🔀 Merge chore/cleanup-readme into main

The README collapsed to API-only prose once the old match/P surface was
dropped. Rebuild its entry-point shape: a quick-start Synopsis walked through
a Contact union, a dedicated Installation section, and a real-world Examples
section (primitive-union dispatch, a fallback, a property union narrowed by
the tagged-union matcher, and the widening variant).

Set the tagline and Description to the library's identity — exhaustive,
type-safe pattern matching for TypeScript — and state the goal Moose-style:
type-safe pattern matching with a lean syntax, accomplished by exhaustive
branches and typed per-branch handler parameters, backed by autocomplete and
a tiny footprint. Drop the F#-style framing and the stale "matches method is
a type guard" and "(not regex)" copy from the README, AGENTS.md and the
package.json description. Every fence is a doc-test, so the examples cannot
drift from the API.

.gitea/workflows/ci.yml

@@ -77,6 +77,10 @@ jobs:
             - run: npm ci
             - run: npm run build
             - run: npm run check
+            # Compile the prose examples into gitignored tests. Kept as an
+            # explicit step (not a `pretest:ci` hook) so it is visible in the
+            # job log and `test:ci` stays a plain command.
+            - run: npm run create:doc-tests
             # Fails the build below 100% coverage on `src/` (`c8 --all --100`);
             # the same run produces the report published below. See
             # development/ci.md § Coverage threshold.

.gitignore

@@ -1,6 +1,10 @@
 node_modules
 dist
 coverage
+
+# Generated doc-tests (scripts/create-doc-tests.ts); the folder is kept via .gitkeep
+src/doc-test/__generated__/*.test.ts
+!src/doc-test/__generated__/.gitkeep
 *.log
 *.tsbuildinfo
 *.local

AGENTS.md

@@ -7,10 +7,11 @@ first-action facts. Do not restate evolving prose here — it will drift.
 
 ## First action
 
-- Project: F#-style pattern matching for TypeScript/ESM. Node `>=26` (pinned via `.node-version`), ESM-only (no CommonJS shim).
+- Project: pattern matching for TypeScript/ESM. Node `>=26` (pinned via `.node-version`), ESM-only (no CommonJS shim).
 - **While iterating:** `npm run test` (`check:tsc` + the unit suite) for fast feedback on the files you changed.
 - **Optional code intelligence:** this repo installs `@spences10/pi-lsp` (pinned in `.pi/settings.json`) as a project-local pi extension. It talks to the repo's own TypeScript 7 via `tsc --lsp --stdio` and exposes **read-only** tools — `lsp_hover`, `lsp_definition`, `lsp_references`, `lsp_find_symbol`, `lsp_document_symbols`, `lsp_diagnostics(_many)`. **When you are looking for a symbol, reach for the LSP before `rg`/`grep`** — `lsp_references` / `lsp_find_symbol` / `lsp_definition` / `lsp_document_symbols` are semantic and cross-file, so they see shadowing, imports and overloads that a text search cannot; use `lsp_hover` to read inferred types on generic-heavy code. Use `rg` for what the LSP cannot see — doc prose, string literals, config, task lists, file discovery — and reconcile the two sets before editing (symbols from the LSP, strings and prose from `rg`). It has no rename / code-action / apply-edit surface — the write side is pi's `edit` tool + `check:tsc`. Treat empty LSP output as _inconclusive_, not success: **`npm run test` / `npm run verify` remain the sole authoritative gate** (see the next bullet). The server keeps running across that gate with a ~5 min idle timeout and registers no file watchers, so if you change `tsconfig.json` / `package.json` mid-session its diagnostics can be stale — when LSP output disagrees with `check:tsc`, trust `check:tsc` and restart pi (or wait out the idle timeout) before concluding the LSP is wrong.
 - **Definition of done — run this before you call the work finished:** `npm run verify`. If all green, commit. If red, look at the output, fix the root cause, and re-run.
+- **Touched a `ts`-tagged fence in `README.md` / `CONTRIBUTING.md`?** Run `npm run create:doc-tests` first: it regenerates the gitignored tests under `src/doc-test/__generated__/`, formats and type-checks them, so `verify` executes the documented example. CI runs it in an explicit step before `test:ci`; the fast local tiers do not. See [development/docs.md](./development/docs.md).
 - **On commit:** write a good message (see [CONTRIBUTING.md § Commit messages](./CONTRIBUTING.md#commit-messages)). Lefthook's pre-commit hook already runs the fast, offline, staged-file checks — don't run them by hand. If the hook fails on style, `npm run fix`, restage, recommit.
 - **Document decisions where the next maintainer will look:** rationale, rejected alternatives and known issues go in `development/<category>.md` (see [development/README.md](./development/README.md)); the actionable rule stays in [CONTRIBUTING.md](./CONTRIBUTING.md) and links to it. Write each fact once — never copy the rule into `development/` or the reason into `CONTRIBUTING.md` — and change both in the same commit when a rule changes.
 - **`npm run maintain` is NOT part of the feature loop.** Its scans are advisory, never a gate; run them only on an explicit maintenance / update-deps branch.

CHANGELOG.md

@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- restore the README's Synopsis and Examples sections: a quick-start recipe plus
+  real-world examples (primitive-union dispatch, a fallback, a property union
+  narrowed by the tagged-union matcher, and a widening variant)
+- document the public API in the README: the four factories, when to use each,
+  what the `W` (widening) suffix means, and examples that bind the handler-map
+  function once
+- add TSDoc to the four public matcher factories
+
 ## [0.8.1] - 2026-09-23
 
 - gate CI at 100% coverage: `test:ci` runs c8 with `--all --100` over `src/`,

CONTRIBUTING.md

@@ -22,6 +22,8 @@ the rules so agents and humans don't diverge.
 - **Test:** `npm run test`, `npm run test:ci`
 - **Watch:** `npm run watch` - re-runs tests on file save, humans only
 - **Checks:** `npm run check`, `npm run fix`
+- **Doc tests:** `npm run create:doc-tests` — compile the `ts`-tagged fences
+  in the prose docs into executed, gitignored tests
 - **Verify:** `npm run verify` — the definition of done
 - **Maintenance:** `npm run maintain` — advisory only
 - **Individual fixes:** `npm run fix:oxfmt`, `npm run fix:oxlint`
@@ -87,6 +89,17 @@ Per [AGENTS.md § Never do](./AGENTS.md#never-do), reach green honestly — fix
 types, never suppress the checks you can't make pass. Full rationale:
 [development/testing.md](./development/testing.md).
 
+## Documentation examples
+
+Every `ts`-tagged fence in `README.md` / `CONTRIBUTING.md` is compiled into an
+executed test, so a documented example cannot drift from the API. Describe each
+fence with the paragraph directly above it (that text becomes the test title),
+and keep its library import self-contained;
+`npm run create:doc-tests` regenerates, formats and type-checks the tests under
+`src/doc-test/__generated__/`. CI runs it in an explicit step before `test:ci`,
+so run it yourself before `npm run verify` when you touched a fence. Why:
+[development/docs.md](./development/docs.md).
+
 ## Code style and formatting
 
 `oxfmt` is the formatter and `oxlint` is the linter (with type-aware rules).
@@ -115,18 +128,21 @@ intended to run. A `<prefix>:<name>` script is implicitly aggregated by a
 `<prefix>` script (if one exists) and run by the corresponding lefthook hook or
 CI step. Pick the prefix that matches the script's lifecycle:
 
-- `create:*` — front doors of the repo's own workflow; these mutate git state
-  rather than the source. `create:branch` opens a unit of work, `create:finish`
+- `create:*` — front doors of the repo's own workflow; these produce or mutate
+  workflow artifacts (git state, generated doc-tests) rather than the
+  hand-written source. `create:branch` opens a unit of work, `create:finish`
   closes the branch half, `create:release` closes the release half
-  (maintainer-only). No bare `create` aggregator on purpose.
+  (maintainer-only), and `create:doc-tests` regenerates the compiled prose
+  examples. No bare `create` aggregator on purpose.
 - `check:*` — read-only verification; never modifies files. Aggregated by
   `npm run check`.
 - `fix:*` — mutating counterpart of a `check:*` script. Aggregated by
   `npm run fix`; the diff is the review surface.
 - `test:*` — test scripts. `test` is the canonical entry point (`check:tsc` +
   unit tests); `test:unit` skips the typecheck for fast local iteration;
-  `test:ci` runs the suite under c8 and fails below 100% coverage on `src/`
-  (CI-only; `verify` stays coverage-free).
+  `test:coverage` runs c8 over the hand-written tests only; `test:doc` runs the
+  generated doc examples without coverage; `test:ci` chains the two and fails
+  below 100% coverage on `src/` (CI-only; `verify` stays coverage-free).
 - `watch:*` — long-running watchers for the manual inner dev loop. Aggregated by
   `watch`.
 - `maintain:*` — advisory repo-maintenance scans: read-only, but whole-project

