🚧 progress: First draft.

Author: make-github-pseudonymous-again

README.md

@@ -4,12 +4,12 @@
 Order validation for JavaScript.
 See [docs](https://comparison-sorting.github.io/is-sorted/index.html).
 
-> :building_construction: Caveat emptor! This is work in progress. Code may be
-> working. Documentation may be present. Coherence may be. Maybe.
-
-> :warning: Depending on your environment, the code may require
-> `regeneratorRuntime` to be defined, for instance by importing
-> [regenerator-runtime/runtime](https://www.npmjs.com/package/regenerator-runtime).
+```js
+import {isSorted} from '@comparison-sorting/is-sorted';
+import {increasing, decreasing} from '@total-order/primitive';
+isSorted(increasing, [1, 2, 3], 0, 3); // true
+isSorted(decreasing, [1, 2, 3], 0, 3); // false
+```
 
 [![License](https://img.shields.io/github/license/comparison-sorting/is-sorted.svg)](https://raw.githubusercontent.com/comparison-sorting/is-sorted/main/LICENSE)
 [![Version](https://img.shields.io/npm/v/@comparison-sorting/is-sorted.svg)](https://www.npmjs.org/package/@comparison-sorting/is-sorted)

package.json

@@ -73,6 +73,7 @@
     "@babel/register": "7.13.16",
     "@commitlint/cli": "12.1.4",
     "@js-library/commitlint-config": "0.0.4",
+    "@total-order/primitive": "^1.0.1",
     "ava": "3.15.0",
     "babel-plugin-transform-remove-console": "6.9.4",
     "babel-plugin-unassert": "3.1.0",

src/firstInversion.js

@@ -0,0 +1,21 @@
+/**
+ * Returns k <= right such that [left,k[ is sorted. If k < right, then
+ * compare( array[k-1] , array[k] ) > 0.
+ *
+ * @param {Function} compare
+ * @param {ArrayLike} array
+ * @param {number} left
+ * @param {number} right
+ * @return {number}
+ */
+export default function firstInversion(compare, array, left, right) {
+	if (left >= right) return right;
+
+	while (++left < right) {
+		if (compare(array[left - 1], array[left]) > 0) {
+			break;
+		}
+	}
+
+	return left;
+}

src/index.js

@@ -1,2 +1,2 @@
-const answer = 42;
-export default answer;
+export {default as firstInversion} from './firstInversion.js';
+export {default as isSorted} from './isSorted.js';

src/isSorted.js

@@ -0,0 +1,14 @@
+import firstInversion from './firstInversion.js';
+
+/**
+ * Returns whether range [left,right[ of array is sorted.
+ *
+ * @param {Function} compare
+ * @param {ArrayLike} array
+ * @param {number} left
+ * @param {number} right
+ * @return {boolean}
+ */
+export default function isSorted(compare, array, left, right) {
+	return firstInversion(compare, array, left, right) === right;
+}

test/src/api.js

@@ -0,0 +1,24 @@
+import test from 'ava';
+
+import {increasing, decreasing} from '@total-order/primitive';
+
+import {firstInversion} from '../../src/index.js';
+
+function macro(t, array, left, right, k1, k2) {
+	const n = array.length;
+
+	t.is(k1, firstInversion(increasing, array, left, right));
+	t.is(k2, firstInversion(decreasing, array, left, right));
+
+	t.is(n, array.length);
+}
+
+macro.title = (_, ...args) => args.join(' , ');
+
+test(macro, [], 0, 0, 0, 0);
+test(macro, [0, 1, 2], 1, 1, 1, 1);
+test(macro, [1, 1, 1], 0, 3, 3, 3);
+test(macro, [1, 2, 3], 0, 3, 3, 1);
+test(macro, [1, 2, 4, 3], 0, 4, 3, 1);
+test(macro, [1, 0, 1, 1, 2, 3, 1, 0, 1], 3, 6, 6, 4);
+test(macro, [1, 0, 1, 1, 2, 3, 1, 0, 1], 0, 9, 1, 2);

test/src/firstInversion.js

@@ -0,0 +1,24 @@
+import test from 'ava';
+
+import {increasing, decreasing} from '@total-order/primitive';
+
+import {isSorted} from '../../src/index.js';
+
+function macro(t, array, left, right, k1, k2) {
+	const n = array.length;
+
+	t.is(k1, isSorted(increasing, array, left, right));
+	t.is(k2, isSorted(decreasing, array, left, right));
+
+	t.is(n, array.length);
+}
+
+macro.title = (_, ...args) => args.join(' , ');
+
+test(macro, [], 0, 0, true, true);
+test(macro, [0, 1, 2], 1, 1, true, true);
+test(macro, [1, 1, 1], 0, 3, true, true);
+test(macro, [1, 2, 3], 0, 3, true, false);
+test(macro, [1, 2, 4, 3], 0, 4, false, false);
+test(macro, [1, 0, 1, 1, 2, 3, 1, 0, 1], 3, 6, true, false);
+test(macro, [1, 0, 1, 1, 2, 3, 1, 0, 1], 0, 9, false, false);