Monad捕获多个异常（不单单失败） [英] Monad to catch multiple exceptions (not just fail on single)

问题描述

我有一个类似的问题，在这里提出的问题（多次或单次尝试抓住），然而在我的情况下，我需要遵循这种模式的功能（而不是性能原因）

I have a similar question to what is asked here (Multiple or Single Try Catch), however in my case I need to follow this pattern for functional (and not performance reasons)

本质上我正在处理Scalatra中的参数错误，我需要一个简单的如果有任何转换失败，那么如果没有第一次失败跳过其余的尝试调用，

Essentially I am handling parameter errors in Scalatra, and I need an easy way to catch if any conversions fail without the first failure skipping the rest of the try calls

换句话说，我需要一些跟随这样的样式

In other words, I need something that follows a pattern like this

  def checkMultiple(a:Seq[Try]):Either[Map[_,Throwable],Map[_,Success]] = {
    ???
  }

我放入了一个try子句的序列。如果其中任何一个失败，它将返回失败的尝试的全部的映射，而不仅仅是第一个（将有失败的尝试的映射及其异常），否则它将返回所有尝试映射的映射与他们的成功值的映射

I put in a Sequence of try clauses. Should any of them fail, it will return back a map of all of the failed try's , not just the first one (which will have a map of the try that failed, along with its exception), else it will return a map of all of the try's mapped with their success values

有没有人知道是否有一个monadic模式本质上已经这样做，或者如果有一些这样做的util库？否则你将如何定义上述函数？

Does anyone know if there is a monadic pattern that already does this in essence, or if there is some util library which does this? Else how would you define the above function?

推荐答案

你可以用简单的Scala来完成一些这样的事情，虽然它有点多工作比Scalaz'验证。

You can accomplish something much like this with plain Scala, though it's a little more work than with Scalaz' Validation.

def checkMultiple[A,B](data: Seq[A])(f: A => B): Either[Map[A,Throwable], Map[A,B]] = {
  val caught = data.map(a => a -> Try(f(a)))
  val wrong = caught.collect{ case (a, Failure(t)) => a -> t }
  if (!wrong.isEmpty) Left(wrong.toMap)
  else Right(caught.map(x => x._1 -> x._2.get).toMap)
}

这里正在工作：

scala> checkMultiple(Seq(1,2,3,4))(x => if (x>4) throw new Exception else x)
res1: scala.util.Either[Map[Int,Throwable],Map[Int,Int]] = 
  Right(Map(1 -> 1, 2 -> 2, 3 -> 3, 4 -> 4))

scala> checkMultiple(Seq(3,4,5,6))(x => if (x>4) throw new Exception else x)
res2: scala.util.Either[Map[Int,Throwable],Map[Int,Int]] = 
  Left(Map(5 -> java.lang.Exception, 6 -> java.lang.Exception))

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