Scala App doesn't run, just finishes with exit code 0 - scala

Question

Full application below - why does this not run with the menu ready for user inputs? Simply returns "Process finished with exit code 0" - I am unsure what I am doing wrong here, the menu should be displayed ready for user input to then return the data from the specified file.
import scala.util.{Try, Success, Failure, Using}
case object MyApp5 {
case class State(name : String
,code : Int
,parties : Array[(String,Int)])
val mapdata = readFile("filename.txt")
def readFile(filename: String): Try[List[State]] = {
val dataRE = "([^(]+) \\((\\d+)\\),(.+)".r
val pVotes = "([^:]+):(\\d+)".r
Using(io.Source.fromFile(filename)) {
_.getLines()
.toList
.collect{ case dataRE(name, code, votes) =>
State(name.trim
,code.toInt
,votes.split(",")
.collect{case pVotes(p,v) => (p,v.toInt)})
}
}
}
class Menu(states: List[State]) {
def apply(key: String): Boolean = {
val (_, op, continue) = lookup(key)
op()
continue
}
private val lookup: Map[String,(String,()=>Unit,Boolean)] =
Map("?" -> ("show this menu", menu _, true)
,"menu" -> ("show this menu", menu _, true)
,"all" -> ("display all voting data", all _, true)
,"st" -> ("vote totals by state", stVotes _, true)
,"x" -> ("exit", done _, false)
,"quit" -> ("exit", done _, false)
).withDefaultValue(("",unknown _, true))
private def done(): Unit = println("bye")
private def unknown(): Unit = println("unknown selection ('?' for main menu)")
private def menu(): Unit =
lookup.keys.toVector.sorted
.map(k => s"$k\t: ${lookup(k)._1}")
.foreach(println)
private def all(): Unit =
states.sortBy(_.name) //alphabetical
.foreach{ st =>
println(st.name) //state name
st.parties
.sortBy(-_._2) //votes in decreasing order
.map{case (p,v) => f"\t$p%-12s:$v%9d"}
.foreach(println)
}
private def stVotes(): Unit =
states.map(st => (st.name, st.parties.map(_._2).sum))
.sortBy(-_._2) //votes in decreasing order
.map{case (state,total) => f"$state%-9s:$total%8d"}
.foreach(println)
}
def main(args: Array[String]): Unit =
args.headOption.map(readFile) match {
case None =>
println(s"usage: ${this.productPrefix} <data_file>")
case Some(Failure(exc)) =>
println(s"Error reading data file: $exc")
case Some(Success(stateData)) =>
val menu = new Menu(stateData)
menu("menu")
Iterator.continually(menu(io.StdIn.readLine(">> ").toLowerCase))
.dropWhile(identity)
.next()
}
}
This is a copy and paste from my scala case object MyApp5 (with the exception of "filename.txt" where I have put the absolute path - what am I missing?

Answer 1

Hard-coding the data file into the program would be a very unfortunate design decision. That way you wouldn't be able to run the program on different data sets, e.g. the results from different elections.
But ... oh well.
def main(args: Array[String]): Unit =
readFile("filename.txt") match {
case Failure(exc) =>
println(s"Error reading data file: $exc")
case Success(stateData) =>
val menu = new Menu(stateData)
menu("menu")
Iterator.continually(menu(io.StdIn.readLine(">> ").toLowerCase))
.dropWhile(identity)
.next()
}
I really don't see any point or advantage in doing it this way.