Make List iterable

src/List.test.ts

@@ -10,7 +10,7 @@ test('List.singleton is not Empty', () => {
     expect(singleton.isEmpty()).toBe(false);
 });
 
-test('List.equals', () => {
+test('List.equals works', () => {
     const empty: List<number> = List.empty();
     const single1 = List.from(1);
     const single2 = List.from(2);
@@ -20,9 +20,17 @@ test('List.equals', () => {
     expect(single1.equals(single1)).toBe(true);
 });
 
-test('List.prepend', () => {
+test('List.prepend works', () => {
     const single1 = List.from(1);
     const prepend1 = List.empty().prepend(1);
     expect(prepend1.equals(single1)).toBe(true);
     expect(single1.prepend(1).equals(single1)).toBe(false);
 });
+
+test('List is iterable', () => {
+    const array = [1, 2, 3];
+    const list = List.from(...array);
+    expect(Array.from(list)).toEqual(array);
+    expect(Array.from(List.empty())).toEqual([]);
+    expect(List.from(...list).equals(list)).toBe(true);
+});

src/List.ts

@@ -2,7 +2,7 @@ type Node<T> = { empty: true } | { empty: false; value: T; next: Node<T> };
 // We can share a single empty node between all lists.
 const EMPTY_NODE = { empty: true };
 
-class List<T> {
+class List<T> implements Iterable<T> {
     private constructor(private readonly _node: Node<T>) {}
 
     public static empty<T>(): List<T> {
@@ -25,6 +25,14 @@ class List<T> {
         return new List({ empty: false, value, next: this._node });
     }
 
+    public *[Symbol.iterator]() {
+        let node = this._node;
+        while (!node.empty) {
+            yield node.value;
+            node = node.next;
+        }
+    }
+
     public equals(that: List<T>): boolean {
         let thisNode = this._node;
         let thatNode = that._node;

tsconfig.json

@@ -1,7 +1,7 @@
 {
     "compilerOptions": {
         "module": "commonjs",
-        "target": "es5",
+        "target": "es6",
         "strictNullChecks": true,
         "declaration": true,
         "outDir": "./dist"