“结合"以功能方式在 javascript 中运行? [英] To "combine" functions in javascript in a functional way?
问题描述
我正在学习函数式编程，我想知道是否有一种方法可以像这样组合"函数:
I'm learning functional programming and I wonder if there is a way to "combine" functions like this:
function triple(x) {
return x * 3;
}
function plusOne(x) {
return x + 1;
}
function isZero(x) {
return x === 0;
}
combine(1); //1
combine(triple)(triple)(plusOne)(1); // 10
combine(plusOne)(triple)(isZero)(-1); // true
如果para是一个函数，它会将该函数组合"到自身中，如果不是则返回最终结果.谢谢！
If the para is a function, it "combines" the function into itself, and if not it will return the final result. Thanks!
推荐答案
传承
这是一个数学概念，称为函数组合.
This is a concept from maths called function composition.
f(x) = y
g(y) = z
g(f(x)) = z
(g•f)(x) = z
最后一行读作x 中的 f 的 g 等于 z".组合函数的优点在于消除了点.注意在 g(f(x)) = z 中，我们接受一个 x 输入并得到一个 z 输出.这会跳过中间点 y.
That last line is read "g of f of x equals z". What's great about composed functions is the elimination of points. Notice in g(f(x)) = z we take an x input and get a z output. This skips the intermediate point, y.
组合是创建高阶函数并保留代码的好方法闪闪发光的干净.很明显为什么我们希望在我们的 Javascript 程序中使用它.
Composition is a great way to create higher-order functions and keep your code sparkly clean. It's plain to see why we'd want this in our Javascript programs.
补偿
JavaScript 是一种多范式语言，具有丰富的函数支持.我们可以创建一个简单的 comp 函数，它结合了两个输入函数，g 和 f，并产生一个 new 功能 -
JavaScript is a multi-paradigm language with rich support for functions. We can create a simple comp function, which combines two input functions, g and f, and results in a new function -
function triple(x) {
return x * 3
}
function plusOne(x) {
return x + 1
}
function comp(g, f) {
return function(x) {
return g(f(x)) // "g of f of x"
}
}
const myfunc =
comp(triple, plusOne)
console.log(myfunc(1))评价
triple(plusOne(1))
triple(2)
6
撰写
正如问题所暗示的那样，我们很可能想要组合两个以上的功能.下面我们编写 compose ，它接受 all 输入函数，并使用上面的简单 comp 将它们reduce.如果没有给出函数，我们返回空函数，identity -
Just as the question suggests, it's likely we will want to combine more than two functions. Below we write compose which takes all of the input functions and reduces them using our simple comp from above. If no functions are given, we return the empty function, identity -
const triple = (x) =>
x * 3
const plusOne = (x) =>
x + 1
const comp = (g, f) =>
x => g(f(x)) // "g of f of x"
const identity = (x) =>
x
const compose = (...all) =>
all.reduce(comp, identity)
const myfunc =
compose(triple, triple, plusOne) // any amount of funcs
console.log(myfunc(1))评价
triple(triple(plusOne(1)))
triple(triple(2))
triple(6)
18
管道
您可以随心所欲地发挥创造力.下面，我们编写 pipe 允许我们的程序以舒适的从左到右的方向阅读 -
You can be as creative as you like. Below, we write pipe which allows our programs to read in a comfortable left-to-right direction -
const triple = (x) =>
x * 3
const plusOne = (x) =>
x + 1
const pipe = x =>
f => pipe(f(x))
pipe(1)(plusOne)(triple)(triple)(console.log) // 18
pipe(3)(triple)(plusOne)(triple)(plusOne)(console.log) // 31表达式一的评估-
f => pipe(f(1))
pipe(plusOne(1))
f => pipe(f(2))
pipe(triple(2))
f => pipe(f(6))
pipe(triple(6))
f => pipe(f(18))
pipe(console.log(18))
18
和表达式二 -
f => pipe(f(3))
pipe(triple(3))
f => pipe(f(9))
pipe(plusOne(9))
f => pipe(f(10))
pipe(triple(10))
f => pipe(f(30))
pipe(plusOne(31))
f => pipe(f(31))
pipe(console.log(31))
31
相关技术
柯里化函数和部分应用是与函数组合结合的概念.上面的 pipe 在 another Q&A 中介绍为 $ 和这里再次演示 -
Curried functions and partial application are concepts that gel with function composition. pipe above is introduced in another Q&A as $ and demonstrated again here -
const $ = x => // "pipe", or whatever name you pick
k => $ (k (x))
const add = x => y => // curried add
x + y
const mult = x => y => // curried mult
x * y
$ (1) // 1
(add (2)) // + 2 = 3
(mult (6)) // * 6 = 18
(console.log) // 18
$ (7) // 7
(add (1)) // + 1 = 8
(mult (8)) // * 8 = 64
(mult (2)) // * 2 = 128
(mult (2)) // * 2 = 256
(console.log) // 256这篇关于“结合"以功能方式在 javascript 中运行?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
