function renderDirectoryContentsTable(pieces: Piece[], folder: Folder): string {
  let table = [
    '<table>',
    '  <thead>',
    '    <th class="first"></th>', // todo image
    '    <th>Name</th>',
    '    <th>Modified</th>',
    '    <th>Size</th>',
    '  </thead>',
    '  <tbody>'
  ].join('\n');

  const sorted = folder.sort(compareFolder);
  let alt: boolean;
  let item: Either<FolderName, File>;
  let name: string;
  let href: string;
  for (let i = 0, len = sorted.length; i < len; i++) {
    alt = (i % 2) === 0;
    item = sorted[i];
    name = isLeft(item) ? (item.value === '' ? '..' : item.value) : item.value.name;
    href = addCurrentDir(pieces, name)
    table += alt ? '<tr class="alt">' : '<tr>\n';
    table += `<td class="first${isLeft(item) ? ' icon-dir' : ''}"></td>\n`;
    table += `<td><a href="${href}">${name}</a></td>\n`;
    table += `<td>${isRight(item) && isJust(item.value.getModified)
      ? formatCalender(item.value.getModified.value) : ''}</td>\n`;
    table += `<td>${isRight(item) ? prettyShow(item.value.size) : ''}</td>\n`;
    table += '</tr>\n';
  }

  table += '  </tbody>\n';
  table += '</table>\n';
  return table;
}

 function go(e: P.Either<E, P.Either<A, B>>): P.Either<P.Either<E, P.Either<A, B>>, P.Either<E, B>> {
   if (P.isLeft(e)) {
     return P.right(e);
   }
   const ret = e.value;
   if (P.isLeft(ret)) {
     return P.left(f(ret.value));
   }
   return P.right(ret);
 }

 return Q.assertTask(T.co(function* () {
   const sup = T.makeSupervisor();
   function action(s: string) {
     return T.delay(20).map(() => s);
   }
   let fib: T.Fiber<string> = yield T.forkWith(sup, action('bar'));
   let fib2: T.Fiber<string> = yield T.forkWith(sup, action('foo'));
   yield T.killAll(new Error('kill All'), sup);
   const s1: P.Either<Error, string> = yield T.attempt(T.joinFiber(fib));
   const s2: P.Either<Error, string> = yield T.attempt(T.joinFiber(fib2));
   return T.pure(P.isLeft(s1) && P.isLeft(s2));
 }));

 const lookupResult: T.Task<P.Either<string, LookupResult>> = T.co(function* () {
   const nonIndexResult: LookupResult  = yield settings.lookupFile(pieces);
   if (nonIndexResult.tag === LookupResultType.LRFILE) {
     return T.pure(P.right(nonIndexResult));
   }
   const eIndexResult: P.Either<string, LookupResult> = yield lookupIndices(
     settings.indices.map(ix => dropLastIfNull(pieces.concat(ix)))
   );
   if (P.isLeft(eIndexResult)) {
     return T.pure(P.left(eIndexResult.value));
   }
   const { value: indexResult } = eIndexResult;
   if (indexResult.tag === LookupResultType.LRNOTFOUND) {
     return T.pure(P.right(nonIndexResult));
   }
   if (indexResult.tag === LookupResultType.LRFILE && settings.redirectToIndex) {
     const file = indexResult.file;
     return T.pure(P.left((function () {
       const repieces = pieces.slice().reverse();
       if (repieces.length === 0) {
         return file.name;
       }
       const lastSegment = repieces[0];
       if (lastSegment == '') return file.name;
       return `${lastSegment}/${file.name}`;
     })()));
   }
   return T.pure(P.right(indexResult));
 });

 return defParser(s => {
   const ret = this.fn(s);
   if (P.isLeft(ret)) {
     return ret.value.pos === s.pos ? other.fn(s) : ret;
   }
   return ret;
 });

    test('reading from an empty Chan blocks', function* () {
      const chan: Q.Chan<number> = yield Q.newChan;
      const r: P.Either<void, number> = yield compete(T.delay(50), Q.readChan(chan));
      assert.ok(P.isLeft(r));

      return T.pure(void 0);
    });

function compareFolder(fa: Either<FolderName, File>, fb: Either<FolderName, File>): 0 | 1 | -1 {
  if (isLeft(fa) && isRight(fb)) {
    return -1;
  }
  if (isRight(fa) && isLeft(fb)) {
    return 1;
  }
  if (isLeft(fa) && isLeft(fb)) {
    return fa.value < fb.value ? -1 : fa.value === fb.value ? 0 : 1;
  }
  if (isRight(fa) && isRight(fb)) {
    let a = fa.value.name, b = fb.value.name;
    return a < b ? -1 : a === b ? 0 : 1;
  }
  // should never reached here
  return 0;
}

export function tailRec<A, B>(
  i: A,
  f: (i: A) => P.Either<A, B>
): B {
  let current = f(i);
  while (P.isLeft(current)) {
    current = f(current.value);
  }
  return current.value;
}

  it('should report error from storage', async function () {
    const middleware = mutter({ getStorage: getTntStorage });
    const form = new FormData();

    form.append('small', file('small0.txt'));

    const result = await T.toPromise(T.attempt(submitForm(middleware, form)));
    assert.ok(isLeft(result));
    assert.equal((result.value as any).message, 'tnt storage handleFile');
  });