Add range() to generate sequences for a given number range

Author: winterbe

README.md

@@ -39,13 +39,22 @@ Sequency is centered around a single class called `Sequence` to process any kind
 Sequences can be created by utilizing one of the following functions:
 
 ```js
-import {sequenceOf, asSequence, emptySequence, generateSequence} from 'sequency';
+import {
+    asSequence,
+    sequenceOf, 
+    emptySequence, 
+    range,
+    generateSequence,
+    extendSequence
+} from 'sequency';
 ```
 
 - `sequenceOf` accepts one or many values and returns a new sequence.
 - `asSequence` accepts an iterable (e.g. an array, set or map) and returns a new sequence.
 - `emptySequence` returns a new empty sequence.
+- `range` returns as number sequence consisting of all numbers between `startInclusive` and `endExclusive`.
 - `generateSequence` returns a sequence generated from the given generator function.
+- `extendSequence` allows extending sequences with user-defined operations (see [example](https://github.com/winterbe/sequency/blob/ac3dbb0f212bb08783d970472c7a76dc921b60ba/test/extendSequence.test.ts)).
 
 Each `Sequence` provides a fluent functional API consisting of intermediate and terminal operations. Intermediate functions (e.g. `filter`, `map`, `sorted`) return a new sequence, thus enabling method chaining. Terminal functions (e.g. `toArray`, `groupBy`, `findLast`) return an arbitrary result. Detailed descriptions of all operations are available in the [API docs](https://winterbe.github.io/sequency/).
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sequency",
-  "version": "0.15.0",
+  "version": "0.16.0",
   "description": "Functional sequences for processing iterable data in JavaScript",
   "main": "lib/Sequence.js",
   "umd:main": "lib-umd/sequency.js",

src/Sequence.ts

@@ -154,3 +154,22 @@ export function generateSequence<T>(a: any, b?: any): Sequence<T> {
         ? createSequence<T>(new GeneratorSeedIterator(seed, b))
         : emptySequence<T>();
 }
+
+export function range(startInclusive: number, endExclusive: number, step: number = 1): Sequence<number> {
+    if (startInclusive >= endExclusive) {
+        throw new Error(`startInclusive [${startInclusive}] must be lower then endExclusive [${endExclusive}]`);
+    }
+    if (startInclusive === endExclusive - 1) {
+        return emptySequence();
+    }
+    let current = startInclusive;
+    return generateSequence(() => {
+        try {
+            return current < endExclusive
+                ? current
+                : undefined;
+        } finally {
+            current += step;
+        }
+    });
+}

test/range.test.ts

@@ -0,0 +1,22 @@
+import {range} from "../src/Sequence";
+
+describe("range", () => {
+    it("should create range of numbers with step = 1", () => {
+        const numbers = range(0, 5).toArray();
+        expect(numbers).toEqual([0, 1, 2, 3, 4]);
+    });
+
+    it("should create range of numbers with step = .5", () => {
+        const numbers = range(0, 4, .5).toArray();
+        expect(numbers).toEqual([0, .5, 1, 1.5, 2, 2.5, 3, 3.5]);
+    });
+
+    it("should create empty sequence", () => {
+        const numbers = range(0, 1).toArray();
+        expect(numbers).toEqual([]);
+    });
+
+    it("should throw on invalid boundaries", () => {
+        expect(() => range(1, 0)).toThrow();
+    });
+});