在Clojure中序列和集合之间有什么区别 [英] What's the difference between a sequence and a collection in Clojure

问题描述

我是一个Java程序员，是Clojure的新人。从不同的地方，我看到序列和收集在不同的情况下使用。但是，我不知道他们之间的确切差异。

I am a Java programmer and am new to Clojure. From different places, I saw sequence and collection are used in different cases. However, I have no idea what the exact difference is between them.

对于一些示例：

1）在Clojure的文档中， Sequence ：

1) In Clojure's documentation for Sequence:

The Seq interface
(first coll)
  Returns the first item in the collection. 
  Calls seq on its argument. If coll is nil, returns nil.
(rest coll)
  Returns a sequence of the items after the first. Calls seq on its argument. 
  If there are no more items, returns a logical sequence for which seq returns nil.
(cons item seq)
  Returns a new seq where item is the first element and seq is the rest.

正如你所看到的，当描述Seq接口时，前两个函数'coll'这似乎表明这是一个集合，而'cons'函数使用'seq'，这似乎表明这是一个序列。

As you can see, when describing the Seq interface, the first two functions (first/rest) use 'coll' which seems to indicate this is a collection while the 'cons' function use 'seq' which seems to indicate this is a sequence.

称为coll？和seq？可用于测试值是集合还是序列。

2) There are functions called "coll?" and "seq?" that can be used to test if a value is a collection or a sequence. It is clearly collection and sequence are different.

3）在Clojure的文档中，关于'

3) In Clojure's documentation about 'Collections', it is said:

由于集合支持seq函数，所以序列
函数可用于任何集合

Because collections support the seq function, all of the sequence functions can be used with any collection

这是否意味着所有集合都是序列？

Does this mean all collections are sequences?

(coll? [1 2 3]) ; => true 
(seq? [1 2 3]) ; => false

上面的代码告诉我这不是这种情况，因为[1 2 3]不是一个序列。

The code above tells me it is not such case because [1 2 3] is a collection but is not a sequence.

我认为这是一个很基本的问题Clojure，但我不能找到一个地方解释清楚他们的区别是什么，我在不同的情况下使用。

I think this is a pretty basic question for Clojure but I am not able to find a place explaining this clearly what their difference is and which one should I use in different cases. Any comment is appreciated.

推荐答案

每个序列都是一个集合，但不是每个集合都是序列。

Every sequence is a collection, but not every collection is a sequence.

seq 函数可以转换序列中的集合。例如。对于地图，您会得到其条目的列表。该列表条目与地图本身不同。

The seq function makes it possible to convert a collection in a sequence. E.g. for a map you get a list of its entries. That list of entries is different from the map itself, though.

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