scalaz 验证和列表 monad [英] scalaz validation and list monad

问题描述

我正在尝试提出类似于以下内容的内容:

I am trying to come up with something similar to the following:

val s: Validation[String, Int] = 1.success
def s2(i: Int): Validation[String, Int] = i.success

val result = for {
  i <- s
  j <- List(1, 2)
  k <- s2(j)
} yield "fine";

以上代码无法编译，我理解，在语法上没有意义.

The above code does not compile and I understand, syntactically it does not make sense.

我正在尝试以一元方式执行验证列表.我如何做到这一点?

I am trying to execute a list of validations in a monadic way. How do I achieve that?

推荐答案

如果你有一个A的验证列表，你可以把它变成一个A列表的验证code> 使用 sequence:

If you have a list of validations of A, you can turn it into a validation of lists of A using sequence:

List(1, 2).map(s2).sequence[({type l[a]=Validation[String, a]})#l, Int] 

(如果我理解正确的话).所以你得到

(if I understand the question correctly). So you get

val result = for {
  i <- s
  k <- List(1, 2).map(s2).sequence[({type l[a]=Validation[String, a]})#l, Int] 
} yield "fine"

这篇关于scalaz 验证和列表 monad的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！