javascript - 带有嵌套流的 flatMapConcat

Question

我在这里询问了“如何将流映射到延迟 promise 流”，并发限制为 1:map a stream to lazy promise stream 。答案是flatMapConcat。

现在我有两个嵌套流，需要并发限制为 1，并且 flatMapConcat 不再起作用。

var getPromise = function(value) {
  console.log('resolving ' + value);
  return new RSVP.Promise(function(resolve, reject) {
      setTimeout(function() {
        resolve(value);
      }, 1000);
  });
};


var stream = Bacon.fromArray([1,2,3]).flatMapConcat(function(value) {
  return Bacon.fromPromise(getPromise(value));
});

//stream.log();
// nice sequential
// resolving 1
// 1
// resolving 2
// 2
// resolving 3
// 3

var secondStream = stream.flatMapConcat(function(promised) {
  return Bacon.fromPromise(getPromise('second' + promised));
});


secondStream.log();
// mixed up stream and secondStream, not sequential anymore
// resolving 1
// resolving second1
// resolving 2
// second1
// resolving second2
// resolving 3
// second2
// resolving second3
// second3

// Required output:
// resolving 1
// resolving second1
// second1
// resolving 2
// resolving second2
// second2
// resolving 3
// resolving second3
// second3

第一个流很好而且是连续的，但是当我用它构建嵌套流时，flatMapConcat不再起作用。我需要第一个流来等待第二个流。

Answer 1

尝试将第二个 .flatMap 移到第一个内:

var stream = Bacon.fromArray([1,2,3]).flatMapConcat(function(value) {
  return Bacon.fromPromise(getPromise(value)).flatMapConcat(function(promised) {
    return Bacon.fromPromise(getPromise('second' + promised));
  });
});