#facebook-immutable で階乗計算

#facebook-immutable で階乗計算

#facebook-immutable で階乗計算

facebook-immutable で階乗計算

##Range()

http://facebook.github.io/immutable-js/docs/#/Range

>Returns a IndexedSeq of numbers from `start` (inclusive) to `end` (exclusive), by `step`, where `start` defaults to 0, `step` to 1, and `end` to infinity. When `start` is equal to `end`, returns empty range.

>Range(start?: number, end?: number, step?: number): IndexedSeq<number>

```js
Range() // [0,1,2,3,...]
Range(10) // [10,11,12,13,...]
Range(10,15) // [10,11,12,13,14]
Range(10,30,5) // [10,15,20,25]
Range(30,10,5) // [30,25,20,15]
Range(30,30,5) // []
```

##コード

```js
var _ = require('immutable');

var plus = function(a, b)
{
  return a * b;
};
```

階乗を求める関数

```js
var factorial = function(n)
{
  var x = _.Range(1, n + 1) // natural numbers starts from 1 to n
    .reduce(plus);

  return x;
};
```

または、

```js
var factorial = function(n)
{
  var x = _.Range(1); // natural numbers starts from 1
    .take(n)
    .reduce(plus);

  return x;
};
```

表示

```js
console.log(factorial(3)); // 1*2*3 = 6
```