处理 Scalaz6 验证列表 [英] Processing a list of Scalaz6 Validation
问题描述
是否有一种惯用的方法来处理 Scalaz6 中的验证集合?
Is there an idiomatic way to handle a collection of Validation in Scalaz6?
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())
我可以考虑在循环结果时使用折叠,但最终测试呢?
I could think of using a fold when looping on results, but what about the final test?
推荐答案
处理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,它将为空(即 Failure
).
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 (i.e., a Failure
) if there were any errors along the way.
对 Validation
进行排序会在左侧类型的半群中累积错误(与 Either
相反,后者会立即失败).这就是为什么您经常看到使用 ValidationNEL
(其中 NEL
代表 NonEmptyList
)而不是简单的 Validation
.例如,如果您有以下结果类型:
Sequencing a Validation
accumulates errors (as opposed to Either
, which fails immediately) in the semigroup of the left-hand type. This is why you often see ValidationNEL
(where the NEL
stands for NonEmptyList
) used instead of simply Validation
. So for example if you have this result type:
import scalaz._, Scalaz._
type ExceptionsOr[A] = ValidationNEL[Exception, A]
还有一些结果:
val results: Seq[ExceptionsOr[Int]] = Seq(
"13".parseInt.liftFailNel, "42".parseInt.liftFailNel
)
测序将为您提供以下信息:
Sequencing will give you the following:
scala> results.sequence
res0: ExceptionsOr[Seq[Int]] = Success(List(13, 42))
另一方面,如果我们有一些这样的错误:
If we had some errors like this, on the other hand:
val results: Seq[ExceptionsOr[Int]] = Seq(
"13".parseInt.liftFailNel, "a".parseInt.liftFailNel, "b".parseInt.liftFailNel
)
我们最终会遇到 Failure
(请注意,我已重新格式化输出以使其在此处清晰易读):
We'd end up with a Failure
(note that I've reformatted the output to make it legible here):
scala> results.sequence
res1: ExceptionsOr[Seq[Int]] = Failure(
NonEmptyList(
java.lang.NumberFormatException: For input string: "a",
java.lang.NumberFormatException: For input string: "b"
)
)
所以在你的情况下你会写这样的东西:
So in your case you'd write something like this:
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", _)
)
}
查看我的回答这里和此处 了解有关 sequence
和 Validation
的更多详细信息.
See my answers here and here for more detail about sequence
and about Validation
more generally.
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