Clojure“map”功能排序保證？

Question

map文檔說：

user=> (doc map)

clojure.core/map
([f] [f coll] [f c1 c2] [f c1 c2 c3] [f c1 c2 c3 & colls])
  Returns a lazy sequence consisting of the result of applying f to
  the set of first items of each coll, followed by applying f to the
  set of second items in each coll, until any one of the colls is
  exhausted.  Any remaining items in other colls are ignored. Function
  f should accept number-of-colls arguments. Returns a transducer when
  no collection is provided.
nil

applying f to the set使我不確定是否f被施加到傳遞，得到的結果序列的第n個元素的每個集合的第n個元素的序列 。

換一種說法：

有保證嗎？

(map str [ "1" "2" "3" ] [ "a" "b" "c" ] )

永遠都會回來

("1a" "2b" "3c")

永不

("a1" "b2" "3c")

？

Answer 1

是的， (map str ["1" "2" "3"] ["a" "b" "c"])將始終返回("1a" "2b" "3c") 。

從源代碼這里你可以看到它調用函數(first s1) (first s2) ，然后調用(map f (rest s1) (rest s2)) ，所以它總是按順序處理它們：

https://github.com/clojure/clojure/blob/master/src/clj/clojure/core.clj#L2756

在它開始之前，它會在每個集合上調用seq 。 對於像向量這樣的有序集合，生成的seq中的元素將始終與原始集合具有相同的順序。 對於無序集合，您不能指望它們按特定順序排列，但事實並非如此。