与 Clojure 的序列不一致? [英] Inconsistency with Clojure's sequences?

问题描述

Clojure:

1:13 user=> (first (conj '(1 2 3) 4))
4
1:14 user=> (first (conj [1 2 3] 4))
1
; . . .
1:17 user=> (first (conj (seq [1 2 3]) 4))
4

我明白发生了什么，但是这应该以不同的方式工作吗?

I understand what is going on, but should this work differently?

推荐答案

conj 的文档(来自 clojure.org):

conj[oin].返回一个带有 xs 的新集合'添加'.(conj nil item) 返回 (item).添加"可能发生在不同的地方"，具体取决于具体类型.

conj[oin]. Returns a new collection with the xs 'added'. (conj nil item) returns (item). The 'addition' may happen at different 'places' depending on the concrete type.

将元素添加"到向量的末尾更有效，而在列表的开头这样做更有效.conj 使用最有效的数据结构.

It's more efficient to "add" elements to the end of a vector, while it's more efficient to do so at the beginning of lists. conj uses whatever is the most efficient for the data structure you give it.

在你给出的例子中，'(1 2 3) 和 (seq [1 2 3]) 都实现了 ISeq(见seq? 的文档)，而 [1 2 3] 没有.

In the examples you give, '(1 2 3) and (seq [1 2 3]) both implement ISeq (see documentation for seq?), while [1 2 3] doesn't.

Clojure 的 conj 最终会在底层数据结构；对于向量 (PersistentVector)，cons 将元素添加到末尾，而对于列表，它们被添加到前面(cons 方法用于 PersistentLists 返回一个新列表，以新元素为头，现有列表为尾.

Clojure's conj ultimately calls the cons method (not to be confused with the cons function - this method is internal clojure code) on the underlying data structure; for vectors (PersistentVector), cons adds elements to the end, while for lists they're added to the front (the cons method for PersistentLists returns a new list with the new element as its head, and the existing list as its tail).

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