Project Euler Problem 2

problem2.scala

  /*
  * http://projecteuler.net/problem=2
  * http://odz.sakura.ne.jp/projecteuler/index.php?cmd=read&page=Problem%202
  */
  val fib: List[Int] => List[Int] = {xs =>
    xs match {
      case Nil => throw new IllegalArgumentException
      case i::Nil => throw new IllegalArgumentException
      case _ => {
        val nextNum = xs.head + xs.tail.head
        if (nextNum >= 4000000) {
          xs
        } else {
          fib(nextNum :: xs)
        }
      }
    }
  }

  fib(List(2, 1)).filter(_ % 2 == 0).sum