export const sequence = <T, U>(fn: ($: T) => Promise<U>) => async (L: T[]) => {
    for (const o of L)
        await fn(o);
};

export const parallel = <T, U>(fn: ($: T) => Promise<U>) => async (L: T[]) => {
    await Promise.all(L.map(fn));
};


export const notUndefined: <T>($: T | undefined) => T = $ => {
    if ($ === undefined)
        throw Error('the value is undefined!');
    else
        return $;
};