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2025 tmu
+Copyright (c) 2026 tmu
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -1,15 +1,53 @@
 # tiny-pattern-ts
 
-Pattern matching for TypeScript/ESM environments (F#-style, not regex).
+Exhaustive, type-safe pattern matching for TypeScript.
+
+## Synopsis
+
+```ts
+import { getTaggedUnionMatcher } from "tiny-pattern-ts";
+
+// 1. We have a union type
+type Contact =
+    | { kind: "email"; address: string }
+    | { kind: "phone"; number: string }
+    | { kind: "messenger"; username: string };
+
+// 2. Create a matcher providing the discriminant property
+const matchContact = getTaggedUnionMatcher<Contact>()("kind");
+
+// 3. Define handlers for each branch of the union
+const formatContact = matchContact({
+    email: (e) => `MAIL: ${e.address}`,
+    phone: (p) => `PHONE: ${p.number}`,
+    messenger: (m) => `MESSENGER: @${m.username}`,
+});
+
+// 4. Call the matcher with a value
+const mailOutput = formatContact({ kind: "email", address: "ada@example.com" });
+assert.equal(mailOutput, "MAIL: ada@example.com");
+
+const phoneOutput = formatContact({ kind: "phone", number: "+1 555 0100" });
+assert.equal(phoneOutput, "PHONE: +1 555 0100");
+```
 
 ## Description
 
-`tiny-pattern-ts` brings F#-style pattern matching to TypeScript. Patterns are
-ordinary objects whose `matches` method is a TypeScript type guard, so narrowing
-composes the way any other guard does. It is deliberately not a regex engine and
-not a macro: there is no transpiler and no DSL to learn, and the type-level
-contract is the feature — see [development/library.md](./development/library.md)
-for the design decisions and [Caveats](#caveats) for the limits.
+`tiny-pattern-ts` is a pattern-matching library for TypeScript.
+
+The main goal of `tiny-pattern-ts` is to make pattern matching type-safe with a
+lean syntax. This is accomplished by being exhaustive and passing typed
+parameters per branch to the handlers — supported by an outstanding
+autocomplete and a tiny footprint.
+
+See [development/library.md](./development/library.md) for the design decisions
+and [Caveats](#caveats) for the limits.
+
+## Installation
+
+```sh
+npm install tiny-pattern-ts
+```
 
 ## Requirements
 
@@ -19,9 +57,202 @@ for the design decisions and [Caveats](#caveats) for the limits.
   both resolve on TS >= 5.0 in `node10` / `node16` / `nodenext` / `bundler`.
 - The package is **ESM-only** (no CommonJS shim).
 
+## Examples
+
+A few real-world recipes. Each binds the handler-map function once and reuses
+it, so the matcher is allocated a single time.
+
+### Dispatch on a primitive union
+
+A result code is itself a finite union, so `getPrimitiveUnionMatcher` keys a
+handler on each member:
+
+```ts
+import { getPrimitiveUnionMatcher } from "tiny-pattern-ts";
+
+type ResultCode = "ok" | "created" | "no-content";
+
+const toStatus = getPrimitiveUnionMatcher<ResultCode>()({
+    ok: () => 200,
+    created: () => 201,
+    "no-content": () => 204,
+});
+
+assert.equal(toStatus("ok"), 200);
+assert.equal(toStatus("created"), 201);
+assert.equal(toStatus("no-content"), 204);
+```
+
+### Leave cases to a fallback
+
+Pass a fallback as the second argument to handle only part of the universe; it
+receives the members the map leaves uncovered — here the parameter is
+`"deprecated" | "gateway-timeout"`:
+
+```ts
+import { getPrimitiveUnionMatcher } from "tiny-pattern-ts";
+
+type Status = "active" | "beta" | "deprecated" | "gateway-timeout";
+
+const rollout = getPrimitiveUnionMatcher<Status>()(
+    { active: () => "enabled", beta: () => "enabled" },
+    (status) => `blocked (${status})`,
+);
+
+assert.equal(rollout("active"), "enabled");
+assert.equal(rollout("deprecated"), "blocked (deprecated)");
+```
+
+### Dispatch on a property union
+
+The value does not have to be the union itself. When a single property carries a
+finite union, the tagged-union matcher keys on it and narrows the whole record to
+the selected value:
+
+```ts
+import { getTaggedUnionMatcher } from "tiny-pattern-ts";
+
+interface Invoice {
+    readonly currency: "eur" | "usd" | "jpy";
+    readonly amount: number;
+}
+
+const matchCurrency = getTaggedUnionMatcher<Invoice>()("currency");
+
+const symbolOf = matchCurrency({
+    eur: (i) => `€${i.amount.toFixed(2)}`,
+    usd: (i) => `$${i.amount.toFixed(2)}`,
+    jpy: (i) => `¥${i.amount.toFixed(0)}`,
+});
+
+assert.equal(symbolOf({ currency: "usd", amount: 12.5 }), "$12.50");
+assert.equal(symbolOf({ currency: "jpy", amount: 900 }), "¥900");
+```
+
+### Widen the return type
+
+When the handlers return different types, reach for the widening `W` variant: the
+matcher's return is their union rather than one common type — here
+`string | string[] | undefined`:
+
+```ts
+import { getPrimitiveUnionMatcherW } from "tiny-pattern-ts";
+
+type Field = "name" | "tags" | "note";
+
+const parse = getPrimitiveUnionMatcherW<Field>()({
+    name: () => "Ada",
+    tags: () => ["admin", "beta"],
+    note: () => undefined,
+});
+
+assert.equal(parse("name"), "Ada");
+assert.deepEqual(parse("tags"), ["admin", "beta"]);
+assert.equal(parse("note"), undefined);
+```
+
 ## API
 
-Yet to be implemented
+The package exports four factories. Two axes pick one:
+
+- **Universe** — a _primitive-union_ matcher matches a value that is itself a
+  finite union (`"yes" | "no"`); a _tagged-union_ matcher matches an object
+  discriminated by a property (`{ kind: … }`).
+- **Return** — the _strict_ variant gives every handler one common return type
+  `R`; the _widening_ variant (`W`) widens the return value to the union of the
+  handler returns.
+
+| Factory                          | Use when                                                                  | Return                |
+| -------------------------------- | ------------------------------------------------------------------------- | --------------------- |
+| `getPrimitiveUnionMatcher<T>()`  | the value is the union and all handlers return the same type              | one common `R`        |
+| `getPrimitiveUnionMatcherW<T>()` | the value is the union and handlers return different types                | union of the handlers |
+| `getTaggedUnionMatcher<T>()`     | the value is a discriminated object and all handlers return the same type | one common `R`        |
+| `getTaggedUnionMatcherW<T>()`    | the value is a discriminated object and handlers return different types   | union of the handlers |
+
+Bind the function that takes the handler map to a `match…` variable once and
+reuse it; the [Examples](#examples) do this, so the builder is allocated once.
+
+### Primitive-union matchers
+
+`getPrimitiveUnionMatcher<T>()` takes the finite universe `T` and returns a
+builder. Calling the builder with a handler map keyed by `T`'s members returns a
+matcher: a function from `T` to the common return type.
+
+```ts
+import { getPrimitiveUnionMatcher } from "tiny-pattern-ts";
+
+const matchAnswer = getPrimitiveUnionMatcher<"yes" | "no">();
+
+const reply = matchAnswer({
+    yes: () => "agreed",
+    no: () => "declined",
+});
+
+const answer = reply("yes");
+assert.equal(answer, "agreed");
+```
+
+Add a fallback as the second argument to leave members unhandled; the fallback
+receives the remainder:
+
+```ts
+import { getPrimitiveUnionMatcher } from "tiny-pattern-ts";
+
+const matchLabel = getPrimitiveUnionMatcher<"yes" | "no" | "maybe">();
+
+const label = matchLabel(
+    { yes: () => "agreed", no: () => "declined" },
+    (other) => `not sure: ${other}`, // other: "maybe"
+);
+
+const answer = label("yes");
+assert.equal(answer, "agreed");
+
+const fallback = label("maybe");
+assert.equal(fallback, "not sure: maybe");
+```
+
+`getPrimitiveUnionMatcherW` is the same builder, but the matcher's return type
+is the union of the handler return types rather than one common `R`.
+
+### Tagged-union matchers
+
+`getTaggedUnionMatcher<T>()` takes a discriminated union `T`. The returned
+function takes the discriminant property's name and returns the handler-map
+builder, keyed by that property's tags.
+
+```ts
+import { getTaggedUnionMatcher } from "tiny-pattern-ts";
+
+type Shape =
+    { kind: "circle"; radius: number } | { kind: "square"; side: number };
+
+const matchShape = getTaggedUnionMatcher<Shape>()("kind");
+
+const area = matchShape({
+    circle: (s) => Math.PI * s.radius ** 2,
+    square: (s) => s.side ** 2,
+});
+
+const circleArea = area({ kind: "circle", radius: 2 });
+assert.equal(circleArea, Math.PI * 4);
+
+const squareArea = area({ kind: "square", side: 3 });
+assert.equal(squareArea, 9);
+```
+
+`getTaggedUnionMatcherW` is the widening counterpart, exactly as in the
+primitive-union pair. The discriminant key is restricted to properties whose
+values are tags; see [Caveats](#caveats) for the supported tags and the
+`boolean` / `null` / `undefined` key projection.
+
+### The universe
+
+The primitive universe `T` must be a finite union of literals with no
+value/stringification collision. A broad member (`string`, `number`, a template
+literal) or a colliding pair (`true | "true"`, `1 | "1"`) is rejected at the
+factory. The reasons and the rejected alternatives are in
+[development/library.md](./development/library.md).
 
