Option — make absence a value, not a guess

Effect v3.12.0

In TypeScript, the array's find method hands you the value or nothing, and the type admits it: Account or undefined. The trouble is that second half. Reach for the name directly and it will not compile, so you reach for the exclamation mark to silence the error, and now an absent account crashes at runtime. The type warned you, then you talked it into staying quiet.

Effect gives absence a name. Option.fromNullable takes that maybe-undefined value and returns an Option: Some when the account is there, None when it is not. The hole in the type closes. found is now Option of Account, and there is no undefined left to forget, because reading the value means dealing with None first.

And it composes. Option.map runs only when there is a value, so you turn the account into its name with no question-mark-dot. When it is None, map is skipped and Option.getOrElse supplies the fallback. The whole chain collapses to one honest type, id to string, and the absent case is handled once, not at every step.

// Plain TypeScript: Array.prototype.find returns T | undefined. The "| undefined"
// is the half everyone forgets — reach for the value directly and the type lies
// about whether it is there.
interface Account {
  id: number;
  name: string;
}

const accounts: Account[] = [
  { id: 1, name: "Ada" },
  { id: 2, name: "Linus" },
];

const found = accounts.find((u) => u.id === 3);
//    ^? Account | undefined

// found.name would not compile; found!.name would compile and crash at runtime.
console.log(found?.name ?? "no user"); // no user

❚❚ beat