✨ feat: Add method reversed().

Fixes #107.

Author: make-github-pseudonymous-again

README.md

@@ -60,7 +60,8 @@ Parent is [@aureooms/js-persistent](https://github.com/aureooms/js-persistent).
     * [`Tree#takeUntil(Function) -> Tree`](#treetakeuntilfunction---tree)
     * [`Tree#dropUntil(Function) -> Tree`](#treedropuntilfunction---tree)
   * [:flying_saucer: Visit](#flying_saucer-visit)
-    * [`TreeSymbol.iterator -> Iterable`](#treesymboliterator---iterable)
+    * [`Tree[Symbol.iterator]() -> Iterable`](#treesymboliterator---iterable)
+    * [`Tree#reversed() -> Iterable`](#treereversed---iterable)
 * [:scroll: References](#scroll-references)
 * [:link: Links](#link-links)
 
@@ -306,6 +307,14 @@ Returns an iterator on the values of the tree in left-to-right order.
 for ( const x of tree ) console.log( x ) ;
 ```
 
+#### `Tree#reversed() -> Iterable`
+
+Returns an iterator on the values of the tree in right-to-left order.
+
+```js
+for ( const x of tree.reversed() ) console.log( x ) ;
+```
+
 
 ## :scroll: References
 

src/1-digit/0-Digit.js

@@ -13,3 +13,7 @@ Digit.prototype._nodes_with_list = function (M, list, other) {
 Digit.prototype[Symbol.iterator] = function () {
 	return this._list()[Symbol.iterator]();
 };
+
+Digit.prototype.reversed = function () {
+	return this._list().reverse()[Symbol.iterator]();
+};

src/2-node/2-Node2.js

@@ -10,6 +10,10 @@ Node2.prototype[Symbol.iterator] = function () {
 	return [this.a, this.b][Symbol.iterator]();
 };
 
+Node2.prototype.reversed = function () {
+	return [this.b, this.a][Symbol.iterator]();
+};
+
 Node2.prototype.measure = function () {
 	return this.v;
 };

src/2-node/3-Node3.js

@@ -11,6 +11,10 @@ Node3.prototype[Symbol.iterator] = function () {
 	return [this.a, this.b, this.c][Symbol.iterator]();
 };
 
+Node3.prototype.reversed = function () {
+	return [this.c, this.b, this.a][Symbol.iterator]();
+};
+
 Node3.prototype.measure = function () {
 	return this.v;
 };

src/3-tree/implementations/0-Empty.js

@@ -49,6 +49,8 @@ Empty.prototype[Symbol.iterator] = function () {
 	return _EMPTY;
 };
 
+Empty.prototype.reversed = function* () {};
+
 /**
  * It is assumed that p(i+|this|) is true.
  */

src/3-tree/implementations/1-Single.js

@@ -57,9 +57,11 @@ Single.prototype.concat = function (other) {
 	return other.cons(this.a);
 };
 
-Single.prototype[Symbol.iterator] = function* () {
-	yield this.a;
-};
+Single.prototype[Symbol.iterator] =
+	// eslint-disable-next-line no-multi-assign
+	Single.prototype.reversed = function* () {
+		yield this.a;
+	};
 
 /**
  * It is assumed that p(i+|this|) is true.

src/3-tree/implementations/2-Deep.js

@@ -120,6 +120,12 @@ Deep.prototype[Symbol.iterator] = function* () {
 	yield* this.right;
 };
 
+Deep.prototype.reversed = function* () {
+	yield* this.right.reversed();
+	for (const node of this.middle.reversed()) yield* node.reversed();
+	yield* this.left.reversed();
+};
+
 /**
  * It is assumed that p(i+|this|) is true.
  */

src/4-lazy/0-Lazy.js

@@ -63,3 +63,7 @@ Lazy.prototype.concat = function (other) {
 Lazy.prototype[Symbol.iterator] = function () {
 	return this.force()[Symbol.iterator]();
 };
+
+Lazy.prototype.reversed = function () {
+	return this.force().reversed();
+};

test/src/methods/reversed.js

@@ -0,0 +1,28 @@
+import test from 'ava';
+
+import {Measures} from '@aureooms/js-measure';
+const {COUNTER} = Measures;
+
+import {list, range, tee, reversed} from '@aureooms/js-itertools';
+
+import {from} from '../../../src/index.js';
+
+const macro = (t, iterable) => {
+	const [copy1, copy2] = tee(iterable, 2);
+	const expected = list(reversed(copy1));
+	const actual = list(from(COUNTER, copy2).reversed());
+	t.deepEqual(actual, expected);
+};
+
+macro.title = (title, iterable) =>
+	`from(COUNTER, ${title || JSON.stringify(iterable)})`;
+
+test(macro, []);
+test('range(0)', macro, range(0));
+test(macro, [0]);
+test(macro, 'ab');
+test(macro, '724');
+test(macro, 'abcd');
+test('range(9)', macro, range(9));
+test('range(1000)', macro, range(1000));
+test('range(100000)', macro, range(100000));