From 4e5dfd7134dd6a314c58580ecd1ea898f9ddd205 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Herv=C3=A9=20BECHER?= <hbdu68@gmail.com>
Date: Sun, 19 Oct 2025 14:41:58 +0200
Subject: [PATCH] add cartesian product

---
 src/async/impl.ts  | 48 ++++++++++++++++++++++++++++++++++++++++++++++
 src/async/types.ts |  1 +
 src/sync/impl.ts   | 48 ++++++++++++++++++++++++++++++++++++++++++++++
 src/sync/types.ts  |  1 +
 4 files changed, 98 insertions(+)

diff --git a/src/async/impl.ts b/src/async/impl.ts
index ee85c95..965d078 100644
--- a/src/async/impl.ts
+++ b/src/async/impl.ts
@@ -664,6 +664,10 @@ export abstract class BaseAsyncSequence<TElement> extends AsyncSequenceMarker im
     return new ZippedAsyncSequence<TElement, TOther>(this, wrap(sequence));
   }
 
+  cartesianProduct<TOther>(sequence: MaybeAsyncIterable<TOther>): AsyncSequence<[TElement, TOther]> {
+    return new CartesianProductAsyncSequence<TElement, TOther>(this, wrap(sequence));
+  }
+
   indexed(): AsyncSequence<[number, TElement]> {
     return new IndexedAsyncSequence<TElement>(this);
   }
@@ -1022,6 +1026,10 @@ export class DelegatedAsyncSequence<TElement> extends AsyncSequenceMarker implem
     return this.#sequence.zip(wrap(sequence));
   }
 
+  cartesianProduct<TOther>(sequence: MaybeAsyncIterable<TOther>): AsyncSequence<[TElement, TOther]> {
+    return this.#sequence.cartesianProduct(wrap(sequence));
+  }
+
   indexed(): AsyncSequence<[number, TElement]> {
     return this.#sequence.indexed();
   }
@@ -1821,6 +1829,46 @@ class ZippedAsyncSequence<T, U> extends BaseAsyncSequence<[T, U]> {
   }
 }
 
+export class CartesianProductAsyncSequence<T, U> extends BaseAsyncSequence<[T, U]> {
+  readonly #first: AsyncSequence<T>;
+  readonly #second: AsyncSequence<U>;
+
+  constructor(first: AsyncSequence<T>, second: AsyncSequence<U>) {
+    super();
+
+    this.#first = first;
+    this.#second = second;
+  }
+
+  override async nonEnumeratedCount() {
+    const n1 = await this.#first.nonEnumeratedCount();
+
+    if (n1 < 0) {
+      return -1;
+    }
+
+    const n2 = await this.#second.nonEnumeratedCount();
+
+    if (n2 < 0) {
+      return -1;
+    }
+
+    return n1 * n2;
+  }
+
+  override async maxCount() {
+    return await this.#first.maxCount() * await this.#second.maxCount();
+  }
+
+  override async *iterator() {
+    for await (const firstObj of this.#first) {
+      for await (const secondObj of this.#second) {
+        yield [firstObj, secondObj] as [T, U];
+      }
+    }
+  }
+}
+
 class UnionAsyncSequence<T> extends BaseAsyncSequence<T> {
   readonly #first: AsyncSequence<T>;
   readonly #second: AsyncSequence<T>;
diff --git a/src/async/types.ts b/src/async/types.ts
index 767ffd9..f1b194a 100644
--- a/src/async/types.ts
+++ b/src/async/types.ts
@@ -108,6 +108,7 @@ export interface AsyncSequence<TElement> extends AsyncIterable<TElement> {
   forEach(action: MaybeAsyncAction<TElement>): Promise<void>;
 
   zip<TOther>(sequence: MaybeAsyncIterable<TOther>): AsyncSequence<[TElement, TOther]>;
+  cartesianProduct<TOther>(sequence: MaybeAsyncIterable<TOther>): AsyncSequence<[TElement, TOther]>;
 
   indexed(): AsyncSequence<[number, TElement]>;
 
diff --git a/src/sync/impl.ts b/src/sync/impl.ts
index e706638..2b1e3b0 100644
--- a/src/sync/impl.ts
+++ b/src/sync/impl.ts
@@ -673,6 +673,10 @@ export abstract class BaseSequence<TElement> extends SequenceMarker implements S
     return new ZippedSequence<TElement, TOther>(this, wrap(sequence));
   }
 
+  cartesianProduct<TOther>(sequence: Iterable<TOther>): Sequence<[TElement, TOther]> {
+    return new CartesianProductSequence<TElement, TOther>(this, wrap(sequence));
+  }
+
   indexed(): Sequence<[number, TElement]> {
     return new IndexedSequence<TElement>(this);
   }
@@ -1039,6 +1043,10 @@ export class DelegatedSequence<TElement> extends SequenceMarker implements Seque
     return this.#sequence.zip(sequence);
   }
 
+  cartesianProduct<TOther>(sequence: Iterable<TOther>) {
+    return this.#sequence.cartesianProduct(sequence);
+  }
+
   indexed() {
     return this.#sequence.indexed();
   }
@@ -2094,6 +2102,46 @@ export class ZippedSequence<T, U> extends BaseSequence<[T, U]> {
   }
 }
 
+export class CartesianProductSequence<T, U> extends BaseSequence<[T, U]> {
+  readonly #first: Sequence<T>;
+  readonly #second: Sequence<U>;
+
+  constructor(first: Sequence<T>, second: Sequence<U>) {
+    super();
+
+    this.#first = first;
+    this.#second = second;
+  }
+
+  override nonEnumeratedCount() {
+    const n1 = this.#first.nonEnumeratedCount();
+
+    if (n1 < 0) {
+      return -1;
+    }
+
+    const n2 = this.#second.nonEnumeratedCount();
+
+    if (n2 < 0) {
+      return -1;
+    }
+
+    return n1 * n2;
+  }
+
+  override maxCount() {
+    return this.#first.maxCount() * this.#second.maxCount();
+  }
+
+  override *iterator() {
+    for (const firstObj of this.#first) {
+      for (const secondObj of this.#second) {
+        yield [firstObj, secondObj] as [T, U];
+      }
+    }
+  }
+}
+
 class UnionSequence<T> extends BaseSequence<T> {
   readonly #first: Sequence<T>;
   readonly #second: Sequence<T>;
diff --git a/src/sync/types.ts b/src/sync/types.ts
index b27bb0b..fc2cb02 100644
--- a/src/sync/types.ts
+++ b/src/sync/types.ts
@@ -111,6 +111,7 @@ export interface Sequence<TElement> extends Iterable<TElement> {
   forEach(action: Action<TElement>): void;
 
   zip<TOther>(sequence: Iterable<TOther>): Sequence<[TElement, TOther]>;
+  cartesianProduct<TOther>(sequence: Iterable<TOther>): Sequence<[TElement, TOther]>;
 
   indexed(): Sequence<[number, TElement]>;