tmu
aaeeef1e11
Record why open universes and value/stringification collisions are rejected, the `Member<T, K>` inversion, and the findings from the rejected open-universe attempt so they are not re-run.
53 lines
2.3 KiB
Markdown
53 lines
2.3 KiB
Markdown
# tiny-pattern-ts
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Pattern matching for TypeScript/ESM environments (F#-style, not regex).
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## Description
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`tiny-pattern-ts` brings F#-style pattern matching to TypeScript. Patterns are
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ordinary objects whose `matches` method is a TypeScript type guard, so narrowing
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composes the way any other guard does. It is deliberately not a regex engine and
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not a macro: there is no transpiler and no DSL to learn, and the type-level
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contract is the feature — see [development/library.md](./development/library.md)
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for the design decisions and [Caveats](#caveats) for the limits.
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## Requirements
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- **Node.js >= 26** (`engines` field; pinned via `.node-version`).
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- **TypeScript >= 5.0** to consume the published declarations. The emitted `.d.ts`
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use `const` type parameters (TS 5.0) and keep their relative `.ts` specifiers;
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both resolve on TS >= 5.0 in `node10` / `node16` / `nodenext` / `bundler`.
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- The package is **ESM-only** (no CommonJS shim).
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## API
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Yet to be implemented
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## Caveats
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- **Only finite universes are supported.** The factory must be given a finite
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union of literals; `string`, `number` and template literals are rejected. This
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is what lets the exhaustive overload be proven, so the runtime `dispatch`
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throw stays unreachable through the typed API.
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- **A value and its stringification must not both be present.** Object keys
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stringify, so a universe containing both a member and the string it
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stringifies to — `1 | "1"`, `true | "true"`, `null | "null"` — is rejected at
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the factory. Either form alone is fine, and one value's string form may
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coexist with a _different_ value's bare form (`"true" | false`).
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- **`symbol` and `bigint` are not supported.** A `symbol` brand is a
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compile-time phantom with nothing to match at runtime, and a `bigint` is not a
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valid property key; neither satisfies the matcher's universe constraint.
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- **`NaN` and `-0` cannot be matched specifically.** They have no literal type,
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so both stay part of `number`.
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## License
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MIT © 2025 tmu. See [LICENSE](./LICENSE).
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## Contributing
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Contributions are documented in [CONTRIBUTING.md](./CONTRIBUTING.md); the
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reasons behind the project's decisions, rejected alternatives, and known issues
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live in [development/](./development/README.md). AI coding agents start at
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[AGENTS.md](./AGENTS.md).
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