Scala: match and parse an integer string?

This is better IMHO:

val IntRegEx = "(\\d+)".r
def getValue(s: String): Option[Int] =
  s match {
    case "inf"         => Some(Int.MaxValue)
    case IntRegEx(num) => Some(num.toInt)
    case _             => None
  }

getValue("inf")          // Some(2147483647)
getValue("123412")       // Some(123412)
getValue("not-a-number") // None

Of course, it doesn't throw any exceptions, but if you really want it, you may use:

getValue(someStr).getOrElse(error("NaN"))

Define an extractor

object Int {
  def unapply(s : String) : Option[Int] = try {
    Some(s.toInt)
  } catch {
    case _ : java.lang.NumberFormatException => None
  }
}

Your example method

def getValue(s: String): Int = s match {
  case "inf" => Integer.MAX_VALUE 
  case Int(x) => x
  case _ => error("not a number")
}

And using it

scala> getValue("4")
res5: Int = 4

scala> getValue("inf")
res6: Int = 2147483647

scala> getValue("helloworld")
java.lang.RuntimeException: not a number
at scala.Predef$.error(Predef.scala:76)
at .getValue(<console>:8)
at .<init>(<console>:7)
at .<clinit>(<console>)
at RequestResult$.<init>(<console>:4)
at RequestResult$.<clinit>(<console>)
at RequestResult$result(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Na...