export function eachObjLim<A, B>(
  n: number,
  ms: Record<string, A>,
  fn: (a: A, i: string) => T.Task<B>
): T.Task<Record<string, B>> {
  return n <= 0 ? T.raise(new Error('1 arguments to eachObjLim must be greater than zero'))
    : newQSem(n).chain(qsem => eachObjPar(ms, (v, i) => withQSem(qsem, fn(v, i))));
}

 .chain(stat => {
   if (stat.isFile()) {
     let time = H.fromDate(stat.mtime);
     let date = H.formatHttpDate(time);
     return T.pure(new FileInfo(path, stat.size, time, date));
   }
   return T.raise(new Error(`getInfo: ${path}  isn't a file`));
 });

 return fcache.read.chain(cache => {
   const there = HM.lookup(hash, path, cache);
   if (isJust(there)) {
     const entry = there.value;
     return entry.tag === EntryType.NEGATIVE ? T.raise(new Error('FileInfoCache:getAndRegisterInfo'))
       : T.pure(entry.finfo);
   }
   return T.rescue(positive(fcache, hash, path), () => negative(fcache, hash, path));
 });

  return getSessionImpl(storage, sess.id).chain(oldSess => {
    if (oldSess) return T.raise(new SessionAlreadyExists(oldSess, sess));
    const sk = storage.sessionKey(sess.id);
    let commands: string[][] = [['hmset', sk].concat(printSession(sess))];
    // ttl
    let ttl = expireSession(sess, storage);
    if (ttl !== null) commands.push(ttl);

    // auth
    if (sess.authId)
      commands.push(['sadd', storage.authKey(sess.authId), sk]);

    return transaction(commands, storage.redis).map(absurd);
  });

 destroy(sessId: string) {
   return T.raise(new TNTExplosion('destroy', { sessId }));
 }

 get(sessId: string) {
   return T.raise(new TNTExplosion('get', { sessId }));
 }

 function onlyTiny0(ctx: any, file: FileUpload): T.Task<boolean> {
   return file.fieldname === 'tiny0' ? T.pure(true) : T.raise(new Error('only tiny0 allowed'));
 }

 return send(W.responseStream(200, headers, () => T.raise(new Error('should not evaluated'))));

 replace(session: SS.Session) {
   return T.raise(new TNTExplosion('replace', session));
 }