Hari 28: Functional Programming Lanjutan

Functor, Monad & Either Pattern

// Maybe Monad — menangani null/undefined dengan aman
class Maybe {
    constructor(value) { this._value = value; }
    static of(value) { return new Maybe(value); }
    isNothing() { return this._value === null || this._value === undefined; }
    map(fn) { return this.isNothing() ? this : Maybe.of(fn(this._value)); }
    getOrElse(defaultVal) { return this.isNothing() ? defaultVal : this._value; }
    toString() { return this.isNothing() ? "Nothing" : `Just(${this._value})`; }
}

// Gunakan tanpa khawatir null
const nama = Maybe.of(null)
    .map(s => s.trim())
    .map(s => s.toUpperCase())
    .getOrElse("TAMU");
console.log(nama); // "TAMU"

const email = Maybe.of("  budi@example.com  ")
    .map(s => s.trim())
    .map(s => s.toLowerCase())
    .getOrElse("unknown");
console.log(email); // "budi@example.com"