Option Patterns

The Null Virus

const phone = user.phone ?? null;        // null spreads
const carrier = getCarrier(phone) ?? null; // spreads more

Option: Explicit Absence

import { Option } from "effect";

// Convert at boundary
const phone: Option.Option<string> = Option.fromNullable(user.phoneNumber);

// Pattern match - compiler enforces both cases
const display = Option.match(phone, {
  onNone: () => "No phone",
  onSome: (p) => `Phone: ${p}`,
});

// Get with fallback
const phoneOrDefault = Option.getOrElse(phone, () => "N/A");

// For API responses (JSON needs null, not Option)
const apiPhone = Option.getOrNull(phone); // string | null

Schema Integration

import { Schema } from "effect";

const User = Schema.Struct({
  id: Schema.String,
  // nullable API field -> Option in domain
  phone: Schema.OptionFromNullOr(Schema.String),
});

type User = typeof User.Type;
// { id: string; phone: Option<string> }

Domain Rules

Boundaries

// INPUT: nullable -> Option
const phone = Option.fromNullable(request.body.phone);

// OUTPUT: Option -> nullable for JSON
const response = { phone: Option.getOrNull(user.phone) };