# Functional Programming 筆記
## Library

- [Ramda](https://www.npmjs.com/package/ramda)
- [fp-ts](https://www.npmjs.com/package/fp-ts)


## 值 vs Functor

^ f	  ^ g		^ composition 		^
| pure	  | pure	| compose(f, g)		|
| effects | pure(unary)	| f.map(g)		|
| effects | pure(n-ary)	| f1.map(g).ap(f2)	|
| effects | effects	| m.chain(f).chain(g)	|


## Functor


^	ADT	^	Effect			^
|	Either		|	處理錯誤情境		|
|	Future		|	#TODO			|
|	Identity	|	#TODO			|
|	IO		|	處理永不失敗的同步計算	|
|	Maybe		|	處理無值情境		|
|	Reader		|	#TODO			|
|	Tuple		|	#TODO			|
|	State		|	#TODO			|


### Either

  * 處理錯誤情境
  * 分成 `Either.Right` 和 `Either.Left`
  * `Either.Right` 會繼續跑，而 `Either.Left` 則會忽略後續運算，執意將手上的值傳下去
  * <https://ithelp.ithome.com.tw/articles/10279389>

```javascript
const addOne = num => Right(R.add(1));
const error = () => Left(new Error('error'))

Right(10)
    .chain(addOne)
    .map(R.add(2))
    .inspect() // Right(13)
    
Right(10)
    .chain(error)
    .map(R.add(2))
    .inspect() // Left(Error: error)

```

### Future

> TODO


### Identity

> TODO


### IO

  * 處理永不失敗的同步計算
  * <https://ithelp.ithome.com.tw/articles/10278925>

### Maybe

  * 處理無值情境 ( null || undefined )
  * <https://ithelp.ithome.com.tw/articles/10277399>

### Reader
  * 用來避免中間傳送無用的 `dep`
  * <https://ithelp.ithome.com.tw/articles/10280177>

### Tuple

> TODO


### State

    * <https://ithelp.ithome.com.tw/articles/10280554>




## Articles

- <https://ithelp.ithome.com.tw/users/20140431/ironman/4122?page=1>
- <https://medium.com/hannah-lin/9edc7d705c3f>
- <https://medium.com/@mirkomariani/e83e54fcd86b>
- <https://medium.com/let-s-learn/5db457997554>