如何理解这个猫的例子？

Question

clojuredocs.com

中有猫的例子

(into [] (comp cat cat (map inc)) [[[1] [2]] [[3] [4]]])

据我所知，comp 从左到右应用 fn，但上面的示例似乎是从右到左应用的。我该如何阅读？

Answer 1

"secret" 在 comp 函数中，它从右到左应用函数，但对于 transducers it is left to right。

既然你在转换，(comp cat cat (map inc))有点像
(fn [xs] (map inc (sequence cat (sequence cat xs))))（注意，cat 的版本中没有 coll）

Answer 2

简短回答：comp-ing transducers 基本上运行它们 left-to-right。

来自上面的文档：

Transducers compose with ordinary function composition. A transducer performs its operation before deciding whether and how many times to call the transducer it wraps. The recommended way to compose transducers is with the existing comp function:
(def xf
  (comp
    (filter odd?)
    (map inc)
    (take 5)))
The transducer xf is a transformation stack that will be applied by a process to a series of input elements. Each function in the stack is performed before the operation it wraps. Composition of the transformer runs right-to-left but builds a transformation stack that runs left-to-right (filtering happens before mapping in this example).

As a mnemonic, remember that the ordering of transducer functions in comp is the same order as sequence transformations in ->>. The transformation above is equivalent to the sequence transformation:
(->> coll
     (filter odd?)
     (map inc)
     (take 5))

如何理解这个猫的例子？

How to understand this example of cat?

clojure

cat