 ## Caveats
 
@@ -55,7 +286,7 @@ cover. The type-level cost of supporting open universes is recorded in
 
 ## License
 
-MIT © 2025 tmu. See [LICENSE](./LICENSE).
+MIT © 2026 tmu. See [LICENSE](./LICENSE).
 
 ## Contributing
 

backlog.tasks

@@ -8,10 +8,10 @@ Setup:
 ☐ Split off template into separate package => pi --session 01a07dde-7050-7054-bb36-1606d7eb2bc3 @low
 
 v1.0:
-☐ API surface is stable and fully typed
-    ☐ Finalize public exports in `src/index.ts`
-    ☐ Document all exported types and functions
-    ☐ Add JSDoc for public APIs
+✔ API surface is stable and fully typed @done
+    ✔ Finalize public exports in `src/index.ts` @done
+    ✔ Document all exported types and functions @done
+    ✔ Add JSDoc for public APIs @done
 ✔ Test coverage meets threshold @done
     ✔ Achieve 100% branch coverage on `src/primitive-union.ts` @done
     ✔ Achieve 100% branch coverage on `src/index.ts` @done
@@ -23,14 +23,16 @@ Matcher:
     ✔ optional discriminant (`{ type?: "x" }`) is the same hole: the boolean/nullish change now admits the `undefined` tag, so the factory accepts the key, but `Extract<T, Record<K, V>>` still passes `never` to both the `x` and `undefined` handlers @done
 
 Documentation:
-☐ Bring README.md back to its previous form — synopsis and examples restored, in the correct place
+✔ Bring README.md back to its previous form — synopsis and examples restored, in the correct place @done
     → previous section order: title, tagline, Synopsis, Description, Requirements, Examples, API, License, Contributing
     → previous Examples order: literal/exhaustive, typeof, structural/discriminated unions, when, any
 ☐ Create `examples/` directory with runnable snippets
 ☐ Add comparison section vs. other TS pattern-matching libs in Readme.md
-☐ Write migration guide for users coming from discriminated unions
-☐ Create backlog tasks for implementation
-☐ Validate code fences in Markdown (start with README.md) — compile the TypeScript examples against `src/` so the docs cannot drift from the API
+    ☐ Why do we do this? => exhaustiveness encoded type safe
+    ☐ Why this form? little syntax, data last, very small, autocomplete, strict typing in the handler; for more features use ts-pattern
+✔ Write migration guide for users coming from discriminated unions @done (9/24/2026, 10:21:17 PM)
+✔ Create backlog tasks for implementation @done (9/24/2026, 10:21:16 PM)
+✔ Validate code fences in Markdown (start with README.md) — compile the TypeScript examples against `src/` so the docs cannot drift from the API @done
 
 Maintenance:
 ☐ Serve CI coverage over a tiny self-hosted webserver (replace the zip artifact) @low

development/README.md

@@ -24,6 +24,7 @@ One file per category:
 | [workflow.md](./workflow.md)     | Branching and merging, script prefixes, feedback tiers, commit messages |
 | [tooling.md](./tooling.md)       | Toolchain choices and configuration, editor setup                       |
 | [testing.md](./testing.md)       | Test strategy and type-driven development                               |
+| [docs.md](./docs.md)             | Validating the Markdown code fences in the prose docs                   |
 | [ci.md](./ci.md)                 | CI pipeline, runner image, coverage serving                             |
 | [publishing.md](./publishing.md) | Release and npm publishing                                              |
 

development/docs.md

@@ -0,0 +1,61 @@
+# Docs
+
+Why the prose documentation is maintained the way it is. The actionable rules
+are in [CONTRIBUTING.md](../CONTRIBUTING.md); this file records the rationale.
+
+## Validating Markdown code fences
+
+#### Decision (2026-11)
+
+Compile every `ts / `typescript fence in the prose docs into a real
+`node:test` case under `src/doc-test/__generated__/`, typechecked by a scoped
+`tsc` project and executed by `node --test`.
+
+#### Why
+
+- A documented example is a promise about the API. Left unchecked it drifts the
+  moment a signature changes, and a reader copies broken code.
+- The repo runs TypeScript 7, the native/Go compiler. It exposes **no legacy JS
+  compiler API** (`ts.createProgram`, `ts.transpileModule`, `ts.createSourceFile`
+  are all `undefined`; `Object.keys(require("typescript"))` is
+  `["version", "versionMajorMinor"]`). So `@typescript/vfs`, the type-aware
+  `eslint-plugin-markdown` and `docs-ts` / `@effect/docgen` cannot run here.
+- `node --check` parses as JS and rejects valid TS type annotations, so it is not
+  a gate. The only faithful validator is the `tsc` **CLI**, which means emitting
+  real `.ts` files and letting the existing `check:tsc` / `node --test` pipeline
+  judge them.
+
+#### Rejected
+
+- **A packaged doc-test tool** (see above) — no usable compiler API on TS 7.
+- **Embedding a typecheck in the generator** — duplicates the gate, and would
+  not exercise the repo's own resolution.
+- **`node --check`** — wrong language level.
+
+#### Known issue
+
+- Scanned sources are hard-coded to `README.md` and `CONTRIBUTING.md`. A
+  `docs/` + `examples/` list is the natural extension; `development/` must never
+  be scanned (its fences are illustrative, not compilable).
+- The generator hoists and merges leading imports, rewrites `tiny-pattern-ts` to
+  the `#test-tiny-pattern-ts` source alias, and rejects an example that imports
+  `node:assert` / `node:test` (the prelude already binds both). Titles are the
+  immediately preceding paragraph; a fence with no such paragraph is a fatal
+  error, which keeps every example described.
+- `oxlint src/doc-test` reports "No files found" because the generated
+  `*.test.ts` are gitignored. That is cosmetic: the files are still typechecked
+  and run.
+- The generated tests are `*.test.ts`, which c8's default excludes already keep
+  out of the `--100` gate. Do not add an `--exclude` for them: passing any
+  `--exclude` replaces the defaults, so every hand-written test file and
+  `__tests__/` helper re-enters coverage and the gate fails.
+- Generated examples must not run under `c8`: an example could cover a line no
+  hand-written test reaches, so the coverage gate would pass on documentation
+  alone. `test:coverage` therefore runs c8 over the tracked tests only
+  (`git ls-files 'src/*.test.ts'` — the generated files are untracked), and
+  `test:doc` runs the examples in a separate process without c8. `test:ci`
+  chains the two, so correctness and coverage stay independent.
+- The CI `build` job runs `npm run create:doc-tests` as an explicit step before
+  `npm run test:ci`, not a `pretest:ci` lifecycle hook: the hook hides the step
+  from the job log and makes `test:ci` behave differently under npm than when
+  run directly.

development/library.md

@@ -5,8 +5,39 @@ user-facing reference is [README § API](../README.md#api).
 
 The matchers are implemented in `src/primitive-union.ts` (`getPrimitiveUnionMatcher` /
 `getPrimitiveUnionMatcherW`) and `src/tagged-union.ts` (`getTaggedUnionMatcher` /
-`getTaggedUnionMatcherW`), re-exported from `src/index.ts`; the rest of the
-library is placeholder code.
+`getTaggedUnionMatcherW`), re-exported from `src/index.ts`; the rest of `src/`
+is implementation detail.
+
+## Public surface
+
+#### Decision (2026-09)
+
+`src/index.ts` exports the four factories and nothing else. Every exported
+function carries TSDoc; the builder types and the `matcher-shared.ts`
+vocabulary stay internal.
+
+#### Why
+
+- The factories are the whole contract: a consumer calls one and never needs to
+  name the builder type it returns.
+- The builder interfaces are already the inferred return types, so they travel
+  into the emitted `.d.ts` regardless. Exporting them would only make them
+  nameable while freezing the internal `Strict` / `Widening` overload split as
+  API.
+- TSDoc travels into the emitted declarations, so editor hovers and the
+  published package document the API without a hand-written `.d.ts`.
+
+#### Rejected
+
+- **Exporting the builder types** (`PrimitiveUnionMatcher`, …). Nameable, but it
+  grows the surface for no call-site benefit and pins the `Strict` / `Widening`
+  split.
+- **Exporting the `matcher-shared.ts` vocabulary** (`Matchable`, `UnaryFn`,
+  `PatternKey`, `Member`, `PatternReturns`, …). They appear in the public
+  signatures, but a consumer never needs to name them; exporting them would
+  freeze plumbing as API.
+- **A hand-written `.d.ts` or a separate API document.** It would drift from the
+  implementation; TSDoc is generated from the source.
 
 ## Matcher shape
 

development/workflow.md

@@ -96,7 +96,8 @@ aggregator.
 
 #### Why
 
-- Both members create something real: a branch, a release.
+- Every member creates something real: a branch, a release, the compiled
+  doc-tests.
 - It joined both lists in [CONTRIBUTING.md](../CONTRIBUTING.md) alongside its
   first members, so it could not go invisible the way the retired `use:` prefix
   did.

package-lock.json

@@ -23,6 +23,7 @@
                 "expect-type": "1.4.0",
                 "knip": "^6.34.0",
                 "lefthook": "^2.1.12",
+                "mdast-util-from-markdown": "^2.0.3",
                 "oxfmt": "^0.70.0",
                 "oxlint": "^1.83.0",
                 "oxlint-tsgolint": "^7.0.2001",
@@ -2358,6 +2359,16 @@
                 "tslib": "^2.4.0"
             }
         },
+        "node_modules/@types/debug": {
+            "version": "4.1.13",
+            "resolved": "https://registry.npmjs.org/@types/debug/-/debug-4.1.13.tgz",
+            "integrity": "sha512-KSVgmQmzMwPlmtljOomayoR89W4FynCAi3E8PPs7vmDVPe84hT+vGPKkJfThkmXs0x0jAaa9U8uW8bbfyS2fWw==",
+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "@types/ms": "*"
+            }
+        },
         "node_modules/@types/istanbul-lib-coverage": {
             "version": "2.0.6",
             "resolved": "https://registry.npmjs.org/@types/istanbul-lib-coverage/-/istanbul-lib-coverage-2.0.6.tgz",
@@ -2365,6 +2376,23 @@
             "dev": true,
             "license": "MIT"
         },
+        "node_modules/@types/mdast": {
+            "version": "4.0.4",
+            "resolved": "https://registry.npmjs.org/@types/mdast/-/mdast-4.0.4.tgz",
+            "integrity": "sha512-kGaNbPh1k7AFzgpud/gMdvIm5xuECykRR+JnWKQno9TAXVa6WIVCGTPvYGekIDL4uwCZQSYbUxNBSb1aUo79oA==",
+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "@types/unist": "*"
+            }
+        },
+        "node_modules/@types/ms": {
+            "version": "2.1.0",
+            "resolved": "https://registry.npmjs.org/@types/ms/-/ms-2.1.0.tgz",
+            "integrity": "sha512-GsCCIZDE/p3i96vtEqx+7dBUGXrc7zeSK3wwPHIaRThS+9OhWIXRqzs4d6k1SVU8g91DrNRWxWUGhp5KXQb2VA==",
+            "dev": true,
+            "license": "MIT"
+        },
         "node_modules/@types/node": {
             "version": "26.6.2",
             "resolved": "https://registry.npmjs.org/@types/node/-/node-26.6.2.tgz",
@@ -2375,6 +2403,13 @@
                 "undici-types": "~8.9.0"
             }
         },
+        "node_modules/@types/unist": {
+            "version": "3.0.3",
+            "resolved": "https://registry.npmjs.org/@types/unist/-/unist-3.0.3.tgz",
+            "integrity": "sha512-ko/gIFJRv177XgZsZcBwnqJN5x/Gien8qNOn0D5bQU/zAzVf9Zt3BlcUiLqhV9y4ARk0GbT3tnUiPNgnTXzc/Q==",
+            "dev": true,
+            "license": "MIT"
+        },
         "node_modules/@typescript/typescript-aix-ppc64": {
             "version": "7.0.2",
             "resolved": "https://registry.npmjs.org/@typescript/typescript-aix-ppc64/-/typescript-aix-ppc64-7.0.2.tgz",
@@ -2887,6 +2922,17 @@
                 "node": ">=10"
             }
         },
+        "node_modules/character-entities": {
+            "version": "2.0.2",
+            "resolved": "https://registry.npmjs.org/character-entities/-/character-entities-2.0.2.tgz",
+            "integrity": "sha512-shx7oQ0Awen/BRIdkjkvz54PnEEI/EjwXDSIZp86/KKdbafHh1Df/RYGBhn4hbe2+uKC9FnT5UCEdyPz3ai9hQ==",
+            "dev": true,
+            "license": "MIT",
+            "funding": {
+                "type": "github",
+                "url": "https://github.com/sponsors/wooorm"
+            }
+        },
         "node_modules/check-outdated": {
             "version": "3.0.0",
             "resolved": "https://registry.npmjs.org/check-outdated/-/check-outdated-3.0.0.tgz",
@@ -3332,6 +3378,62 @@
                 "node": ">=22.12.0"
             }
         },
+        "node_modules/debug": {
+            "version": "4.4.3",
+            "resolved": "https://registry.npmjs.org/debug/-/debug-4.4.3.tgz",
+            "integrity": "sha512-RGwwWnwQvkVfavKVt22FGLw+xYSdzARwm0ru6DhTVA3umU5hZc28V3kO4stgYryrTlLpuvgI9GiijltAjNbcqA==",
+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "ms": "^2.1.3"
+            },
+            "engines": {
+                "node": ">=6.0"
+            },
+            "peerDependenciesMeta": {
+                "supports-color": {
+                    "optional": true
+                }
+            }
+        },
+        "node_modules/decode-named-character-reference": {
+            "version": "1.3.0",
+            "resolved": "https://registry.npmjs.org/decode-named-character-reference/-/decode-named-character-reference-1.3.0.tgz",
+            "integrity": "sha512-GtpQYB283KrPp6nRw50q3U9/VfOutZOe103qlN7BPP6Ad27xYnOIWv4lPzo8HCAL+mMZofJ9KEy30fq6MfaK6Q==",
+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "character-entities": "^2.0.0"
+            },
+            "funding": {
+                "type": "github",
+                "url": "https://github.com/sponsors/wooorm"
+            }
+        },
+        "node_modules/dequal": {
+            "version": "2.0.3",
+            "resolved": "https://registry.npmjs.org/dequal/-/dequal-2.0.3.tgz",
+            "integrity": "sha512-0je+qPKHEMohvfRTCEo3CrPG6cAzAYgmzKyxRiYSSDkS6eGJdyVJm7WaYA5ECaAD9wLB2T4EEeymA5aFVcYXCA==",
+            "dev": true,
+            "license": "MIT",
+            "engines": {
+                "node": ">=6"
+            }
+        },
+        "node_modules/devlop": {
+            "version": "1.1.0",
+            "resolved": "https://registry.npmjs.org/devlop/-/devlop-1.1.0.tgz",
+            "integrity": "sha512-RWmIqhcFf1lRYBvNmr7qTNuyCt/7/ns2jbpp1+PalgE/rDQcBT0fioSMUpJ93irlUhC5hrg4cYqe6U+0ImW0rA==",
+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "dequal": "^2.0.0"
+            },
+            "funding": {
+                "type": "github",
+                "url": "https://github.com/sponsors/wooorm"
+            }
+        },
         "node_modules/emoji-regex": {
             "version": "8.0.0",
             "resolved": "https://registry.npmjs.org/emoji-regex/-/emoji-regex-8.0.0.tgz",
@@ -4024,6 +4126,508 @@
                 "url": "https://github.com/chalk/chalk?sponsor=1"
             }
         },
+        "node_modules/mdast-util-from-markdown": {
+            "version": "2.0.3",
+            "resolved": "https://registry.npmjs.org/mdast-util-from-markdown/-/mdast-util-from-markdown-2.0.3.tgz",
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+            "dev": true,
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+                "@types/unist": "^3.0.0",
+                "decode-named-character-reference": "^1.0.0",
+                "devlop": "^1.0.0",
+                "mdast-util-to-string": "^4.0.0",
+                "micromark": "^4.0.0",
+                "micromark-util-decode-numeric-character-reference": "^2.0.0",
+                "micromark-util-decode-string": "^2.0.0",
+                "micromark-util-normalize-identifier": "^2.0.0",
+                "micromark-util-symbol": "^2.0.0",
+                "micromark-util-types": "^2.0.0",
+                "unist-util-stringify-position": "^4.0.0"
+            },
+            "funding": {
+                "type": "opencollective",
+                "url": "https://opencollective.com/unified"
+            }
+        },
+        "node_modules/mdast-util-to-string": {
+            "version": "4.0.0",
+            "resolved": "https://registry.npmjs.org/mdast-util-to-string/-/mdast-util-to-string-4.0.0.tgz",
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+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT",
+            "dependencies": {
+                "micromark-util-symbol": "^2.0.0"
+            }
+        },
+        "node_modules/micromark-util-decode-string": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-decode-string/-/micromark-util-decode-string-2.0.1.tgz",
+            "integrity": "sha512-nDV/77Fj6eH1ynwscYTOsbK7rR//Uj0bZXBwJZRfaLEJ1iGBR6kIfNmlNqaqJf649EP0F3NWNdeJi03elllNUQ==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT",
+            "dependencies": {
+                "decode-named-character-reference": "^1.0.0",
+                "micromark-util-character": "^2.0.0",
+                "micromark-util-decode-numeric-character-reference": "^2.0.0",
+                "micromark-util-symbol": "^2.0.0"
+            }
+        },
+        "node_modules/micromark-util-encode": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-encode/-/micromark-util-encode-2.0.1.tgz",
+            "integrity": "sha512-c3cVx2y4KqUnwopcO9b/SCdo2O67LwJJ/UyqGfbigahfegL9myoEFoDYZgkT7f36T0bLrM9hZTAaAyH+PCAXjw==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT"
+        },
+        "node_modules/micromark-util-html-tag-name": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-html-tag-name/-/micromark-util-html-tag-name-2.0.1.tgz",
+            "integrity": "sha512-2cNEiYDhCWKI+Gs9T0Tiysk136SnR13hhO8yW6BGNyhOC4qYFnwF1nKfD3HFAIXA5c45RrIG1ub11GiXeYd1xA==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT"
+        },
+        "node_modules/micromark-util-normalize-identifier": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-normalize-identifier/-/micromark-util-normalize-identifier-2.0.1.tgz",
+            "integrity": "sha512-sxPqmo70LyARJs0w2UclACPUUEqltCkJ6PhKdMIDuJ3gSf/Q+/GIe3WKl0Ijb/GyH9lOpUkRAO2wp0GVkLvS9Q==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT",
+            "dependencies": {
+                "micromark-util-symbol": "^2.0.0"
+            }
+        },
+        "node_modules/micromark-util-resolve-all": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-resolve-all/-/micromark-util-resolve-all-2.0.1.tgz",
+            "integrity": "sha512-VdQyxFWFT2/FGJgwQnJYbe1jjQoNTS4RjglmSjTUlpUMa95Htx9NHeYW4rGDJzbjvCsl9eLjMQwGeElsqmzcHg==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT",
+            "dependencies": {
+                "micromark-util-types": "^2.0.0"
+            }
+        },
+        "node_modules/micromark-util-sanitize-uri": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-sanitize-uri/-/micromark-util-sanitize-uri-2.0.1.tgz",
+            "integrity": "sha512-9N9IomZ/YuGGZZmQec1MbgxtlgougxTodVwDzzEouPKo3qFWvymFHWcnDi2vzV1ff6kas9ucW+o3yzJK9YB1AQ==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT",
+            "dependencies": {
+                "micromark-util-character": "^2.0.0",
+                "micromark-util-encode": "^2.0.0",
+                "micromark-util-symbol": "^2.0.0"
+            }
+        },
+        "node_modules/micromark-util-subtokenize": {
+            "version": "2.1.0",
+            "resolved": "https://registry.npmjs.org/micromark-util-subtokenize/-/micromark-util-subtokenize-2.1.0.tgz",
+            "integrity": "sha512-XQLu552iSctvnEcgXw6+Sx75GflAPNED1qx7eBJ+wydBb2KCbRZe+NwvIEEMM83uml1+2WSXpBAcp9IUCgCYWA==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT",
+            "dependencies": {
+                "devlop": "^1.0.0",
+                "micromark-util-chunked": "^2.0.0",
+                "micromark-util-symbol": "^2.0.0",
+                "micromark-util-types": "^2.0.0"
+            }
+        },
+        "node_modules/micromark-util-symbol": {
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/micromark-util-symbol/-/micromark-util-symbol-2.0.1.tgz",
+            "integrity": "sha512-vs5t8Apaud9N28kgCrRUdEed4UJ+wWNvicHLPxCa9ENlYuAY31M0ETy5y1vA33YoNPDFTghEbnh6efaE8h4x0Q==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT"
+        },
+        "node_modules/micromark-util-types": {
+            "version": "2.0.2",
+            "resolved": "https://registry.npmjs.org/micromark-util-types/-/micromark-util-types-2.0.2.tgz",
+            "integrity": "sha512-Yw0ECSpJoViF1qTU4DC6NwtC4aWGt1EkzaQB8KPPyCRR8z9TWeV0HbEFGTO+ZY1wB22zmxnJqhPyTpOVCpeHTA==",
+            "dev": true,
+            "funding": [
+                {
+                    "type": "GitHub Sponsors",
+                    "url": "https://github.com/sponsors/unifiedjs"
+                },
+                {
+                    "type": "OpenCollective",
+                    "url": "https://opencollective.com/unified"
+                }
+            ],
+            "license": "MIT"
+        },
         "node_modules/minimatch": {
             "version": "10.2.6",
             "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-10.2.6.tgz",
@@ -4060,6 +4664,13 @@
                 "node": ">=4"
             }
         },
+        "node_modules/ms": {
+            "version": "2.1.3",
+            "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
+            "integrity": "sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA==",
+            "dev": true,
+            "license": "MIT"
+        },
         "node_modules/mz": {
             "version": "2.7.0",
             "resolved": "https://registry.npmjs.org/mz/-/mz-2.7.0.tgz",
@@ -4798,6 +5409,20 @@
                 "node": ">=4"
             }
         },
+        "node_modules/unist-util-stringify-position": {
+            "version": "4.0.0",
+            "resolved": "https://registry.npmjs.org/unist-util-stringify-position/-/unist-util-stringify-position-4.0.0.tgz",
+            "integrity": "sha512-0ASV06AAoKCDkS2+xw5RXJywruurpbC4JZSm7nr7MOt1ojAzvyyaO+UxZf18j8FCF6kmzCZKcAgN/yu2gm2XgQ==",
+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "@types/unist": "^3.0.0"
+            },
+            "funding": {
+                "type": "opencollective",
+                "url": "https://opencollective.com/unified"
+            }
+        },
         "node_modules/v8-to-istanbul": {
             "version": "9.3.0",
             "resolved": "https://registry.npmjs.org/v8-to-istanbul/-/v8-to-istanbul-9.3.0.tgz",

package.json

@@ -1,7 +1,7 @@
 {
     "name": "tiny-pattern-ts",
     "version": "0.8.1",
-    "description": "Pattern matching for TypeScript/ESM environments (F#-style, not regex)",
+    "description": "Exhaustive, type-safe pattern matching for TypeScript",
     "keywords": [
         "adt",
         "algebraic-data-types",
@@ -28,7 +28,8 @@
     "type": "module",
     "sideEffects": false,
     "imports": {
-        "#test-utils/*": "./src/util/__tests__/*"
+        "#test-utils/*": "./src/util/__tests__/*",
+        "#test-tiny-pattern-ts": "./src/index.ts"
     },
     "exports": {
         ".": {
@@ -47,7 +48,8 @@
         "check:oxfmt": "oxfmt --check ${LEFTHOOK_FILES:-.}",
         "check:oxlint": "oxlint ${LEFTHOOK_FILES:-src scripts}",
         "check:tsc": "tsc",
-        "clean": "rm -rf dist coverage",
+        "clean": "rm -rf dist coverage src/doc-test/__generated__/*.test.ts",
+        "create:doc-tests": "node --strip-types scripts/create-doc-tests.ts && sh -c 'oxfmt src/doc-test/__generated__/*.test.ts' && tsc -p src/doc-test/tsconfig.json",
         "fix": "npm run fix:oxlint && npm run fix:oxfmt",
         "fix:oxfmt": "oxfmt ${LEFTHOOK_FILES:-.}",
         "fix:oxlint": "oxlint --fix src scripts",
@@ -58,7 +60,9 @@
         "maintain:knip": "knip --include dependencies,exports,files",
         "maintain:outdated": "check-outdated --ignore-pre-releases --ignore-packages @types/node",
         "test": "npm run check:tsc && node --test --strip-types \"src/**/*.test.ts\"",
-        "test:ci": "c8 --all --include \"src/**/*.ts\" --reporter=text --reporter=lcov --reporter=html --100 node --test --strip-types \"src/**/*.test.ts\"",
+        "test:ci": "npm run test:coverage && npm run test:doc",
+        "test:coverage": "c8 --all --include \"src/**/*.ts\" --reporter=text --reporter=lcov --reporter=html --100 node --test --strip-types $(git ls-files 'src/*.test.ts')",
+        "test:doc": "node --test --strip-types \"src/doc-test/__generated__/*.test.ts\"",
         "test:unit": "node --test --strip-types \"src/**/*.test.ts\"",
         "verify": "npm run check && npm run test:unit",
         "watch": "npm run watch:test",
@@ -83,6 +87,7 @@
         "expect-type": "1.4.0",
         "knip": "^6.34.0",
         "lefthook": "^2.1.12",
+        "mdast-util-from-markdown": "^2.0.3",
         "oxfmt": "^0.70.0",
         "oxlint": "^1.83.0",
         "oxlint-tsgolint": "^7.0.2001",

