maybe-type.ts

enum MaybeType {
  Just = 'maybe-type__just',
  Nothing = 'maybe-type__nothing',
}

interface Just<T> {
  type: typeof MaybeType.Just
  value: T
}

interface Nothing {
  type: typeof MaybeType.Nothing
}

type Maybe<T>
  = Just<T>
  | Nothing

const Nothing = (): Nothing => ({
  type: MaybeType.Nothing,
})

const Just = <T> (value: T): Just<T> => ({
  type: MaybeType.Just,
  value,
})