Example

interface User {
    name: string;
    id: string;
    score: number;
}
interface Bulk {
    users: readonly User[];
}
const extractFromBulk = (id: string) =>
    local((bulk: Bulk): Option<User> => {
        const found = bulk.users.find((elem) => elem.id === id);
        if (!found) {
            return Option.none();
        }
        return Option.some(found);
    });
const scoreReport = (id: string): Reader<Bulk, string> =>
    Cat.cat(ask<Option.Option<User>>())
        .feed(
            map(
                Option.mapOr("user not found")(({ name, score }) =>
                    `${name}'s score is ${score}!`
                ),
            ),
        )
        .feed(extractFromBulk(id)).value;

const bulk: Bulk = {
    users: [
        {
            name: "John",
            id: "1321",
            score: 12130,
        },
        { name: "Alice", id: "4209", score: 320123 },
    ],
};
expect(run(scoreReport("1321"))(bulk)).toStrictEqual("John's score is 12130!");
expect(run(scoreReport("4209"))(bulk)).toStrictEqual("Alice's score is 320123!");
Copy