震惊小伙伴的单行代码●CoffeeScript篇

几年前,函数式编程的复兴正值巅峰,一篇介绍 Scala 中 10 个单行函数式代码的博文在网上走红。很快地,一系列使用其他语言实现这些单行代码的文章也随之出现,比如 Haskell, Ruby, Groovy, Clojure, Python, C#, F#, CoffeeScript

每篇文章都令人印象深刻的揭示了这些语言中一些出色优秀的编程特征。编程高手们利用这些技巧提高编程速度、改进软件质量,编程初学者能从这些简洁的预防中学到各种编程语言的真谛。本《震惊小伙伴的单行代码系列》将逐一介绍这些各种编程语言单行代码文章,供大家学习参考。

1. 让列表中的每个元素都乘以2

[1..10].map (i) -> i*2

i * 2 for i in [1..10]

2. 求列表中的所有元素之和

[1..1000].reduce (t, s) -> t + s

(reduce == reduceLeft, reduceRight 也可以)

3. 判断一个字符串中是否存在某些词

wordList = ["coffeescript", "eko", "play framework", "and stuff", "falsy"]
tweet = "This is an example tweet talking about javascript and stuff."

wordList.some (word) -> ~tweet.indexOf word

下面的例子会返回匹配的单词:

wordList.filter (word) -> ~tweet.indexOf word

~ is not a special operator in CoffeeScript, just a dirty trick. It is the bitwise NOT operator, which inverts the bits of it’s operand. In practice it equates to -x-1. Here it works on the basis that we want to check for an index greater than -1, and -(-1)-1 == 0 evaluates to false.

4. 读取文件

fs.readFile 'data.txt', (err, data) -> fileText = data

同步版本:

fileText = fs.readFileSync('data.txt').toString()

In node.js land this is only acceptable for application start-up routines. You should use the async version in your code.

5. 祝你生日快乐!

[1..4].map (i) -> console.log "Happy Birthday " + (if i is 3 then "dear Robert" else "to You")

下面这一版读起来更像是伪代码:

console.log "Happy Birthday #{if i is 3 then "dear Robert" else "to You"}" for i in [1..4]

6. 过滤列表中的数值

(if score > 60 then (passed or passed = []) else (failed or failed = [])).push score for score in [49, 58, 76, 82, 88, 90]

更函数式的方法:

[passed, failed] = [49, 58, 76, 82, 88, 90].reduce ((p,c,i) -> p[+(c < 60)].push c; p), [[],[]]

7. 获取XML web service数据并分析

这里用json代替XML:

request.get { uri:'path/to/api.json', json: true }, (err, r, body) -> results = body

8. 找到列表中最小或最大的一个数字

Math.max.apply @, [14, 35, -7, 46, 98] # 98
Math.min.apply @, [14, 35, -7, 46, 98] # -7

9. 并行处理

Not there yet. You can create child processes on your own and communicate with them, or use the WebWorkers API implementation. Skipping over.

10. “Sieve of Eratosthenes”算法

下面的代码可以写成一行吗?

sieve = (num) ->
    numbers = [2..num]
    while ((pos = numbers[0]) * pos) <= num
        delete numbers[i] for n, i in numbers by pos
        numbers.shift()
    numbers.indexOf(num) > -1

跟紧凑的版本:

primes = []
primes.push i for i in [2..100] when not (j for j in primes when i % j == 0).length

真正的一行实现:

(n) -> (p.push i for i in [2..n] when not (j for j in (p or p=[]) when i%j == 0)[0]) and n in p
(n) -> (p.push i for i in [2..n] when !(p or p=[]).some((j) -> i%j is 0)) and n in p
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