feat(zip): add zip function

Author: djcsdy

index.test.ts

@@ -47,7 +47,8 @@ import {
     take,
     takeWhile,
     toArray,
-    unshift
+    unshift,
+    zip
 } from "./index";
 
 test("tail", async t => {
@@ -375,3 +376,11 @@ test("scan", async t => {
 test("scan1", async t => {
     t.deepEqual(await toArray(scan1(asyncIterable([1, 2, 3]), (a, e, i) => a + e * i)), [1, 3, 9]);
 });
+
+test("zip", async t => {
+    t.deepEqual(await toArray(zip(asyncIterable([1, 2, 3]), asyncIterable([6, 5, 4, 3, 2, 1]))), [
+        [1, 6],
+        [2, 5],
+        [3, 4]
+    ]);
+});

index.ts

@@ -988,3 +988,31 @@ export function scan1Fn<T>(
 ): (iterable: AsyncIterableLike<T>) => AsyncIterable<T> {
     return iterable => scan1(iterable, f);
 }
+
+export async function* zip<T, U>(
+    a: AsyncIterableLike<T>,
+    b: AsyncIterableLike<U>
+): AsyncIterable<readonly [T, U]> {
+    const ait = asyncIterator(a);
+    const bit = asyncIterator(b);
+
+    let ar = await ait.next();
+    let br = await bit.next();
+
+    while (ar.done !== true && br.done !== true) {
+        yield [ar.value, br.value];
+
+        ar = await ait.next();
+        br = await bit.next();
+    }
+}
+
+export const asyncZip = zip;
+
+export function zipFn<T, U>(
+    b: AsyncIterableLike<U>
+): (a: AsyncIterableLike<T>) => AsyncIterable<readonly [T, U]> {
+    return a => zip(a, b);
+}
+
+export const asyncZipFn = zipFn;