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.