diff --git a/packages/algorithm/src/chain.ts b/packages/algorithm/src/chain.ts
index 20db1c872..18e6844c7 100644
--- a/packages/algorithm/src/chain.ts
+++ b/packages/algorithm/src/chain.ts
@@ -28,7 +28,7 @@
  * Array.from(stream);  // [1, 2, 3, 4, 5, 6]
  * ```
  */
-export function* chain<T>(...objects: Iterable<T>[]) {
+export function* chain<T>(...objects: Iterable<T>[]): IterableIterator<T> {
   for (const object of objects) {
     for (const value of object) {
       yield value;
diff --git a/packages/algorithm/src/empty.ts b/packages/algorithm/src/empty.ts
index a7c580382..2bb1c3d19 100644
--- a/packages/algorithm/src/empty.ts
+++ b/packages/algorithm/src/empty.ts
@@ -23,6 +23,6 @@
  * ```
  */
 // eslint-disable-next-line require-yield, @typescript-eslint/no-unused-vars
-export function* empty<T>() {
+export function* empty<T>(): IterableIterator<T> {
   return;
 }
diff --git a/packages/algorithm/src/enumerate.ts b/packages/algorithm/src/enumerate.ts
index 9765ff614..6ab1347be 100644
--- a/packages/algorithm/src/enumerate.ts
+++ b/packages/algorithm/src/enumerate.ts
@@ -28,7 +28,10 @@
  * Array.from(stream);  // [[1, 'foo'], [2, 'bar'], [3, 'baz']]
  * ```
  */
-export function* enumerate<T>(object: Iterable<T>, start = 0) {
+export function* enumerate<T>(
+  object: Iterable<T>,
+  start = 0
+): IterableIterator<[number, T]> {
   for (const value of object) {
     yield [start++, value];
   }
diff --git a/packages/algorithm/src/filter.ts b/packages/algorithm/src/filter.ts
index 2eee493f9..e0d9ac873 100644
--- a/packages/algorithm/src/filter.ts
+++ b/packages/algorithm/src/filter.ts
@@ -31,7 +31,7 @@
 export function* filter<T>(
   object: Iterable<T>,
   fn: (value: T, index: number) => boolean
-) {
+): IterableIterator<T> {
   let index = 0;
   for (const value of object) {
     if (fn(value, index++)) {
diff --git a/packages/algorithm/src/map.ts b/packages/algorithm/src/map.ts
index 575416993..59469e396 100644
--- a/packages/algorithm/src/map.ts
+++ b/packages/algorithm/src/map.ts
@@ -30,7 +30,7 @@
 export function* map<T, U>(
   object: Iterable<T>,
   fn: (value: T, index: number) => U
-) {
+): IterableIterator<U> {
   let index = 0;
   for (const value of object) {
     yield fn(value, index++);
diff --git a/packages/algorithm/src/range.ts b/packages/algorithm/src/range.ts
index cc314e31a..e3df6c3c1 100644
--- a/packages/algorithm/src/range.ts
+++ b/packages/algorithm/src/range.ts
@@ -34,7 +34,11 @@
  * Array.from(stream);  // [2, 3]
  * ```
  */
-export function* range(start: number, stop?: number, step?: number) {
+export function* range(
+  start: number,
+  stop?: number,
+  step?: number
+): IterableIterator<number> {
   if (stop === undefined) {
     stop = start;
     start = 0;
diff --git a/packages/algorithm/src/repeat.ts b/packages/algorithm/src/repeat.ts
index a2869cbd9..499736713 100644
--- a/packages/algorithm/src/repeat.ts
+++ b/packages/algorithm/src/repeat.ts
@@ -26,7 +26,7 @@
  * Array.from(stream);  // [7, 7, 7]
  * ```
  */
-export function* repeat<T>(value: T, count: number) {
+export function* repeat<T>(value: T, count: number): IterableIterator<T> {
   while (0 < count--) {
     yield value;
   }
@@ -48,6 +48,6 @@ export function* repeat<T>(value: T, count: number) {
  * Array.from(stream);  // [7]
  * ```
  */
-export function* once<T>(value: T) {
+export function* once<T>(value: T): IterableIterator<T> {
   yield value;
 }
diff --git a/packages/algorithm/src/stride.ts b/packages/algorithm/src/stride.ts
index c4babd5b4..e32e385ef 100644
--- a/packages/algorithm/src/stride.ts
+++ b/packages/algorithm/src/stride.ts
@@ -29,7 +29,10 @@
  * Array.from(stream);  // [1, 3, 5];
  * ```
  */
-export function* stride<T>(object: Iterable<T>, step: number) {
+export function* stride<T>(
+  object: Iterable<T>,
+  step: number
+): IterableIterator<T> {
   let count = 0;
   for (const value of object) {
     if (0 === count++ % step) {
diff --git a/packages/algorithm/src/take.ts b/packages/algorithm/src/take.ts
index 021408017..f62b3a302 100644
--- a/packages/algorithm/src/take.ts
+++ b/packages/algorithm/src/take.ts
@@ -31,7 +31,10 @@
  * Array.from(stream);  // [5, 4, 3]
  * ```
  */
-export function* take<T>(object: Iterable<T>, count: number) {
+export function* take<T>(
+  object: Iterable<T>,
+  count: number
+): IterableIterator<T> {
   for (const value of object) {
     if (0 < count--) {
       yield value;
diff --git a/packages/algorithm/src/zip.ts b/packages/algorithm/src/zip.ts
index c3f09fe7b..c426b2b86 100644
--- a/packages/algorithm/src/zip.ts
+++ b/packages/algorithm/src/zip.ts
@@ -30,7 +30,7 @@ import { every } from './iter';
  * Array.from(stream);  // [[1, 4], [2, 5], [3, 6]]
  * ```
  */
-export function* zip<T>(...objects: Iterable<T>[]) {
+export function* zip<T>(...objects: Iterable<T>[]): IterableIterator<T[]> {
   const iters = objects.map(obj => obj[Symbol.iterator]());
   let tuple = iters.map(it => it.next());
   for (; every(tuple, item => !item.done); tuple = iters.map(it => it.next())) {