Sample solution to standard bowling kata (http://codingdojo.org/cgi-bin/wiki.pl?KataBowling) using Scala pattern matching and extractors

BowlingKataRunner.scala

// Idiomatic solution using extrators
// Extractors allow us to bind parameters to an object and are usable in pattern matches to see if a pattern can apply to the params submitted. 
// Note this is simialr to case classes, but works against an Object (which are like 'static' classes in Java). Also it incurs some performance penalties
// as opposed to using case classes
class BowlingForExtractors() {

    def score(bowls:List[Int]) = scoreFrames(bowls).slice(0,10).sum    // take the first 10 elements from the List and sum them..any additional elements are the result of additional strikes

    def scoreFrames(bowls:List[Int]) : List[Int] = bowls match {
        case Nil => List(0)
        case isStrike() =>
            bowls.slice(0,3).sum :: scoreFrames(bowls drop 1) // :: is the cons operator and is right associative. Basically it prepends
        case isSpare() =>
            bowls.slice(0,3).sum :: scoreFrames(bowls drop 2) // elements to the left to the start of a List. the drop 'infix' operator 
        case _ =>
            bowls.slice(0,2).sum :: scoreFrames(bowls drop 2) // removes the named number of elements from the start of the List
    }

    object isStrike {  // typical extractors would implement an apply method for creating an object instance based on params passed in..
        def unapply(bowls:List[Int]) = bowls match {
            case 10::_ => true
            case _ => false
        }
    }

    object isSpare {
        def unapply(bowls:List[Int]) = bowls match {
            case a::b::_ if a+b == 10 => true
            case _ => false
        }
    }
}


object BowlingKataRunner {

    val allFoursAndFives = List(4,5,4,5,4,5,4,5,4,5,4,5,4,5,4,5,4,5,4,5) // Should == 90
    val allFives = List(5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5) // Should == 150
    val allStrikes = List(10,10,10,10,10,10,10,10,10,10,10,10) // Should == 300

    def main(args: Array[String]) {
		
        val extractorSolution = new BowlingForExtractors()

        println("Testing Bowling using extractors....")
        println("4s and 5s: " + ((extractorSolution score allFoursAndFives) == 90))
	println("All 5s: " + ((extractorSolution score allFives) == 150) )
	println("All Strikes: " + ((extractorSolution score allStrikes) == 300) )

    }

}