Question

I‘m learning Scala by the book Programming in Scala. When I try to run the code given in the book, it gives me the following error:

Exception in thread "main" java.lang.RuntimeException: Cannot figure out how to run target: File2
    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)

How do I solve this?

Here’s my code:

object Files2 {
  def filesHere = (new java.io.File(".")).listFiles
  def filesMatching(query: String, matcher: (String, String) => Boolean) = {
    for (file <- filesHere; if matcher(file.getName, query))
      yield file
  }

  def filesEnding(query: String) = filesMatching(query, _.endsWith(_))
  def filesContaining(query: String) = filesMatching(query, _.contains(_))
  def filesRegex(query: String) = filesMatching(query, _.matches(_))

  def main(args: Array[String]) {
    println("filesEnding(\"scala\").toList [" + filesEnding("scala").toList + "]")
    println("filesContaining(\"Files1\").toList [" + filesContaining("Files1").toList + "]")
    println("filesRegex(\".*Re.ex.*\").toList [" + filesRegex(".*Re.ex.*").toList + "]")  
  }
}

Answer 1

I just pasted your code into a file called test.scala and then ran it with scala test.scala and it worked fine.

dhg ~$ scala test.scala
filesEnding("scala").toList [List(./test.scala)]
filesContaining("Files1").toList [List()]
filesRegex(".*Re.ex.*").toList [List()]