【Note】fp-ts 库函数备忘

"个人关于 fp-ts 的库函数的一些笔记。"

1. chain = flatMap

chain 做的事情（mapping and then flattening）：

  1. 检查是否有值
  2. 如果有值，则将该值传入函数，并返回一个新的被包装的类型
import * as O from 'fp-ts/Option'


pipe(
    ns,
    head,
    O.map(inverse)
    O.flatten
)


// 等价于
pipe(
    ns,
    head,
    O.chain(inverse)
)

2. fromPredicate

const isEven = (n: number) => n % 2 === 0


const getEven = O.fromPredicate(isEven) // Option<number>


type Shape = Circle | Square


const isCircle = (shape: Shape): shape is Circle => shape.kind === 'circle'


const getCircle = O.fromPredicate(isCircle) // Option<Shape>

【END】

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