Add limit and limitAsync (#1)

* Fix tests for iterable

* Add limit and limitAsync functions

iterable.ts

@@ -48,6 +48,38 @@ export function* range(a: number, b?: number, c?: number) {
         yield i
 }
 
+/**
+ * Given an iterable, yields the first `count` items, then returns.
+ * @author MindfulMinun
+ * @since 2022-07-07
+ */
+export function* limit<T>(count: number, iterable: Iterable<T>) {
+    let i = 0
+    for (const value of iterable) {
+        if (i < count) {
+            yield value
+            i++
+        } else break
+    }
+    return iterable
+}
+
+/**
+ * Given an async iterable, yields the first `count` items, then returns.
+ * @author MindfulMinun
+ * @since 2022-07-07
+ */
+export async function* limitAsync<T>(count: number, iterable: AsyncIterable<T>) {
+    let i = 0
+    for await (const value of iterable) {
+        if (i < count) {
+            yield value
+            i++
+        } else break
+    }
+    return iterable
+}
+
 /**
  * Removes elements from an array. Non-destructive, as all array operations should be :D
  *
@@ -106,7 +138,7 @@ export function shuffle<T>(arr: T[]): T[] {
  * @since 2020-07-19
  */
 export function swap<T>(arr: T[], i: number, j: number): void {
-    let carry = arr[i]
+    const carry = arr[i]
     arr[i] = arr[j]
     arr[j] = carry
 }
@@ -217,7 +249,7 @@ export async function once<T>(source: AsyncIterable<T>, predicate: (value: T) =>
  * @author MindfulMinun
  * @since 2022-06-05
  */
-export function pinkyPromise<T>(): [Promise<T>, (value: T) => void, (error: any) => unknown] {
+export function pinkyPromise<T>(): [Promise<T>, (value: T) => void, (error: unknown) => unknown] {
     let resolve: (value: T) => void
     let reject: (error: unknown) => void
 

tests/iterable.test.ts

@@ -1,5 +1,5 @@
 import {
-    choose, fill, range, removeFromArraybyIndexes, shuffle, swap, once
+    choose, fill, range, limit
 } from "../iterable.ts"
 
 import { assertThrows, assertEquals, assert } from "https://deno.land/[email protected]/testing/asserts.ts"
@@ -29,12 +29,47 @@ Deno.test("range: one arg", () => {
     assert(iter.next().done)
 })
 
-
 Deno.test("range: two args", () => {
-    const iter = range(50_000)
-    for (let i = 0; i < 50_000; i++) {
+    const iter = range(40, 50)
+    for (let i = 40; i < 50; i++) {
         const next = iter.next()
         assertEquals(next.value, i)
     }
     assert(iter.next().done)
 })
+
+Deno.test("range: three args", () => {
+    const iter = range(60, 80, 4)
+    for (let i = 60; i < 80; i += 4) {
+        const next = iter.next()
+        assertEquals(next.value, i)
+    }
+    assert(iter.next().done)
+})
+
+
+Deno.test("limit: limits to the first n elements", () => {
+    const values: number[] = []
+    const truth = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181]
+    const count = truth.length
+    for (const value of limit(count, fibonacci())) {
+        values.push(value)
+    }
+    assertEquals(values.length, count)
+    truth.forEach((val, i) => {
+        assertEquals(values[i], val)
+    })
+})
+
+function* fibonacci() {
+    let back2 = 0
+    let back1 = 1
+    yield back2
+    yield back1
+    while (true) {
+        const sum = back2 + back1
+        back2 = back1
+        back1 = sum
+        yield sum
+    }
+}