Merge pull request #1 from lambdalisue/fix-range

Throw an error when the 3rd argument of `range()` is 0

Author: lambdalisue

builtins.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from "./deps_test.ts";
+import { assertThrows, describe, expect, it } from "./deps_test.ts";
 import {
   all,
   any,
@@ -254,6 +254,16 @@ describe("range", () => {
     expect(Array.from(range(5, 1, -1))).toEqual([5, 4, 3, 2]);
     expect(Array.from(range(5, -3, -2))).toEqual([5, 3, 1, -1]);
   });
+
+  it("step cannot be 0", () => {
+    assertThrows(
+      () => {
+        range(0, 1, 0);
+      },
+      undefined,
+      "range() arg 3 must not be zero",
+    );
+  });
 });
 
 describe("reduce", () => {

builtins.ts

@@ -187,8 +187,11 @@ export function min<T>(
  * Internal helper for the range function
  */
 function _range(start: number, stop: number, step: number): Iterable<number> {
+  if (step === 0) {
+    throw new Error("range() arg 3 must not be zero");
+  }
   const counter = count(start, step);
-  const pred = step >= 0 ? (n: number) => n < stop : (n: number) => n > stop;
+  const pred = step > 0 ? (n: number) => n < stop : (n: number) => n > stop;
   return takewhile(counter, pred);
 }
 

deps_test.ts

@@ -1,4 +1,5 @@
 export { expect } from "https://deno.land/x/[email protected]/mod.ts";
+export * from "https://deno.land/[email protected]/testing/asserts.ts";
 
 const currentScopes: string[] = [];