✨ feat(enumerate): First draft.

Author: make-github-pseudonymous-again

src/_enumerate.js

@@ -0,0 +1,14 @@
+import {list, map} from '@aureooms/js-itertools';
+
+export default function* _enumerate(elements, n = elements.length) {
+	if (n === 0) yield [];
+	else {
+		const last = elements[n - 1];
+		for (const partition of _enumerate(elements, n - 1)) {
+			yield partition.concat([[last]]);
+			for (const part of partition) {
+				yield list(map((p) => (p === part ? p.concat([last]) : p), partition));
+			}
+		}
+	}
+}

src/enumerate.js

@@ -0,0 +1,7 @@
+import {list} from '@aureooms/js-itertools';
+
+import _enumerate from './_enumerate';
+
+export default function enumerate(elements) {
+	return _enumerate(list(elements));
+}

src/index.js

@@ -1,12 +1,16 @@
+import _enumerate from './_enumerate';
 import count from './count';
+import enumerate from './enumerate';
 import isPartition from './isPartition';
 import sequence from './sequence';
 
 /* eslint import/no-anonymous-default-export: [2, {"allowObject": true}] */
 export default {
+	_enumerate,
 	count,
+	enumerate,
 	isPartition,
 	sequence,
 };
 
-export {count, isPartition, sequence};
+export {_enumerate, count, enumerate, isPartition, sequence};

test/src/enumerate.js

@@ -0,0 +1,23 @@
+import test from 'ava';
+
+import {range, list, map} from '@aureooms/js-itertools';
+import {enumerate} from '../../src';
+
+const macro = (t, n, expected) => {
+	const elements = range(n);
+	t.deepEqual(list(map(list, enumerate(elements))), expected);
+};
+
+macro.title = (title, n, expected) =>
+	`enumerate(range(${n})) = ${JSON.stringify(expected)}`;
+
+test(macro, 0, [[]]);
+test(macro, 1, [[[0]]]);
+test(macro, 2, [[[0], [1]], [[0, 1]]]);
+test(macro, 3, [
+	[[0], [1], [2]],
+	[[0, 2], [1]],
+	[[0], [1, 2]],
+	[[0, 1], [2]],
+	[[0, 1, 2]],
+]);