Question

继续阅读硕士论文[1]以学习Scala中的解析，但无法弄清楚如何使这个例子有效（参见第28-29页）：

import util.parsing.combinator.JavaTokenParsers

trait ArithParser extends JavaTokenParsers {
    def expr: Parser[Any] = term ~ rep("+" ~ term | "-" ~ term)
    def term              = factor ~ rep("*" ~ factor | "/" ~ factor)
    def factor            = floatingPointNumber ^^ {_.toDouble} | "(" ~> expr <~ ")"
}

object ArithParserCLI extends ArithParser {
    def main(args: Array[String]) {
        for (arg <- args) {
            println("Input: " + arg)
            println("Output: " + parseAll(expr, arg))
        }
    }
}

[1] E. Labun, “Combinator Parsing in Scala,” Technische Hochschule Mittelhessen, 2012.

不幸的是我不能让它在Scala 2.9.3或Scala 2.11.0-M4中运行：

> scala29 ArithParserCLI "10.5 - 4*2"
Exception in thread "main" java.lang.RuntimeException: Cannot figure out how to
run target: ArithParserCLI
        at scala.sys.package$.error(package.scala:27)
        at scala.tools.nsc.GenericRunnerCommand.scala$tools$nsc$GenericRunnerCommand$$guessHowToRun(GenericRunnerCommand.scala:38)
        at scala.tools.nsc.GenericRunnerCommand$$anonfun$2.apply(GenericRunnerCommand.scala:48)
        at scala.tools.nsc.GenericRunnerCommand$$anonfun$2.apply(GenericRunnerCommand.scala:48)
        at scala.Option.getOrElse(Option.scala:108)
        at scala.tools.nsc.GenericRunnerCommand.<init>(GenericRunnerCommand.scala:48)
        at scala.tools.nsc.GenericRunnerCommand.<init>(GenericRunnerCommand.scala:17)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:33)

        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

然后尝试使用2.11 scalac和scala：

> scala ArithParserCLI "10.5 - 4*2"
No such file or class on classpath: ArithParserCLI

Answer 1

您的代码没有任何问题 - 您是否在运行之前使用scalac进行编译？

 scalac ArithParserCLI.scala  # or whatever your source file is named
 scala ArithParserCLI "10.5 - 4*2"

顺便说一句，如果您打算在Scala中进行任何重要编码，强烈建议使用sbt。您也可以在sbt中运行以下代码：

 # Assuming the current directory contains only one scala source file with a 
 # main method:
 sbt 'run "10.5 - 4*2"'

Answer 2

实际上，我刚刚接受了源代码而没有任何更改，并完成了以下操作：

[root@centos scala]# scalac parser.scala
[root@centos scala]# scala ArithParserCLI "10.5 - 4*2"
Input: 10.5 - 4*2
Output: [1.11] parsed: ((10.5~List())~List((-~(4.0~List((*~2.0))))))

scala版本2.9.2。因此，错误可能在您的本地配置中。

在Scala中按名称编译和运行函数？

2 个答案: