📝 Restore and rewrite the README entry point

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.
2026-09-24 21:55:51 +00:00
1 parent 28d87b3387
commit 8261759190
@@ -7,7 +7,7 @@ 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.
@@ -7,6 +7,9 @@ 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
@@ -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

@@ -19,6 +57,100 @@ 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

 The package exports four factories. Two axes pick one:
@@ -38,7 +170,7 @@ The package exports four factories. Two axes pick one:
 | `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 below do this, so the builder is allocated once.
+reuse it; the [Examples](#examples) do this, so the builder is allocated once.

 ### Primitive-union matchers

@@ -23,7 +23,7 @@ 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
@@ -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",