Is Scala functional programming slower than traditional coding?

Question

In one of my first attempts to create functional code, I ran into a performance issue.

I started with a common task - multiply the elements of two arrays and sum up

Answer 1

I am not an expert Scala programmer, so there is probably a more efficient method, but what about something like this. This can be tail call optimized, so performance should be OK.

def multiply_and_sum(l1:List[Int], l2:List[Int], sum:Int):Int = {
    if (l1 != Nil && l2 != Nil) {
        multiply_and_sum(l1.tail, l2.tail, sum + (l1.head * l2.head))
    }
    else {
        sum
    }
}

val first = Array(1,2,3,4,5)
val second = Array(6,7,8,9,10)
multiply_and_sum(first.toList, second.toList, 0)  //Returns: 130