add cached function

src/lib/index.ts

@@ -170,6 +170,18 @@ export function init_array<T, D extends readonly number[]>(
 	return result as ArrayType<T, D>;
 }
 
+const cache = new Map<string, unknown>();
+export function cached<T>(func: () => T, key: string): T {
+	if (cache.has(key)) {
+		return cache.get(key) as T;
+	} else {
+		const result = func();
+		cache.set(key, result);
+		return result;
+	}
+}
+
+
 /**
  * Cyclically pairs the elements of a given list.
  *

src/tests/index.test.ts

@@ -18,6 +18,7 @@ import {
 	unthrow,
 	noop,
 	fake_use,
+	cached,
 	init_array,
 	maybe_global,
 	at,
@@ -37,6 +38,19 @@ it('Pairs', () => {
 	]);
 }, 1000);
 
+it("Cached", () => {
+	let x = 5;
+	const impure_function = () => {
+		x++;
+		return x;
+	};
+	assert.equal(impure_function(), 6);
+	assert.equal(impure_function(), 7);
+	assert.equal(cached(() => impure_function(), "key1"), 8);
+	assert.equal(cached(() => impure_function(), "key1"), 8);
+	assert.equal(cached(() => impure_function(), "key2"), 9);
+})
+
 it('Unthrow', () => {
 	const f = (x: number) => {
 		if (x < 0) {