scripts/create-doc-tests.ts

@@ -0,0 +1,445 @@
+import fs from "node:fs";
+import path from "node:path";
+
+import type { Code, Heading, Paragraph, PhrasingContent, Root } from "mdast";
+import { fromMarkdown } from "mdast-util-from-markdown";
+
+/**
+ * Compile the TypeScript examples embedded in the prose docs into runnable
+ * tests, so a doc fence that drifts from the API fails CI. Every ```ts fence in
+ * the scanned Markdown becomes a `test(...)` in a generated
+ * `src/doc-test/__generated__/<Name>.test.ts`; the file is typechecked by
+ * `tsc` and executed by `node --test` exactly like a hand-written test.
+ *
+ * Usage: node --strip-types scripts/create-doc-tests.ts
+ *
+ * Why regenerate-then-typecheck instead of a lint plugin: development/docs.md §
+ * Validating Markdown code fences. The repo is TypeScript 7 (the native
+ * compiler), which does not expose the legacy JS compiler API, so the only
+ * faithful check is to emit real `.ts` files and let the existing `check:tsc` /
+ * `node --test` pipeline judge them.
+ */
+
+/** The package's public entry, as spelled inside the examples. */
+const LIBRARY_SOURCE = "tiny-pattern-ts";
+
+/** Matches the library specifier (single- or double-quoted) inside an import. */
+const LIBRARY_SPECIFIER = new RegExp(
+    `(?<quote>["'])${LIBRARY_SOURCE}\\k<quote>`,
+    "g",
+);
+
+/**
+ * A source specifier resolved to `src/index.ts` by `package.json#imports`.
+ * Examples import `from "tiny-pattern-ts"`, which neither `node` nor `tsc`
+ * resolves to source before `dist/` exists, so the generator rewrites it.
+ */
+const PRELUDE_IMPORT_SOURCE = "#test-tiny-pattern-ts";
+
+/** Markdown files to scan, relative to the repo root. */
+const SOURCES = ["README.md", "CONTRIBUTING.md"];
+
+/** Directory the generated tests are written to (gitignored contents). */
+const OUTPUT_DIR = "src/doc-test/__generated__";
+
+/** Fences whose info-string matches one of these are compiled; others skipped. */
+const TYPESCRIPT_LANGS: ReadonlySet<string> = new Set(["ts", "typescript"]);
+
+/**
+ * Modules the generated file already imports. An example that imports one of
+ * these would collide with the prelude binding (duplicate `test` / `assert`), so
+ * it is surfaced as a fatal error and the example is rewritten.
+ */
+const PRELUDE_MODULES: ReadonlySet<string> = new Set([
+    "node:assert",
+    "node:test",
+]);
+
+/** One line of the prelude every generated file starts with. */
+const PRELUDE_TEST = 'import { test } from "node:test";';
+const PRELUDE_ASSERT = 'import { strict as assert } from "node:assert";';
+
+/** Indentation applied to every fence body line inside the `test` callback. */
+const INDENT = "    ";
+
+const EMPTY = "";
+const INITIAL_COUNT = 0;
+const WRITE_INCREMENT = 1;
+const FIRST_ITEM = 0;
+const FAILURE_EXIT_CODE = 1;
+
+/** Strip all leading blank lines so the import scan starts at real content. */
+const LEADING_BLANK_LINES = /^(?:[ \t]*\r?\n)+/;
+/** Collapse the plain text of a title paragraph to one line. */
+const WHITESPACE = /\s+/g;
+/** Split an info-string like `ts title="x"` into its bare language. */
+const LANG_SEPARATOR = /\s+/;
+
+/** One leading `import` statement, including a multi-line named import. */
+const IMPORT_STATEMENT =
+    /^import\s+(?:(?:type\s+)?[\w$*{}\s,]+?\s+from\s+)?["'][^"'\n]+["']\s*;?[ \t]*(?:\r?\n|$)/;
+
+/** `import { a, b } from "src";`, with an optional `type` keyword. */
+const NAMED_IMPORT =
+    /^import\s+(?<isType>type\s+)?\{(?<specifiers>[^}]*)\}\s+from\s+["'](?<source>[^"']+)["']\s*;?$/;
+
+/** The module in a `… from "src"` statement. */
+const FROM_SOURCE = /from\s+["'](?<source>[^"']+)["']/;
+
+/** The module in a side-effect `import "src"` statement. */
+const SIDE_EFFECT_SOURCE = /^import\s+["'](?<source>[^"']+)["']/;
+
+type Block = Root["children"][number];
+
+class DocTestError extends Error {
+    public constructor(message: string) {
+        super(message);
+        this.name = "DocTestError";
+    }
+}
+
+/** Merge named specifiers that target the same module into one import. */
+interface NamedImportGroup {
+    readonly source: string;
+    readonly isType: boolean;
+    readonly names: string[];
+}
+
+/** One compiled fence, ready to be wrapped in a `test(...)`. */
+interface DocCase {
+    readonly title: string;
+    readonly body: string;
+}
+
+/** Accumulator threaded through the Markdown walk. */
+interface BuilderState {
+    readonly named: Map<string, NamedImportGroup>;
+    readonly passthrough: Set<string>;
+    readonly cases: DocCase[];
+    title: string | undefined;
+}
+
+/** Read one capture group, tolerating the type-level `groups` optionality. */
+const groupOf = (match: RegExpExecArray, name: string): string | undefined => {
+    const { groups } = match;
+    return groups === undefined ? undefined : groups[name];
+};
+
+/** Recursively concatenate the literal text of a single inline node. */
+const inlineText = (node: PhrasingContent): string => {
+    if ("value" in node) {
+        return node.value;
+    }
+    if ("children" in node) {
+        return node.children.map(inlineText).join(EMPTY);
+    }
+    return EMPTY;
+};
+
+/** Render a paragraph/heading node to its plain text for use as a test title. */
+const textOf = (node: Paragraph | Heading): string =>
+    node.children.map(inlineText).join(EMPTY).replace(WHITESPACE, " ").trim();
+
+/**
+ * Split a fence into its leading `import` statements and the executable body.
+ * Only a contiguous run of imports at the very top is hoisted; anything after
+ * the first non-import line stays in the body verbatim.
+ */
+const splitImports = (code: string): { imports: string[]; body: string } => {
+    const imports: string[] = [];
+    let rest = code.replace(LEADING_BLANK_LINES, EMPTY);
+    let match = IMPORT_STATEMENT.exec(rest);
+    while (rest.startsWith("import") && match !== null) {
+        const statement = match[FIRST_ITEM] ?? EMPTY;
+        imports.push(statement.trim());
+        rest = rest.slice(statement.length).replace(LEADING_BLANK_LINES, EMPTY);
+        match = IMPORT_STATEMENT.exec(rest);
+    }
+    return { imports, body: rest.trim() };
+};
+
+/** The module an import statement points at, or `undefined` if unreadable. */
+const importSource = (statement: string): string | undefined => {
+    const fromMatch = FROM_SOURCE.exec(statement);
+    if (fromMatch !== null) {
+        return groupOf(fromMatch, "source");
+    }
+    const sideEffectMatch = SIDE_EFFECT_SOURCE.exec(statement);
+    return sideEffectMatch === null
+        ? undefined
+        : groupOf(sideEffectMatch, "source");
+};
+
+/**
+ * Reject an example that imports a harness-provided module, then rewrite the
+ * library specifier to the source alias so the emitted file resolves.
+ */
+const normalizeImport = (statement: string): string => {
+    const source = importSource(statement);
+    if (source !== undefined && PRELUDE_MODULES.has(source)) {
+        throw new DocTestError(
+            `example imports "${source}", which the harness injects; remove the line:\n  ${statement.trim()}`,
+        );
+    }
+    return statement.replace(
+        LIBRARY_SPECIFIER,
+        `$<quote>${PRELUDE_IMPORT_SOURCE}$<quote>`,
+    );
+};
+
+/** Split the `{ a, b }` contents of a named import into trimmed specifiers. */
+const specifiersOf = (raw: string): string[] =>
+    raw
+        .split(",")
+        .map((name) => name.trim())
+        .filter((name) => name.length > INITIAL_COUNT);
+
+/** Add named specifiers to the group for `(isType, source)`, merging. */
+const addNamedImport = (
+    named: Map<string, NamedImportGroup>,
+    ref: Pick<NamedImportGroup, "source" | "isType">,
+    names: readonly string[],
+): void => {
+    const key = `${ref.isType ? "type:" : "value:"}${ref.source}`;
+    const existing = named.get(key);
+    if (existing === undefined) {
+        named.set(key, {
+            source: ref.source,
+            isType: ref.isType,
+            names: [...names],
+        });
+        return;
+    }
+    for (const name of names) {
+        if (!existing.names.includes(name)) {
+            existing.names.push(name);
+        }
+    }
+};
+
+/** Sort each hoisted import into a merged named group or a passthrough set. */
+const collectImports = (
+    statements: readonly string[],
+    named: Map<string, NamedImportGroup>,
+    passthrough: Set<string>,
+): void => {
+    for (const raw of statements) {
+        const statement = normalizeImport(raw);
+        const match = NAMED_IMPORT.exec(statement);
+        if (match === null) {
+            passthrough.add(statement);
+        } else {
+            addNamedImport(
+                named,
+                {
+                    source: groupOf(match, "source") ?? EMPTY,
+                    isType: groupOf(match, "isType") !== undefined,
+                },
+                specifiersOf(groupOf(match, "specifiers") ?? EMPTY),
+            );
+        }
+    }
+};
+
+/** Render the hoisted imports: merged named groups first, then the rest. */
+const renderImports = (
+    named: ReadonlyMap<string, NamedImportGroup>,
+    passthrough: ReadonlySet<string>,
+): string[] => {
+    const lines: string[] = [];
+    for (const group of named.values()) {
+        const keyword = group.isType ? "import type" : "import";
+        lines.push(
+            `${keyword} { ${group.names.join(", ")} } from "${group.source}";`,
+        );
+    }
+    for (const statement of passthrough) {
+        lines.push(statement);
+    }
+    return lines;
+};
+
+/** The bare language of a fence's info-string, e.g. `ts` in `ts title="x"`. */
+const typescriptLang = (code: Code): string =>
+    (code.lang ?? EMPTY).trim().split(LANG_SEPARATOR)[FIRST_ITEM] ?? EMPTY;
+
+/** Set the title a following fence will inherit. */
+const handleTitleNode = (
+    state: BuilderState,
+    node: Paragraph | Heading,
+): void => {
+    state.title = textOf(node);
+};
+
+/** Report and reset a non-TS fence that was skipped. */
+const skipFence = (state: BuilderState, name: string, code: Code): void => {
+    process.stderr.write(
+        `${name}: skipped non-TypeScript fence (lang="${code.lang ?? EMPTY}")\n`,
+    );
+    state.title = undefined;
+};
+
+/** Compile a described TS fence into a case, or reject it. */
+const compileFence = (
+    state: BuilderState,
+    name: string,
+    code: Code,
+): DocCase => {
+    const { title } = state;
+    if (title === undefined) {
+        const lang = typescriptLang(code);
+        throw new DocTestError(
+            `${name}: a \`\`\`${lang} fence has no preceding paragraph or ` +
+                `heading to use as its test title — describe the example.`,
+        );
+    }
+    const { imports, body } = splitImports(code.value);
+    collectImports(imports, state.named, state.passthrough);
+    return { title, body };
+};
+
+/** Compile one TS fence into a case, or reject/skip it. */
+const handleCodeNode = (
+    state: BuilderState,
+    name: string,
+    code: Code,
+): void => {
+    const lang = typescriptLang(code);
+    if (!TYPESCRIPT_LANGS.has(lang)) {
+        skipFence(state, name, code);
+        return;
+    }
+    state.cases.push(compileFence(state, name, code));
+};
+
+/** Route one Markdown block, preserving the "described fence" invariant. */
+const handleNode = (state: BuilderState, name: string, node: Block): void => {
+    if (node.type === "paragraph" || node.type === "heading") {
+        handleTitleNode(state, node);
+    } else if (node.type === "code") {
+        handleCodeNode(state, name, node);
+    } else {
+        // Only a paragraph/heading introduces a fence; any other block breaks
+        // the "immediately preceded" chain.
+        state.title = undefined;
+    }
+};
+
+/** Walk one Markdown file and collect its cases and hoisted imports. */
+const parseDoc = (
+    name: string,
+    markdown: string,
+): Omit<BuilderState, "title"> => {
+    const state: BuilderState = {
+        named: new Map(),
+        passthrough: new Set(),
+        cases: [],
+        title: undefined,
+    };
+    for (const node of fromMarkdown(markdown).children) {
+        handleNode(state, name, node);
+    }
+    return {
+        named: state.named,
+        passthrough: state.passthrough,
+        cases: state.cases,
+    };
+};
+
+/** Indent a fence body one level for the body of the `test` callback. */
+const indentBody = (body: string): string =>
+    body
+        .split("\n")
+        .map((line) =>
+            line.length > INITIAL_COUNT ? `${INDENT}${line}` : line,
+        )
+        .join("\n");
+
+/** Wrap one compiled fence in an executed `test(...)`. */
+const renderCase = (docCase: DocCase): string => {
+    const indented = indentBody(docCase.body);
+    return `test(${JSON.stringify(docCase.title)}, () => {\n${indented}\n});`;
+};
+
+/** Build the prelude + hoisted imports that top every generated file. */
+const buildHeader = (name: string, imports: readonly string[]): string[] => {
+    const header = [
+        "// Generated by scripts/create-doc-tests.ts — do not edit by hand.",
+        `// Source: ${name}`,
+        EMPTY,
+        PRELUDE_TEST,
+        PRELUDE_ASSERT,
+    ];
+    if (imports.length > INITIAL_COUNT) {
+        header.push(EMPTY, ...imports);
+    }
+    header.push(EMPTY);
+    return header;
+};
+
+/** Turn one Markdown file into the source of its generated test file. */
+const buildTestFile = (name: string, markdown: string): string => {
+    const parsed = parseDoc(name, markdown);
+    if (parsed.cases.length === INITIAL_COUNT) {
+        return EMPTY;
+    }
+    const imports = renderImports(parsed.named, parsed.passthrough);
+    const header = buildHeader(name, imports);
+    const blocks = parsed.cases.map(renderCase);
+    return `${header.join("\n")}\n${blocks.join("\n\n")}\n`;
+};
+
+/** Map a source Markdown path to its generated test path under OUTPUT_DIR. */
+const outputFor = (source: string): string =>
+    path.join(
+        OUTPUT_DIR,
+        `${path.basename(source, path.extname(source))}.test.ts`,
+    );
+
+/** Write a generated file when there is content, else clear a stale one. */
+const writeIfAny = (dest: string, name: string, out: string): boolean => {
+    if (out === EMPTY) {
+        process.stderr.write(`${name}: no TypeScript fences\n`);
+        fs.rmSync(dest, { force: true });
+        return false;
+    }
+    fs.writeFileSync(dest, out);
+    return true;
+};
+
+/** Generate the doc-test for one source; return whether a file was written. */
+const generateFor = (root: string, source: string): boolean => {
+    const abs = path.join(root, source);
+    if (!fs.existsSync(abs)) {
+        process.stderr.write(`skipped missing ${source}\n`);
+        return false;
+    }
+    const name = path.basename(source);
+    const out = buildTestFile(name, fs.readFileSync(abs, "utf8"));
+    return writeIfAny(path.join(root, outputFor(source)), name, out);
+};
+
+const main = (): void => {
+    const root = process.cwd();
+    fs.mkdirSync(path.join(root, OUTPUT_DIR), { recursive: true });
+    let written = INITIAL_COUNT;
+    for (const source of SOURCES) {
+        if (generateFor(root, source)) {
+            written += WRITE_INCREMENT;
+        }
+    }
+    process.stdout.write(
+        `created doc-tests for ${written} file(s) under ${OUTPUT_DIR}/\n`,
+    );
+};
+
+try {
+    main();
+} catch (error) {
+    if (error instanceof DocTestError) {
+        process.stderr.write(`${error.message}\n`);
+        process.exitCode = FAILURE_EXIT_CODE;
+    } else {
+        throw error;
+    }
+}

