柯里化与偏函数

1. 柯里化（Currying）

1.1 定义

柯里化是将一个接受多个参数的函数转换为一系列只接受单个参数的函数：

f(a, b, c) → f(a)(b)(c)

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(this, args);
    }
    return function (...moreArgs) {
      return curried.apply(this, args.concat(moreArgs));
    };
  };
}

const add = curry((a, b, c) => a + b + c);
console.log(add(1)(2)(3)); // 6
console.log(add(1, 2)(3)); // 6

1.2 实际应用

// 日志函数
const log = curry((level, timestamp, message) => {
  console.log(`[${level}] ${timestamp}: ${message}`);
});
const infoLog = log('INFO');

// 过滤器
const filter = curry((predicate, array) => array.filter(predicate));
const isEven = (n) => n % 2 === 0;
const filterEven = filter(isEven);
console.log(filterEven([1, 2, 3, 4, 5, 6])); // [2, 4, 6]

2. 偏函数（Partial Application）

function partial(fn, ...presetArgs) {
  return function (...laterArgs) {
    return fn(...presetArgs, ...laterArgs);
  };
}

const greet = (greeting, name, punctuation) => `${greeting}, ${name}${punctuation}`;

const hello = partial(greet, 'Hello');
console.log(hello('World', '!')); // "Hello, World!"

3. 柯里化 vs 偏函数