY-5:feat/higher-kinded-types
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feat: Higher-Kinded Types prototype (parser + RFC)#63390
Sai Asish Y (SAY-5) wants to merge 1 commit into
microsoft:mainfrom
SAY-5:feat/higher-kinded-types

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@SAY-5

@SAY-5 Sai Asish Y (SAY-5) commented Apr 12, 2026

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This is a prototype exploring parser support for higher-kinded type parameters (<F<_>> syntax), along with an RFC document laying out a phased approach to full HKT support.

Parser changes recognize type parameters that are themselves generic. The RFC covers syntax design, kind inference, and how checker integration would work in a follow-up.

Included test cases cover the patterns people typically want HKTs for: Functor, Monad, Bifunctor, natural transformations.

This is intentionally scoped to parser + design — checker integration is a separate, much larger effort.

Phase 1 of Higher-Kinded Types (#1213):
- Parser: recognize <F<_>> in type parameter positions
- Types: isHigherKinded/hktParameters on TypeParameterDeclaration
- RFC: design doc with phased plan
- Tests: Functor, Monad, Bifunctor syntax cases
@RyanCavanaugh

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This repo is closed to development.

Also, https://github.com/microsoft/TypeScript/blob/main/CONTRIBUTING.md#use-of-ai-assistance

@github-project-automation github-project-automation Bot moved this from Not started to Done in PR Backlog Apr 14, 2026
@typescript-bot TypeScript Bot (typescript-bot) added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Apr 14, 2026
@typescript-bot

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This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

@SAY-5

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Understood. Apologies for not reading the contributing guidelines properly.

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