function listForInPar_<A, B>(xs: P.list.List<A>, fn: (_: A) => T.Task<B>): T.Task<void> {
  return P.list.foldr((a, b) => T.apSecond(fn(a).parallel(), b), T.Parallel.of(void 0), xs).sequential();
}

    it('saveSession can replace old session with new one', async function () {
      const storage = await T.toPromise(emptyMockStorage);

      const state = SS.createServerSessionState(storage);

      const m1 = { a: 'b' };
      const sess1 = await T.toPromise(SS.saveSession(state, { sess: null, now: fakenow }, m1));

      const m2 = SO.insert(state.authKey, 'John', m1);
      const sess2 = await T.toPromise(SS.saveSession(state, { sess: sess1, now: fakenow }, m2));

      const m3 = SO.insert(SS.forceInvalidateKey, SS.ForceInvalidate.ALL_SESSION_IDS_OF_LOGGED_USER, m2 as any);
      const sess3 = await T.toPromise(SS.saveSession(state, { sess: sess2, now: fakenow }, m3));

      await getMockOperation(storage);

      const m4 = SO.insert('x', 'y', m2);
      const sess4 = await T.toPromise(SS.saveSession(state, { sess: sess3, now: fakenow }, m4));
      assert.deepEqual(sess4, SO.assign({}, sess3, { data: SO.remove(state.authKey, m4) }));

      const op = await getMockOperation(storage);
      assert.deepEqual(op, L.fromArray([
        { tag: 'replace', session: sess4 }
      ]));
    });

 function go(xs: L.List<[number, L.List<A>]>, acc: L.List<[number, L.List<A>]>): T.Task<L.List<[number, L.List<A>]>> {
   if (L.isEmpty(xs)) return T.pure(acc);
   const [k, s] = xs.head;
   return prune(s, f).chain(mt =>
     isNothing(mt)   ? go(xs.tail, acc)
     /* otherwise */ : go(xs.tail, L.cons([k, mt.value] as [number, L.List<A>], acc)));
 }

    it('saveSession can create new session', async function () {
      const storage = await T.toPromise(emptyMockStorage);
      const state = SS.createServerSessionState(storage);

      const m1 = { a: 'b' };
      const session = await T.toPromise(SS.saveSession(state, { sess: null, now: fakenow }, m1));
      assert.ok(session != null);
      assert.equal((session as any).authId, null);
      assert.deepEqual((session as any).data, m1);

      const op = await getMockOperation(storage);
      assert.deepEqual(op, L.singleton({ session, tag: 'insert' }));
    });

 return L.concat(I.foldrWithKey((_, v, xs) => L.cons(v, xs), L.nil, m));

 return p.chain(a =>
   sep.chain(() => sepEndBy(p, sep).map(as => L.cons(a, as)))
     .alt(Parser.of(L.singleton(a)))

 return p.chain(head => many(p).map(xs => L.cons(head, xs)));

function nel<A>(xs: L.List<A>): Maybe<L.List<A>> {
  return L.isEmpty(xs) ? nothing : just(xs);
}