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  • 9 commits
  • 17 files changed
  • 2 contributors

Commits on Mar 15, 2026

  1. Add higher-kinded types (HKTs) — v0 proof of concept 

    Introduce first-class support for abstracting over type constructors via
kind annotations in type parameter syntax: `<F : * -> *>`.

This enables writing generic abstractions like Functor and Monad that
work across Array, Promise, user-defined types, and any type constructor
of the right kind — eliminating the need for defunctionalization hacks.

What works:
- Kind annotation syntax parsed from `<F : * -> *>` (no new tokens)
- `Functor<Array>`, `Monad<Box>` — concrete and user-defined constructors
- `F<A>` type application resolves to `Array<A>` when F = Array
- Monad<F> extends Functor<F> — HKT params forwarded through inheritance
- Generic functions: lift, when, sequence all typecheck
- Type inference: `boxMonad.pure(42)` infers `Box<number>`
- Invariant assignability for abstract constructor applications
- Arity checking: `F<A, B>` errors when `F : * -> *`
- Full backward compatibility with existing TypeScript code
- 12 test cases passing in the standard test suite

Compiler changes:
- parser.ts: parseKindAnnotation() for `* -> *` syntax
- types.ts: kindArity on TypeParameterDeclaration and TypeParameter;
  hktConstructorSymbol and hktTypeArguments on Type
- checker.ts: TypeConstructorRef and HKTApplicationType representations
  (both piggyback on TypeFlags.Substitution); HKT-aware type argument
  resolution, instantiation, assignability, and inference

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  2. Add HKT playground — interactive browser demo 

    Self-contained HTML page that loads the custom TypeScript compiler and
provides a live type-checking editor with example buttons for Functor,
Monad, Sequence, and error cases.

Serve from repo root: python3 -m http.server 8080
Open: http://localhost:8080/hkt-playground.html

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  3. Upgrade HKT playground to Monaco editor 

    Replace textarea with Monaco editor for full IDE experience: syntax
highlighting, bracket matching, error squigglies, line numbers, and
click-to-navigate on diagnostic locations.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  4. Add custom hover provider using HKT-aware compiler 

    Replace Monaco's built-in TypeScript hover (which shows `any` for HKT
types) with a custom hover provider that queries our compiler's type
checker. Hovering over `fa: F<A>` now shows the correct type from our
HKT-aware checker, and type parameters with kind annotations display
their kind (e.g., `F : * -> *`).

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  5. Change kind syntax to uncurried form with tuple parameters 

    Replace Haskell-style curried kind arrows with explicit tuple syntax:
- `* -> *` for one-arg constructors (unchanged)
- `(*, *) -> *` for two-arg constructors (was `* -> * -> *`)
- `(*) -> *` is sugar for `* -> *`
- `(* -> *) -> *` parses but errors: "Higher-order kinds are not yet
  supported"

The parser now handles a full kind grammar with parens, commas, and
right-associative arrows. Internally, a KindNode tree is stored on
the AST alongside the simple kindArity count. The checker validates
that all kind parameters and return are `*`, rejecting higher-order
kinds with a clear diagnostic (TS2900).

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  6. Support higher-order kinds: (* -> *) -> * and beyond 

    Remove the "not yet supported" restriction on higher-order kinds.
Type constructors can now take other type constructors as parameters:

  type ApplyToArray<F : (* -> *) -> *> = F<Array>
  interface Wrapper<F : * -> *> { wrap<A>(a: A): F<A> }

Changes:
- Store full KindNode tree on TypeParameter (alongside kindArity)
- Add kind utilities: kindsMatch(), getKindOfType(), getKindOfSymbol(),
  kindToString() for recursive kind comparison
- resolveTypeConstructorArgument now uses full kind matching instead
  of simple arity equality
- isHKTTypeArgumentContext handles TypeParameter parents (F<Array>
  where F is itself a higher-kinded parameter)
- Force-resolve type alias symbols in isHKTTypeArgumentContext to
  ensure typeParameters are populated

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  7. Update HKT.md with higher-order kinds and new syntax 

    Reflect current state: uncurried kind syntax, higher-order kinds
supported, 18 tests passing, live demo link.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  8. Add Bifunctor and Higher-Order examples to playground 

    New example tabs showing (*, *) -> * with Pair/Bifunctor and
(* -> *) -> * with ApplyToNumber, NaturalTransformation, and
nested kind aliases.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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  9. Improve Higher-Order example with Nat composition 

    Show natural transformations (Nat<F, G> where F, G : * -> *) and
composition of natural transformations (composeNat with three * -> *
params), demonstrating genuine higher-kinded programming.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
    @rkirov @claude
    rkirov and claude committed Mar 15, 2026
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