[learn FP with Kirby using `fp-ts`] Array

basic.ts

/**
 * Array
 * ===
 * Basic array
 */

import { pipe } from "fp-ts/lib/function";
import * as Array from "fp-ts/Array";

const foo = [1, 2, 3, 4, 5];
describe("array support basic operation like js array", () =>
  pipe(
    foo,
    Array.map((x) => x - 1),
    Array.filter((x) => x % 2 === 0),
    Array.reduce(0, (a, b) => a + b)
  ));

lookup.ts

/**
 * lookup
 * ===
 * lookup provide array element access but with type safety
 */

import { pipe } from "fp-ts/function";
import * as Array from "fp-ts/Array";

const foo = [1, 2, 3];
describe("lookup item which exist", () =>
  pipe(
    foo,
    Array.lookup(1)
    //
  )); // { _tag: 'Some', value: 2 }

describe("lookup item which not exist", () =>
  pipe(
    foo,
    Array.lookup(3)
    //
  )); // { _tag: 'None' }

/**
 * Because it returns an Option, we are forced to deal with the possible none case.
 */

/**
 * head
 * ===
 * get the first element with option
 */

describe("head get the first element if array not empty", () => {
  const foo = [1, 2, 3];
  if (foo.length > 0) {
    const firstElement = Array.head(foo); // { _tag: 'Some', value: 1 }
  }
});

import * as NEA from "fp-ts/NonEmptyArray";

describe("NonEmptyArray head get first element without option", () => {
  if (Array.isNonEmpty(foo)) {
    const firstElement = NEA.head(foo); // 1
  }
});

zip.ts

/**
 * zip
 * ===
 * combine two array into one
 */

import { pipe } from "fp-ts/function";
import * as Array from "fp-ts/Array";

const foo = [1, 2, 3, 4, 5];
const bar = ["a", "b", "c", "d", "e"];
describe("array provide additional function like 'zip'", () =>
  pipe(
    foo,
    Array.zip(bar)
    //
  ));