一个在JavaScript中支持“模式匹配技术”的Babel插件
【一个在JavaScript中支持“模式匹配技术”的Babel插件】模式匹配(pattern matching)是 lisp 、rust 、scala 、erlang 等语言中的常见语法，不过 JavaScript 一直未支持这个特性，虽然 tc39 早有相关的题案https://github.com/tc39/proposal-pattern-matching，不过目前进展缓慢，遂研发了一个Babel插件用于在JavaScript中支持模式匹配的语法
babel-plugin-proposal-pattern-matching
安装
使用 npm:
npm install --save-dev babel-plugin-proposal-pattern-matching设置 .babelrc
{
"plugins": ["babel-plugin-proposal-pattern-matching"]
}一些演示 简单使用
import match from 'babel-plugin-proposal-pattern-matching/match'
const fib = n=>match(n)(
(v=1)=>1,
(v=2)=>1,
_=>fib(_-1)+fib(_-2)
)console.log(fib(10))
// -> 55直接返回一个函数，配合函数式编程
import match from 'babel-plugin-proposal-pattern-matching/match'
const fib = fnmatch(
(v = 1) => 1,
(v = 2) => 1,
_ => fib(_ - 1) + fib(_ - 2)
)console.log(fib(10))// -> 55const arr = [1, 2, 3]console.log(
arr.map(
fnmatch(
(v = 1) => 'one',
(v = 2) => 'two',
(v = 3) => 'three'
)
)
)// -> [ 'one', 'two', 'three' ]数据类型判断
import { match , T} from 'babel-plugin-proposal-pattern-matching/match'const getType = item => match(item)(
(v = T.number) => 'number',
(v = T.string) => 'string',
(v = T.nullish) => 'nullish',
_ => `${_} undefined type`
)console.log(getType('a'))
// -> stringconsole.log(getType(1))
// -> numberconsole.log(getType(undefined))
// -> nullishconsole.log(getType(null))
// -> nullish实例判断
import { match, instanceOf } from 'babel-plugin-proposal-pattern-matching/match'const getType = val => match(val)(
(v=instanceOf(RegExp))=>'RegExp',
(v=instanceOf(Array))=>'Array',
(v=instanceOf(Object))=>'Object',
)console.log(getType(/111/))
// -> RegExp
console.log(getType([1,2,3]))
// -> Array
console.log(getType({a:1}))
// -> Object解构，这里支持无限嵌套
import { match } from 'babel-plugin-proposal-pattern-matching/match'
const sum = x => match(x)(
([x, ...xs]) => x + sum(xs),
([]) => 0
)console.log(sum([1, 2, 3]))
// -> 6for (let i = 1;
i <= 15;
i++) {
console.log(
match({a: i % 3, b: i % 5})(
({a = 0, b = 0}) => 'FizzBuzz',
({a = 0, b}) => 'Fizz',
({a, b = 0}) => 'Buzz',
_ => i
)
)
}
// ->
// 1
// 2
// Fizz
// 4
// Buzz
// Fizz
// 7
// 8
// Fizz
// Buzz
// 11
// Fizz
// 13
// 14
// FizzBuzz非运算
import { match, not, or, T } from 'babel-plugin-proposal-pattern-matching/match'const toNumber = n => match(n)(
(v = not(T.boolean)) => v,
(v = true) => 1,
(v = false) => 0
)console.log(
[true, false, 0, 1, 2, 3].map(toNumber)
)
// -> [ 1, 0, 0, 1, 2, 3 ]或运算
import { match, or } from 'babel-plugin-proposal-pattern-matching/match'
const fib = n => match(n)(
(v = or(1, 2)) => 1,
_ => fib(_ - 1) + fib(_ - 2)
)console.log(fib(10))
// -> 55与运算
import { match, and, not } from 'babel-plugin-proposal-pattern-matching/match'
const fib = n => match(n)(
(_ = and(not(1), not(2))) => fib(_ - 1) + fib(_ - 2),
_ => 1
)console.log(fib(10))
// -> 55
