4 files changed, 78 insertions, 0 deletions
diff --git a/src/utils/anonymous.test.ts b/src/utils/anonymous.test.ts
index 2da613f..45896bf 100644
--- a/src/utils/anonymous.test.ts
+++ b/src/utils/anonymous.test.ts
@@ -9,6 +9,7 @@ import {
   identity,
   instanciate,
   pass,
+  transform,
 } from "./anonymous.ts";
 import { assertSpyCalls, spy } from "@std/testing/mock";
 import { FALSE, TRUE } from "../../tests/fixtures/test_data.ts";
@@ -128,3 +129,34 @@ describe("extremeBy", () => {
     assertEquals(extremeBy(data, "min"), Infinity);
   });
 });
+
+describe("transform", () => {
+  it("applies the function to the input", () => {
+    const result = transform(5, (x) => x * 2);
+    assertEquals(result, 10);
+  });
+
+  it("works with strings", () => {
+    const result = transform("hello", (x) => x.toUpperCase());
+    assertEquals(result, "HELLO");
+  });
+
+  it("works with objects", () => {
+    const input = { a: 1, b: 2 };
+    const result = transform(input, ({ a, b }) => a + b);
+    assertEquals(result, 3);
+  });
+
+  it("returns the correct type", () => {
+    const TRUE = true;
+    const FALSE = false;
+    const result = transform(TRUE, (x) => !x);
+    assertEquals(result, FALSE);
+  });
+
+  it("works with identity function", () => {
+    const input = [1, 2, 3];
+    const result = transform(input, identity);
+    assertEquals(result, input);
+  });
+});
diff --git a/src/utils/anonymous.ts b/src/utils/anonymous.ts
index ddd28bd..58e5a0a 100644
--- a/src/utils/anonymous.ts
+++ b/src/utils/anonymous.ts
@@ -23,3 +23,4 @@ export const pass = <T>(fn: (x: T) => void): (x: T) => T => (x: T): T => {
 export const equal = <T>(x: T): (y: T) => boolean => (y: T): boolean => x === y;
 export const extremeBy = (arr: number[], mode: "max" | "min"): number =>
   Math[mode](...arr);
+export const transform = <T, U>(x: T, y: (x: T) => U): U => y(x);
diff --git a/src/utils/datetime.ts b/src/utils/datetime.ts
index c32fde0..be2ce08 100644
--- a/src/utils/datetime.ts
+++ b/src/utils/datetime.ts
@@ -1,3 +1,5 @@
+import { createRanges } from "./iterator.ts";
+
 export function toIso8601Full(date: Date): string {
   const yearN = date.getFullYear();
   const isNegativeYear = yearN <= 0;
@@ -66,3 +68,19 @@ export function getRelativeTimeUnit(
   if (Math.abs(minutes) >= 1) return [Math.round(minutes), "minute"];
   return [Math.round(seconds), "second"];
 }
+
+export function listDates(dates: Date[], { date, locale, list }: {
+  date: Intl.DateTimeFormatOptions;
+  locale: Intl.LocalesArgument;
+  list: Intl.ListFormatOptions;
+}): string {
+  const formatter = new Intl.DateTimeFormat(locale, date);
+  return new Intl.ListFormat(locale, list).format(dates.map(formatter.format));
+}
+
+export function listYearsWithRanges(years: number[], { locale, list }: {
+  locale: Intl.LocalesArgument;
+  list: Intl.ListFormatOptions;
+}): string {
+  return new Intl.ListFormat(locale, list).format(createRanges(years));
+}
diff --git a/src/utils/iterator.ts b/src/utils/iterator.ts
index fa58fc9..43437b6 100644
--- a/src/utils/iterator.ts
+++ b/src/utils/iterator.ts
@@ -50,3 +50,30 @@ export async function findMapAsync<T, R>(
 
   return await tryNext(0);
 }
+
+export function createRanges(nums: Iterable<number>): string[] {
+  const ns = new Set(nums).values().toArray().sort((
+    a,
+    b,
+  ) => a - b);
+
+  const result = [];
+  let start = ns[0];
+  let end = ns[0];
+
+  for (let i = 1; i <= ns.length; i++) {
+    if (ns[i] === end + 1) {
+      end = ns[i];
+    } else {
+      if (start === end) {
+        result.push(`${start}`);
+      } else {
+        result.push(`${start}-${end}`);
+      }
+      start = ns[i];
+      end = ns[i];
+    }
+  }
+
+  return result;
+}