Other patterns of [zerosum's answer](https://gist.github.com/4578404)

Euler0009_1.scala

/** try to use Tuple */
object Euler0009 {

  private val max = 1000

  def main(args: Array[String]) {
    println(
      triplet(1, 2).filter{ case(a, b, c) => a*a + b*b == c*c}
                        .map{case (a, b, c) => a * b * c}
    )
  }

  def triplet(a: Int, b: Int, triplets: List[(Int, Int, Int)] = Nil): List[(Int, Int, Int)] = {
    val c = max - a - b

    if(a > max/3) {
      triplets
    } else if(b < c) {
      triplet(a, b+1, (a, b, c) :: triplets)
    } else {
      triplet(a+1, a+2, triplets)
    }
  }
}

Euler0009_2.scala

/** try to use pattern match */
object Euler0009 {
 
  private val max = 1000
 
  def main(args: Array[String]): Unit = {
    println(
      triplet(1, 2).filter{case a :: b :: c :: Nil => a*a + b*b == c*c}
                        .map(_.product)
      )
  }
 
  def triplet(a: Int, b: Int, triplets: List[List[Int]] = Nil): List[List[Int]] = {
    val c = max - a - b
 
    if(a > max/3) {
      triplets
    } else if(b < c) {
      triplet(a, b+1, List(a, b, c) :: triplets)
    } else {
      triplet(a+1, a+2, triplets)
    }
  }
}