A Scala 'signs are opposite' function (positive, negative)

Here's the source code for a Scala function to determine whether signs (positive, negative) of two values are opposite:

   * The "signs are opposite" helper function.
  def signsAreOpposite(x: Double, y: Double): Boolean = {
    if (x < 0 && y > 0) return true
    else if (x > 0 && y < 0) return true
    else return false

Bear in mind that part of this solution depends on how you want to handle the situation where one (or both) of the values are zero.