✅ List tests

Author: UltiRequiem

src/language/list.test.ts

@@ -0,0 +1,53 @@
+import { assertEquals, assertThrows } from "../../deps.ts";
+import {
+  arrayToList,
+  arrayToListFor,
+  arrayToListReduce,
+  nth,
+  prepend,
+} from "./list.ts";
+
+const EXAMPLE_LIST = {
+  value: 1,
+  rest: {
+    value: 2,
+    rest: {
+      value: 3,
+      rest: null,
+    },
+  },
+};
+
+Deno.test("[arrayToList]", () => {
+  assertEquals(arrayToList([1, 2, 3]), EXAMPLE_LIST);
+});
+
+Deno.test("[arrayToListFor]", () => {
+  assertEquals(arrayToListFor([1, 2, 3]), EXAMPLE_LIST);
+});
+
+Deno.test("[arrayToListReduce]", () => {
+  assertEquals(arrayToListReduce([1, 2, 3]), EXAMPLE_LIST);
+});
+
+Deno.test("[nth]", () => {
+  const nth3 = nth(EXAMPLE_LIST, 2);
+  assertEquals(nth3, 3);
+
+  assertThrows(
+    () => {
+      nth(EXAMPLE_LIST, 5);
+    },
+    RangeError,
+    "Index out of range",
+  );
+});
+
+Deno.test("[prepend]", () => {
+  const prepended = prepend(4, EXAMPLE_LIST);
+
+  assertEquals(prepended, {
+    value: 4,
+    rest: EXAMPLE_LIST,
+  });
+});

src/language/list.ts

@@ -16,13 +16,15 @@ export function arrayToListReduce<T>(values: T[]) {
 }
 
 export function arrayToListFor<T>(values: T[]) {
-  let rest = {};
+  let rest: List<T> | null = null;
 
-  for (let i = values.length - 1; i >= 0; i--) {
-    rest = { value: values[i], rest };
+  const reversedItems = values.reverse();
+
+  for (const value of reversedItems) {
+    rest = { value, rest };
   }
 
-  return rest as List<T>;
+  return rest;
 }
 
 export function prepend<T>(value: T, rest: List<T>): List<T> {
@@ -34,5 +36,9 @@ export function nth<T>(list: List<T>, index: number): T {
     return list.value;
   }
 
-  return nth(list.rest!, index - 1);
+  if (list.rest === null) {
+    throw new RangeError("Index out of range.");
+  }
+
+  return nth(list.rest, index - 1);
 }