functional/predicates.test.ts

import { expect, test } from "./deps.test.ts";
import { always, and, never, not, or } from "./predicates.ts";

test("always", () => {
  expect(always()).toBe(true);
  expect(always(true)).toBe(true);
  expect(always(false)).toBe(true);
});

test("never", () => {
  expect(never()).toBe(false);
  expect(never(true)).toBe(false);
  expect(never(false)).toBe(false);
});

test("not", () => {
  const iseven = (x: number) => x % 2 == 0;
  const isodd = not(iseven);
  expect(iseven(0)).toBe(true);
  expect(isodd(0)).toBe(false);
  expect(iseven(1)).toBe(false);
  expect(isodd(1)).toBe(true);
  expect(iseven(2)).toBe(true);
  expect(isodd(2)).toBe(false);
});

test("and", () => {
  const f = and((x: number) => x % 2 == 0, (x: number) => x > 5);
  expect(f(0)).toBe(false);
  expect(f(2)).toBe(false);
  expect(f(8)).toBe(true);
  expect(f(9)).toBe(false);
  expect(f(10)).toBe(true);
});

test("or", () => {
  const f = or((x: number) => x % 2 == 0, (x: number) => x > 5);
  expect(f(0)).toBe(true);
  expect(f(1)).toBe(false);
  expect(f(2)).toBe(true);
  expect(f(8)).toBe(true);
  expect(f(9)).toBe(true);
});