1 files changed, 40 insertions, 0 deletions
diff --git a/u/types/collections/cons.ts b/u/types/collections/cons.ts
new file mode 100644
index 0000000..05dbe7c
--- /dev/null
+++ b/u/types/collections/cons.ts
@@ -0,0 +1,40 @@
+import { IOptional, Mapper, Optional } from '@emprespresso/pengueno';
+
+export interface ICons<T> extends Iterable<T> {
+    readonly value: T;
+    readonly next: IOptional<ICons<T>>;
+
+    readonly replace: Mapper<T, ICons<T>>;
+    readonly before: Mapper<IOptional<ICons<T>>, ICons<T>>;
+}
+
+export class Cons<T> implements ICons<T> {
+    constructor(
+        public readonly value: T,
+        public readonly next: IOptional<ICons<T>> = Optional.none(),
+    ) {}
+
+    public before(head: IOptional<ICons<T>>): ICons<T> {
+        return new Cons<T>(this.value, head);
+    }
+
+    public replace(_value: T): ICons<T> {
+        return new Cons<T>(_value, this.next);
+    }
+
+    *[Symbol.iterator]() {
+        for (let cur = Optional.some<ICons<T>>(this); cur.present(); cur = cur.flatMap((cur) => cur.next)) {
+            yield cur.get().value;
+        }
+    }
+
+    static addOnto<T>(items: Iterable<T>, tail: IOptional<ICons<T>>): IOptional<ICons<T>> {
+        return Array.from(items)
+            .reverse()
+            .reduce((cons, value) => Optional.from<ICons<T>>(new Cons<T>(value, cons)), tail);
+    }
+
+    static from<T>(items: Iterable<T>): IOptional<ICons<T>> {
+        return Cons.addOnto(items, Optional.none());
+    }
+}