Scala中解析器成功的模式匹配 [英] Pattern matching on Parsers Success In Scala

问题描述

我是Scala的新手，并且一直在尝试使用其出色的组合器解析器库.我一直在尝试编译此代码:

I'm new to Scala, and have been trying to use its excellent combinator parser library. I've been trying to get this code to compile:

import scala.util.parsing.combinator._
...
val r:Parsers#ParseResult[Node] = parser.parseAll(parser.suite,reader)
r match {
  case Success(r, n) => println(r)
  case Failure(msg, n) => println(msg)
  case Error(msg, n) => println(msg)
}
...

但是我不断收到这些错误:

But I keep getting these errors:

TowelParser.scala:97: error: not found: value Success
  case Success(r, n) => println(r)
       ^
TowelParser.scala:98: error: not found: value Failure
  case Failure(msg, n) => println(msg)

TowelParser.scala:99: error: object Error is not a case class constructor, nor does it have an unapply/unapplySeq method
  case Error(msg, n) => println(msg)

我尝试了很多不同的事情，例如:

I've tried lots of different things like:

case Parsers#Success(r, n) => println(r)

和

case Parsers.Success(r, n) => println(r)

和

import scala.util.parsing.combinator.Parsers.Success

但是我似乎无法编译它.我敢肯定我可能会遗漏一些明显的东西，但是我已经有一段时间了，而Google似乎没有很好的例子.

But I can't seem to get this to compile. I'm sure there's probably something obvious I'm missing, but I've been at it for a while, and google doesn't seem to have any good examples of this.

谢谢！

推荐答案

您需要指定ParseResult的完整路径，其中包括Parsers实例.例如:

You need to specify the full path for the ParseResult, which includes your Parsers instance. For example:

import scala.util.parsing.combinator._

object parser extends RegexParsers { def digits = "\\d+".r ^^ (_.toInt) }

val res = parser.parseAll(parser.digits, "42")

res match {
  case parser.Success(r, n) => println(r)
  case parser.Failure(msg, n) => println(msg)
  case parser.Error(msg, n) => println(msg)
}

请注意，如果您想要一点语法上的方便，也可以导入这些内容:

Note that you could also import these if you want a little extra syntactic convenience:

import parser.{ Error, Failure, Success }

现在，您的原始版本将按预期运行.

Now your original version will work as expected.

这篇关于Scala中解析器成功的模式匹配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！