Scalaz 验证失败的地图 [英] Map on Scalaz Validation failure

问题描述

import scalaz._
import Scalaz._

"abc".parseInt

这将返回一个 Validation[NumberFormatException, Int].有没有办法可以在失败端应用函数(例如 toString)来获得 Validation[String, Int]?

This will return a Validation[NumberFormatException, Int]. Is there a way I can apply a function on the failure side (such as toString) to get a Validation[String, Int]?

推荐答案

<-: 和 :-> 定义了一对方法>MAB[M[_,_], A, B] 任何M[A, B]的左右两边只要有的映射双函子[M].Validation 恰好是一个双函子，所以你可以这样做:

There is a pair of methods <-: and :-> defined on MAB[M[_,_], A, B] that map on the left and right side of any M[A, B] as long as there is a Bifunctor[M]. Validation happens to be a bifunctor, so you can do this:

((_:NumberFormatException).toString) <-: "123".parseInt

Scala 的类型推断一般从左到右流动，所以这实际上更短:

Scala's type inference generally flows from left to right, so this is actually shorter:

"123".parseInt.<-:(_.toString)

并且需要更少的注释.

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