type Either<T, U> = {
  hasRight: boolean,
  left: T,
  right: U
};

function eitherLeft<T, U>(left: T): Either<T, U> {
  return { hasRight: false, left: left, right: undefined };
}

function eitherRight<T, U>(right: U): Either<T, U> {
  return { hasRight: true, left: undefined, right: right };
}

export { Either, eitherLeft, eitherRight };