✨ Add primitive union pattern matchers

Curried matchers over string|number literal unions in four variants
(exhaustive/partial x strict/widened return inference), per the header
matrix in src/primitive.ts.

- Adds type-fest for Simplify/ValueOf.
- Deliberate oxlint escape hatches (as any dispatch) until a cast-free
  formulation lands; see the file comments.

package-lock.json

@@ -8,6 +8,9 @@
             "name": "tiny-pattern-ts",
             "version": "0.1.8",
             "license": "MIT",
+            "dependencies": {
+                "type-fest": "^5.9.0"
+            },
             "devDependencies": {
                 "@arethetypeswrong/cli": "^0.18.5",
                 "@runwisp/pubv": "^1.5.1",
@@ -4622,6 +4625,18 @@
                 "url": "https://github.com/chalk/supports-hyperlinks?sponsor=1"
             }
         },
+        "node_modules/tagged-tag": {
+            "version": "1.0.0",
+            "resolved": "https://registry.npmjs.org/tagged-tag/-/tagged-tag-1.0.0.tgz",
+            "integrity": "sha512-yEFYrVhod+hdNyx7g5Bnkkb0G6si8HJurOoOEgC8B/O0uXLHlaey/65KRv6cuWBNhBgHKAROVpc7QyYqE5gFng==",
+            "license": "MIT",
+            "engines": {
+                "node": ">=20"
+            },
+            "funding": {
+                "url": "https://github.com/sponsors/sindresorhus"
+            }
+        },
         "node_modules/test-exclude": {
             "version": "8.0.0",
             "resolved": "https://registry.npmjs.org/test-exclude/-/test-exclude-8.0.0.tgz",
@@ -4705,6 +4720,21 @@
             "license": "0BSD",
             "optional": true
         },
+        "node_modules/type-fest": {
+            "version": "5.9.0",
+            "resolved": "https://registry.npmjs.org/type-fest/-/type-fest-5.9.0.tgz",
+            "integrity": "sha512-yANm3Jr3GiJ1qgJlxGAVxTOIcEOk1rhQHamlXtnrCK7EHP4HeM9OGxtMg/W7HFdrVzw/ZWJKGVIJusVH85sLtw==",
+            "license": "(MIT OR CC0-1.0)",
+            "dependencies": {
+                "tagged-tag": "^1.0.0"
+            },
+            "engines": {
+                "node": ">=20"
+            },
+            "funding": {
+                "url": "https://github.com/sponsors/sindresorhus"
+            }
+        },
         "node_modules/typescript": {
             "version": "7.0.2",
             "resolved": "https://registry.npmjs.org/typescript/-/typescript-7.0.2.tgz",

package.json

@@ -65,6 +65,9 @@
         "setup": "npm run setup:git-commit-message",
         "setup:git-commit-message": "git config commit.template commit-message-template"
     },
+    "dependencies": {
+        "type-fest": "^5.9.0"
+    },
     "devDependencies": {
         "@arethetypeswrong/cli": "^0.18.5",
         "@runwisp/pubv": "^1.5.1",

src/primitive.ts

@@ -0,0 +1,61 @@
+import type { Simplify, ValueOf } from "type-fest";
+
+type UnaryFn<T, R> = (shape: T) => R;
+
+// ============================================================================
+// ✔️ Exhaustive
+// ❌ ReturnsStrict
+// ============================================================================
+type PatternPrimitiveUnion<R, T extends string | number> = {
+    [K in T]: UnaryFn<K, R>;
+};
+
+type PatternReturns<
+    P extends Record<string | number, UnaryFn<never, unknown>>,
+> = ReturnType<ValueOf<P>>;
+
+export const getPrimitiveUnionMatcherW: <T extends string | number>() => <
+    P extends PatternPrimitiveUnion<unknown, T>,
+>(
+    pattern: Simplify<P>,
+) => UnaryFn<T, PatternReturns<P>> = () => (pattern) => (shape) =>
+    // oxlint-disable-next-line typescript/no-explicit-any typescript/no-unsafe-type-assertion
+    (pattern[shape] as any)(shape);
+
+// ============================================================================
+// ✔️ Exhaustive
+// ✔️ ReturnsStrict
+// ============================================================================
+export const getPrimitiveUnionMatcher: <T extends string | number>() => <R>(
+    pattern: Simplify<PatternPrimitiveUnion<R, T>>,
+) => UnaryFn<T, R> = getPrimitiveUnionMatcherW;
+
+// ============================================================================
+// ❌ Exhaustive
+// ✔️ ReturnsStrict
+// ============================================================================
+type PatternPrimitiveUnionPartial<R, T extends string | number> =
+    | PatternPrimitiveUnion<R, T>
+    | (Partial<PatternPrimitiveUnion<R, T>> & {
+          _: UnaryFn<T, R>;
+      });
+
+export const getPrimitiveUnionMatcherPartial: <T extends string | number>() => <
+    R,
+>(
+    pattern: Simplify<PatternPrimitiveUnionPartial<R, T>>,
+) => UnaryFn<T, R> = () => (pattern) => (shape) =>
+    // oxlint-disable-next-line typescript/no-explicit-any typescript/no-unsafe-type-assertion
+    (pattern[shape] ?? (pattern as any)["_"])(shape);
+
+// ============================================================================
+// ❌ Exhaustive
+// ❌ ReturnsStrict
+// ============================================================================
+export const getPrimitiveUnionMatcherPartialW: <
+    T extends string | number,
+>() => <P extends PatternPrimitiveUnionPartial<unknown, T>>(
+    pattern: Simplify<P>,
+
+    // oxlint-disable-next-line typescript/no-explicit-any typescript/no-unsafe-type-assertion
+) => UnaryFn<T, PatternReturns<P>> = getPrimitiveUnionMatcherPartial as any;