src/doc-test/README.md

@@ -0,0 +1,12 @@
+# Generated doc-tests
+
+`__generated__/` is the output of [`scripts/create-doc-tests.ts`](../../scripts/create-doc-tests.ts):
+each `*.test.ts` is compiled from the ```ts fences in a prose doc and is
+**gitignored**, not edited by hand. `npm run create:doc-tests` regenerates them,
+formats them with `oxfmt`, then type-checks them with
+[`tsconfig.json`](./tsconfig.json) — the scoped config that relaxes
+`noUnusedLocals` so example-only locals (and the injected `assert`) compile.
+
+CI regenerates them in an explicit step before `test:ci`; the fast local `test` /
+`verify` tiers do not. See [development/docs.md](../../development/docs.md) for why the
+generator is shaped this way.

src/doc-test/tsconfig.json

@@ -0,0 +1,10 @@
+{
+    "extends": "../../tsconfig.json",
+    "compilerOptions": {
+        "noEmit": true,
+        "noUnusedLocals": false,
+        "noUnusedParameters": false
+    },
+    "include": ["__generated__/**/*.test.ts"],
+    "exclude": []
+}

src/index.ts

@@ -1,3 +1,11 @@
+/**
+ * The public entry point of `tiny-pattern-ts`.
+ *
+ * Exports the four matcher factories and nothing else; the builder types they
+ * return and the rest of `src/` are implementation detail.
+ *
+ * @module
+ */
 export {
     getPrimitiveUnionMatcher,
     getPrimitiveUnionMatcherW,

src/primitive-union.ts

@@ -96,9 +96,50 @@ const dispatch =
             shape as never,
         );
 
+/**
+ * Create a matcher for a finite primitive universe, with one common return
+ * type.
+ *
+ * Use it when the value itself is the union (`"yes" | "no"`) and every handler
+ * returns the same type.
+ *
+ * The returned builder takes a handler map keyed by the members; supplying a
+ * second fallback argument allows a partial map and receives the unhandled
+ * remainder.
+ *
+ * @typeParam T - The finite universe of primitive members to match.
+ * @returns A builder for the handler map, or the handler map plus a fallback.
+ * @example
+ *     const matchAnswer = getPrimitiveUnionMatcher<"yes" | "no">();
+ *     const describe = matchAnswer({
+ *         yes: () => "agreed",
+ *         no: () => "declined",
+ *     });
+ *     describe("yes"); // "agreed"
+ */
 export const getPrimitiveUnionMatcher = <
     T extends Matchable,
 >(): PrimitiveUnionMatcherStrict<T> => dispatch;
+
+/**
+ * Create a matcher for a finite primitive universe whose return type is the
+ * union of every handler's return type.
+ *
+ * Use it when the value itself is the union (`"yes" | "no"`) and the handlers
+ * return different types. The `W` (widening) counterpart of
+ * {@link getPrimitiveUnionMatcher}; the universe constraint and the optional
+ * fallback are identical.
+ *
+ * @typeParam T - The finite universe of primitive members to match.
+ * @returns A builder for the handler map, or the handler map plus a fallback.
+ * @example
+ *     const matchReply = getPrimitiveUnionMatcherW<"yes" | "no">();
+ *     const reply = matchReply({
+ *         yes: () => 1,
+ *         no: () => "declined",
+ *     });
+ *     // reply: (shape: "yes" | "no") => number | string
+ */
 export const getPrimitiveUnionMatcherW = <
     T extends Matchable,
 >(): PrimitiveUnionMatcherWidening<T> => dispatch;

src/tagged-union.ts

@@ -152,10 +152,56 @@ const dispatch =
         );
     };
 
+/**
+ * Create a matcher for a discriminated union, with one common return type.
+ *
+ * Use it when the value is an object discriminated by a property
+ * (`{ kind: "circle" } | { kind: "square" }`) and every handler returns the
+ * same type.
+ *
+ * The first call fixes the union `T`; the returned function takes the
+ * discriminant property's name (`K`, restricted to properties whose values are
+ * tags), and that returns the handler-map builder. Supplying a second fallback
+ * argument to the builder allows a partial map and receives the members whose
+ * tag was not handled. A `boolean`, `null` or `undefined` tag is keyed by its
+ * stringified form (`true` -> `"true"`); see README § Caveats.
+ *
+ * @typeParam T - The discriminated-union type to match.
+ * @returns A function that takes the discriminant property's name.
+ * @example
+ *     type Shape =
+ *         | { kind: "circle"; radius: number }
+ *         | { kind: "square"; side: number };
+ *
+ *     const matchShape = getTaggedUnionMatcher<Shape>()("kind");
+ *     const area = matchShape({
+ *         circle: (s) => Math.PI * s.radius ** 2,
+ *         square: (s) => s.side ** 2,
+ *     });
+ */
 export const getTaggedUnionMatcher = <
     T extends object,
 >(): TaggedUnionMatcherFactory<T> => dispatch;
 
+/**
+ * Create a matcher for a discriminated union whose return type is the union of
+ * every handler's return type.
+ *
+ * Use it when the value is a discriminated object and the handlers return
+ * different types. The `W` (widening) counterpart of
+ * {@link getTaggedUnionMatcher}; the curried key step and the optional fallback
+ * are identical.
+ *
+ * @typeParam T - The discriminated-union type to match.
+ * @returns A function that takes the discriminant property's name.
+ * @example
+ *     const matchShape = getTaggedUnionMatcherW<Shape>()("kind");
+ *     const describe = matchShape({
+ *         circle: () => "round",
+ *         square: () => 4,
+ *     });
+ *     // describe: (shape: Shape) => string | number
+ */
 export const getTaggedUnionMatcherW = <
     T extends object,
 >(): TaggedUnionMatcherWideningFactory<T> => dispatch;

tsconfig.json

@@ -8,5 +8,6 @@
         "allowImportingTsExtensions": true,
         "verbatimModuleSyntax": true
     },
-    "include": ["src", "scripts"]
+    "include": ["src", "scripts"],
+    "exclude": ["src/doc-test"]
 }