[英]Processing a list of Scalaz6 Validation
Is there an idiomatic way to handle a collection of Validation in Scalaz6? 是否有一种惯用的方法来处理Scalaz6中的验证集合?
val results:Seq[Validation[A,B]]
val exceptions = results.collect{case Failure(exception)=>exception}
exceptions.foreach{logger.error("Error when starting up ccxy gottware",_)}
val success = results.collect{case Success(data)=>data}
success.foreach {data => data.push}
if (exceptions.isEmpty)
containers.foreach( _.start())
I could think of using a fold when looping on results, but what about the final test? 我可以考虑在循环结果时使用折叠,但最终测试呢?
The usual way to work with a list of validations is to use sequence
to turn the list into a Validation[A, List[B]]
, which will be be empty (ie, a Failure
) if there were any errors along the way. 使用验证列表的常用方法是使用
sequence
将列表转换为Validation[A, List[B]]
,如果在此过程中出现任何错误,则Validation[A, List[B]]
将为空(即Failure
)。
Sequencing a Validation
accumulates errors (as opposed to Either
, which fails immediately) in the semigroup of the left-hand type. 排序
Validation
累积了左手类型半群中的错误(与Either
相反,后者立即失败)。 This is why you often see ValidationNEL
(where the NEL
stands for NonEmptyList
) used instead of simply Validation
. 这就是为什么你经常看到使用
ValidationNEL
(其中NEL
代表NonEmptyList
)而不是简单的Validation
。 So for example if you have this result type: 例如,如果您有此结果类型:
import scalaz._, Scalaz._
type ExceptionsOr[A] = ValidationNEL[Exception, A]
And some results: 还有一些结果:
val results: Seq[ExceptionsOr[Int]] = Seq(
"13".parseInt.liftFailNel, "42".parseInt.liftFailNel
)
Sequencing will give you the following: 排序将为您提供以下内容:
scala> results.sequence
res0: ExceptionsOr[Seq[Int]] = Success(List(13, 42))
If we had some errors like this, on the other hand: 如果我们有这样的错误,另一方面:
val results: Seq[ExceptionsOr[Int]] = Seq(
"13".parseInt.liftFailNel, "a".parseInt.liftFailNel, "b".parseInt.liftFailNel
)
We'd end up with a Failure
(note that I've reformatted the output to make it legible here): 我们最终会
Failure
(注意我已经重新格式化输出以使其在这里清晰可见):
scala> results.sequence
res1: ExceptionsOr[Seq[Int]] = Failure(
NonEmptyList(
java.lang.NumberFormatException: For input string: "a",
java.lang.NumberFormatException: For input string: "b"
)
)
So in your case you'd write something like this: 所以在你的情况下,你会写这样的东西:
val results: Seq[ValidationNEL[A, B]]
results.sequence match {
case Success(xs) => xs.foreach(_.push); containers.foreach(_.start())
case Failure(exceptions) => exceptions.foreach(
logger.error("Error when starting up ccxy gottware", _)
)
}
See my answers here and here for more detail about sequence
and about Validation
more generally. 有关
sequence
和Validation
更多详细信息,请参阅此处和此处的答案。
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