S99 P22 Create a list containing all integers within a given range.

S9922.scala

import scala.annotation.tailrec

/*
 * S99 P22 http://aperiodic.net/phil/scala/s-99/
 *  
 * Create a list containing all integers within a given range.
 * Example:
 * scala> range(4, 9)
 * res0: List[Int] = List(4, 5, 6, 7, 8, 9)
 * 
 * D. Holbrook 2012-04-18
 */

object S9922 extends App {

  def range(lower: Int, upper: Int): List[Int] = {
    @tailrec
    def loop(l: Int, u: Int, a: List[Int]): List[Int] = {
      if (l > u) a.reverse
      else loop(l + 1, u, l :: a)
    }
    loop(lower, upper, List[Int]())
  }

  println(range(10, 30))

}