详解JS中的reduce fold unfold用法

const addReducer = (x, y) => x + y;

[1, 2, 3, 4, 5].reduce(addReducer, 0) // 15

const reduce = (f, init, arr) => {
  let acc = init;
  for (const item of arr) {
    acc = f(acc, item);
  }
  return acc
}
// 执行
reduceFor(addReducer, 0, [1, 2, 3, 4, 5])  // 15

reduce = (f, init, arr) => {
  let acc = init;
  let current;
  let i = 0;
  while ((current = arr[i++])) {
    acc = f(acc, current);
  }
  return acc;
}

// 执行
reduceFor(addReducer, 0, [1, 2, 3, 4, 5])  // 15

function reduce(f, init, arr) {
  if (arr.length === 0) return init;
  const [head, ...rest] = arr;
  return reduceRecursion(f, f(init, head), rest);
}

// 执行
reduceFor(addReducer, 0, [1, 2, 3, 4, 5])  // 15

range(0, 100, 5)

range = (first, last, step) => {
  const n = (last - first) / step + 1;
  return Array.from({ length: n - 1 })
            .map((_, index) => first + index * step);
}
// 也可以使用from的第二个参数
// Array.from({ length: n }, (_, i) => first + i * step);

function* range(first, last, step) {
  let acc = first;
  while (acc < last) {
    yield acc;
    acc = acc + step;
  }
}
[...range(0, 100, 5)]

function unfold(f, init) {
  const g = (f, next, acc) => {
    const result = f(next);
    const [head, last] = result || [];
    console.log(last);
    return result ? g(f, last, acc.concat(head)) : acc;
  };
  return g(f, init, []);
}

range = R.curry((first, last, step) =>
  unfold(next => next < last && [next, next + step], 0)
)

// 执行
range(0, 100, 5)