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clojure学习3

最近更新：2024-11-11 | 字数总计：916 | 阅读估时：4分钟 | 阅读量：次

Function Functions
prue function
Function Composition Instead of Attribute Mutation
1. comp
2. memoize

Function Functions

complement

一个布尔函数的否定返回

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(defn identify-humans  [social-security-numbers]
(filter #(not (vampire? %))
(map vampire-related-details social-security-numbers)))

(def not-vampire? (complement vampire?))
;;可以使用complement
(defn identify-humans  [social-security-numbers]
(filter not-vampire?
(map vampire-related-details social-security-numbers)))

#

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(defn parse  "Convert a CSV into rows of columns"  [string]
    (map #(clojure.string/split % #",")
    (clojure.string/split string #"\n")))

#"," 是这个于创建正则表达式字面量

(ns fwpd.core)

(def filename "suspects.csv")

(def vamp-keys [:name :glitter-index])

(defn str->int [str] (Integer. str))

(def conversions {:name identity, :glitter-index str->int})

(Defn convert [vamp-key value] ((get conversions vamp-key) value))

(defn parse
  "Convert a CSV into rows of columns"
  [string]
  (map #(clojure.string/split % #",") (clojure.string/split string #"\n")))

(defn mapify
  "Return a seq of maps like {:name \"Edward Cullen\" :glitter-index 10}"
  [rows]
  (map (fn [unmapped-row]
         (reduce (fn [row-map [vamp-key value]]
                   (assoc row-map vamp-key (convert vamp-key value)))
           {}
           (map vector vamp-keys unmapped-row)))
    rows))

(defn glitter-filter  [minimum-glitter records]
  (filter #(>= (:glitter-index %) minimum-glitter) records))

(glitter-filter 3 (mapify (parse (slurp filename))))

;; ({:name "Edward Cullen", :glitter-index 10} {:name "Jacob Black", :glitter-index 3} {:name "Carlisle Cullen", :glitter-index 6})

prue function

如果给定相同的参数，则始终返回相同的结果
它不会引起任何副作用(该函数不能进行任何可在函数本身之外观察到的更改)

Living with Immutable Data Structures

不可变的数据结构可确保您的代码不会产生副作用

Recursion Instead of for/while

var wrestlers = getAlligatorWrestlers();
var totalBites = 0;
var l = wrestlers.length;
for(var i=0; i < l; i++){
    totalBites += wrestlers[i].timesBitten;
}

对totalBites 会产生副作用,但是是内部的，无害的，没有跟改外部的

但clojure的核心数据结构甚至不允许这些无害的更改

1 2	(def great-baby-name "Rosanthony") great-baby-name ; => "Rosanthony"(let [great-baby-name "Bloodthunder"] great-baby-name); => "Bloodthunder"great-baby-name; => "Rosanthony"

clojure 执行递归使用recur

clojure 不提供尾优化

Function Composition Instead of Attribute Mutation

函数组合而不是属性更改

class GlamourShotCaption
attr_reader :text
def initialize(text)
@text = text    clean!  end  private  def clean!    text.trim!    text.gsub!(/lol/, "LOL")
endendbest = GlamourShotCaption.new("My boa constrictor is so sassy lol!  ")best.text
; => "My boa constrictor is so sassy LOL!"

(require '[clojure.string :as s])
(defn clean  [text]  (s/replace (s/trim text) #"lol" "LOL"))
(clean "My boa constrictor is so sassy lol!  ")
; => "My boa constrictor is so sassy LOL!"

通过函数组合,而不是属性更改

像这样组合函数（以便将一个函数的返回值作为参数传递给另一个函数）称为函数组合
通常，函数式编程鼓励您通过组合更简单的函数来构建更复杂的函数

一旦您有信心使用不可变数据结构来完成工作，您就会感到更加自信，因为您不必担心哪些肮脏的代码可能会沾上您珍贵的可变变量

comp

creating a new function from the composition of any number of functions

1	((comp inc *)2 3); => 7

(def character  {:name "Smooches McCutes"
:attributes {:intelligence 10    :strength 4     :dexterity 5}})

(def c-int (comp :intelligence :attributes))
(def c-str (comp :strength :attributes))
(def c-dex (comp :dexterity :attributes))

(c-int character); => 10
(c-str character); => 4
(c-dex character); => 5

(fn [c] (:strength (:attributes c)))

(defn spell-slots  [char]  (int (inc (/ (c-int char) 2))))

(def spell-slots-comp (comp int inc #(/ % 2) c-int))

(spell-slots character)
; => 6

1	(defn two-comp [f g] (fn [& args] (f (apply g args))))

memoize

记忆化

(+ 3 (+ 5 8))

(defn sleepy-identity
"Returns the given value after 1 second"
[x]  (Thread/sleep 1000)  x)
(sleepy-identity "Mr. Fantastico") ; => "Mr. Fantastico" after 1 second
(sleepy-identity "Mr. Fantastico") ; => "Mr. Fantastico" after 1 second

(def memo-sleepy-identity (memoize sleepy-identity))

(memo-sleepy-identity "Mr. Fantastico"); => "Mr. Fantastico" after 1 second
(memo-sleepy-identity "Mr. Fantastico"); => "Mr. Fantastico" immediately

未完待续……

2024-11-09 该篇文章被 apple115 打上标签: lang